We are already accustomed to the main parameters of the capacitor: capacitance and operating voltage. But recently, its equivalent series resistance (ESR) has become an equally important parameter. What is it and what does it affect?

Since EPS most strongly affects the operation of electrolytic capacitors, in the future we will talk about them. Now we will analyze the electrolytic capacitor by bones and find out what secrets it hides.

Any electronic component is not perfect. This also applies to the capacitor. The totality of its properties is shown by a conditional diagram.

As you can see, a real capacitor consists of a capacitance C , which we are used to seeing on diagrams in the form of two vertical stripes. Next resistor Rs , which symbolizes the active resistance of the wire leads and the contact resistance of the lead - lining. The photo shows how the wire leads are attached to the plates by riveting.

Since any, even a very good dielectric, has a certain resistance (up to hundreds of megaohms), a resistor is shown parallel to the plates Rp . It is through this "virtual" resistor that the so-called leakage current flows. Naturally, there are no resistors inside the capacitor. This is for illustration and convenience purposes only.

Due to the fact that the plates of the electrolytic capacitor are twisted and installed in an aluminum case, an inductance is formed L.

This inductance exhibits its properties only at frequencies above the resonant frequency of the capacitor. The approximate value of this inductance is tens of nanohenries.

So, from all this, we select what is included in the EPS of an electrolytic capacitor:

Resistance, which is caused by losses in the dielectric due to its inhomogeneity, impurities and the presence of moisture;

Ohmic resistance of wire leads and plates. Active resistance of wires;

Contact resistance between plates and leads;

This can also include the resistance of the electrolyte, which increases due to the evaporation of the electrolyte solvent and changes in its chemical composition due to its interaction with the metal plates.

All these factors are summed up and form the resistance of the capacitor, which was called the equivalent series resistance - abbreviated as EPS, but in a foreign manner ESR (E equivalent S serial R existence).

As you know, an electrolytic capacitor, due to its design, can only work in DC and pulsating current circuits due to its polarity. Actually, it is used in power supplies to filter ripples after the rectifier. Let's remember this feature of the capacitor - to pass current pulses.

And if ESR is, in fact, resistance, then heat will be released on it during the flow of current pulses. Think about the power of the resistor. Thus, the larger the EPS, the more the capacitor will heat up.

Heating an electrolytic capacitor is very bad. Due to heating, the electrolyte begins to boil and evaporate, the capacitor swells. Probably, you have already noticed a protective notch on the top of the case on electrolytic capacitors.

With prolonged operation of the capacitor and an elevated temperature inside it, the electrolyte begins to evaporate and put pressure on this notch. Over time, the pressure inside increases so much that the notch breaks, releasing gas out.

"Slammed" capacitor on the power supply board (reason - exceeding the permissible voltage)

Also, the protective notch prevents (or weakens) the explosion of the capacitor when the permissible voltage is exceeded or its polarity is changed.

In practice, it happens the other way around - the pressure pushes the insulator away from the terminals. The photo below shows a capacitor that has dried up. Its capacitance decreased to 106 uF, and the ESR when measured was 2.8Ω, while the normal ESR value for a new capacitor with the same capacitance lies in the range of 0.08 - 0.1Ω.

Electrolytic capacitors are produced at different operating temperatures. For aluminum electrolytic capacitors, the lower temperature limit starts from -60 0 C, and the upper limit is +155 0 C. But for the most part, such capacitors are designed to operate in the temperature range from -25 0 C to 85 0 C and from -25 0 C to 105 0 С. Sometimes only the upper temperature limit is indicated on the label: +85 0 С or +105 0 С.

The presence of EPS in a real electrolytic capacitor affects its operation in high-frequency circuits. And if for ordinary capacitors this influence is not so pronounced, then for electrolytic capacitors it plays a very important role. This is especially true for their operation in circuits with a high level of ripple, when a significant current flows and heat is generated due to ESR.

Take a look at the photo.

Swollen electrolytic capacitors (due to prolonged operation at elevated temperatures)

This is the motherboard of a personal computer that has stopped turning on. As you can see, there are four swollen electrolytic capacitors on the printed circuit board next to the processor heatsink. Long-term operation at elevated temperatures (external heating from a radiator) and a decent service life led to the fact that the capacitors “slammed”. This is due to heat and ESR. Poor cooling negatively affects not only the operation of processors and microcircuits, but, as it turns out, also electrolytic capacitors!

Reducing the ambient temperature by 10 0 C prolongs the service life of the electrolytic capacitor by almost half.

A similar picture is observed in failed PC power supplies - electrolytic capacitors also swell, which leads to a drawdown and ripples in the supply voltage.

Faulty capacitors in the ATX PC PSU (caused by poor quality capacitors)

Often, due to long-term operation, switching power supplies for access points, Wi-Fi routers, and all kinds of modems also fail due to “popped” or lost capacitors. Let's not forget that when heated, the electrolyte dries up, and this leads to a decrease in capacity. I described an example from practice.

From all that has been said, it follows that electrolytic capacitors operating in high-frequency pulse circuits (power supplies, inverters, converters, switching stabilizers) operate in rather extreme conditions and fail more often. Knowing this, manufacturers produce special series with low ESR. On such capacitors, as a rule, there is an inscription Low ESR , which means "low EPS".

It is known that the capacitor has capacitive or reactance, which decreases with increasing frequency of the alternating current.

Thus, as the frequency of the alternating current increases, the reactance of the capacitor will drop, but only until it approaches the value of the equivalent series resistance (ESR). That is what needs to be measured. Therefore, many devices - ESR meters (ESR-meters) measure ESR at frequencies of several tens - hundreds of kilohertz. This is necessary in order to "remove" the reactance value from the measurement results.

It is worth noting that the ESR value of a capacitor is affected not only by the current ripple frequency, but also by the voltage on the plates, ambient temperature, and workmanship. Therefore, it is impossible to say unequivocally that the ESR of a capacitor, for example, is 3 ohms. At different operating frequencies, the ESR value will be different.

ESR meter

When checking capacitors, especially electrolytic ones, you should pay attention to the ESR value. There are many commercially available instruments for testing capacitors and measuring ESR. The photo shows a universal radio component tester (LCR-T4 Tester), the functionality of which supports measuring the ESR of capacitors.

In radio engineering magazines, you can find descriptions of home-made devices and attachments for multimeters for measuring ESR. You can also find highly specialized ESR meters on sale that are capable of measuring capacitance and ESR without soldering them out of the board, as well as discharging them before that in order to protect the device from damage by the high residual voltage of the capacitor. Such devices include, for example, such as ESR-micro v3.1, ESR-micro V4.0s, ESR-micro v4.0SI.

When repairing electronics, you often have to change electrolytic capacitors. At the same time, parameters such as capacitance and ESR are measured to assess their quality. In order to have something to compare with, an ESR table was compiled, which indicates the ESR of new electrolytic capacitors of different capacities. This table can be used to evaluate the suitability of a particular capacitor for further service.

Tell in:

The interest of our readers and authors in the development and manufacture of devices for measuring ESR (ESR) of oxide capacitors does not weaken. The prefix offered below for the 83x series multimeters continues this theme. Multimeters, further instruments, the 83x series are very popular among radio amateurs due to their affordable price and acceptable measurement accuracy.

Articles on expanding the capabilities of these devices have been repeatedly published on the pages of the Radio magazine, for example,. When developing the proposed attachment, as well as in, the task was not to use an additional power source. The attachment diagram is shown in rice. one.

Fig.1

Devices built on ICL71x6 ADC chips or their analogues have an internal stabilized voltage source of 3 V with a maximum load current of 3 mA. From the output of this source, the power supply is supplied to the set-top box through the "COM" connector (common wire) and the external "NPNc" socket, which is part of the eight-pin socket for connecting low-power transistors in the mode of measuring the static current transfer coefficient. The EPS measurement method is similar to that used in a digital meter, which is described in the article. Compared with this device, the proposed prefix differs significantly in the simplicity of the circuit, the small number of elements and their low price.

Main technical characteristics
EPS measurement interval, Ohm:
with open contacts of switch SA1 0.1... 199.9
with its contacts closed (position "x0.1") 0.01...19.99
Capacitance of tested capacitors, not less than, uF 20
Current consumption, mA 1.5

When working with a prefix, the switch for the type of operation of the device is set to the position for measuring DC voltage with a limit of "200 mV". The external plugs of the prefix "COM", "VΩmA", "NPNc" are connected to the corresponding sockets of the device. The timing diagram is shown in rice. 2. The generator, assembled on a logic element DD1.1 - a Schmitt trigger, a VD1 diode, a capacitor C1 and resistors R1, R2, generates a sequence of positive pulses with a duration of t r = 4 μs with a pause of 150 μs and a stable amplitude of about 3 V ( rice. 2, a). These pulses can be observed with an oscilloscope relative to the common wire of the "COM" jack. During each pulse, a stable current, set by resistors R4, R5, flows through the capacitor under test, connected to the "Cx" sockets of the set-top box, which is equal to 1 mA with open contacts of the switch SA1 or 10 mA with its closed contacts (position "x0.1").

Let's consider the operation of the units and elements of the attachment with the capacitor being checked connected from the moment the next pulse of duration t r appears at the output of the DD1.1 element. From the low-level pulse inverted by the DD1.2 element with a duration of t r, the transistor VT1 closes for 4 μs. After charging the drain-source capacitance of the closed transistor VT1, the voltage at the terminals of the tested capacitor will depend practically only on the current flowing through its EPS. On the logic element DD1.3, resistor R3 and capacitor C2, a node delaying the front of the generator pulse for 2 μs is assembled. During the delay time t 3, the drain-source capacitance of the closed transistor VT1, shunting the capacitor under test, has time to charge and practically does not affect the accuracy of the measurement process following after t 3 (Fig. 2b). From the generator pulse delayed by 2 μs and shortened in duration to 2 μs, a high-level measuring pulse with a duration t meas = 2 μs (Fig. 2, c) is formed at the output of the DD1.4 inverter. The transistor VT2 opens from it, and the storage capacitor C3 begins to charge from the voltage drop across the EPS of the tested capacitor through resistors R6, R7 and the open transistor VT2. At the end of the measuring pulse and the pulse from the generator output from a high level at the output of element DD1.2, transistor VT1 opens, and VT2 closes from a low level at the output of element DD1.4. The described process is repeated every 150 μs, which leads to the charging of the capacitor C3 until the voltage drops on the ESR of the tested capacitor after several tens of periods. The indicator of the device displays the value of the equivalent series resistance in ohms. With the switch position SA1 "x0.1", the indicator readings must be multiplied by 0.1. The transistor VT1, open between the pulses of the generator, eliminates the increase in voltage (charge) on the capacitive component of the tested capacitor to values ​​below the minimum sensitivity of the device, equal to 0.1 mV. The presence of the input capacitance of the transistor VT2 leads to a zero shift of the device. To eliminate its influence, resistors R6 and R7 are used. By selecting these resistors, they achieve the absence of voltage on the capacitor C3 with closed sockets "Cx" (zero setting).

On measurement errors. First, there is a systematic error, reaching approximately 6% for resistances close to the maximum in each interval. It is associated with a decrease in the testing current, but is not so important - capacitors with such EPS are subject to rejection. Secondly, there is a measurement error, depending on the capacitance of the capacitor.
This is explained by the increase in voltage during the pulse from the generator to the capacitive component of the capacitors: the smaller the capacitance, the faster its charging. This error is easy to calculate, knowing the capacity, current and charging time: U \u003d M / C. So, for capacitors with a capacity of more than 20 microfarads, it does not affect the measurement result, but for 2 microfarads, the measured value will be more than the real value by about 1.5 Ohms (respectively, 1 microfarad - 3 Ohms, 10 microfarads - 0.3 Ohms, etc.). P.).

Devil w PCB shown on rice. 3. Three holes for the pins should be drilled so that the latter fit into them with little effort.

This will facilitate the process of soldering them to the pads. Pin "NPNc" - gold-plated from a suitable connector, a piece of tinned copper wire is also suitable. A hole for it is drilled in a suitable place after installing the "COM" and "VΩmA" pins. The latter - from failed measuring probes. Capacitor SZ is desirable to use from the TKE group no worse than H10 (X7R). Transistor IRLML6346 (VT1) can be replaced with IRLML6246, IRLML2502, IRLML6344 (in descending order). Replacement criteria - open channel resistance no more than 0.06 Ohm at a gate-source voltage of 2.5 V, drain-source capacitance - no more than 300 ... 400 pF. But if we limit ourselves only to the interval 0.01 ... 19.00 Ohm (switch SA1 in this case is replaced by a jumper, resistor R5 is removed), then the maximum drain-source capacitance can reach 3000 pF. We will replace the 2N7000 (VT2) transistor with 2N7002, 2N7002L, BS170C with a threshold voltage of not more than 2 ... 2.2 V. Before mounting the transistors, check that the location of the pins matches the conductors of the printed circuit board. Nests XS1, XS2 in the copy of the author - screw terminal block 306-021-12.

Before setting up, the set-top box should not be connected to a multimeter, so as not to disable it, but to an independent 3 V power source, for example, to two series-connected galvanic cells. The plus of this source is temporarily connected to the "NPNc" pin of the set-top box (without connecting this pin to the multimeter), and the minus is connected to its common wire. The consumed current is measured, which should not exceed 3 mA, after which the autonomous source is turned off. The sockets "Cx" are temporarily closed with a short piece of copper wire with a diameter of at least 1 mm. The pins of the attachment are inserted into the sockets of the same name on the device. By selecting resistors R6 and R7, zero readings of the device are set at both positions of the SA1 switch. For convenience, these resistors can be replaced with one trimmer, and after zero adjustment, resistors R6 and R7 are soldered with a total resistance equal to the trimmer.

Remove the piece of wire that closes the "Cx" sockets. A resistor 1 ... 2 0m is connected to them when SA1 is closed, then - 10 ... 20 Ohms when open. Compare the readings of the device with the resistances of the resistors. If necessary, select R4 and R5, achieving the desired measurement accuracy. The appearance of the console is shown in the photo rice. four.
The prefix can be used as a low resistance ohmmeter. It can also measure the internal resistance of small-sized galvanic or rechargeable cells and batteries through a series-connected capacitor with a capacity of at least 1000 μF, observing the polarity of its connection. From the obtained measurement result, it is necessary to subtract the ESR of the capacitor, which must be measured in advance.

LITERATURE
1. Nechaev I. Attachment to a multimeter for measuring the capacitance of capacitors. - Radio, 1999, No. 8, pp. 42,43.
2. Chudnov V. Attachment to a multimeter for measuring temperature. - Radio, 2003, No. 1, p. 34.
3. Podushkin I. Generator + single vibrator = three attachments to the multimeter. - Radio, 2010, No. 7, p. 46, 47; No. 8, p. 50-52.
4. Datasheet ICL7136 http://radio-hobby.org/modules/datasheets/2232-icl7136
5. Biryukov S. Digital ESR meter. - Circuitry, 2006, No. 3, p. 30-32; No. 4, p. 36.37.

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In recent years, specialists and radio amateurs have found the usefulness of evaluating the equivalent series resistance (ESR) of oxide capacitors, especially in the repair practice of pulsed power supplies, high-quality UMZCH and other modern equipment. This article proposes a meter that has a number of advantages.

In recent years, specialists and radio amateurs have found the usefulness of evaluating the equivalent series resistance (ESR) of oxide capacitors, especially in the repair practice of pulsed power supplies, high-quality UMZCH and other modern equipment. This article proposes a meter that has a number of advantages.

A scale close to logarithmic, convenient for a device with a pointer indicator, allows you to determine the ESR values ​​approximately in the range from fractions of an ohm to 50 ohms, while the value of 1 ohm is on the scale section corresponding to 35 ... 50% of the total deviation current. This makes it possible to estimate ESR values ​​with acceptable accuracy in the range of 0.1 ... 1 Ohm, which, for example, is necessary for oxide capacitors with a capacity of more than 1000 μF, and with less accuracy - up to 50 Ohm.

Full galvanic isolation of the measurement circuit protects the device from failure when checking an accidentally charged capacitor - a common situation in practice. Low voltage on the measuring probes (less than 70 mV) allows measurements in most cases without desoldering the capacitors. Power supply of the device from one galvanic cell with a voltage of 1.5 V is accepted as the most optimal option (low cost and small dimensions). There is no need to calibrate the device and monitor the voltage of the element, since a built-in stabilizer and automatic switch are provided when the supply voltage is less than the permissible limit with a blocking of switching on. And finally, quasi-touch switching on and off the device with two miniature buttons.

Main technical characteristics
Interval of measured resistance, Ohm .......... 0.1 ... 50
Measuring pulse frequency, kHz .............................120
The amplitude of the pulses on the probes of the meter, mV ........ 50 ... 70
Supply voltage, V
nominal.................1.5
admissible ..............0.9...3
Consumption current, mA, not more than .......................... 20

The circuit diagram of the device is shown in fig. one

A step-up voltage converter from 1.5 to 9 V is assembled on transistors VT1, VT2 and transformer T1. Capacitor C1 - filtering.

The output voltage of the converter is supplied through an electronic switch on the trinistor VS1, which, in addition to manually turning the device on and off, automatically turns it off at a reduced supply voltage, goes to a micropower stabilizer assembled on a DA1 chip and resistors R3, R4. A stabilized voltage of 4 V feeds a pulse generator assembled according to a typical circuit on six elements AND-NOT of the DD1 microcircuit. The R6C2 circuit sets the test pulse frequency to approximately 100...120 kHz. LED HL1 - indicator of turning on the device.

Through the separating capacitor C3, the pulses are fed to the transformer T2. The voltage from its secondary winding is applied to the tested capacitor and to the primary winding of the measuring current transformer ТЗ. From the secondary winding of the TK, the signal enters through a half-wave rectifier on the diode VD3 and capacitor C4 to the pointer microammeter RA1. The larger the ESR of the capacitor, the smaller the deviation of the meter needle.

The trinistor switch operates as follows. In the initial state, the gate of the field-effect transistor VT3 has a low voltage, since the trinistor VS1 is closed, as a result of which the power supply circuit of the device is disconnected along the negative wire. At the same time, the load resistance of the boost converter is almost infinite and it does not work in this mode. In this state, the current consumption from the battery G1 is almost zero.

When the contacts of the SB2 button are closed, the voltage converter receives a load formed by the transition resistance of the control electrode-cathode of the trinistor and resistor R1. The converter starts up and its voltage opens the trinistor VS1. The field-effect transistor VT3 opens, and the negative power supply circuit of the stabilizer and generator is connected to the converter through a very low resistance of the channel of the field-effect transistor VT3. The SB1 off button, when pressed, shunts the anode and cathode of the VS1 trinistor, as a result, the VT3 transistor also closes, turning off the device. Automatic shutdown at low battery voltage occurs when the current through the trinistor becomes less than the hold-on current. The voltage at the output of the boost converter, at which this happens, is selected so that it is sufficient for the normal operation of the stabilizer, i.e., so that the minimum allowable difference between the voltage values ​​​​at the input and output of the DA1 microcircuit is always maintained.

Construction and details

All parts of the device, with the exception of a microammeter and two buttons, are located on a single-sided printed circuit board measuring 55x80 mm. The drawing of the board is shown in fig. 2. The body of the device is made of foil-coated getinaks. Miniature TV buttons are installed under the microammeter.

All transformers are wound on rings made of 2000NM ferrite, size K10x6x4.5, but these dimensions are not critical. Transformer T2 has two windings: primary - 100 turns, secondary - one turn. In a TK transformer, the primary winding consists of four turns, and the secondary winding of 200 turns. The diameter of the wires of the windings of transformers T2 and TK is not critical, but it is desirable to wind those that are included in the measuring circuit with a thicker wire - about 0.8 mm, other windings of these transformers are wound with PEV-2 wire with a diameter of 0.09 mm.

Transistors VT1 and VT2 - any of the KT209 series. it is desirable to select them with the same base current transfer coefficient. Capacitors can be used any suitable in size: resistors - MLT with a power of 0.125 or 0.25 W. Diodes VD1 and VD2 - any medium power. Diode VD3 - D311 or any of the D9 series. The field-effect transistor VT3 is almost any p-channel with a low open channel resistance and a low gate-source threshold voltage; for compact mounting, part of the base has been removed from the IRF740A transistor

The LED is suitable for any increased brightness, the glow of which is already visible at a current of 1 mA.

Microammeter RA1 - M4761 from an old reel-to-reel tape recorder, with a total arrow deflection current of 500 μA. A piece of shielded wire 20 cm long was used as a probe. A suitable body of a ballpoint pen is put on it, and thin steel needles are soldered to the end of the central core and to the screen braid of the wire. The needles are temporarily fixed at a distance of 5 mm from each other, the probe body is slightly pushed over them and the junction is filled with hot glue; the joint is molded in the form of a ball with a diameter slightly less than a centimeter. Such a probe, in my opinion, is the most optimal for such meters. It is easy to connect to a capacitor by placing one needle on one terminal of the capacitor and the other touching the second terminal, similar to working with compasses.

About setting up the device.

First of all, the operation of the boost converter is checked. As a load, you can temporarily connect a 1 kΩ resistor to the output of the converter. Then temporarily connect the anode and cathode of the trinistor with a jumper and set the resistor R3 at the output of the stabilizer DA1 to a voltage of approximately 4 V. The generator frequency should be within 100 ... 120 kHz.

Next, the probe needles are closed with a conductor and by adjusting the tuning resistor R3, the microammeter needle is set slightly below the maximum position, then, trying to change the phasing of one of the measurement windings, they achieve the maximum readings of the device and leave the windings in such a connection. By adjusting the resistor R3, set the arrow to the maximum. By connecting a non-wire resistor with a resistance of 1 Ohm to the probes, the position of the arrow is checked (it should be approximately in the middle of the scale) and, if necessary, by changing the number of turns in the primary winding of the TK transformer, the scale stretching is changed. At the same time, every time setting the arrow of the microammeter to the maximum by adjusting R3.

The most optimal scale seems to be on which EPS readings of no more than 1 Ohm occupy approximately 0.3 ... 0.5 of its entire length, that is, readings from 0.1 to 1 Ohm every 0.1 Ohm are freely distinguishable. Any other microammeters with a total deviation current of not more than 500 μA can be used in the device: for more sensitive ones, it will be necessary to reduce the number of turns of the secondary winding of the TK transformer.

Next, a shutdown node is established by selecting a resistor R1, instead of it, you can temporarily solder a tuning resistor with a resistance of 6.8 kOhm. After applying power to the DA1 input from an external regulated source, the voltage at the DA1 output is monitored by a voltmeter. You should find the smallest input voltage of the stabilizer, at which the output does not start to fall yet - this is the minimum operating input voltage. It must be borne in mind that the lower the minimum operating voltage, the more fully the resource of the battery will be used.

Further, by selecting the resistor R1, an abrupt closing of the trinistor is achieved at a supply voltage slightly higher than the minimum allowable. This is clearly seen from the deviation of the arrow of the device. It should, with the probes closed, drop sharply from the maximum to zero, while the LED goes out. The trinistor must close earlier than the field effect transistor VT3; otherwise there will be no abrupt switching. Next, re-check the manual switching on and off with the buttons SB1 and SB2.

In conclusion, the meter scale is calibrated using non-wire resistors of the appropriate ratings. The use of the device in the practice of repair showed its greater efficiency and convenience compared to other similar devices. They can also successfully check the contact resistance of the contacts of various buttons, reed switches and relays.

The article is taken from the site www.radio-lubitel.ru

Start

Yes, this topic has been discussed many times, including here. I have compiled two versions of the scheme Ludens and they have proven themselves very well, however, all the options previously proposed have drawbacks. Instrument scales with dial indicators are very non-linear and require many low-resistance resistors for calibration, these scales must be drawn and inserted into the heads. Instrument heads are large and heavy, fragile, and the cases of small-sized plastic indicators are usually soldered and they often have a small scale. The weak point of almost all previous designs is their low resolution. And for LowESR capacitors, it is just necessary to measure hundredths of an ohm in the range from zero to half an ohm. Devices based on microcontrollers with a digital scale were also proposed, but not everyone deals with microcontrollers and their firmware, the device turns out to be unreasonably complex and relatively expensive. Therefore, in the Radio magazine they made a reasonable rational scheme - any radio amateur has a digital tester, and it costs a penny.

I made minimal changes. Housing - from a faulty "electronic choke" for halogen lamps. Power - battery "Krona" 9 Volt and stabilizer 78L05. I removed the switch - it is very rare to measure LowESR in the range up to 200 Ohms (if I feel like it, I use a parallel connection). Changed some details. Chip 74HC132N, transistors 2N7000(to92) and IRLML2502(sot23). Due to the increase in voltage from 3 to 5 volts, there was no need to select transistors.
During testing, the device worked normally from a fresh battery voltage of 9.6 V to a fully discharged 6 V.

In addition, for convenience, I used smd resistors. All smd elements are perfectly soldered with the EPSN-25 soldering iron. Instead of a serial connection R6R7, I used a parallel connection - it’s more convenient, on the board I provided for connecting a variable resistor in parallel with R6 to adjust zero, but it turned out that “zero” is stable over the entire range of voltages I indicated.

The surprise was that in the design "developed in the magazine" the polarity of the VT1 connection was reversed- the drain and the source are mixed up (correct if I'm wrong). I know that transistors will work even with this inclusion, but such errors are unacceptable for editors.

Total

This device has been working for me for about a month, its readings when measuring capacitors with ESR in units of ohms coincide with the device according to the scheme Ludens .
It has already been tested in combat conditions, when my computer stopped turning on due to the capacitances in the power supply, while there were no obvious signs of “burnout”, and the capacitors were not swollen.

The accuracy of readings in the range of 0.01 ... 0.1 Ohm made it possible to reject dubious ones and not to throw away old soldered capacitors, but having a normal capacity and ESR. The device is easy to manufacture, parts are available and cheap, the thickness of the tracks allows them to be drawn even with a match.
In my opinion, the scheme is very successful and deserves repetition.

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▼ 🕗 25/09/11 ⚖️ 14.22 Kb ⇣ 668 Hello reader! My name is Igor, I'm 45, I'm a Siberian and an avid amateur electronics engineer. I came up with, created and maintain this wonderful site since 2006.
For more than 10 years, our magazine exists only at my expense.

Good! The freebie is over. If you want files and useful articles - help me!

To search for such capacitors, a device designed and manufactured by the author with high accuracy and resolution is proposed. For greater convenience of using the device, the possibility of its joint operation with almost any digital voltmeter (multimeter) is provided. Considering the affordability of prices for "folk" digital multimeters of the 8300 series, the proposed design is a kind of "find" for many radio amateurs, especially when you consider that the circuit does not contain any scarce or expensive components and even coil units.

Oxide (electrolytic) capacitors are used everywhere. They affect the reliability and quality of operation of radio electronic equipment (RES). In terms of quality and purpose, capacitors are characterized by many indicators. First, the performance and scope of capacitors were evaluated in terms of capacitance, operating voltage, leakage current, and weight and size indicators. The power has increased and the frequencies at which electrolytic capacitors are used have increased. Modern switching power supplies for RES have a power of tens to hundreds of watts (or more) and operate at frequencies of tens to hundreds of kilohertz. The currents flowing through the capacitors have increased, respectively, the requirements for their parameters have also increased.

Unfortunately, in mass production, quality indicators do not always meet the standards. First of all, this affects such a parameter as equivalent series resistance (ESR), or ESR. Not enough attention is paid to this issue, especially in amateur radio literature, although there are more and more malfunctions arising from the fault of EPS capacitors. It's a shame, but even among brand new capacitors, specimens with increased EPS are increasingly encountered.

Foreign capacitors are also no exception. As measurements have shown, the ESR value for capacitors of the same type can differ several times. Having an ESR meter at your disposal, you can select capacitors with the smallest ESR value for installation in the most critical device nodes.

We should not forget that electrochemical processes take place inside the capacitor, which destroy the contacts in the zone of connection of the plates with aluminum contacts. If the new capacitor has an overestimated ESR value, then its operation does not contribute to its reduction. On the contrary, EPS increases with time. As a rule, the more ESR the capacitor had before installation, the sooner its value will increase. The ESR of a faulty capacitor can increase from a few ohms to several tens of ohms, which is equivalent to the appearance of a new element - a resistor inside a faulty capacitor. Since thermal power is dissipated on this resistor, the capacitor heats up, and electrochemical processes in the contact zone proceed faster, contributing to a further increase in ESR.

Repair specialists of various RESs are well aware of the defects in switching power supplies associated with an increase in the ESR of capacitors. Measurement of capacitance with widely used instruments often does not give the desired results. Unfortunately, it is not possible to identify capacitors defective in terms of ESR with such devices (C-meters). The capacity will be within normal limits or only slightly lower. With an ESR value not exceeding 10 ohms, the readings of the capacitance meter do not give grounds for suspicion (such an ESR value practically does not affect the measurement accuracy), and the capacitor is considered serviceable.

Technical requirements for the EPS meter. Increased requirements for the quality of capacitors are primarily imposed in switching power supplies, where such capacitors are used as filters at frequencies up to 100 kHz or in switching circuits of power elements. The ability to measure ESR allows not only to detect failed capacitors (except in cases of leakage and short circuit), but also, which is very important, to make an early diagnosis of REM defects that have not yet manifested themselves. To be able to measure the ESR, the process of measuring the complex resistance of the capacitor is carried out at a sufficiently high frequency, where the capacitance is much less than the allowable value of the ESR. So, for example, for a capacitor with a capacitance of 5 μF, the capacitance is 0.32 ohms at a frequency of ) 00 kHz. As you can see, the capacitance even of a low-capacity electrolytic capacitor is many times less than the ESR of a defective capacitor. The ESR value of faulty capacitors with a capacity of up to 200 microfarads significantly exceeds 1 ohm.

By the value of ESR, one can confidently assess the suitability of a capacitor for certain purposes. When buying capacitors, using a portable ESR meter, you can choose the best copies. It is important that the ESR measurement process can be carried out without dismantling the tested capacitors. In this case, it is necessary that the capacitor is not shunted by a resistor having a resistance commensurate with the EPS. The maximum voltage on the probes of the device should be limited so as not to disable the elements of the REM being repaired. Semiconductor devices should not affect the readings of the EPS meter. This means that the voltage on the measured capacitor must be minimal in order to exclude the influence of the active elements of the RES.

When working in stationary conditions, the device must be operated from the mains (you can, for example, use an appropriate switch and an external power supply). To prevent reverse polarity of an external power supply or charger, protection must be provided. To prevent deep discharge of the batteries, cut-out protection or at least a battery voltage monitoring indication should be provided. To stabilize the parameters of the device, you must use the built-in voltage regulator. This stabilizer must meet at least two requirements: to be economical, i.e. have a low own current consumption, and provide a fairly stable output voltage when the input supply voltage changes in the range of at least 7 ... 10 V.

Of great importance is the indicator of the EPS readings. ESR meters with discrete indication, for example, on LEDs, are of little use for rejecting (selecting) capacitors from large batches and have huge errors in measuring ESR. EPS meters with non-linear scales cause problems with the implementation of the new scale, with the reading of indications and have a large measurement error. New circuits on programmable "chips" (microcontrollers), sadly to say, are not yet available to most radio amateurs. At the price of the microcontroller alone, you can purchase all the components for the manufacture of the EPS meter considered below.

As part of the EPS meter, it is convenient to have a pointer measuring device with a linear scale that does not require any alterations, using, for example, one common scale 0 ... 100 for all subranges of the device. During long and intensive work with the EPS meter, it is very convenient to use a digital scale. However, independent production of a digital device is not profitable due to the complexity of the design as a whole and the high cost. It is better to provide for the possibility of working the meter in conjunction with a widely used and cheap digital multimeter of the 8300 series, such as the M830B. Any other digital voltmeter with similar characteristics that has a DC voltage measurement range of 0 ... 200 mV or 0 ... 2000 mV will do. For the price of one microcontroller, you can purchase one or even two of these multimeters. The digital indicator of the ESR meter allows you to quickly sort out capacitors. The pointer (built-in) meter is useful in cases where there is no digital tester at hand.

Perhaps the most important parameter is the reliability of the device. And it, one way or another, depends on the human factor. What kind of device is it that fails if the capacitor being tested is not discharged? In a hurry, equipment repairers often discharge capacitors not with resistors, but with wire jumpers, which adversely affects the life of the electrolytic capacitors themselves. The device must not fail and discharge capacitors with extra currents.

The ESR meter must have a wide range of measurement of the ESR value. It is very good if it measures EPS from 10 ohms to almost zero. Measurement of ESR over 10 ohms is irrelevant, since specimens of electrolytic capacitors with such an ESR are already completely substandard, especially for operation in pulse circuits, especially at frequencies of tens to hundreds of kilohertz. It is convenient to have a device that allows you to measure ESR values ​​​​less than 1 Ohm. In this case, an "exclusive" opportunity is provided to select the best examples of capacitors among the best types with the largest capacity.

As the main power source, a battery was used, made up of disk nickel-cadmium batteries of the D-0.26D type. They are more reliable and energy-intensive than 7D-0.1. It is possible to recharge the batteries.

Specifications

• Ranges of measured resistances......0...1 Ohm, 0...10 Ohm
• Measuring signal frequency used..........77 kHz
• Supply voltage...........7... 15 V
• Consumed current, no more.......................4.5 mA

Schematic diagram of the EPS meter of electrolytic capacitors is shown in Fig.1. The design of the device is based on an ohmmeter operating on alternating current. It is not necessary to increase the frequency more than ] 00 kHz because of the upper cut-off frequency (100 kHz) of the K157DA1 chip detector, which is used in this device design, moreover, not all types of electrolytic capacitors are designed to operate at frequencies over 100 kHz.
The generator of the device is made on a DD1 chip of the K561TL1 type. The choice of this type of IC is due solely to considerations of increasing the efficiency of the device. In this situation, you can use other generators made on more common ICs, in particular on K561LA7 or K561LE5. This will increase the current consumption from the power supply.

The generator has two requirements: amplitude stability and frequency stability. The first requirement is more important than the second, since the change in the amplitude of the output voltage of the generator is a greater destabilizing factor than the change in frequency. Therefore, there is no need to use quartz resonators, as well as to accurately set the frequency, which is exactly 77 kHz. The operating frequency of the device can be selected within 60...90 kHz. Tuning and operation of the device must be carried out at the same operating frequency, since the stable parameters of the tuned device are stored in a rather narrow frequency range.

From the output of the generator, a rectangular signal is fed through the elements R17-R19, C8 to the tested capacitor Cx (terminals 1 and 2). From the capacitor Cx, the signal enters the amplifier, from the amplifier - to the detector, then rectified - to the pointer measuring device RA1 and a digital voltmeter (XS2 connector). The flow of current through the capacitor under test causes a voltage drop across it. To measure low resistances, a high sensitivity of the detector is required, not to mention its linearity. If you significantly increase the current flowing through the capacitor under test, then the current consumed from the power source will also increase sharply.

In the author's version, the current through the tested capacitor is approximately 1 mA, i.e. each millivolt of voltage drop corresponds to 1 ohm of the ESR of the capacitor. With ESR equal to 0.1 Ohm, it is necessary to deal with measuring voltages of 100 μV! Since this device is capable of measuring an order of magnitude smaller ESR values, we are already talking about tens of microvolts, which should be clearly recorded by the meter.
It is obvious that the signal must be amplified for the normal operation of the detector. This task is performed by an amplifying stage: on a low-noise transistor VT7, an amplifier is made according to the scheme with OE (the gain at the operating frequency is 20), on the transistor VT8, a buffer amplifier is made, assembled according to the scheme with OK.

Capacitor C9 is an element of the HPF. The selected capacitance value of the SU capacitor actually prevents the R24C10 circuit from operating at low frequencies. With such simple methods, a significant blockage of the frequency response in the bass region is realized. The drop in frequency response in the LF region is additionally formed by the choice of capacitances C1 and C12 in the detector circuit. In H interference is additionally limited by resistor R23 (protective elements are also taken into account).

In order for the tested capacitor (undischarged) not to disable the generator IC, protective elements VD1, VD2, R19 are provided in the circuit. A similar circuit, consisting of elements R22, VD3, VD4, protects the input of the amplifier. In the operating mode (when measuring ESR), the diodes practically do not have any shunting effect on the signal. When the capacitor under test Cx is disconnected from terminals 1 and 2, the diodes limit the signal amplitude at the amplifier input, although a signal of this level does not lead to amplifier failure. This device protection scheme, despite the simplicity of implementation, has confirmed its high efficiency in practice.

The EPS meter of electrolytic capacitors is unpretentious in operation. The values ​​of the resistors R19 and R22 are chosen in such a way as to ensure a reliable discharge of the tested capacitors that work in almost any household equipment. Therefore, protective diodes must effectively discharge the tested capacitors, and at the same time be reliably protected from overcurrent when the capacitors are discharged. The SA1.2 toggle switch section with the SA4 button and resistors R20 and R21 are used to calibrate the device.

The most difficult thing was the choice of the detector scheme. Here there were specific problems. Practical tests of many widely used diode detectors only confirmed their unsuitability for linear voltage detection in a wide range of amplitudes. Nothing suitable from a circuit design simple, implemented on discrete elements, on which one could rely, could not be found in the literature.

The very idea of ​​using the K157DA1 chip in the EPS meter detector arose by chance. I recalled that the IC type K157DA1 was widely used in indicators of the recording level of various domestic tape recorders. First of all, my attention was attracted by the relative simplicity of the circuit connection of this IC. The current consumed by the IC from the power source was also suitable, as was the appropriate operating frequency range. It is also allowed to operate this IC with unipolar power supply. However, the typical inclusion K157DA1 is not suitable in this case. As a result, it was necessary not only to modify the IC switching circuit in comparison with the typical one, but also to change the values ​​\u200b\u200bof the strapping elements several times.

This IC incorporates a two-channel full-wave rectifier. The second channel in the considered design is not used. Prototyping confirmed the linearity of IC detection at frequencies up to 100 kHz. Some copies of the IC even had a certain margin for the upper cut-off frequency (two of the ten tested ICs - up to 140 kHz). A further increase in frequency caused a sharp decrease in the rectified voltage of the IC. The non-linearity of IC detection manifested itself at the minimum signal levels and at a significant amplification of the IC. The quiescent output voltage (at pin 12 of the IC) was no less annoying, which, according to the reference data, can reach 50 mV, which could not be reconciled with if it was already decided to make a measuring device, and not an EPS indicator.

Some time later, this problem was successfully overcome. Between the pins of the microcircuit 14 and 2, a resistor R3 with a resistance of 33 kOhm is installed in a typical connection. It is connected to the artificial midpoint of a voltage divider formed by resistors R1 and R2 (Fig. 1). This is an option for using ICs with a unipolar power supply.

As it turned out later, the linearity of detection is significantly dependent on the value of the resistance of the resistor R3 precisely in the region of small amplitudes. Reducing the resistance R3 by several times provides the necessary linearity of the detector, and, no less important, the resistance of this resistor also affects the value of the DC quiescent voltage (pin 12 of the IC). The presence of this voltage makes it difficult to carry out measurements normally at low ESR values ​​(you will have to deal with the mathematical operation of subtraction with each measurement). Hence the importance of setting the "zero* potential at the output of the detector.

The correct choice of resistor R3 practically eliminates this problem. In the proposed version, the resistance of the resistor is more than three times less than the typical rating. It makes sense to further reduce the value of this resistance, but in this case, the input resistance of the detector is also significantly reduced. It is now almost completely determined by the resistance of the resistor R3.

On transistors VT1 and VT2, protection is made for the pointer meter RA1. Such inclusion of transistors provides a clear response threshold and does not shunt the PA1 head at all in the range of PA1 operating currents, which increases its reliability and increases its service life.

Switch SA3 is used for operational control of the battery voltage and allows you to measure it under load, i.e. directly during operation of the device. This is important because for many batteries over time, even with a deep discharge (no load), the voltage may be normal or close to the nominal, but it is worth connecting a load, even a few milliamps, as the voltage of such a battery drops sharply.
On transistors VT3-VT6, a micropower voltage regulator (CH) is made, which feeds all the elements of the device. When using an unstabilized power source, all instrument parameters change. Reducing the voltage (discharging) of the battery also significantly "knocks down" the entire setting. The detector, by the way, turned out to be the most resistant to changes in the supply voltage. The most dependent on the supply voltage (the amplitude of the rectangular voltage varies greatly) is the generator, which makes it impossible to operate the device.
The use of a microchip CH causes irrational current consumption by the stabilizer itself, so it soon had to be abandoned. After experimenting with various circuits on discrete elements, the author settled on the CH circuit shown in Fig.1. In appearance, this CH is very simple, but its presence in this circuit is quite enough for all the technical parameters of the EPS meter to remain stable when the battery voltage changes from 7 to 10V. At the same time, it is possible to power the device from an external power supply unit, even an unstabilized one, with a voltage of up to 15 V.

Own power consumption CH is determined by the value of the collector current of the transistor VT6 and was selected within 100...300 μA. An analogue of a low-power zener diode is made on the VT6 transistor. Its voltage determines the value of the output voltage CH, which is less than the stabilization voltage of the zener diode by the value of the base-emitter transition voltage of the transistor VT3.

Details. Resistors R1-R3, R5, R7, R15, R29 -10 kOhm, R4, R6, R8, R10, R11, R13, R24, R30-1kOhm, R9-39kOhm, R12-100 Ohm, R14-680 kOhm, R16 - 100 kOhm, R17, R25 - 2.4 kOhm, R18 - 4.7 kOhm, R19, R22 - 330 kOhm, R20 -1 Ohm, R21 - 10 Ohm, R23 - 3.3 kOhm, R26 - 150 kOhm, R27 - 820 kOhm, R28 - 20 kOhm. Capacitors C1, C3, C6, C10, C12 - 0.1 uF, C2, C4, C5, C11 - 5 uFx16 V, C7 -150 pF, C8 - 0.47 uF, C9-0.01 uF.

Resistors R4, R10, R16, R17, R20, R21, R24, R25 type C2-13, tuning resistors type SP-38V, the rest - MLT. Capacitor C7 type KSO-1; C1, C3, C6, C9 - K10-17, the rest K73-17 and K50-35. Transistors VT2, VT3, VT7 type BC549C. In position VT7, a transistor with a maximum h21e should be used. VS549 transistors are interchangeable with domestic KT3102 or KT342. Transistors VT1, VT4, VT8 type BC557C. Instead of them, domestic KTZ107 (K, L) were also used. KP10ZE was used as a field effect transistor in the stable current generator. Capacitor C6 is soldered on the side of the printed conductors, directly on the terminals DD1. Resistor R24 ​​on the amplifier board is conventionally not shown. It is soldered in series with capacitor C10.

Diodes VD5, VD6 - KD212, VD1-VD4 -1 N4007. There are no special requirements for the VD6 diode, it can be any silicon. Diode VD5 must withstand the maximum charging current of the batteries. The situation is different with diodes VD 1-VD4. If the input of the device will not be connected to the TV power supply module (its electrolytic capacitor) that has just been turned off, then instead of 1 N4007, you can install D220, D223, KD522, etc. As these diodes, instances with minimal capacitances and a permissible current of more than 1 A are best suited.

Switch SA1 type MT-3, SA2, SA3 -MT-1, SA4 - KM2-1. The small-sized pointer measuring device is designed for a current of 100 μA and has an internal resistance of 3 kOhm. With success, almost any pointer measuring instruments for a current of 100 μA will fit. With a higher current, a corresponding reduction in the values ​​​​of resistors R7 and R8 will be required.

Design. The task of creating a miniature device was not set; it was necessary to place the device and the D-0.26D battery in a plastic case measuring 230x80x35 mm. The device is structurally made on four separate printed circuit boards. The amplifier board and the location of parts on it are shown in Fig. 2, the generator board and the location of parts on it - in Fig. 3, the voltage regulator board and the location of parts on it - in Fig. 4, the detector board and the location of parts on it - in Fig. .5.

This version of the device is caused by the replacement of individual blocks with new ones as a result of the experiments and upgrades of the device. Modular-block design always leaves a chance to "retreat". In this embodiment, it is much easier to upgrade or repair. After all, it is easier to replace one small block than to re-create a new design on one large printed circuit board. Before being placed in the specified case, the dimensions of all the boards were reduced (the boards were carefully cut with metal scissors).

In order to ensure the possibility of measuring the minimum resistance values, it is necessary to minimize the resistance connecting the input of the device with Cx. To do this, it is not enough to use short wires. The device is mounted in such a way that the common wires of the generator circuits, the amplifier and the connection point Cx are at a minimum distance from each other.

Poor installation will easily disrupt the normal operation of the device in the 1 ohm range, turning it into a very inconvenient and mediocre meter in this range. It is for the sake of this range that the author undertook the development of this device, since it is possible to implement the "traditional" ESR measurement range using simpler schemes. The range of 0 ... 1 Ohm allows you to very quickly "deal" with such capacitors as 10,000 microfarads or more.

Setting. Despite the presence in the circuit of six tuning resistors and other elements that require selection, setting up the device is not a difficult process. Initially, the sliders of all tuning resistors are set to the position corresponding to the maximum resistance. At the time of tuning, multi-turn resistors of the SP5-3 type were used, although the printed circuit boards were developed for the SP-38V version. After setting up the device, they were all replaced by fixed resistors.

The setting starts with CH. A resistor MLT-0.25 with a resistance of 1.2 kOhm is connected to the CH output. By selecting the resistor R13, the minimum possible current through the transistor VT6 is reached, at which the CH maintains stable operation at an input voltage of 7 to 15 V. You should not get involved in an excessive decrease in this current. Its recommended value is 100...500 µA. After setting this current, proceed to the selection of the resistor R14. The output voltage of the CH depends on it, the value of which was set within 6 ... 6.3 V. You can additionally reduce the voltage drop across the CH by replacing the resistor R12 with a wire jumper (after setting up the entire device). However, the MV then loses its current limitation in case of abnormal situations in the MV load.

Setting up the amplifier on transistors VT7, VT8 consists in selecting the resistance of the resistor R24 ​​to achieve a voltage gain of approximately 20 times (at the operating frequency). The accuracy of the specified value is not important here. Much more important is the stability of the gain, which most of all depends on the stability of the elements C10, R24, R25, VT7. Shown in the diagram in Fig. 1 position of the switch contacts SA1 corresponds to the range of 10 ohms. Close the contacts of the SA4 pushbutton switch. Thus, instead of the capacitor Cx, a highly stable calibration resistor R21 with a resistance of 10 ohms is connected to the input of the device. Then, resistor R18 sets a voltage of 10 mV across resistor R21 (and 200 mV, if necessary, by selecting R24 on the VT8 emitter). Reducing the resistance of the resistor R5, set the arrow of the meter RA1 to the final mark of its scale (100 μA). Trimmer resistor R11 set the readings of a digital voltmeter 100mV. If necessary, reduce the resistance of the resistor R7. The presence of calibration resistors allows you to quickly evaluate the performance of a well-established device.

It is also necessary to decide on the adjustment of the PA1 protection unit. This scheme has its own subtleties. In order not to install any additional elements - indicators of turning on the device (which certainly consume electricity, spent time and complicate the circuit), the author used the "hysteresis" of the protection circuit in terms of indicating the inclusion of the device. Using resistor R8, the protection operation current is set to 130 ... 150 μA.

After the protection is triggered (both transistors are open), the arrow PA1 returns to a certain average position of the scale. By changing the resistance R8, it is possible to achieve such an on state of the transistor VT2 that the arrow of the RA1 device can be "pulled" into almost any working section of the RA1 scale. This state of the protection node circuit is very stable, requiring no subsequent adjustment. In many ways, the circuit owes this to the use of these types of transistors.

The position of the arrow in the working sector does not interfere with measurements, since the protection is not tied to the value of the working current RA1. Shorting the terminals Cx of the device or connecting a serviceable capacitor Cx immediately causes the arrow to be set to the position corresponding to the value of the measured resistance. And only an overestimated value of the current through PA1 again activates the protection. Such remarkable protection can be equipped with many measuring instruments. The protection is set up once and the resistance of the resistor R8 is not changed more. Otherwise, additional adjustment of the device will be required due to a change in the total resistance of resistors R7 and R8.
Next, switch the SA1 switch to the position corresponding to the 1 ohm range. In the same way as when setting up the device in the 10 Ohm range, but more carefully, the SA4 leads are shorted. Despite the fact that precision calibration resistors were used in the design, they had to be selected. The reason for this was the presence of significant resistance introduced by wires and contacts SA4, SA 1.2. Therefore, in the range of 1 Ohm, when setting, the contacts of both switches are already closed (with a button, the adjustment is inconvenient, so its contacts were short-circuited even when setting in the range of 10 Ohms). The fact is that the device easily fixes the transient resistance of the contacts of switches SA1.2 and SA4.

In this circuit, contacts SA1 and SA4 carry almost no current load. For this purpose, a push-button version of the SA4 design was used, which actually excludes the supply of energy from an undischarged capacitor Cx to these switches. This means that their transient resistances will be long-term stable. As a result, they can be stably "neutralized" by reducing the resistances R20, R21. In the author's version of the device, a 22 Ohm resistor (MLT-0.5) is connected in parallel with R20 and a 130 Ohm resistor (MLT-0.5) is connected in parallel with R21.

Adjustment operations are repeated to ensure maximum measurement accuracy on both ranges. Of course, the device should not indicate completely different readings on different ranges with the same connected capacitor Cx. In the range of 1 ohm, the setting requires setting the voltage on the digital voltmeter display to 100 mV using the tuning resistor R6. Since this resistor is connected in parallel with resistor R5, we should not forget about the dependence of the 1 ohm range setting on the 10 ohm setting. This switching option is simpler in circuitry and in practice (instead of three wires, only two are suitable for the board). Last of all, the value of the resistor R9 is selected so that 100mV on the digital multimeter corresponds to 10V of the battery voltage.

Instrument upgrade. If the device is needed only for stationary operating conditions, then the CH is removed from the circuit. With the exclusion of the pointer meter RA1, the circuit is also simplified, the elements R8, VT1, VT2 are removed. Instead of the resistor R8, a wire jumper is installed. This option (without the PA1 meter) allows you to slightly reduce the power consumption of the device due to the detector circuit. After removing the pointer head, given the large input impedance of the digital tester, the values ​​of the resistors R7, R10, R11 are increased by 10 times. Thus, the output of the IC is unloaded, which favorably affects the operation of the IC. Capacitor C4 is replaced by non-electrolytic K10-17-2.2 uF. However, in order to increase the reliability of the device, all electrolytic capacitors were subsequently replaced by non-electrolytic ones (K10-17-2.2 μF).

In the case of sharing this device with a digital multimeter having a range of 0 ... 200 mV or 0 ... 2000 mV, it is easy to expand the range of measured resistances "up", i.e. up to 20 ohm. You just need to re-select the values ​​​​of the elements R7 and R10.

Clarification. In the specification of the parts used in the device, which is given in the first part of the article (RA 3/2005, p. 24, 3rd column, 3rd paragraph from the top), the resistance of the resistors R19, R22 should not be 330 kOhm, but 330 Ohm. We apologize.

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