Do-it-yourself capacitor capacitance meter. Description and configuration of the device

DIY capacitor capacitance meter- below is a diagram and a description of how, without much effort, you can independently make a device for testing the capacitance of capacitors. Such a device can be very useful when buying containers in the electronic market. With its help, a low-quality or defective element of the accumulation of an electric charge is detected without problems. The schematic diagram of this ESR, as most electronics engineers usually call it, is nothing complicated and even a novice radio amateur can assemble such an apparatus.

Moreover, the capacitor capacitance meter does not imply a long time and large financial costs for its assembly; it takes literally two to three hours to manufacture a probe of equivalent series resistance. Also, it is not necessary to run to the radio store - for sure, any radio amateur will have unused parts suitable for this design. All you need to repeat this circuit is a multimeter of almost any model, it is only desirable that it be digital and with a dozen parts. There is no need to make any alterations or modernization of the digital tester, all that needs to be done with it is to solder the leads of the parts to the necessary sites on its board.

Schematic diagram of the ESR device:

The list of elements required for the assembly of the meter:

One of the main components of the device is a transformer, which should have a ratio of turns 11/1. Ferrite ring core M2000NM1-36 K10x6x3, which must first be wrapped with insulating material. Then wind the primary winding on it, arranging the turns according to the principle - turn to turn, while filling the entire circle. The secondary winding must also be carried out with a uniform distribution around the entire perimeter. The approximate number of turns in the primary winding for the K10x6x3 ring will be 60-90 turns, and the secondary should be eleven times less.

You can use almost any silicon diode with a reverse voltage of at least 40v, if you don’t really need super accuracy in measurements, then the KA220 is quite suitable. For a more accurate determination of the capacitance, you will have to put a diode with a small voltage drop in the direct connection option - Schottky. The protective suppressor diode D2 must be rated for reverse voltage from 28v to 38v. Low-power silicon p-n-p transistor: for example, KT361 or its equivalent.

Measure the EPS value in the voltage range of 20v. When the external meter connector is connected, the ESR add-on to the multimeter immediately enters the capacitance test operation mode. In this case, a reading of about 35v will be visually displayed on the device in the test range of 200v and 1000v (this depends on the use of a suppressor diode). In the case of a capacitance test at 20 volts, the reading will be displayed as “out of measurement limit”. When the connector of the external meter is disconnected, the EPS set-top box instantly switches to the mode of operation as an ordinary multimeter.

Conclusion

The principle of operation of the device - to start the device, you need to connect the adapter to the network, while the ESR meter turns on, when the ESR is turned off, the multimeter automatically switches to the standard functions. To calibrate the device, you need to select a constant resistor so that it matches the scale. For clarity, the picture is below:

When the probes are shorted, 0.00-0.01 will be displayed on the multimeter scale, this reading means the instrument's error in the measurement range up to 1 ohm.

Masters repairing radio equipment most often encounter a breakdown of capacitors or a decrease in capacitance. To find out if the part is working or not, you need to measure the capacitance of the capacitor. There are various devices for this.

The device and characteristics of the capacitor

The capacitor contains two metal plates, between which a dielectric is placed. Air, plastic, mica, cardboard, ceramic materials are used for the dielectric.

In more modern parts, instead of metal, foil is used, which is rolled up. Thus, with smaller dimensions of the capacitor, it is possible to increase its capacitance.

Capacitors are classified according to dielectric material, mounting methods, plate shape, etc. By polarity, they are divided into:

electrolytic, or oxide, having polarity;
nonpolar.

Electrolytic capacitor elements require obligatory observance of polarity when turned on. The dielectric in them is an oxide layer formed on a tantalum (aluminum) anode. The cathode is an electrolyte in the form of a liquid or gel. The measurement of the capacitance of this type of capacitor must be carried out, taking into account the marking of the poles of the part.

The main property of a capacitor is the accumulation of an electric charge, due to which it is widely used in various filters. With it, you can transfer a signal between amplification stages, separate high and low frequencies, etc.

Capacitor parameters:

Capacity. The ability to accumulate a charge, depending on the area of the plates, the distance between them, the nature of the material used as an electrolyte. Measured in farads;
Rated voltage. Shows at what voltage long and stable operation of the element is possible. If the parameter is exceeded, breakdown may occur.

Possible Capacitor Faults

There are several types of capacitor failures that affect the operation of the electrical circuit:

complete breakdown (short circuit between the plates);
violation of external tightness from mechanical damage;
capacity reduction;
increase in internal resistance;
a decrease in voltage at which a reversible breakdown of the element occurs.

In most cases, parts fail due to prolonged operation in conditions of overheating. It is always important to ensure the optimal temperature regime for the operation of the equipment.

How to check the health of the capacitor

At the first stage, it is necessary to make a visual inspection of the part for mechanical damage, body deformation, color changes. For electrolytic cells, this is swelling in the upper part, which may be small, but noticeable in comparison with serviceable counterparts. Most of the time, the part looks normal on the outside. Then, to check it, special devices will be required:

a multimeter with a capacitance measurement function;
a special capacitor capacitance meter;
LC meter;
ESR device.

Using a multimeter, it is sometimes difficult to make a conclusion about a malfunction, since the capacitance of a damaged capacitor element is reduced by very small amounts. With the help of LC meters or special devices, its value can be determined more accurately. ESR instruments are used to measure the capacitance of electrolytic capacitors. Moreover, measurements are made without soldering parts from the circuit.

If there is no special device, then capacitive measurements of non-polar elements can be made with a multimeter that measures resistance. At the same time, they are soldered out of the board.

On the scale of the multimeter, set the limit to "200 kOhm". The scale limit varies depending on the capacitance rating;
Discharge the soldered capacitor elements, as there may be a residual charge. The discharge is produced by short-circuiting their terminals;
Connect the probes of the device to the capacitor terminals and observe its readings. Try not to touch the contact part of the probes with your hands.

The resistance value that appears on the screen will gradually increase, and then show “1”, which means “infinity” on a digital device. For capacitors with a small capacitance, the process of changing the resistance is accelerated so that it can not be fixed.

Important! A properly charged capacitor element has "infinite" resistance.

If the part is faulty, immediately, without a previous increase, the values \u200b\u200bof "1" will be visible, indicating a break inside the part, or "0" - an internal short circuit. A smooth increase in resistance is observed due to the charging of the part from the multimeter battery.

You can also use old analog testers for capacitive measurements. At the same time, observations are made of the movements of the arrow. It should immediately deviate to the right with a speed depending on the capacitance, continuing its slow movement to the limits of the scale. If she does not twitch or, having deviated, stops, this indicates damage. The same is signaled by a sharp throw to the limit figures.

Important! Capacitor elements with a capacity of up to 0.25 microfarads can be tested with a multimeter. For smaller parameters, the test is carried out on LC meters.

Measurement of actual capacitive values

Using the method described above, it is impossible to determine quantitative capacitive values, one can only conclude that the capacitor element is in good condition. According to instruments that measure capacitance in farads, its deviation from the nominal parameter is immediately determined. A zero value indicates a breakdown, a reduced value also signals that the part needs to be replaced.

Indirectly, the value of capacitance can be judged by the rate of increase in resistance at the time of connection to the multimeter. The lower it is, the greater the capacity. You can calculate its approximate value by connecting serviceable capacitor elements with a previously known capacitance and measuring the time in seconds for which the resistance reaches "infinity". The conclusion is made on the basis of a comparison with the tested capacitor element.

On the front panel of a multimeter designed for capacitive measurements, there are special CX input connectors marked "plus" and "minus". Ordinary probes may be present instead. For measurement, capacitor elements are inserted into these connectors with the obligatory observance of the polarity of the electrolytic parts. Marking is also present on the capacitors themselves. For non-polar elements, this does not matter. The limit value of the scale of the measured capacitance must be set based on the capacitor parameters.

Important! Before connecting to the device, it is necessary to remove the residual charge from the capacitor.

ESR measurement

ESR stands for Equivalent Series Resistance, a very important parameter for an electrolytic capacitor. When this resistance increases, the charging current decreases, causing the electrical circuit to malfunction. Moreover, the capacity measured by traditional methods may not go beyond the limits of the norm. Especially the effect of equivalent resistance is noticeable in parts with a capacity of more than 5 microfarads. For stable operation, the parameter should not exceed 1 ohm.

When checking capacitor elements without desoldering from the board, such an apparatus gives more accurate results. Attempts to similarly measure the parameters of a part with a multimeter will not give a reliable picture. Next to the capacitor, there are other elements: inductances, resistances, etc., which introduce a distorting effect. Usually, a conclusion is made about the health of the capacitor element using indirect measurements, or another one with identical characteristics is soldered in parallel with it. This is only possible in low voltage circuits.

Capacitor Breakdown Voltage Reduction

Radio amateur masters may encounter a case when all the characteristics of the capacitor are normal when measured with a multimeter, but when working in the circuit, there are signs of its breakdown. This occurs when the breakdown voltage drops below the nominal value. If the part is designed for a voltage of 25 V, and the breakdown occurs at 15 V, then when measuring with a multimeter, a malfunction of the capacitor element will not be detected, since the breakdown is reversible.

To determine such a malfunction, it is necessary to use a constant current source with the ability to regulate the voltage level. By connecting a part to it and gradually increasing the input voltage, it turns out the presence of damage, noticeable by a sharp increase in current until the protective shutdown of the power supply is triggered.

Measurements of capacitance can be carried out in different ways. You can simply detect a faulty element with an ohmmeter, more accurate results are obtained using LC meters and ESR devices.

Video

From the title of the article it is clear that today we will talk about a device for measuring the capacitance of capacitors. Not every simple multimeter has this feature. But when making another homemade product, we very often think: will it work, are the capacitors that we used in good condition, how to check them. Yes, and just during the repair process, this device will be needed. Of course, you can check the integrity of the electrolytic capacitor with a tester. But we will find out whether it is alive or not, but we will not be able to determine the capacity, how dry it is.

Some cheap multimeters on the market today have this feature. But the measurement limit is limited to 200 microfarads. Which is clearly not enough. You need at least four thousand microfarads. But such multimeters cost an order of magnitude higher. So I finally decided to buy capacitor capacitance meter. I chose the cheapest with acceptable characteristics. I opted for the XC6013L:

This device comes in a beautiful box. True, on the box is an image of another multimeter:

And on top is a sticker with a model of this device, probably the Chinese do not have enough boxes:

The device is enclosed in a protective yellow casing made of soft plastic, similar to rubber. The hands feel weighty, which indicates the seriousness of the device. On the bottom side there is a folding stand, which may not be useful to many:

The capacitance meter is powered by a 9 volt krone battery, which is supplied in the kit:

The characteristics of the device are simply amazing. It can measure from 200 picofarads to 20,000 microfarads. Which is quite enough for amateur radio purposes:

On top of the device is a large and informative LCD display. Below it are two buttons. On the left is a red button, with which you can fix the current capacity reading on the display. And on the right is a blue button, which made me very happy, with a screen backlight, which is undoubtedly a plus of this device. Between the buttons there is a connector for measuring small capacitors. True, it is impossible to check bush capacitors soldered from donor boards, since the pads are located quite deep. Therefore, this connector can only be used when checking capacitors with long leads:

Under the measuring range selector there is a connector for connecting probes. By the way, the probes are made of the same material as the protective casing of the device; they are quite soft to the touch:

Undoubtedly, the most important function of the device is also located there - this is the setting of zero readings when measuring capacitances in the picofarad discharge. This is clearly seen in the following two photos. Here, one probe is deliberately removed and zero is set using the regulator:

Here the dipstick is in place. As you can see, the capacitance of the probes affects the readings. Now it is enough to set zero with the regulator and take measurements, which will be quite accurate:

Now let's test the device in operation and see what it is capable of.

Testing a capacitor capacitance meter

To begin with, we will check capacitors that are known to be good, new and removed from donor boards. The first will be a test subject at 120 microfarads. This is a new copy. As you can see, the readings are slightly underestimated. By the way, I have 4 such capacitors, and none of them showed 120 microfarads. Possible device error. Or maybe they are doing one non-standard now:

Here is one thousand microfarads, quite accurately:

Two thousand two hundred microfarads, not bad either:

And here are ten microfarads:

Well, now a hundred microfarads, very good:

Let's look at the readings of the device, which it will show when checking for defective capacitors that were removed during the repair. As you can see, the difference is noticeable:

Here are the results. Of course, in some cases, the malfunction of the electrolytic capacitor is visible visually. But in most cases, it is difficult to do without a device. In addition, I tested this device on two boards, checking the capacitors without soldering them. The device showed good results, only in some cases it is necessary to observe the polarity. Therefore, I advise you to buy such a device, and you can measure the capacitance of capacitors with your own hands.

Almost two years ago I bought a digital capacitance meter, I took, one might say, the first thing that came across. I was so tired of the inability of the Mastech MY62 multimeter to measure the capacitance of capacitors more than 20 microfarads, and it did not measure correctly less than 100 picofarads. I liked two factors in the SM-7115A:

Measures the entire required range
Compactness and convenience

Paid 750 rubles. He sincerely believed that he was not worth the money, and the price was "inflated" due to the complete absence of competitive products. The country of origin is, of course, China. He was afraid that he would “fake”, more than that he was sure of this - but in vain.

The capacitance meter and wires to it were packed in polyethylene, each in its own sheath and enclosed in a box of thick cardboard, the free space was filled with foam. Also in the box was an instruction in English. Overall dimensions of the device 135 x 72 x 36 mm, weight 180 grams. The body color is black, the front panel with a lilac tint. It has a liquid crystal indicator, nine measurement ranges, two power off positions, a zero setting regulator, 15 cm, different colors (red - black) wires, with which the measured capacitor is connected to the device, ends with crocodile clips, and sockets on the device case , for their connection, are marked with a color designation of the corresponding polarity, it is additionally possible to measure without them (which increases the accuracy), for which there are two oblong sockets, which are signed with the symbol of the measured capacitor. A 9 volt battery is used, there is a function for automatically indicating its discharge. Three-digit liquid crystal indicator +1 decimal place, the measurement range declared by the manufacturer is from 0.1 pF to 20,000 μF, with the possibility of adjustment on the measurement range from 0 to 200 pF, to set zero, within +/- 20 pF, one measurement time 2-3 seconds.

Table of permissible errors in measurements, individually by ranges. Provided by the manufacturer.

There is an integrated stand on the back half of the case. It makes it possible to place the meter more compactly at the workplace and improves the visibility of the liquid crystal indicator.

The battery compartment is made completely autonomously, to change the battery, it is enough to move its cover to the side. Convenience from the category of inconspicuous, when it is.

In order to remove the back cover of the case, it is enough to unscrew one self-tapping screw. The heaviest PCB component is the 500mA fuse.

The operation of the measuring device is based on the method of double integration. It is assembled on logical counters HEF4518BT - 2 pcs, key HEF4066BT, decimal counter with decoder HCF4017 and smd transistors: J6 - 4 pcs, M6 - 2 pcs.

Having unscrewed six more screws, you can see the other side of the printed circuit board. The variable resistor with which the setting is made to "0" is so that it can be easily replaced if necessary. On the left are the pins for connecting the measured capacitor, those above are for direct connection (without wires).

The device is set to the zero reference point not immediately, but the set reading holds. With the wires disconnected, this is much easier to do.

For a visual demonstration of the difference in measurement accuracy with different measurement methods (with and without wires), I took small capacitors with factory markings - 8.2 pF

Video review of the device

Without wires With wires
#1 8 pF 7.3 pF
#2 7.6pF 8.3pF
#3 8.1 pF 9.3 pF

Everything is clear, unambiguously without wires, measurements will be more accurate, although the discrepancy is practically within 1 pF. I also repeatedly measured the capacitors on the boards - the measurement readings of the serviceable ones are quite adequate according to the denomination indicated on them. If not to be a very big nitpick, then it is quite possible to say that the quality factor of the measurement of the device is quite high.

Disadvantages of the device

setting to zero is not done immediately,
the petals of the contacts, for measuring without wires, have no elasticity, after unclenching they do not return to their original position,
The meter is not equipped with a calibration container.

conclusions

In general, I am satisfied with the device. It measures well, it is compact (it easily fits in a pocket), so on the radio market I take not what they give, but what I need. I plan, as there will be time, to finalize: to replace the potentiometer and contacts for direct measurement. His scheme, or something similar, can be searched in the section. He told “everything as it is”, and you already decide for yourself whether it is worth replenishing your home laboratory with such a device. Author - Babay.

This circuit, despite its apparent complexity, is quite simple to repeat, since it is assembled on digital microcircuits and, in the absence of errors in installation and the use of known-good parts, practically does not require adjustment. However, the capabilities of the device are quite large:

measurement range - 0.01 - 10000 uF;
4 subranges - 10, 100, 1000, 10,000 uF;
subrange selection – automatic;
result indication – digital, 4 digits with floating decimal point;
measurement error - unit of the least significant digit;

Consider the device circuit:

click to enlarge

On the DD1 chip, more precisely on its two elements, a crystal oscillator is assembled, the operation of which does not require explanation. Next, the clock frequency goes to the divider, assembled on microcircuits DD2 - DD4. Signals from it with frequencies of 1000, 100, 10 and 1 kHz are sent to the DD6.1 multiplexer, which is used as an automatic subband selection node.

The main measurement unit is a single vibrator assembled on elements DD5.3, DD5.4, the pulse duration of which directly depends on the capacitor connected to it. The principle of capacitance measurement is to count the number of pulses during the operation of a single vibrator. On the elements DD5.1, DD5.2, a node is assembled to prevent bounce of the contacts of the "Start measurement" button. Well, the last part of the circuit is a four-digit line of binary-decimal counters DD9 - DD12 with output to four seven-segment indicators.

Consider the algorithm of the meter. When the SB1 button is pressed, the DD8 binary counter is reset and switches the range node (DD6.1 multiplexer) to the lowest measurement range - 0.010 - 10.00 uF. In this case, one of the inputs of the electronic key DD1.3 receives pulses with a frequency of 1 MHz. An enabling signal from a single vibrator passes to the second input of the same switch, the duration of which is directly proportional to the capacitance of the measured capacitor connected to it.

Thus, pulses with a frequency of 1 MHz begin to arrive on the counting decade DD9 ... DD12. If a decade overflow occurs, then the transfer signal from DD12 increases the DD8 counter by one and allows zero to be written to the DD7 trigger at input D. This zero turns on the DD5.1, DD5.2 shaper, and it, in turn, resets the counting decade, sets DD7 again to "1" and restarts the one-shot. The process is repeated, but a frequency of 100 kHz is now supplied to the counting decade through the switch (the second range has turned on).

If, before the end of the pulse from the one-shot, the counting decade is overflowed again, then the range changes again. If the single vibrator turned off earlier, then the count stops and you can read the value of the capacitance connected for measurement on the indicator. The final touch is the decimal point control block, which indicates the current measurement subrange. Its functions are performed by the second part of the DD6 multiplexer, which illuminates the desired point, depending on the included subband.

IV6 vacuum fluorescent indicators are used as indicators in the circuit, so the power supply of the meter must produce two voltages: 1 V for incandescence and +12 V for anode power supply of lamps and microcircuits. If the indicators are replaced by LCDs, then one + 9V source can be dispensed with, while the use of LED matrices is impossible due to the low load capacity of the DD9 ... DD12 microcircuits.

It is better to use a multi-turn resistor as a calibration resistor R8, since the measurement error of the device will depend on the accuracy of the calibration. The remaining resistors can be MLT-0.125. As for microcircuits, any of the K1561, K564, K561, K176 series can be used in the device, but it should be borne in mind that the 176 series is very reluctant to work with a quartz resonator (DD1).

Setting up the device is quite simple, but it should be done with great care.

Temporarily disable the SB1 button from DD8 (pin 13).
Apply rectangular pulses with a frequency of approximately 50-100 Hz to the connection point of R3 with R2 (any simplest generator on a logic chip will do).
In place of the measured capacitor, connect an exemplary one, the capacitance of which is known and lies in the range of 0.5 - 4 μF (for example, K71-5V 1 μF ± 1%). If possible, it is better to measure the capacitance using a measuring bridge, but you can also rely on the capacitance indicated on the case. Here you need to keep in mind that how accurately you calibrate the device, so it will measure you in the future.
Using the trimmer resistor R8, set the indicator readings as accurately as possible in accordance with the capacitance of the reference capacitor. After calibration, it is better to lock the tuning resistor with a drop of varnish or paint.

Based on the materials of "Radio amateur" No. 5, 2001.