Multimeter attachment – ESR meter
It is no secret that most of the failures of modern equipment are caused by oxide capacitors. This is not only a breakage, loss of capacitance, short circuit, but also a defect expressed as an increase in the capacitor’s active component.
An ideal capacitor operating on alternating current should have only reactive (capacitive) resistance. The active component should be close to zero. Actually, a good oxide (electrolytic) capacitor should have an active resistance (ESR) of no more than 0.5-5 ohms (depends on the capacitance and nominal voltage). Practically, in equipment, which has worked for several years, it is possible to meet a seemingly serviceable capacitor with capacity of 10 μF with ESR up to 100 Ohm or more. Such a capacitor, in spite of the presence of capacitance, is not good and is most likely the cause of malfunction or poor performance of the apparatus in which it operates.
Figure 1 shows a diagram of a multimeter attachment for measuring the ESR of oxide capacitors. In order to measure the active component of the capacitor resistance, it is necessary to choose a measurement mode in which the reactive component is very small. As you know, the reactive capacitance decreases with increasing frequency. For example, at a frequency of 100 kHz with a capacitance of 10 μF the reactive component will be less than 0.2 Ohm. That is, by measuring the resistance of an oxide capacitor with a capacity of more than 10 μF by its AC voltage drop at a frequency of 100 kHz or more, it can be stated that. with a given error of 10-20%, the measurement result can practically only be taken as the value of the active resistance. And so, the circuit shown in Figure 1 is a 120 kHz pulse generator, made on the D1 chip logic inverters, a voltage divider consisting of resistors R2, R3 and the capacitor CX under test, and an AC voltage meter at CX, consisting of detector VD1-VD2 and a multimeter included in the measurement of small DC voltages. The frequency is set by the circuit R1-C1. The element D1.3 is a matching element, and the output stage is made on elements D1.4-D1.6.
By adjusting the resistance R2 the device is adjusted. Since in the popular M838 multimeter there is no mode of measuring small alternating voltages (and this is the device with which the author works), in the circuit of the probe there is a detector on germanium diodes VD1-VD2. The multimeter measures the DC voltage at C4. The power supply is a “Krona”. This is the same battery as the one used to power the multimeter, but the device must be powered from a separate battery. The parts of the device are assembled on a printed circuit board, the layout and location of parts of which are shown in Figure 2. Structurally, the set-top box is made in one case with a power supply. The multimeter’s own probes are used for connection to the multimeter. The housing is an ordinary soapbox. From the points X1 and X2 are made short probes. One of them is rigid, shaped like an awl, and the other is flexible, not more than 10 cm long, shanked with the same pointed stylus. These probes can be connected to capacitors, both unassembled and located on the board (there is no need to unsolder them), which greatly simplifies the search for a defective capacitor when repairing. It is desirable to pick up “crocodiles” to these probes for the convenience of checking unassembled (or dismantled) capacitors.
Microcircuit K561LN2 can be replaced with similar K1561LN2, EKR561LN2, and with changes in the board – K564LN2, CD4049. Diode D9B – any hormanium, for example, any D9, D18, GD507. You can also try to use silicon diodes. The switch S1 is a microtumbler presumably made in China. It has flat leads for PCB mounting. Adjustment of the device. After testing the installation and its functionality, connect a multimeter. It is desirable to check the frequency at X1-X2 with a frequency meter or oscilloscope. If it is within the range of 120-180 kHz, it is normal. If not, adjust R1 resistance. Prepare a set of fixed resistors of 1 Ohm, 5 Ohm, 10 Ohm, 15 Ohm, 25 Ohm, 30 Ohm, 40 Ohm, 60 Ohm, 70 Ohm, and 80 Ohm (or so). Prepare a piece of paper. Connect a 1 ohm resistor in place of the capacitor under test. Turn the slider R2 until the multimeter reads 1 mV. Write on the paper “1 Ohm = 1mV”. Next, connect other resistors, and without changing the position of R2, make similar entries (e.g. “60 ohms = 17mV”). You will get a table of decoding multimeter readings. This table should be carefully drawn up (manually or on a computer) and glued to the body of the device so that it is easy to use. If the table is paper, stick scotch tape on its surface to protect the paper from abrasion. Now, when checking the capacitors, you read the multimeter in millivolts, then use the table to roughly determine the ESR of the capacitor and make a decision about its suitability. I want to note that this attachment can also be adapted to measure the capacitance of oxide capacitors. To do this, you need to significantly reduce the frequency of the multivibrator by connecting a capacitor with a capacity of 0.01 μF in parallel to C1. For convenience you can make a switch “C / ESR”. You also need to make another table, – with the values of the capacitance. It is desirable to use a shielded cable to connect to the multimeter, in order to eliminate the influence of interference on the readings of the multimeter.
The apparatus, on the board of which you are looking for a faulty capacitor, should be turned off at least half an hour before the start of the search (so that the capacitors present in its circuitry are discharged). The attachment can be used not only with a multimeter, but also with any instrument capable of measuring millivolts of DC or AC voltage. If your device is capable of measuring a small AC voltage (millivoltmeter AC or expensive multimeter) you can not make a detector on diodes VD1 and VD2, and measure the AC voltage directly on the capacitor under test. Naturally, the plate should be made for the specific device with which you plan to work in the future. And in case you use a device with an arrow indicator you can put an additional scale on its scale to measure the ESR.
Literature: 1 S. Rychikhin. A Tester of Oxide Capacitors Radio, #10, 2008, pp.14-15.
ESR Capacitor Meter
A review of several popular circuits of homemade capacitor ESR meters and new promising developments.
Recently in the radio amateur and professional literature a lot of attention is paid to such devices as electrolytic capacitors. And it is not surprising, because frequencies and power are growing “before our eyes”, and on these capacitors is a huge responsibility for the performance of individual nodes, and the circuit as a whole.
I will not enumerate all destabilizing factors in work of these workmen, (it now unless unless only on a fence do not write), we shall consider better in brief one of parameters – ESR and designs of several simple devices for quality estimation of electrolytic capacitors which were successfully repeated by me, something is changed, but the main, and most valuable, is certainly experience which I shall share with you in the given article. This article is written for beginners, so the presentation will be simple, without any formulas.
I want to warn you right away that most of the connections and circuit decisions were taken from forums and magazines, so I do not claim any authorship on my part, on the contrary, I want to help beginners to determine the endless schemes and variations of meters and testers. All circuits presented here were not once assembled and tested in the work, and the corresponding conclusions about the work of this or that design were made.
So, the first circuit, which has become almost a classic for beginners ESR Metro builders “Manfred” – so it is kindly called by forum members, by the name of its creator, Manfred Ludens ludens.cl/Electron/esr/esr.html
It has been repeated by hundreds, maybe thousands, of radio amateurs, and they are mostly happy with the result. Its main advantage is a series measurement scheme, so that the minimum ESR corresponds to the maximum voltage on the shunt resistor R6, which in turn has a useful effect on the operation of the detector diodes.
I have not repeated this circuit myself, but came to a similar one by trial and error. Of the drawbacks can be noted “walking” zero from the temperature, and the dependence of the scale on the parameters of diodes and Op-Amp. Increased supply voltage required for operation of the device. The sensitivity of the device can be easily increased by reducing resistors R5 and R6 to 1-2 ohms and respectively increasing the gain of Op-Amp, you may have to replace it with 2 more high-speed.
My first EPOS tester, which works properly to this day.
The schematic has not been saved, and it can be said that it was not, collected from the whole world by thread, what I was satisfied with schematically, however, for the basis was taken this scheme from a magazine radio:
The following changes were made:
1. Supply from a lithium battery from a cell phone 2. no regulator, because the range of the working voltage of the lithium battery is rather narrow 3. transformers TV1 and TV2 were shunted with 10 and 100 ohm resistors to reduce the emissions when measuring small capacitance 4. The output of 561Ln2 was buffered by two complementary transistors.
So I got such a device:
After assembling and calibration of the device I repaired 5 Meredian digital telephone sets, which were lying in the box for about 6 years with the label “hopeless”. Everyone in the department began to make themselves similar probes :).
For greater versatility, I added additional features:
1. infrared receiver for visual and auditory check of remote controls (a very popular feature for TV repairs) 2. backlighting of the capacitor probe contact area 3. “vibrator” from a cell phone, helps to localize bad soldering and microphonic effect in the parts .
And recently on the forum “radiokot.ru” Mr. Simurg posted an article on a similar device. In it he applied low-voltage power, bridge measuring circuit, which allowed to measure capacitors with ultra-low ESR.
His colleague RL55 took Simurg’s circuit as a basis and simplified the device to the maximum, according to his statements, without worsening its parameters. His circuit looks like this:
The device below, I had to collect at short notice, as they say “for the need”. I was on a visit to my relatives where the TV set broke and nobody could repair it. When I visited my in-laws, they could not repair it, but it took no more than a week, the TV-switchboard transistor kept burning, and the TV set scheme was out of order. Then I remembered that I had seen a simple tester on the forums, I remembered the schematic by heart, my relative also did a little radio hobby, he “riveted” audio amplifiers, so all the details were quickly found. A couple of hours of huffing and puffing with a soldering iron, and such a little device was born:
Were in 5 minutes localized and replaced 4 dried up electrolytics, which multimeter determined as normal, drank for the success of a noble drink. The TV after repair has been working properly for 4 years.
The device of this type has become a panacea for all those times when I do not have a good tester with me. It is assembled quickly, repaired, and finally presented to the owner as a keepsake and a “just in case”. After such a ceremony the soul of the paying person as a rule opens twice, or even three times wider:)
I wanted something synchronous, began to think about the scheme of implementation, and then in the magazine “Radio 2011”, as if by magic the article was published, even without having to think. I decided to check what kind of a beast it was. I assembled it and it turned out like this:
Particular delight product has not caused, works almost as well as all the previous, there is certainly a difference in the readings in 1-2 divisions in certain cases. May be its readings are more reliable, but a probe is a probe, on the quality of defects it almost does not affect. Also equipped with LED to watch “where you put it?
In general, for the soul and repairs can be done. And for exact measurements we should look for a more solid ESR meter circuit.
Well, and after all, on the site monitor.net, the participant buratino posted a simple project, how from a common cheap digital multimeter you can make a probe ESR. I was so intrigued by the project that I decided to try it, and this is what I got out of it.
I used a case from a marker pen.
I scratched out the board with a scalpel, the feeler pins were from an mcu48 relay.
I wound the transformer on a CFL ring and assembled the rest on the breadboard.
In the case I glued the board with duplex adhesive tape.
The frequency of ADC oscillator is a little bit low, so by decreasing the capacity from 100 to 33 picofarads I managed to get it to about 40-45 kilohertz, which is more or less acceptable.
From here we take the rectangular pulses. We change the capacitor under the white wire to a smaller value, in the range of 30-40 picofarads is not critical
Let’s assemble everything in the case.
There is a small disadvantage, you have to multiply the readings by 10, but you get used to it quickly. And finally a list of recommended sites to watch. Review prepared by – [email protected]