Very often, the cause of failures of various electronic equipment is electrolytic capacitors, and not the loss of their capacity, but an increase in their internal resistance.
This parameter plays a major role in the operation of pulse devices, and conventional capacitance meters, for the most part, do not see this parameter.
I decided to try to assemble a tester for electrolytic capacitors on a regular bulk, without any MK and displays, simple, reliable in operation and easily repeatable.
Several such devices were made, and here is a diagram of the last, very successful option, which allows, with a certain degree of probability, to check electrolytic capacitors without soldering them from the circuit, if the supply voltage in this circuit is 5 volts or more.
Principle of operation.
When the power is turned on, the capacitor C9 is charged (with a capacity of 100-47 μF), after pressing the SA3 button, the relay contacts P1 are briefly activated and the capacitor under test is charged through the low-resistance resistor R2 (R5), a short pulse is created on it and it opens through the divider R3, R4 (or does not open if it is not enough) thyristor, as indicated by the VD3 LED.
If the internal resistance of the capacitor is more than 0.05 (0.1) ohm, then the voltage drop is not enough to open and this indicates a malfunction of the electrolytic capacitor.
The resistor R4 adjusts the sensitivity of the device, the switch SA1 switches the sensitivity. Resistor R1 serves to gently discharge the capacitor.
The setting comes down to setting the response threshold for a film capacitor of 1 μF (it was taken from the line scan of an old monitor, when tested with an industrial device, it showed an internal resistance of 0 Ohm, with a lower measurement limit of the device of 0.01 Ohm), this allows for a more sensitive limit (switch SA1 is open ) test electrolytic capacitors up to 47uF, and at a less sensitive limit (SA1 closed) capacitors more than 47uF, although very high quality electrolytic capacitors and smaller capacities operate at this limit.
The results were compared with an industrial internal resistance meter.
Before setting up the device, you need to set the potentiometer to the extreme right position according to the diagram, close the measuring probes, and periodically pressing the "Start" button, rotate the potentiometer until the LED fires. This is to check the health of the circuit, then we connect a 1 uF film capacitor to the probes and slowly rotate further by pressing the "Start" button. The moment the LED is triggered will be the desired threshold.
I didn’t bother with the case and design, the task was to assemble a workable device.
I took the case for it from an old computer UPS, so do not particularly "kick" for the appearance. Likewise with print. Since there are not many details in the circuit, I made the installation in a hinged way.
All radio elements for the circuit were taken from old technology. Any network transformer, with an output voltage of 10-14 volts, rated for a secondary winding current of 0.2-0.5A, any diode bridge for about the same current, a 5-volt voltage regulator of any of the LM7805, KA7805 series.
Capacitors C2-C6 need good ones, taken from an old motherboard, pre-checked for serviceability. For good performance of the device, it is better to take more capacitors in parallel, must be in parallel!
The relay was taken from an old uninterruptible power supply with a 9 volt winding, it can also be 12 volts, the main thing is that it would work for a short time from the capacitor C9, if the relay winding is with little resistance, then you may have to pick up the capacitance of the capacitor C9 (increasing).
The thyristor was taken from the old switching power supply of the 3USCT TV (linear scan), a high-speed thyristor is needed.
For the accuracy of measurements, the circuits where the measuring currents flow cannot be performed with a thin wire. I used wires with a cross section of 0.75 sq. mm., It is also desirable to make the probes of the device not long 30-40 cm. Any LEDs that anyone likes, preferably large bright ones.
Yes, the only thing that needs to be observed when checking electrolytic capacitors is the polarity of their connection to the device.
Recently, in amateur and professional literature, a lot of attention has been paid to such devices as electrolytic capacitors. And it is not surprising, because frequencies and powers are growing “before our eyes”, and these capacitors bear a huge responsibility for the performance of both individual nodes and the circuit as a whole.
I want to warn you right away that most of the nodes and circuit designs were taken from forums and magazines, so I don’t declare any authorship on my part, on the contrary, I want to help novice repairmen decide on endless circuits and variations of meters and probes. All the schemes provided here have been repeatedly assembled and tested in the work, and appropriate conclusions have been drawn on the operation of a particular design.
So, the first scheme, which has become almost a classic for beginners ESR Metro builders "Manfred" - as the forum users kindly call it, after its creator, Manfred Ludens ludens.cl/Electron/esr/esr.html
It was repeated by hundreds, maybe thousands of radio amateurs, and were mostly satisfied with the result. Its main advantage is a sequential measurement circuit, due to which the minimum ESR corresponds to the maximum voltage across the shunt resistor R6, which, in turn, has a beneficial effect on the operation of the detector diodes.
I did not repeat this scheme myself, but came to a similar one through trial and error. Among the shortcomings, one can note the “walking” of zero on temperature, and the dependence of the scale on the parameters of the diodes and the op-amp. Increased supply voltage required for the operation of the device. The sensitivity of the device can be easily increased by reducing the resistors R5 and R6 to 1-2 ohms and, accordingly, increasing the gain of the op-amp, you may have to replace it with 2 faster ones.
My first EPS probe, working properly to this day.
The circuit has not been preserved, and it can be said that it did not exist, I collected from all over the world one by one, what suited me in terms of circuitry, however, such a circuit from the radio magazine was taken as a basis:
The following changes have been made:
1. Powered by mobile phone lithium battery
2. the stabilizer is excluded, since the operating voltage limits of the Lithium Battery are quite narrow
3. TV1 TV2 transformers are shunted with 10 and 100 ohm resistors to reduce emissions when measuring low capacities
4. The 561bn2 output was buffered by 2 complementary transistors.
In general, it turned out such a device:
After assembling and calibrating this device, 5 Meredian digital telephone sets were immediately repaired, which had been lying in a box with the inscription “hopeless” for 6 years already. Everyone in the department started making similar samples for themselves :).
For greater universality, I have added additional functions:
1. Infrared receiver, for visual and auditory testing of remote controls, (a very popular feature for TV repairs)
2. Illumination of the place where the probes touch the capacitors
3. "vibration" from a mobile phone, helps to localize bad soldering and microphone effect in detail.
Remote control video
And recently, on the radiokot.ru forum, Mr. Simurg posted an article on a similar device. In it, he applied a low-voltage power supply, a bridge measurement circuit, which made it possible to measure capacitors with an ultra-low ESR level.
His colleague RL55, taking the Simurg circuit as a basis, extremely simplified the device, according to his statements, without worsening the parameters. His schema looks like this:
The device below, I had to assemble in a hurry, as they say "as needed." I was visiting relatives, so the TV broke down there, no one could repair it. Or rather, it was possible to repair it, but not more than for a week, the horizontal scanning transistor burned all the time, there was no TV circuit. Then I remembered that I had seen a simple probe on the forums, I remembered the circuit by heart, my relative also did a little amateur radio, I “riveted” audio amplifiers, so all the details were quickly found. A couple of hours of puffing with a soldering iron, and such a device was born:
In 5 minutes, 4 dried electrolytics were localized and replaced, which were determined as normal by a multimeter, a certain amount of a noble drink was drunk for success. The TV after repair has been working properly for 4 years.
A device of this type has become like a panacea in difficult times when there is no normal tester with you. It is assembled quickly, repairs are made, and finally solemnly presented to the owner as a keepsake, and, “just in case”. After such a ceremony, the soul of the person who pays, as a rule, opens twice, or even three times wider :)
I wanted something synchronous, I began to think about the implementation scheme, and now in the Radio 1 2011 magazine, as if by magic, an article was published, I didn’t even have to think. I decided to check what kind of animal. Collected, it turned out like this:
The product did not cause much enthusiasm, it works almost like all the previous ones, there is, of course, a difference in readings of 1-2 divisions, in certain cases. Maybe his testimony is more reliable, but a probe is a probe, it almost does not affect the quality of fault detection. Also supplied with an LED to watch “where are you sticking it?”.
In general, for the soul and repairs can be done. And for accurate measurements, you need to look for a more impressive ESR meter circuit.
Well, and finally, on the monitor.net website, a member buratino posted a simple project on how to make an ESR probe from a regular cheap digital multimeter. The project intrigued me so much that I decided to try it, and this is what came out of it.
Hull adapted from the marker
How to test a capacitor. Theoretical information about capacitors |
Basically, according to the design, capacitors are of two types: polar and non-polar. Electrolytic capacitors are polar, while all other capacitors are non-polar. Polar capacitors got their name from the fact that using them in various homemade products, it is necessary to observe the polarity, if it is accidentally broken, then the capacitor will most likely have to be thrown away. Since the explosion of the container is not only beautiful with its effects, but also very dangerous.
But don’t be scared right away, only Soviet-type capacitors explode, but it’s already hard to find them, and the imported one only “farts” a little. For capacitor test you have to remember, namely: the fact that the capacitor passes only alternating current, it passes direct current only at the very beginning for a few microseconds (this time depends on its capacitance), and then it does not pass. In order to check the capacitor with a multimeter, you need to remember that its capacitance must be from 0.25 uF.
How to test a capacitor. Practical experiments and experiences |
We take a multimeter and set it to continuity or to measure resistance, and connect the probes to the terminals of the capacitor.
Since a direct current is supplied from the multimeter, we will charge the capacitor. And since we charge it, its resistance begins to increase until it is very large. If, when we connect the probes to the capacitor, the multimeter starts to beep and show zero resistance, then we throw it out. And if we immediately show a one on the multimeter, then a break has occurred inside the capacitor and it should also be thrown out
PS: Large capacities in this way you will not be able to check :(
In modern circuits, the role of capacitors has increased markedly, because both the power and frequency of operation of devices have increased. And therefore it is very important to check this parameter for all electrolytes before assembling the circuit or during the diagnosis of a malfunction.
Equivalent Series Resistance - equivalent series resistance is the sum of series-connected ohmic resistances of the leads and electrolyte contacts with electrolytic capacitor plates.
ESR meter based on Sunwa YX-1000A pointer multimeter
The circuit works on the principle of testing a capacitor with an alternating current of a given value. Then the voltage drop across the capacitor is directly proportional to the modulus of its complex resistance. Such a device will determine not only the increased internal resistance, but also the loss of capacitance. The circuit consists of three main parts of a rectangular pulse generator, a converter and an indication
The rectangular pulse generator is assembled on a digital microcircuit consisting of six logical NOT elements. The role of the AC-to-DC converter is performed by DA2, and the indication on the DA3 chip and 10 LEDs.
The ESR meter scale is non-linear. For the possibility of expanding the measurement range, there is a range switch. made in Sprint Layout is also available.
Oxide electrolyte can be simplified in the form of two aluminum tape plates separated by a spacer made of a porous material impregnated with a special composition - electrolyte. The dielectric in such elements is a very thin oxide film formed on the surface of aluminum foil when a voltage of a certain polarity is applied to the plates. Wire leads are attached to these tape plates. The tapes are rolled up, and all this is placed in a sealed case. Due to the very small thickness of the dielectric and the large area of the plates, oxide capacitors with small dimensions have a sufficiently large capacitance.
Eight negative feedback op amps form the basis of this circuit, and are in a stable operating position if their two inputs match the applied voltage. Amplifiers 1A and 1B generate oscillations with a frequency of 100 kHz, which is set by the chain C1 and R1. Diodes D2 and D3 are designed to limit the lower and upper amplitude of the output signal, so the level and frequency are resistant to changes in the battery supply voltage.
This amateur radio circuit allows you to control EPS in circuits up to 600 volts, but only if the circuit does not have an alternating voltage with a frequency of more than 100 Hz.
The output of op amp 1B is loaded by resistor R8F. The tested capacitor is connected through the probes. Capacitor C3 blocking. Diodes D4 and D5 protect the device from the charging current of capacitor C3. Resistor R7 is designed to discharge C3 after measurement. The DC bias voltage from diode D1 and the signal from resistor R9F are summed at the input of op-amp 1D. Each of the three stages has a gain of 2.8.
Details: 1. LM324N op amp. 2. "F" resistors 1% accuracy; all others-5% 3. R7 from 0.5 watts, the rest 0.25 watts. 4. R21 establishes linearity in the middle of the scale: 330 to 2.2 ohms. 5. R24 corrects the DC offset at ESR infinity. 6. R26 helps zero (full scale): 68 to 240 ohms. 7. R6F=150 ohm, R12F=681 ohm
ESR meter on available radio components |
The probe circuit consists of: a generator, a measuring circuit, an amplifier, an indicator. T1 is a composite transistor. A self-made LED scale was used as an indicator.
To speed up the assembly process, a probe for testing capacitors is made on a breadboard and placed in a case from a piece of cable channel. The screws are made of copper wire.
The delivery set includes the measuring device itself, three probes for it and four legs for the board. The Esr meter is designed to operate on a 14500 type lithium battery with a voltage of 3.7 volts, but you can not order it, but take it from an old laptop battery, and do not care that it is larger in size.
About the management of the ESR meter.
1 - USB for power and battery charging. The device for checking electrolytic capacitors can also be used without a lithium battery, using external power, but then the error of the device increases slightly.
2 - turn on the device
3 - Operation indicator. Lights up after the probe enters test mode
4 - Button to start the measurement process. We press it only after connecting the measured capacitance to the contacts
5 - Connectors for connecting measuring probes, or suitable size transistors
6 - Socket for measuring small radio components, the legs of which can enter the hole
7 - Contact pads for checking SMD.
The MG328 is designed to operate on a 14500 battery, but I decided to install a 18650 battery there. To do this, I unsoldered the native holder and directly soldered the 18650 element in its place. In terms of dimensions, everything fit into the standard dimensions of the finished board.
After power is supplied to the board from usb, the charging indicator starts to glow. The device has a self-test mode. To start it, you need to connect all three probes together, and press the test button. After that, DIY MG328 will switch to self-test mode. In addition, this mode can be accessed through the menu. To do this, you will need to press the test button for two seconds.
To navigate the menu, you need to press the test button to select any of the items, and then hold down the same button for a few seconds. A pleasant surprise was the found menu item - frequency generator.
The photographs below show examples of measuring various types of radio components.
In general, the measuring device is happy as an elephant. Already in many of my repairs I found dead capacitors, without external signs of problems.
Thank you very much for the work you have done. Another conclusion based on what I read: The 1 mA head turned out to be stupid for such a detector. after all, it is the inclusion in series with the head of the resistor that stretches the scale. Since great accuracy is not needed, you can try the head from the tape recorder. (one trouble, it is pretty electrified, it touched a little with the sleeve of the sweater and the arrow itself jumps to the floor of the scale) and the total deviation current is about 240 μA (the exact name is M68501)
In general, is it not enough to scale the ohm to 10-12 in order to reject the capacitor?
Prefix to the multimeter - meterESR
An ideal capacitor, operating on alternating current, should have only reactive (capacitive) resistance. The active component should be close to zero. In reality, a good oxide (electrolytic) capacitor should have an active resistance (ESR) of no more than 0.5-5 ohms (depending on capacitance, rated voltage). In practice, in equipment that has worked for several years, you can find a seemingly serviceable capacitor with a capacity of 10 microfarads with an ESR of up to 100 ohms or more. Such a capacitor, despite the presence of a capacitance, is unusable, and most likely is the cause of a malfunction or poor-quality operation of the apparatus in which it operates.
Figure 1 shows a diagram of an attachment to a multimeter for measuring the ESR of oxide capacitors. To measure the active component of the capacitor resistance, it is necessary to select a measurement mode in which the reactive component will be very small. As you know, capacitance reactance decreases with increasing frequency. For example, at a frequency of 100 kHz with a capacitance of 10 microfarads, the reactive component will be less than 0.2 ohms. That is, by measuring the resistance of an oxide capacitor with a capacity of more than 10 μF by the drop of an alternating voltage with a frequency of 100 kHz or more on it, it can be argued that. with a given error of 10-20%, the measurement result can be accepted practically only as a value of active resistance.
And so, the circuit shown in Figure 1 is a 120 kHz frequency pulse generator, made on logical inverters of the D1 chip, a voltage divider consisting of resistances R2, R3 and a tested capacitor CX, and an AC voltage meter on CX, consisting of a detector VD1 -VD2 and a multimeter included in the measurement of low DC voltages.
The frequency is set by the R1-C1 circuit. Element D1.3 is a matching element, and an output stage is made on elements D1.4-D1.6.
By adjusting the resistance R2, the device is adjusted. Since the popular M838 multimeter does not have a mode for measuring small alternating voltages (namely, the author works with a prefix with this device), the probe circuit has a detector on germanium diodes VD1-VD2. The multimeter measures the DC voltage at C4.
The power source is Krona. This is the same battery as the one that powers the multimeter, but the set-top box must be powered by a separate battery.
Attachment parts are mounted on a printed circuit board, the wiring and arrangement of parts of which are shown in Figure 2.
Structurally, the prefix is made in one housing with a power source. To connect to the multimeter, the multimeter's own probes are used. The body is an ordinary soap dish.
Short probes are made from points X1 and X2. One of them is rigid, in the form of an awl, and the second is flexible, not more than 10 cm long, with the same pointed probe. These probes can be connected to capacitors, both unmounted and located on the board (they do not need to be soldered), which greatly simplifies the search for a defective capacitor during repair. It is advisable to pick up "crocodiles" for these probes for the convenience of checking unmounted (or dismantled) capacitors.
The K561LN2 chip can be replaced with a similar K1561LN2, EKR561LN2, and with changes in the board - K564LN2, CD4049.
Diodes D9B - any harmonic, for example, any D9, D18, GD507. You can try to use silicon.
Switch S1 is a micro toggle switch, presumably made in China. It has flat PCB leads.
Setting up the fixture. After checking the installation and operation, connect the multimeter. It is advisable to check the frequency at X1-X2 with a frequency meter or oscilloscope. If it lies in the range of 120-180 kHz, it is normal. If not, - pick up the resistance R1.
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 sheet of paper. Connect a 1 Ω resistor instead of the capacitor under test. Turn the R2 slider so that the multimeter reads 1 mV. On paper, write down "1 ohm = 1mV". Next, connect other resistors, and without changing the position of R2, make similar entries (for example, “60Ω = 17mV”).
You will get a table for decoding the readings of the multimeter. This table must be carefully formatted (manually or on a computer) and glued to the body of the set-top box, so that the table is convenient to use. If the table is paper, stick adhesive tape on its surface to protect the paper from abrasion.
Now, when checking capacitors, you read the multimeter readings in millivolts, then roughly determine the ESR of the capacitor from the table and decide on its suitability.
I want to note that this prefix 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 0.01 uF capacitor in parallel with C1. For convenience, you can make a switch "C / ESR". You will also need to make another table - with the values of the capacities.
It is advisable to use a shielded cable to connect to the multimeter in order to exclude the effect of interference on the multimeter readings.
The device on the board of which you are looking for a faulty capacitor must be turned off at least half an hour before the start of the search (so that the capacitors in its circuit are discharged).
The prefix can be used not only with a multimeter, but also with any device capable of measuring millivolts of direct or alternating voltage. If your device is capable of measuring a small alternating voltage (ac millivoltmeter or an expensive multimeter), you can not do a detector on diodes VD1 and VD2, but measure the alternating voltage directly on the capacitor under test. Naturally, the plate must be made for a specific device with which you plan to work in the future. And in the case of using a device with a dial indicator, you can apply an additional scale to measure ESR on its scale.
Radio designer, 2009, No. 01 pp. 11-12 Stepanov V.
Literature:
1 S Rychikhin. Probe of oxide capacitors Radio, No. 10, 2008, pp. 14-15.
For more than a year I have been using the device according to the scheme of D. Telesh from the magazine "Schemotechnics" No. 8, 2007, pp. 44-45.
On the millivoltmeter M-830V in the range of 200 mV, the readings, without an installed capacitor, are 165 ... 175 mV.
Supply voltage 3 V (2 AA batteries worked for more than a year), measurement frequency from 50 to 100 kHz (set 80 kHz by selecting capacitor C1). In practice, I measured capacitances from 0.5 to 10,000 μF and ESR from 0.2 to 30 (when calibrated, the instrument readings in mV correspond to resistors of the same rating in ohms). Used to repair switching power supplies PC and BREA.
A practically ready-made circuit for checking the EPS, if assembled on a CMOS, it will also work from 3 volts ....
ESR meter
That is, a device for measuring EPS - equivalent series resistance.
As it turned out, the performance of (electrolytic - in particular) capacitors, especially those that work in power pulse devices, is largely affected by the internal equivalent series resistance to alternating current. Different manufacturers of capacitors have different attitudes to the frequency at which the ESR value should be determined, but this frequency should not be lower than 30 kHz.
The value of the ESR is to some extent related to the main parameter of the capacitor - capacitance, but it has been proven that the capacitor can be faulty due to the large intrinsic value of the ESR, even with the declared capacitance.
outside view
The KR1211EU1 microcircuit was used as a generator (the frequency at ratings in the circuit is about 70 kHz), phase inverter transformers from the BP AT / ATX can be used - the same parameters (transformation ratios in particular) from almost all manufacturers. Attention!!! In transformer T1, only half of the winding is used.
The head of the device has a sensitivity of 300 μA, but other heads can be used. It is preferable to use more sensitive heads.
The scale of this device is extended by a third when measured up to 1 ohm. The tenth Ohm is easily distinguishable from 0.5 Ohm. The scale fits 22 ohms.
Stretch and range can be varied by adding turns to the measuring winding (with probes) and / or to windings III of one or another transformer.
http://www. matei. ro/emil/links2.php
http://www. . au/cms/gallery/article. html? slideshow=0&a=103805&i=2
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When a working capacitor is connected, the LED should go out completely, since short-circuited turns completely disrupt generation. With faulty capacitors, the LED remains on or dims slightly, depending on the ESR value.
The simplicity of this probe allows you to assemble it in a case from an ordinary felt-tip pen, the main place in it is given to the battery, the power button and the LED protruding above the case. The diminutiveness of the probe allows you to place one of the probes in the same place, and make the second one as short as possible, which will reduce the effect of the inductance of the probes on the readings. In addition, you do not need to turn your head to visually control the indicator and install probes, which is often inconvenient during operation.
Construction and details.
The transformer coils are wound on one ring, preferably the smallest, its magnetic permeability is not very important, the generator coils have a number of turns of 30 vit. each, indicator - 6 vit. and measuring 4 vit. or 3 vit. (selected during setup), the thickness of all wires is 0.2-0.3mm. The measuring winding should be wound with a wire of at least 1.0 mm. (A mounting wire is quite suitable - as long as the winding fits on the ring.) R1 regulates the frequency and current consumption within a small range. Resistor R2 limits the short circuit current created by the tested capacitor; for reasons of protection against a charged capacitor that will discharge through it and the winding, it must be 2 watts. By varying its resistance, one can easily distinguish resistance from 0.5 ohms and higher by the glow of the LED. Any low power transistor will do. Power is supplied from one 1.5 volt battery. During the testing of the device, it was even possible to power it from two probes of a pointer ohmmeter, switched on by units of ohms.
Detail ratings:
Rom
R2* - 1om
C1- 1uF
C2- 390pF
Setting.
Presents no difficulty. A properly assembled generator starts working immediately at a frequency of 50-60 kHz, if the LED does not light up, you need to change the polarity of the switch on. Then, by connecting a resistor of 0.5-0.3 Ohm to the measuring winding instead of a capacitor, they achieve a barely noticeable glow by selecting turns and resistor R2, but usually their number ranges from 3 to 4. At the end of everything, they check on a known good and faulty capacitor. With little skill, the ESR of a capacitor is easily recognized up to 0.3-0.2 Ohm, which is quite enough to find a faulty capacitor, from a capacitance of 0.47 to 1000 microfarads. Instead of one LED, you can put two and turn on a 2-3 volt zener diode in the circuit of one of them, but you will need to increase the winding, and the device will become more structurally complicated. You can make two probes coming out of the case at once, but you should provide a distance between them so that it is convenient to measure capacitors of different sizes. (for example - for SMD capacitors, you can use the idea of \u200b\u200bSW. Barbos "a - and constructively make a probe in the form of tweezers)
Another application of this device: it is convenient for them to check control buttons in audio and video equipment, because over time, some buttons give false commands due to increased internal resistance. The same applies to checking the printed conductors for a break or checking the contact resistance of the contacts.
I hope that the probe will take its rightful place in the ranks of the “beetle builder” assistant devices.
Impressions of using this probe:
- I forgot what a faulty capacitor is;
- 2/3 of the old capacitors had to be thrown out.
Well, the best part is that I don’t go to the store and the market without a probe.
Capacitor sellers are very unhappy.
Capacitance and inductance meter
E. Terentiev
Radio, 4, 1995
http://www. *****/shem/schematics. html? di=54655
The proposed pointer meter allows you to determine the parameters of most of the inductors and capacitors encountered in the practice of a radio amateur. In addition to measuring the parameters of elements, the device can be used as a fixed frequency generator with a ten-day division, as well as a label generator for radio engineering measuring instruments.
The proposed capacitance and inductance meter differs from similar ("Radio", 1982, 3, p. 47) simplicity and low labor intensity of manufacture. The measurement range is divided ten days into six sub-ranges with capacitance limits of 100 pF - 10 μF for capacitors and inductance 10 μH - 1 H for inductors. The minimum values of the measured capacitance, inductance and the measurement accuracy of parameters at the limit of 100 pF and 10 μH are determined by the constructive capacitance of the terminals or sockets for connecting the leads of the elements. On the remaining sub-ranges, the measurement error is mainly determined by the accuracy class of the pointer measuring head. The current consumed by the device does not exceed 25 mA.
The principle of operation of the device is based on measuring the average value of the discharge current of the capacitance of the capacitor and the EMF of the self-induction of the inductance. The meter, the schematic diagram of which is shown in Fig. 1, consists of a master oscillator based on elements DD1.5, DD1.6 with quartz frequency stabilization, a line of frequency dividers on microcircuits DD2 - DD6 and buffer inverters DD1.1 - DD1.4. Resistor R4 limits the output current of the inverters. A circuit of elements VD7, VD8, R6, C4 is used when measuring capacitance, and a circuit VD6, R5, R6, C4 is used when measuring inductance. Diode VD9 protects the PA1 microammeter from overload. The capacitance of the capacitor C4 is chosen relatively large in order to reduce the jitter of the needle at the maximum measurement limit, where the clock frequency is minimal - 10 Hz.
The instrument uses a measuring head with a total deflection current of 100 μA. If you apply a more sensitive one - by 50 μA, then in this case you can reduce the measurement limit by 2 times. The ALS339A seven-segment LED indicator is used as an indicator of the measured parameter, it can be replaced by the ALS314A indicator. Instead of a quartz resonator at a frequency of 1 MHz, you can turn on a mica or ceramic capacitor with a capacitance of 24 pF, however, in this case, the measurement error will increase by 3-4%.
It is possible to replace the D20 diode with D18 or GD507 diodes, the KS156A zener diode with KS147A, KS168A zener diodes. Silicon diodes VD1-VD4, VD9 can be any with a maximum current of at least 50 mA, and the transistor VT1 can be any of the types KT315, KT815. Capacitor CZ - ceramic K10-17a or KM-5. All element values and quartz frequency may differ by 20%.
The device setup starts in the capacitance measurement mode. Switch SB1 to the upper position according to the diagram and set the range switch SA1 to the position corresponding to the measurement limit of 1000 pF. By connecting an exemplary capacitor with a capacity of 1000 pF to the terminals XS1, XS2, the engine of the trimming resistor R6 is brought to a position in which the pointer of the PA1 microammeter is set to the final division of the scale. Then the switch SB1 is switched to the mode of measuring the inductance and, having connected an inductor of 100 μH to the terminals, in the same position of the switch SA1, a similar calibration is performed with a tuning resistor R5. Naturally, the accuracy of instrument calibration is determined by the accuracy of the reference elements used.
It is advisable to start measuring the parameters of the elements with a device from a larger measurement limit in order to avoid a sharp overshoot of the arrow of the device head. To power the meter, you can use a DC voltage of 10...15 V or an alternating voltage from a suitable winding of the power transformer of another device with a load current of at least 40...50 mA. The power of a separate transformer must be at least 1 W.
If the device is powered by a battery of batteries or galvanic cells with a voltage of 9 V, it can be simplified and more economical by eliminating the diodes of the supply voltage rectifier, indicator HG1 and switch SB1 by bringing three terminals (sockets) to the front panel of the device from points 1, 2, 3 indicated on the concept. When measuring capacitance, the capacitor is connected to terminals 1 and 2; when measuring inductance, the coil is connected to terminals 1 and 3.
Editorial note. The accuracy of an LC meter with a pointer indicator to a certain extent depends on the section of the scale, therefore, the introduction of a switchable frequency divider by 2, 4 or a similar change in the frequency of the master oscillator (for the version without a quartz resonator) into the circuit makes it possible to reduce the requirements for dimensions and accuracy class of the indicating device.
LC Meter Attachment to Digital Voltmeter
http:///izmer/izmer4.php
The digital measuring instrument in the amateur radio laboratory is no longer a rarity. However, it is not often possible for them to measure the parameters of capacitors and inductors, even if it is a multimeter. The simple prefix described here is intended for use in conjunction with multimeters or digital voltmeters (for example, M-830V, M-832 and the like) that do not have a mode for measuring the parameters of reactive elements.
To measure the capacitance and inductance using a simple attachment, the principle described in detail in the article by A. Stepanov "Simple LC-meter" in "Radio" No. 3 for 1982 was used. The proposed meter is somewhat simplified (instead of an oscillator with a quartz resonator and a decade frequency divider, multivibrator with a switchable generation frequency), but it allows, with sufficient accuracy for practice, to measure capacitance within 2 pF ... 1 μF and inductance 2 μH ... 1 H. In addition, it generates a rectangular voltage with fixed frequencies of 1 MHz, 100 kHz, 10 kHz, 1 kHz, 100 Hz and adjustable amplitude from 0 to 5 V, which expands the scope of the device.
The master oscillator of the meter (Fig. 1) is made on the elements of the DD1 (CMOS) microcircuit, the frequency at its output is changed using the SA1 switch within 1 MHz - 100 Hz by connecting capacitors C1-C5. From the generator, the signal is fed to an electronic key assembled on a transistor VT1. Switch SA2 select the measurement mode "L" or "C". In the position of the switch shown in the diagram, the attachment measures the inductance. The measured inductor is connected to sockets X4, X5, the capacitor - to X3, X4, and the voltmeter - to sockets X6, X7.
During operation, the voltmeter is set to the DC voltage measurement mode with an upper limit of 1 - 2V. It should be noted that the voltage at the output of the set-top box varies within 0 ... 1 V. On the sockets X1, X2 in the capacitance measurement mode (switch SA2 - in position "C") there is an adjustable rectangular voltage. Its amplitude can be smoothly changed by a variable resistor R4.
The set-top box is powered by a GB1 battery with a voltage of 9 V ("Corundum" or similar) through a stabilizer on a VT2 transistor and a VD3 zener diode.
The K561LA7 microcircuit can be replaced with K561LE5 or K561LA9 (excluding DD1.4), transistors VT1 and VT2 can be replaced with any low-power silicon of the corresponding structure, we will replace the VD3 zener diode with KS156A, KS168A. Diodes VD1, VD2 - any point germanium, for example, D2, D9, D18. Switches are desirable to use miniature.
The case of the device is home-made or ready-made of suitable sizes. Mounting parts (Fig. 2) in the case - hinged on switches, resistor R4 and sockets. The appearance option is shown in the figure. XZ-X5 connectors are self-made, made of sheet brass or copper with a thickness of 0.1 ... 0.2 mm, their design is clear from fig. 3. To connect a capacitor or coil, it is necessary to insert the leads of the part all the way into the wedge-shaped gap of the plates; this achieves fast and reliable fixation of the findings.
The adjustment of the device is carried out using a frequency meter and an oscilloscope. Switch SA1 is moved to the upper position according to the scheme and by selecting capacitor C1 and resistor R1 a frequency of 1 MHz is achieved at the output of the generator. Then the switch is sequentially transferred to subsequent positions and by selecting capacitors C2 - C5, the generation frequencies are set to 100 kHz, 10 kHz, 1 kHz and 100 Hz. Next, the oscilloscope is connected to the collector of the transistor VT1, the SA2 switch is in the capacitance measurement position. By selecting the resistor R3, the oscillation form is achieved, close to the meander on all ranges. Then the switch SA1 is again set to the upper position according to the diagram, a digital or analog voltmeter is connected to the sockets X6, X7, and an exemplary capacitor with a capacity of 100 pF is connected to the sockets X3, X4. By adjusting the resistor R7, a voltmeter reading of 1 V is achieved. Then the SA2 switch is switched to the inductance measurement mode and an exemplary coil with an inductance of 100 μH is connected to the sockets X4, X5, the voltmeter readings are also set to 1 V with resistor R6.
This completes the setup of the device. On the remaining ranges, the accuracy of the readings depends only on the accuracy of the selection of capacitors C2 - C5. From the editor. It is better to start setting up the generator with a frequency of 100 Hz, which is set by selecting the resistor R1, the capacitor C5 is not selected. It should be remembered that capacitors C3 - C5 must be paper or, better, metafilm (K71, K73, K77, K78). With limited possibilities in the selection of capacitors, you can use the switching section SA1.2 resistors R1 and their selection, and the number of capacitors must be reduced to two (C1, C3). The resistance values of the resistors will be in this case: 4.7: 47; 470 k0m.
(Radio 12-98
List of sources on the topic of EPS capacitors in the journal "Radio"
Khafizov R. Probe of oxide capacitors. - Radio, 2003, No. 10, pp. 21-22. Stepanov V. EPS and not only ... - Radio, 2005, No. 8, p. 39,42. Vasiliev V. A device for testing oxide capacitors. - Radio, 2005, No. 10, pp. 24-25. Nechaev I. Estimation of the equivalent series resistance of a capacitor. - Radio, 2005, No. 12, pp. 25-26. Shchus A. ESR meter of oxide capacitors. - Radio, 2006, No. 10, p. 30-31. Kurakin Yu. EPS indicator of oxide capacitors. - Radio, 2008, No. 7, pp. 26-27. Platoshin I. ESR meter of oxide capacitors. - Radio, 2008, No. 8, p. 18-19. Rychikhin S. Probe of oxide capacitors. - Radio, 2008, No. 10, pp. 14-15. Tabaksman V., Felyugin V. ESR meters of oxide capacitors. - Radio, 2009, No. 8, pp. 49-52.
Capacitor capacitance meter
V. Vasiliev, Naberezhnye ChelnyThis device is built on the basis of the device previously described in our magazine. Unlike most of these devices, it is interesting in that it is possible to check the health and capacitance of capacitors without dismantling them from the board. In operation, the proposed meter is very convenient and has sufficient accuracy.
Anyone who repairs household or industrial radio equipment knows that it is convenient to check the health of capacitors without dismantling them. However, many capacitor capacitance meters do not provide such an opportunity. True, one such design was described in. It has a small measuring range, a non-linear scale with a countdown, which reduces accuracy. When designing a new meter, the task of creating a device with a wide range, a linear scale and a direct reading was solved so that it could be used as a laboratory one. In addition, the device must be diagnostic, i.e., capable of checking capacitors shunted by p-n junctions of semiconductor devices and resistor resistances.
The principle of operation of the device is as follows. At the input of the differentiator, in which the capacitor under test is used as a differentiator, a triangular voltage is applied. At the same time, a meander is obtained at its output with an amplitude proportional to the capacitance of this capacitor. Next, the detector selects the amplitude value of the meander and outputs a constant voltage to the measuring head.
The amplitude of the measuring voltage on the probes of the device is approximately 50 mV, which is not enough to open the p-n junctions of semiconductor devices, so they do not have their shunting effect.
The device has two switches. "Scale" limit switch with five positions: 10 µF, 1 µF, 0.1 µF, 0.01 µF, 1000 pF. The "Multiplier" switch (X1000, X100, X10, X1) changes the measurement frequency. Thus, the device has eight capacitance measurement subranges from 10,000 μF to 1,000 pF, which is practically sufficient in most cases.
The triangular oscillation generator is assembled on the op-amp of the DA1.1, DA1.2, DA1.4 microcircuit (Fig. 1). One of them, DA1.1, operates in the comparator mode and generates a rectangular signal, which is fed to the input of the DA1.2 integrator. The integrator converts square waves to triangular. The generator frequency is determined by the elements R4, C1-C4. In the feedback circuit of the generator, there is an inverter on the op-amp DA1.4, which provides a self-oscillating mode. Switch SA1 can set one of the measurement frequencies (multiplier): 1 Hz (X1000), 10 Hz (x100), 100 Hz (x10), 1 kHz (x1).
Rice. 1
Op-amp DA2.1 is a voltage follower, at its output a triangular-shaped signal with an amplitude of about 50 mV, which is used to create a measuring current through the tested capacitor Cx.
Since the capacitance of the capacitor is measured in the board, there may be residual voltage on it, therefore, in order to prevent damage to the meter, two anti-parallel bridge diodes VD1 are connected in parallel to its probes.
Op-amp DA2.2 works as a differentiator and acts as a current-voltage converter. Its output voltage: Uout=(R12...R16) Iin=(R12...R16)Cх dU/dt. For example, when measuring a capacitance of 100 uF at a frequency of 100 Hz, it turns out: Iin \u003d Cx dU / dt \u003d 100 100 mV / 5 ms \u003d 2mA, Uout \u003d R16 Iin \u003d 1 kOhm mA \u003d 2 V.
Elements R11, C5-C9 are necessary for the stable operation of the differentiator. Capacitors eliminate oscillatory processes at the meander fronts, which make it impossible to accurately measure its amplitude. As a result, a square wave with smooth fronts and an amplitude proportional to the measured capacitance is obtained at the DA2.2 output. Resistor R11 also limits the input current when the probes are closed or when the capacitor is broken. For the input circuit of the meter, the following inequality must be fulfilled: (3...5)СхR11<1/(2f).
If this inequality is not met, then in half a period the current Iin does not reach a steady value, and the meander does not reach the corresponding amplitude, and an error occurs in the measurement. For example, in the meter described in, when measuring a capacitance of 1000 uF at a frequency of 1 Hz, the time constant is determined as Cx R25 \u003d 1000 uF 910 Ohm \u003d 0.91 s. Half of the oscillation period T / 2 is only 0.5 s, therefore, on this scale, the measurements will turn out to be noticeably nonlinear.
The synchronous detector consists of a key on a field-effect transistor VT1, a key control unit on an op-amp DA1.3 and a storage capacitor C10. Op-amp DA1.2 issues a control signal to the key VT1 during the positive half-wave of the meander, when its amplitude is set. Capacitor C10 stores the DC voltage emitted by the detector.
From the capacitor C10, the voltage carrying information about the value of capacitance Cx is fed through the DA2.3 repeater to the RA1 microammeter. Capacitors C11, C12 - smoothing. From the engine of the variable calibration resistor R22, voltage is removed to a digital voltmeter with a measurement limit of 2 V.
The power supply (Fig. 2) produces bipolar voltages of ±9 V. The reference voltages form thermally stable zener diodes VD5, VD6. Resistors R25, R26 set the required output voltage. Structurally, the power source is combined with the measuring part of the device on a common circuit board.
Rice. 2
The device uses variable resistors of the SPZ-22 type (R21, R22, R25, R26). Fixed resistors R12-R16 - type C2-36 or C2-14 with a tolerance of ±1%. The resistance R16 is obtained by connecting several selected resistors in series. Other types of resistors R12-R16 can also be used, but they must be selected using a digital ohmmeter (multimeter). The remaining fixed resistors are any with a dissipation power of 0.125 watts. Capacitor C10 - K53-1 A, capacitors C11-C16 - K50-16. Capacitors C1, C2 - K73-17 or other metal-film, SZ, C4 - KM-5, KM-6 or other ceramic capacitors with TKE not worse than M750, they must also be selected with an error of no more than 1%. The rest of the capacitors - any.
Switches SA1, SA2 - P2G-3 5P2N. It is permissible to use the transistor KP303 (VT1) with the letter indices A, B, C, F, I in the design. Transistors VT2, VT3 of voltage stabilizers can be replaced by other low-power silicon transistors of the corresponding structure. Instead of OU K1401UD4, you can use K1401UD2A, but then at the limit of "1000 pF" an error may occur due to the offset of the differentiator input created by the input current DA2.2 to R16.
The power transformer T1 has an overall power of 1 W. It is acceptable to use a transformer with two secondary windings of 12 V each, but then two rectifier bridges are needed.
An oscilloscope is required to set up and debug the device. It's a good idea to have a frequency meter to check the frequencies of the triangular oscillator. Exemplary capacitors will also be needed.
The device begins to be adjusted by setting the voltages to +9 V and -9 V using resistors R25, R26. After that, the operation of the triangular oscillation generator is checked (oscillograms 1, 2, 3, 4 in Fig. 3). In the presence of a frequency meter, the frequency of the generator is measured at different positions of the switch SA1. It is acceptable if the frequencies differ from the values of 1 Hz, 10 Hz, 100 Hz, 1 kHz, but they should differ exactly 10 times from each other, since the correct readings of the device on different scales depend on this. If the generator frequencies are not a multiple of ten, then the required accuracy (with an error of 1%) is achieved by selecting capacitors connected in parallel with capacitors C1-C4. If the capacitances of capacitors C1-C4 are selected with the required accuracy, you can do without measuring frequencies.
As you know, the cause of the vast majority of defects in electronic equipment are faulty electrolytic capacitors. It is they that cause such defects as the failure of a line transistor and a video processor in TVs, burnt through motor drivers in DVD players, an increased background in ULFs, partial or complete inoperability of motherboards ... etc.
Equivalent series resistance (ESR, or Equivalent Series Resistance - ESR) is mainly due to the electrical resistance of the material of the plates and leads of the capacitor and the contact (s) between them, as well as losses in the dielectric. Usually ESR increases with increasing frequency of the current flowing through the capacitor (for example, in the case of using electrolytic capacitors in the filters of switching power supplies), a sufficiently small value of it can be vital for the reliability of the device.
Finding faulty capacitors with a tester or capacitance meter is sometimes quite difficult, because. the capacitance of a failed capacitor may differ slightly from the nominal value, and the ESR value may be quite large. And it is ESR that is the most important parameter to measure when looking for a faulty capacitor. Other capacitor failures, such as a short circuit or low DC resistance, are extremely rare.
The proposed probe is an ohmmeter operating on high frequency alternating current (60-70 kHz).
Scheme
The heart of the device is the K155LA3 (7400) microcircuit, consisting of 4 2I-NOT elements, on which a generator and an amplifier of rectangular pulses with a frequency of 60-70 kHz are assembled.
The generator is assembled on the first two inverters. The frequency is set by the elements C1 and R2. On the third inverter - an intermediate amplifier, and on the fourth - the output. Further, the pulses are fed to the matching step-up transformer T1, wound on a ferrite ring (from the motherboard), with a 0.14 mm wire. The primary winding contains 30 turns, the secondary 300 turns.
Then, through the tuning resistor R3 and the germanium diode D9 - to the measuring head. Also, from R3, the pulses arrive at the primary winding of the measuring transformer T2, wound on the same ring. The primary winding consists of 150 turns of wire with a diameter of 0.14 mm., the secondary has 15 turns of wire 0.5 mm. The device is powered by a Krona battery
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Thank you for your attention!
Igor Kotov, editor-in-chief of Datagor magazine
