With this capacitance meter you can easily measure any capacitance from units of pF to hundreds of microfarads. There are several methods for measuring capacitance. This project uses the integration method.
The main advantage of using this method is that the measurement is based on time measurement, which can be done quite accurately on an MC. This method is very suitable for a homemade capacitance meter, and it can also be easily implemented on a microcontroller.
Working principle of a capacitance meter
Phenomena that occur when the state of a circuit changes are called transient processes. This is one of the fundamental concepts digital circuits. When the switch in Figure 1 is open, the capacitor is charged through resistor R, and the voltage across it will change as shown in Figure 1b. The relationship determining the voltage on the capacitor has the form:
Values are expressed in SI units, t seconds, R ohms, C farads. The time during which the voltage on the capacitor reaches the value V C1 is approximately expressed by the following formula:
From this formula it follows that time t1 is proportional to the capacitance of the capacitor. Therefore, the capacitance can be calculated from the charging time of the capacitor.
Scheme
To measure the charging time, a comparator and a microcontroller timer and a digital logic chip are sufficient. It makes perfect sense to use the AT90S2313 microcontroller ( modern analogue– ATtiny2313). The output of the comparator is used as a flip-flop T C1. The threshold voltage is set by a resistor divider. Charging time does not depend on supply voltage. The charging time is determined by formula 2, therefore it does not depend on the supply voltage because the ratio in the formula VC 1 /E is determined only by the divisor coefficient. Of course, during measurement the supply voltage must be constant.
Formula 2 expresses the time it takes to charge the capacitor from 0 volts. However, it is difficult to work with voltage close to zero due to the following reasons:
- The voltage does not drop to 0 volts. It takes time for the capacitor to fully discharge. This will lead to increased measurement times.
- Time required between startscharging and starting the timer. This will cause measurement error. For AVR this is not critical because this requires only one clock cycle.
- Leakage current at the analog input. According to the AVR datasheet, current leakage increases when the input voltage is close to zero volts.
To prevent these difficulties, two threshold voltages VC 1 (0.17 Vcc) and VC 2 (0.5 Vcc) were used. Surface printed circuit board must be clean to minimize leakage currents. The required supply voltage for the microcontroller is provided by a DC-DC converter powered by a 1.5VAA battery. Instead of a DC-DC converter, it is advisable to use 9 Vbattery and converter 78 L05, preferablyAlsodon't turn offBOD, otherwise problems may arise with EEPROM.
Calibration
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To calibrate the lower range: Using the SW1 button. Next, connect pin #1 and pin #3 on P1, insert a 1nF capacitor and press SW1.
To calibrate the high range: Close pin #4 and #6 of connector P1, insert a 100nF capacitor and press SW1.
The inscription “E4” when turned on means that the calibration value was not found in the EEPROM.
Usage
Automatic ranging
Charging starts through a 3.3M resistor. If the voltage across the capacitor does not reach 0.5 Vcc in less than 130 mS (>57nF), the capacitor discharges and new charger, but through a 3.3 kOhm resistor. If the voltage on the capacitor does not reach 0.5 Vcc in 1 second (>440µF), the inscription “E2”. When time is measured, the capacity is calculated and displayed. The last segment displays the measuring range (pF, nF, µF).
Clamp
You can use part of a socket as a clamp. When measuring small capacitances (units of picofarads), the use of long wires is undesirable.
This article provides an elementary circuit of a capacitance meter on a logic chip. Such a classic and elementary circuit solution can be reproduced quite quickly and easily. Therefore, this article will be useful to a novice radio amateur who is planning to assemble a basic capacitor capacitance meter.
Operation of the capacitance meter circuit:
Figure No. 1 – Capacitance meter circuit List of capacitance meter elements:
R1- R4 – 47 KOhm
R5 – 1.1 KOhm
C3 – 1500 pF
C4 – 12000 pF
C5 –0.1 µF
C meas. – capacitor whose capacitance you want to measure
SA1 – roller switch
DA1 – K155LA3 or SN7400
VD1-VD2– KD509 or analogue 1N903A
PA1 – Pointer indicator head (total deflection current 1 mA, frame resistance 240 Ohm)
XS1- XS2 – crocodile connectors
This version of the capacitor capacitance meter has four ranges, which can be selected using switch SA1. For example, in position “1” you can measure capacitors with a capacity of 50 pF, in position “2” - up to 500 pF, in position “3” - up to 5000 pF, in position “4” - up to 0.05 µF.
The elements of the DA1 microcircuit provide sufficient current to charge the measured capacitor (C measured). It is especially important for measurement accuracy to adequately select diodes VD1-VD2; they must have the same (most similar) characteristics.
Setting up the capacitance meter circuit:
Setting up such a circuit is quite simple; you need to connect C change. with known characteristics (with known capacity). Select the required measurement range with the switch SA1 and rotate the knob of the construction resistor until you achieve the desired reading on the indicator head PA1 (I recommend calibrating it in accordance with your readings, this can be done by disassembling the indicator head and gluing a new scale with new inscriptions)
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 function. But when making another homemade product, we very often think about whether it will work, whether the capacitors we used are working, how to check them. And simply during the repair process, this device will be necessary. Of course, you can check the integrity of the electrolytic capacitor using a tester. But we will find out whether he is alive or not, but we will not be able to determine the container, how dry he is.
Some cheap multimeters currently on the market 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 one with acceptable characteristics. I chose the XC6013L:
This device comes in a beautiful box. True, there is a picture of another multimeter on the box:
And on top is a sticker with the model of this device; the Chinese probably don’t have enough boxes:
The device is enclosed in a protective yellow casing made of soft plastic, similar to rubber. It feels weighty in your hands, which indicates the seriousness of the device. There is a folding stand on the bottom side, which may not be useful to many:
The capacity meter is powered by a 9-volt Krona battery, which is supplied in the kit:
The characteristics of the device are simply excellent. It can measure from 200 picofarads to 20 thousand microfarads. Which is quite enough for amateur radio purposes:
On top of the device there is a large and informative liquid crystal 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 there is a blue button, which I was very pleased with - the screen is backlit, which is undoubtedly an advantage of this device. Between the buttons there is a connector for measuring small capacitors. True, it is not possible to test bush capacitors soldered from donor boards, since the contact pads are located quite deep. Therefore, this connector can only be used when checking capacitors with long leads:
Under the selector for selecting measurement ranges 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:
There is also, undoubtedly, the most important function The device is setting zero readings when measuring capacitances in the picofarad category. As can be clearly seen in the next two photographs. Here one probe is deliberately removed and zero is set using the regulator:
Here the dipstick is put in place. As you can see, the capacitance of the probes affects the readings. Now it’s enough to set zero using the regulator and take measurements, which will be quite accurate:
Now let's test the device in operation and see what it can do.
Testing a 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 the 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 showed 120 microfarads. Possible instrument error. Or maybe now they are doing something substandard:
Here's one thousand microfarads, very accurately:
Two thousand two hundred microfarads is also not bad:
And here are ten microfarads:
Well, now one hundred microfarads, very good:
Let's look at the readings the device will show when checking defective capacitors that were removed during repair. As you can see, the difference is noticeable:
These 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 desoldering 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 capacity meter and, one might say, took the first thing I came across. I was so tired of the inability of the Mastech MY62 multimeter to measure the capacitance of capacitors greater than 20 microfarads, and it did not correctly measure less than 100 picofarads. I liked two things about the SM-7115A:
- Measures the entire required range
- Compact and convenient
Paid 750 rubles. I sincerely believed that it was not worth the money, and the price was “inflated” due to the complete lack of competitive products. The country of origin is, of course, China. He was afraid that he would “fib”; moreover, he was sure of it - but in vain.
The capacitance meter and the wires to it were packed in polyethylene, each in its own shell and placed in a box made of thick cardboard, free space filled with foam. Also in the box were instructions for English. Overall dimensions of the device are 135 x 72 x 36 mm, weight 180 grams. The body color is black, the front panel has a lilac tint. It has a liquid crystal indicator, nine measurement ranges, two power-off positions, a zero adjustment regulator, 15 centimeter, different colored (red - black) wires, with which the measured capacitor is connected to the device, ending with alligator clips, and the sockets on the device body , for their connection, are marked with a color designation of the corresponding polarity; it is additionally possible to measure without them (which increases accuracy), for which there are two elongated sockets, which are signed with the symbol of the capacitor being measured. A 9-volt battery is used and 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 20000 μF, with the ability to adjust the measurement range from 0 to 200 pF, to set zero, within +/- 20 pF, time of one measurement 2-3 seconds.
Table of permissible errors in measurements, individually by range. 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 changes the better side review of the liquid crystal display.
The battery compartment is completely autonomous; to change the battery, just move its cover to the side. Convenience is inconspicuous when it exists.
In order to remove back cover It is enough to unscrew one self-tapping screw on the housing. The heaviest component on the PCB is the 500mA fuse.
The basis of the work measuring instrument The method of double integration is based. 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.
By unscrewing six more screws you can see the other side of the printed circuit board. The variable resistor used to set it to “0” is positioned so that it can be easily replaced if necessary. On the left are the contacts for connecting the capacitor being measured, those above are for direct connection (without wires).
The device is not immediately set to the zero reference point, but the adjusted reading remains. It's much easier to do this with the wires disconnected.
To clearly demonstrate the difference in measurement accuracy when different ways measurements (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 7.6 pF 8.3 pF
№3 8.1 pF 9.3 pF
Everything is clear; measurements will definitely be more accurate without wires, although the discrepancy is practically within 1 pF. I also repeatedly measured the capacitors on the boards - the measurement readings of serviceable ones are quite adequate according to the value indicated on them. Without being too picky, we can say that the measurement quality factor of the device is quite high.
Disadvantages of the device
- zeroing is not done immediately,
- the contact blades, for measuring without wires, lack elasticity and do not return to their original position after unclamping,
- The meter is not equipped with a calibration container.
Conclusions
In general, I am satisfied with the device. It measures well, is compact (easily fits in a pocket), so on the radio market I take not what they give, but what I need. I plan to modify it when I have time: replace the potentiometer and direct measurement contacts. Its diagram, or something similar, can be found in the section. He told it “as it is,” and you can decide for yourself whether it’s worth adding such a device to your home laboratory. Author - Babay.
DIY ESR meter. There is a wide list of equipment breakdowns, the cause of which is precisely electrolytic. The main factor in the malfunction of electrolytic capacitors is “drying out,” familiar to all radio amateurs, which occurs due to poor sealing of the housing. In this case, its capacitive or, in other words, reactance increases as a result of a decrease in its nominal capacity.
In addition, during operation, electrochemical reactions take place in it, which corrode the connection points between the leads and the plates. The contact deteriorates, eventually forming “contact resistance”, sometimes reaching several tens of ohms. This is exactly the same if a resistor is connected in series to a working capacitor, and moreover, this resistor is placed inside it. This resistance is also called “equivalent series resistance” or ESR.
Existence series resistance negatively affects work electronic devices, distorting the operation of capacitors in the circuit. Increased ESR (about 3...5 Ohms) has an extremely strong impact on the performance, leading to the burning of expensive microcircuits and transistors.
The table below shows the average ESR values (in milliohms) for new capacitors of various capacities depending on the voltage for which they are designed.
Material: ABS + metal + acrylic lenses. LED backlight...
It is no secret that reactance decreases with increasing frequency. For example, at a frequency of 100 kHz and a capacitance of 10 μF, the capacitive component will be no more than 0.2 Ohm. Measuring the fall AC voltage having a frequency of 100 kHz and higher, we can assume that with an error in the region of 10...20%, the result of the measurement will be the active resistance of the capacitor. Therefore, it is not at all difficult to assemble.
Description of ESR meter for capacitors
A pulse generator with a frequency of 120 kHz is assembled on logical elements DD1.1 and DD1.2. The generator frequency is determined by the RC circuit on elements R1 and C1.
For coordination, element DD1.3 was introduced. To increase the power of pulses from the generator, elements DD1.4...DD1.6 were introduced into the circuit. Next, the signal passes through the voltage divider across resistors R2 and R3 and goes to the capacitor Cx under study. The alternating voltage measurement unit contains diodes VD1 and VD2 and a multimeter as a voltage meter, for example, M838. The multimeter must be switched to DC voltage measurement mode. The ESR meter is adjusted by changing the R2 value.
The DD1 - K561LN2 microcircuit can be replaced with K1561LN2. Diodes VD1 and VD2 are germanium, it is possible to use D9, GD507, D18.
The radio components of the ESR meter are located on, which you can make yourself. Structurally, the device is made in the same housing with the battery. Probe X1 is made in the form of an awl and attached to the body of the device, probe X2 is a wire no more than 10 cm in length with a needle at the end. Capacitors can be checked directly on the board; there is no need to unsolder them, which makes it much easier to find a faulty capacitor during repairs.
Device setup
1, 5, 10, 15, 25, 30, 40, 60, 70 and 80 ohms.
It is necessary to connect a 1 Ohm resistor to the probes X1 and X2 and rotate R2 until the multimeter reads 1 mV. Then, instead of 1 Ohm, connect the next resistor (5 Ohms) and, without changing R2, record the multimeter reading. Do the same with the remaining resistances. The result is a table of values from which the reactance can be determined.
