Capacitor tester: types of devices and measurement technique

When repairing or radio engineering, you often have to deal with an element such as a capacitor. Its main characteristic is its capacity. Due to the peculiarities of the device and operating modes, the failure of electrolytes becomes one of the main causes of radio equipment malfunctions. Different testing devices are used to determine the capacity of an element. They are easy to purchase in the store, or you can make them yourself.

Physical definition of a capacitor

A capacitor is an electrical element used to store charge or energy. Structurally, a radioelement consists of two plates made of a conductive material, between which a dielectric layer is located. Conductive plates are called plates. They are not connected by a common contact, but each has its own conclusion.

Capacitors have a multilayer appearance, in which the dielectric layer alternates with the layers of the plates. They represent a cylinder or parallelepiped with rounded corners. The main parameter of an electrical element is capacity, the unit of which is farad (F, F). In the diagrams and in the literature, the radio component is indicated by the Latin letter C. After the symbol, the serial number on the diagram and the value of the nominal capacity are indicated.

Since one farad is a rather large value, the real values ​​of the capacitance of the capacitor are much lower. Therefore, when recording it is customary to use conditional abbreviations:

• P - picofarad (pF, pF);
• H - nanofarad (nF, nF);
• M - microfarad (mF, μF).

Principle of operation

The principle of operation of a radio component depends on the type of electrical network. When connected to the terminals of the plates of a direct current source, charge carriers fall on the conductive plates of the capacitor, where they are accumulated. At the same time, a potential difference appears at the terminals of the plates. Its value increases until it reaches a value equal to the current source. As soon as this value is equalized, the charge ceases to accumulate on the plates, and the electrical circuit is broken.

In an AC network, a capacitor is a resistance. Its value is related to the frequency of the current: the higher it is, the lower the resistance, and vice versa. When a radioelement is exposed to a variable current strength, a charge accumulates. Over time, the charge current decreases and disappears completely. During this process, charges of different signs are concentrated on the plates of the device.

A dielectric between them prevents them from moving. At the moment of the half-wave change, the capacitor is discharged through the load connected to its terminals. A discharge current arises, that is, the energy accumulated by the radio element begins to flow into the electrical circuit.

Capacitors are used in almost any electronic circuit. They serve as filter elements for converting the ripple current and cutting off various frequencies. In addition, they compensate for reactive power.

Characteristics and types

Measurements of the parameters of capacitors are associated with finding the values ​​of their characteristics. But among them, the most important is the capacity, which is usually measured. This value indicates the amount of charge that a radioelement can accumulate. In physics, electrical capacity is called a value equal to the ratio of the charge on any plate to the potential difference between them.

In this case, the capacitance of the capacitor depends on the area of ​​the element plates and the thickness of the dielectric. In addition to the capacitance, the radio device is also characterized by the polarity and the value of the internal resistance. Using special devices, these quantities can also be measured. The resistance of the device affects the self-discharge of the element. Besides, the main characteristics of a capacitor include:

1. Leakage resistance. This is the internal impedance through which the discharge of a capacitor that is not connected to an external circuit occurs.
2. Equivalent inductance. This is a parasitic characteristic that affects the operation of the element at high frequencies.
3. Equivalent Series Resistance (ESR). It consists of the generalized resistance of the leads and plates, it is represented as a resistor connected in series with a capacitor.

Capacitors are classified according to different criteria, but first of all they are divided by the type of dielectric. It can be gaseous, liquid and solid. Most often, glass, mica, ceramics, paper and synthetic films are used as it. Besides, capacitors differ in their ability to change the value of the capacitance and can be:

1. Permanent. Capacitors belonging to this type have a constant capacitance value.
2. Variables. These include radioelements, the capacity of which can be changed during the operation of the device. The change occurs due to a change in temperature conditions, electrical parameters of the circuit and mechanical methods.
3. Construction. They allow you to change the capacity when setting up the equipment, while the element should not be connected to a power source.

Also, depending on the purpose, capacitors are of general and special purpose. The first type of devices are low-voltage, and the second - impulse, starting, etc. But regardless of the type and purpose, the principle of measuring their parameters is identical.

Measuring instruments

To measure the parameters of capacitors, both specialized devices and general use are used. By their type, capacity meters are divided into two types: digital and analog. Specialized devices can measure the capacitance of an element and its internal resistance. A simple tester usually diagnoses only a dielectric breakdown or a large leak. In addition, if the tester is multifunctional (multimeter), then the capacity can also be measured with it, but usually its measurement limit is not high.

Thus, as a capacitor tester can be used:

• ESR or RLC meter;
• multimeter;
• tester.

In this case, the diagnosis of an element with a device belonging to the first type can be carried out without desoldering from the circuit. If the second or third type is used, then the element or at least one of its outputs must be disconnected from it.

Using an ESR meter

Measuring ESR is very important when testing a capacitor for performance. The fact is that almost all modern technology is pulsed, using high frequencies in its work. If the equivalent resistance of the capacitor is large, then power is released on it, and this causes the heating of the radio element, leading to its degradation.

Structurally, the specialized meter is a housing with a liquid crystal display. A KRONA battery is used as its power source. The device has two connectors of different colors, to which the probes are connected. A red probe is considered positive, and a black one - negative. This is done in order to be able to correctly measure polar capacitors.

Before measuring ESR resistance, the radio component must be discharged, otherwise the device may fail. For this, the capacitor leads are closed with a resistance of the order of one kilo-ohm for a short time.

Direct measurement takes place by connecting the terminals of the radio component with the probes of the device. In the case of an electrolytic capacitor, it is necessary to observe the polarity, that is, connect plus with plus, and minus with minus. After that, the device turns on, and after a while the results of measuring the resistance and the capacitance of the element appear on its screen.

It should be noted that the bulk of such devices are manufactured in China. Their action is based on the use of a microcontroller, the work of which is controlled by the program. When measuring, the controller compares the signal that has passed through the radio element with the internal one and, based on the differences according to a complex algorithm, outputs data. Therefore, the measurement accuracy of such devices depends mainly on the quality of the components used in their manufacture.

When measuring capacity, you can also use an immittance meter. It looks like an ESR meter, but it can additionally measure inductance. Its principle of operation is based on the passage of the test signal through the measured element and the analysis of the data obtained.

Checking with a multimeter

Almost all basic parameters can be measured with a multimeter, but the accuracy of these results will be lower than when using an ESR instrument. Measuring with a multimeter can be represented as follows:

1. To increase the accuracy of the result, the capacitor is evaporated from the circuit.
2. The multimeter switches to capacitance measurement mode. On the instrument panel, this mode is indicated by the symbol - | (- or Cx.
3. The most suitable value range is selected. If difficulties arise, the maximum possible value is set.
4. The test lead plugs are connected to the COM and VΩmA connectors.
5. The probes touch the legs of the capacitor. Observe polarity if necessary.
6. The multimeter will give a signal to the element, measure the voltage on it and automatically calculate the capacity.

If the tester displays OL or Overload, it means that the capacitance is too high to be measured with a multimeter or the capacitor is broken. When there are several zeros in front of the obtained result, the measurement limit must be lowered.

Tester Application

If you do not have a multimeter at hand that can measure the capacity, then you can take measurements with improvised means. This requires a resistor, a constant output power supply, and a voltage measuring device. It is better to consider the measurement technique with a specific example.

Let there be a capacitor, the capacity of which is unknown. To know her you will need to do the following:

1. The tester measures the voltage of the power supply. For example, this value was 9 volts.
2. A 1K resistor is connected in series with the capacitor to be measured to form an RC network.
3. The capacitor is short-circuited and the RC is connected to the power supply.
4. A multimeter measures the voltage of the circuit. Let's say it hasn't changed and remains equal to nine volts.
5. A value is calculated that is 95% of this voltage. For our case, this value is 8.55 V.
6. At the next stage, the stopwatch is turned on, and at the same time the short-circuit is removed from the capacitor.
7. As soon as the tester reads 8.55 V, the stopwatch stops. Let this time be 60 seconds.
8. Using the formula 3 * t = 3 * R * C, you need to calculate the capacity. For the example under consideration, it will be: C = (60/3) / 1000 = 0.02 F or 20,000 μF.

Such a measurement algorithm cannot be called accurate, but it is quite capable of giving a general idea of ​​the capacity of a radio element.

Diagram of a homemade device

If you have knowledge of radio amateurism, you can assemble a device for measuring the capacity with your own hands. There are many circuitry solutions of various levels of complexity. Many of them are based on measuring the frequency and period of pulses in a circuit with a measured capacitor. Such circuits are complex, so it is easier to use measurements based on calculating the reactance when pulses of fixed frequency are transmitted.

The circuit of such a device is based on a multivibrator, the operating frequency of which is determined by the capacitance and resistance of the resistor, connected to terminals D1.1 and D1.2. The switch S1 sets the measuring range, i.e. changes frequency. From the output of the multivibrator, the pulses are fed to the power amplifier and then to the voltmeter.

The instrument is calibrated at each limit using a reference capacitor. The sensitivity is set by resistor R6.