EPS control device. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Measuring technology

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The device is designed to measure the equivalent series resistance (ESR, in foreign literature - ESR) of capacitors. It has two switchable measurement intervals: on the first one, you can check capacitors with a capacity of more than 1 μF (resistance measurement limits from approximately 1 to 30 ohms), on the second - more than 10 μF (from 0,25 to 10 ohms).

Rice. 1 (click to enlarge)

The scheme of the device is shown in fig. 1. A generator is assembled on the DA1 timer, the frequency of which is set to 100 kHz by the resistor R1 and the capacitor C1. From the output of the generator, an alternating voltage is supplied to the measuring resistors R4, R5, connected in parallel to the probes (contacts XP1, XP2).

A millivoltmeter is assembled on the DA2 chip and the PA1 microammeter, which measures the voltage across resistors R4, R5 (or only R5) connected in parallel and the capacitor being tested. Its sensitivity can be adjusted by selecting the resistor R8: when the resistance decreases, the sensitivity increases.

The variable resistor R9 is used to set the value "∞" on the scale of the microammeter RA1 included in the diagonal of the bridge.

The tested capacitor is connected to the probes, the measured EPS value is read from the scale of the microammeter. Each probe is connected with three wires according to the diagram. The length of these wires should not exceed 25 cm. Such a connection made it possible to obtain a resistance that, when the probes are closed, does not exceed 0,15 Ohm, which is quite enough to test any capacitors with a capacity of at least one microfarad.

The device uses an M4762 measuring head - an indicator of the recording level from tape recorders of old releases - with a total deflection current of 100 ... 150 μA. Diodes VD1, VD2 protect the millivoltmeter when checking undischarged capacitors.

The supply voltage is supplied to the generator and millivoltmeter through the LC filters L1C5 and L2C11, respectively. The inductance of the chokes L1, L2 must be at least 50 μH.

Capacitor C2 can be oxide for a voltage of at least 6,3 V, in which case its positive terminal is connected to terminal 3 of the DA1 microcircuit.

Fig. 2

The device is assembled on two printed circuit boards made of fiberglass foiled on one side: a generator is assembled on one (Fig. 2), and a millivoltmeter is assembled on the second (Fig. 3). Oxide capacitor C12 - K50-16 or imported, the rest - KM, fixed resistors - MLT 0,125, variable - SP3-16. On the generator board, on the side of the printed conductors, a jumper made of insulated wire is soldered, connecting pins 2 and 6 of the DA1 chip. Diodes and resistors are mounted perpendicular to the boards.

Fig. 3

In the absence of a K548UN1A microcircuit, a millivoltmeter can be assembled on transistors of the KT315 series or similar with a current transfer coefficient of at least 100. The circuit of this option is shown in fig. 4. A drawing of a printed circuit board made of fiberglass foiled on one side for a transistor millivoltmeter is shown in fig. 5.

Fig. 4

Structurally, the meter is assembled in a housing of a standard telephone socket. On fig. 6 shows the layout of boards and elements. Resistors R4, R5 are soldered to the contacts of the switch SA1, and the capacitor C10 is soldered to the terminals of the microammeter. The available RJ11 sockets can be used to supply voltage, as well as to connect an external microammeter with a full deviation current of not more than 50 μA or a digital multimeter.

Fig. 5

The device is powered by a voltage of 5 V from a low-power stabilized power supply, for example, a charger for a cell phone, the current consumption does not exceed 8 mA.

Fig. 6

The device with a microcircuit millivoltmeter does not need to be adjusted. In the transistor version, you should make sure that the voltage on the collector of the transistor VT2 is within 2 ... 2,5 V. If necessary, this voltage is set by selecting the resistor R5 - a decrease in the resistance of the resistor leads to an increase in the voltage on the collector of the transistor, and vice versa.

The device is calibrated by connecting resistors with a resistance of 1 to 30 ohms instead of the tested capacitor when the SA1 switch is open. When it is closed, the resistance of the calibration resistors is chosen in the range from 0,25 to 10 ohms.

Author: V. Kalendo

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