Phase meter. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Measuring technology

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In some cases, for example, when adjusting the phase shifters of spatial sound systems, when setting the angle of inclination of the working gaps of magnetic heads in a stereo tape recorder, etc., it is required to accurately determine the phase shift between two voltages of the same frequency.

Unlike phase meters with a detector based on an RS-trigger [1] or according to the XOR scheme [2], a phase meter with a pulsed frequency-phase detector (PFD) allows you to measure not only the phase shift, but also fix the sign of the shift (lead or lag). The proposed phase meter (Fig. 1) is made as an attachment to a digital multimeter (you can also use a conventional avometer).

(click to enlarge)

Rice. 1. Schematic diagram of the phase meter

At the inputs of the phase meter on the operational amplifiers DA1 and DA2, hysteresis comparators (Schmitt triggers) are made. The sensitivity of the comparators is about 30 mV. From the outputs of the comparators, the signals are fed to a pulsed frequency-phase detector with three states, made on D-flip-flops DD1.1, DD1.2 and transistors VT5, VT6. The load of the detector is resistor R17.

To highlight the constant component, proportional to the phase shift, is a second-order low-pass filter on DA3.

The power supply of the detector transistors is chosen to be ±3,6 V, which corresponds to a phase shift of ±360° (i.e., 1 V corresponds to a phase shift of 100°). The measurement accuracy depends on the amplitude of the input signals - the larger it is, the higher the measurement accuracy. At low levels of the studied signals (up to 100...200 mV), their amplitudes should be close in magnitude.

Voltages of ±3,6 V are obtained from stabilized supply voltages of ±5 V using a circuit based on transistors VT1 ... VT4, in which VT1 and VT2 serve for thermal stabilization.

Setting up a phase meter consists in setting, with the help of resistors R7 and R8, voltages of ±3,6 V at the emitters of transistors VT3 and VT4, as well as in balancing DA3. To balance DA3, the same signal is applied to both inputs. Since the phase shift is then zero, there should be no pulses at the output of the detector. Resistor R20 achieves the minimum voltage at the output of the phase meter.

Construction and details

The phase meter is made on a printed circuit board with dimensions of 87x55 mm (Fig. 2). Pin 4 of DD1 is connected to pin 11 with a jumper on top of the chip. Similarly, pin 5 DD1 can be connected to pin 12 and pin 3 to pin 10. In the presence of double-sided fiberglass, the last two connections can be printed from the installation side of the elements. The rest of the connections are made by printed wiring. The assembly drawing of the board is shown in Fig.3. K1UD2A, DA544 - K2UD3 were used as operational amplifiers DA140, DA608. Trigger DD1 -type K561TM2. Electrolytic capacitors - type K50-35 for a voltage of 10 V. Transistors - KT3107B and KT3102B. All microcircuits (digital and analog) are powered by a stabilized bipolar voltage of ±5 V.

Rice. 2. PCB

Rice. 3. Layout of elements

Literature

1. A. Konyukhov, Phase meter in the establishment of a tape recorder. - Radio, 1983, N1, S.Z0.
2. A. Goncharenko, Phase meter on microcircuits. - Radio, 1984, N12, p.29.

Author: A. Petrov, Mogilev; Publication: cxem.net

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