Phase measurement with a multimeter. Scheme, description

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Phase measurement with a multimeter. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Measuring technology

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A simple circuit and a digital multimeter are all that is needed to measure the phase angle of two pulse trains and read its value directly from the display. The error is approximately 1% for output signals in the frequency range from 100 Hz to 200 kHz.

(click to enlarge)

Since the input D of the D-flip-flop of the circuit (1/2 74HC74) is always logic level 1, the rising edge of input signal A will set the trigger output to state 1 (see figure). On the other hand, a narrow negative pulse is generated from the signal B by the circuit R1, C1, ICic, and ICd, resetting the flip-flop to 0. The duration of the pulse generated at the output of the 74CH74 type flip-flop is equal to the time interval between the leading edges of the pulses of sequences A and B. Output voltage , divided by resistors R3, R4, R5 and integrated by the circuit R6, C2, is a constant signal proportional to T1/T.

Initially, the circuit must be set to full scale. This is done by closing the key S3, which leads to the appearance of a logic level 74 at the output of the trigger type 74HC1. Now R4 should be adjusted until the indication of 3,60 V appears on the multimeter indicator. The resolution of the readings is 0,01 V = 1 °. Since the logic zero voltage of the 74HC74 type IC is very close to 0, there is no need to adjust the device at the zero level. By combining the positions of the switches S1 and S2, users can choose different combinations of edges, the phase mismatch between which should be measured (see Table 1).

Table 1

S1	S2	Phase mismatch angle
А	В	Between rising edge A and rising edge B
А	B	Between rising edge A and falling edge B
А	B	Between trailing edge A and rising edge B
А	B	Between falling edge A and falling edge B

Literature

Yongping Xia. Multimeter finds phase angle, ED, 1990, No. 14, pp. 57, 58.

Publication: N. Bolshakov, rf.atnn.ru

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