# Linear AC voltmeter circuit diagram

Posted on Feb 4, 2014

The use of diode rectifiers in AC voltmeters with a low lower limit of measurement range (0. 5. 1 V) leads to significant nonlinearity of the scale because of the nonlinearity of current-voltage characteristics of diodes. The use of electronic amplifiers in rectifier circuits allowing to linearize the scale but requires a power supply. At the same t

ime a linear-bridge rectifier [1, 2] is known, its shoulders are formed by junctions of the collector-emitter of the four transistors, this four transistors is getting the bias voltage from the signal source. The operation of this rectifier is described in detail in [2], a circuit diagram of an AC voltmeter on this basis is shown in Fig. 1. The input (measured) voltage is applied directly to the emitters of the transistors VT1-VT4 (the one of the diagonals of the bridge formed by them), the proportional to this input voltage current is measured by microammeter, connected across collectors of the transistors VT1-VT4 (the other diagonal of the bridge). Testing of this voltmeter showed that the absolute value of the losses in the rectifier at input voltage above 0. 1 V is almost independent of its level and is approximately 40 mV for a load resistance of 10 kilohms (the upper limit of measurement is 1 V) and 60 mV for a load of 5 kilohms (the upper limit of measurement is 0. 5 V). The components for this testing was used the same as described in fig. 1, value of resistors R1-R4 is 10k, microammeter with full-scale deflection of 100 uA. In other words, the scale of the voltmeter was linear in the voltage range of 0. 1. 0. 5V and 0. 1. 1V. The voltmeter was tested with an input sinusoidal signal with a frequency of 10. 10000 Hz. The transfer characteristics (the dependence of the microammeter readings PA1 of the input voltage)...

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