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High impedance voltmeter shows the principle

2015-01-17 13:51  
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Next is the principle of high impedance voltmeter display. The most effective way is to grasp the principle of combining schematic view text, combined with text to understand the principle. See figure: a high input resistance op amp, bridge rectifiers, microampere meter, and other discrete components must be aware of this versatile circuit. This  circuit  can be used to measure the DC, AC RMS, AC peak, or AC peak voltage by simply changing the value of a resistor connected between the inverting input terminal of the operational amplifier and ground. Measured voltage is connected to the non-inverting input of the op amp. Fully deflected generally high input resistance voltmeter circuit shown in display depends on the function switch position is as follows:
(A) 5 v dc in position 1
(b) 5 v AC RMS in position 2
(c) 5 v peak ac at position 3
(d) 5 v AC peak position 4
This circuit is basically a voltage-current converter. The design process is as follows:
Calculated based on the application of Rotary International from one of the following equation:
(A) DC voltmeter: RIA = full EDC / assumptions
(b) rms AC voltmeter (sine wave only): rib = 0.9 overall ERMS / assumptions
(c) peak voltmeter (sine wave only): Rick = 0.636 full EPK / assumptions
(d) between the peak AC voltmeter (sine wave only): Eliminating = 0.318 full EPK-TO-PK / assumptions.
The principle is simple but effective. You can read several times to grasp the principle.
 

TABLE I
Position 1 of Function Switch
Edcinput??? Meter Current
5.00V????? 44 mcA
4.00V?????? 34 mcA
3.00V?????? 24 mcA
2.00V????? 14 mcA
1.00V?????? 4 mcA
TABLE II
Position 2 of Function Switch
Ermsinput??? Meter Current
5V???? 46 mcA
4V?????? 36 mcA
3V????? 26 mcA
2V????? 18 mcA
1V??????? 10 mcA
TABLE III
Position 3 of Function Switch
EPkinput????? Meter Current
5V peak??? 46 mcA
4V peak??? 36 mcA
3V peak??? 26 mcA
2V peak??? 16 mcA
1V peak??? 6 mcA
TABLE IV
Position 4 of Function Switch
EPk-To-PkMeter Current
5V peak to peak???? 46 mcA
4V peak to peak???? 36 mcA
3V peak to peak??? 26 mcA
2V peak to peak???? 16 mcA
1V peak to peak???? 7 mcA

High Resistance Voltmeter

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