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# DC Meter Circuit

IP.com Disclosure Number: IPCOM000077372D
Original Publication Date: 1972-Jul-01
Included in the Prior Art Database: 2005-Feb-25
Document File: 3 page(s) / 60K

IBM

## Related People

Koederitz, F: AUTHOR [+3]

## Abstract

Deviations from a predetermined nominal value within a plurality of positive and negative voltages can be determined with an ammeter used as a so-called zero instrument in a bridge circuit.

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DC Meter Circuit

Deviations from a predetermined nominal value within a plurality of positive and negative voltages can be determined with an ammeter used as a so-called zero instrument in a bridge circuit.

In Fig. 1, a positive reference voltage U is applied via resistor R1 to terminal 1 of meter 2. The other terminal 3 of meter 2 is grounded through resistor R5. Terminal 1 is also grounded through divider resistors R2, R3. Switch S can be shifted to various voltages to be measured. Meter terminal 3 is grounded through contact 5, as shown, while the other contact of switch S connects a divider resistance R4 to point 4 between resistors R2 and R3. An individual divider resistor R4 is provided for each different negative voltage to be measured, and correspondingly an individual divider resistor R6 is provided for each positive voltage to be measured.

Assuming switch S in the position shown in solid lines, terminal 3 of the meter is applied to ground through contact 5. A negative voltage to be measured is applied through a right-hand resistor R4 to point 4 between resistors R2 and R3. Thus, a positive voltage is supplied at terminal 1 of the meter, and the voltages supplied via resistor R1 and R2 compensate each other for zero potential when the negative voltage exactly corresponds to its nominal value. Meter 2 will thus stand at its zero position.

If the positive voltage is to be measured, switch S is shifted right to the position represented by the broken lines. It now connects with one of the resistors R6 for the positive voltage, and contact 9 of the switch S is on a contact 6 unfixed so that point 4 is floating. At terminal 1 of meter 2, the positive reference voltage is found; at terminal 3 there is the positive voltage to be measured. If the test voltage has reached its nominal value, the mutual balancing of the bridge resistors, including the internal meter resistance and resistor R6, ensures that the meter will remain at the zero position.

If the positive voltage is to be measured, switch S is shifted right to the position represented by the broken lines. It now connects with one of the resistors R6 for the positive voltage, and contact 9 of the switch S is on a contact 6 unfixed so that point 4 is floating. At terminal 1 of meter 2, the positive reference voltage is found; at terminal 3 there is the positive voltage to be measured. If the test voltage has reached its nominal value, the mutual balancing of the bridge resistors, including the internal meter resistance and resistor R6, ensures that the meter will remain at the zero position.

It will be noted that ground contacts 5 will be connected in the event switch S at its other slide...