Fluke 8842a instruction manual Ohms Current Source

8842A

Instruction Manual

Resistor R701, precision resistor network Z701, and transistor/zener diode combination U701 are produced as a matched set so that the output of U702A is precisely -7.00000V. This output is remotely sensed at the pins of the custom A/D IC (U101). Diode CR701 prevents the output from going positive at power-up.

U702B functions as an inverter to provide the +7.00000V output and to supply the reference amplifier. The gain of U702B is set by the two 20 kΩ resistors in the resistor network Z702.

5-15. OHMS CURRENT SOURCE

The Ohms Current Source (Figure 5-7) provides a precise test current for the ohms functions. The first stage (U401, R401, and Q401) produces a precise reference current, using precision resistor R401 and a -7.0000V reference voltage from the Precision Voltage Reference.

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Figure 5-7. Ohms Current Source

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