Theory of Operation
Detailed Circuit Description
2
2-15
A1C4, A1C5, and A1C6 provide a filtered power supply for the ac buffer, the ac buffer
switching JFETs, and the rms converter.
2-26. DCmA
Current through A1R2 develops a voltage that is proportional to the input. This dc
voltage is routed through A1R4 to the active filter, then to the a/d converter. The 100
mA current range uses the 3 V range of the a/d converter. See Figure 2-6.
2-27. ACmA
In ACmA, relay A1K3 connects the ac voltage developed across A1R2 to the ac buffer.
The signal is then conditioned as described for ac volts.
2-28. Amps
The dc voltage output of the 10 amp shunt (A1R3) is routed directly to the a/d converter
through the Analog Measurement Processor OVS input (pin 23). For ac amps, the ac
voltage output of the shunt is routed to the rms converter through Analog Measurement
Processor switches S35 and S37.
2-29. Diode/Continuity Test
In Diode Test, the meter front end is in the 300 ohm range configuration. The a/d
converter measures the dc voltage at the binding posts through the OVS input (pin 23).
For the continuity function, the frequency/continuity comparator senses the signal
through Analog Measurement Processor switches S35 and S41. The comparator toggles
when the input goes below about 20 mV.
2-30. Frequency
The frequency/continuity comparator uses the ac volts/ac mA output of the ac buffer as
its input at the Analog Measurement Processor ACBO input (pin 2). In the 10 A ac
range, the signal is routed to the comparator through Analog Measurement Processor
switches S35 and S41.
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