A/D converter
The SourceMeter unit uses a multi-slope charge balance A/D converter with a single-slope
charge balance run-down. The converter is controlled by gate array U610. Commands are issued
by the MPU on the digital board through communications opto-isolators to U610, and U610
sends A/D reading data back through opto-isolators to the digital board for calibration and
processing.
Active guard
The Model 2410 has an active guard or "six-wire ohms" circuit used to measure complex
devices. This circuitry provides a low-current (50mA) equivalent of the voltage on output HI. If
the unit is in the SV mode, th
e low-current equivalent of the source voltage will appear on the
guard terminal. If the unit is in the SI mode, the voltage on output HI is equal to the source
current multiplied by the external resistance value. An equivalent voltage will be generated by
the guard circuit, and a guard sense terminal is provided to sense around the voltage drop in
the guard leads since significant current can flow (50mA).
4-10 Troubleshooting
2410-902-01.book Page 10 Monday, November 7, 2005 2:49 PM
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