| 摘要 |
A plurality of differential analog input channels are multiplexed into a programmable gain amplifier providing four input ranges. The circuit is self-calibrating under microprocessor control with periodic measurements taken of internal channels for analog ground voltage, analog reference voltage and the voltage reference temperature in addition to the analog input signals. The output of the isolation amplifier is fed into a sample and hold circuit and, under the control of an analog input register into an analog to digital converter. An earth barrier separates a primary side which includes the input channels, optically isolated bidirectional MOSFET relays coupled to the input channels, a programmable, selectable gain multiplexer and the input to an isolation amplifier from a secondary side by means of opto isolators bridging the earth barrier. The secondary includes the sample and hold circuit, the power supply, the analog to digital converter, the analog control register, the voltage reference source and decoders.
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