4
Introduction
The 3108 and 3118
8-Channel High-Level Analog Input Cards provide high accuracy analog
measurements. Sampling transformers provide channel-to-RTP System and channel-to-channel
isolation. Very high noise immunity is characteristic of the transformer multiplexer, achieving in
excess of -140 dB of common mode rejection. Immunity to noise is further enhanced with a
double-pole low pass filter.
Analog to digital conversion is performed by a 16-bit switched capacitor successive
approximation A/D converter. Two precision voltage sources provide self-test function for the
card’s amplifiers and A/D converter and can be used to verify accuracy in user application logic.
The card also includes an onboard temperature sensor, which automatically compensates the
analog measurement for higher accuracy. This analog input card also has an internal 12-bit
DAC, which ramps periodically and verifies the operation of the ADC. No field adjustments are
necessary after the initial factory setup.
I/O bus checking diagnostics, card address tests, and configuration tests are performed each
time the controller accesses the card. All data and control transfers are performed twice, once
using the actual data and then using the inverted data. Both versions of the data are compared
to verify that all I/O bus data bits are functioning properly. The configuration code from the card is
compared to the I/O configuration to check that the correct card is installed in the rack. I/O Bus
slot address and control signal contention tests also are performed. Any fault detected sets
status bits in an error detection variable returned to the user application program.
An indicator LED, located near the top of the front panel, indicates the overall health status of the
card. If this LED is on, the card is functioning normally; if it is off, the card is offline. If this LED is
