A-B 1746-NT8 System Overview SLC500 Thermocouple/mV Analog Input Module

System Overview

The module communicates with the SLC 500 processor and receives

+5V dc and +24V dc power from the system power supply through

the parallel backplane interface. No external power supply is

required. You may install as many thermocouple modules in the

system as the power supply can support.

Each module channel can receive input signals from a thermocouple

or a mV analog input device. You configure each channel to accept

either one. When configured for thermocouple input types, the

module converts analog input voltages into cold-junction

compensated and linearized, digital temperature readings. The

module uses National Institute of Standards and Technology (NIST)

ITS-90 for thermocouple linearization.

When configured for millivolt analog inputs, the module converts

analog values directly into digital counts. The module assumes that

the mV input signal is linear.

System Operation

At power-up, the module checks its internal circuits, memory, and

basic functions. During this time the module status LED remains off. If

the module finds no faults, it turns on its module status LED.

After completing power-up checks, the module waits for valid channel

configuration data from your SLC ladder logic program (channel status

LEDs are off). After channel configuration data is transferred and

channel enable bits are set, the enabled channel status LEDs turn on.

Then the channel continuously converts the thermocouple or millivolt

input to a value within the range you selected for the channel.

Each time the module reads an input channel, the module tests that

data for a fault, i.e. over-range or under-range condition.