System Operation

The RTD module has 3 operational states:

· power-up

· module operation

· error (module error and channel error)Power-up

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

functions via hardware and software diagnostics. During this time, the module

status LED remains off, and the channel status LEDs are turned on. If no

faults are found during the power-up diagnostics, the module status LED is

turned on, and the channel status LEDs are turned off.

After power-up checks are complete, the RTD module waits for valid channel

configuration data from your SLC ladder logic program (channel status LEDs

off). After configuration data is written to one or more channel configuration

words and their channel enable bits are set by the user program, the channel

status LEDs go on and the module continuously converts the RTD or

resistance input to a value within the range you selected for the enabled

channels. The module is now operating in its normal state.

Each time a channel is read by the module, that data value is tested by the

module for a fault condition, for example, open-circuit, short-circuit, overrange,

and under range. If such a condition is detected, a unique bit is set in

the channel status word and the channel status LED flashes, indicating a

channel error condition.

The SLC processor reads the converted RTD or resistance data from the

module at the end of the program scan or when commanded by the ladder

program. The processor and RTD module determine that the backplane data

transfer was made without error and the data is used in your ladder program.