Function Blocks
RAI Function Block
Revision 11 HC900 Hybrid Control Designer Function Block Reference Guide 303
2/07
RAI Function Block
Description
The RAI label stands for Analog Input with Remote C/J.
This block is part of the
I/O Blocks category.
Function
This block is used only for Thermocouples when the thermocouple Cold Junction is in a remote location,
i.e., NOT connected at the AI module. Cold Junction compensation is performed using the value presented
at the RCJ input, which is a temperature value in degrees C of the remote junction and which will come
from another AI block. CJ compensation and linearization is performed in the block producing a value in
engineering units at the OUT pin. Fail status of the AI block measuring the Remote CJ can be applied to the
RSTAT pin. (i.e. if the RCJ measurement Fails, the Thermocouple measurement fails)
Input
Analog value from specified real I/O address.
DIS = disable the AI channel
RCJ = Remote CJ Value - This would come from an AI block Output.
RSTAT = Remote CJ Status - This would come from the AI block Fail Pin.
Output
OUT
= Analog Input value in engineering units.
WARN = Warning Input Indication - Sensor failure possibility. If AI input wiring or sensor exceeds
100 ohms of resistance, the WARNing pin will energize. There also will be a warning if the
value of RCJ is outside the limits -30 to +90 C
FAIL = Digital status of channel
Digital Low (0) = OK
Digital High (1) = Open sensor or failed input channel or RSTAT input is ON indicating a
Failed RCJ AI block
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