Publication 1746-UM022B-EN-P - January 2005
Programming Examples 5-3
Automatic Monitoring
Thermocouples and CJC
Sensors
The following example explains how to change data in the channel
configuration word when the channel is currently enabled.
Example - Execute a dynamic configuration change to channel 0 of
the thermocouple module located in slot 1 of a 1746 chassis.
Periodically (e.g., every 60 seconds) change from monitoring an
external type K thermocouple to monitoring the CJC sensors mounted
on the terminal block. The CJC reading gives a good indication of
what the temperature is inside the control cabinet. Finally, set channel
0 back to type K thermocouple.
Verifying Configuration
Changes
When executing a dynamic channel configuration change, there is
always a delay from the time the ladder program makes the change to
the time the 1746-NT8 supplies a data word using that new
configuration information. Also, the ladder program should use the
thermocouple temperature data location N10:20 for thermocouple
temperature readings and data location N10:12 for CJC temperature
readings.
IMPORTANT
During configuration alteration, the state of each
modified channel can not be determined until after
one module update time.
TIP
N10:2/1 through N10:2/4 have the input type for
type K Thermocouple (0001). N10:8/1 through
N10:8/4 have the input type for CJC Temperature
Sensor (1111).
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