Interfacing To The Pid Instruction - Allen-Bradley 1746-NT8 User Manual

Interfacing to the PID
Instruction
calibration time to ensure that the new input data matches the channel
configuration requested. The above table shows how to calculate the
update time and auto-calibration time for the channel configuration
being used.
The thermocouple module was designed to interface directly to the
SLC 5/02 or later processor PID instruction without the need for an
intermediate scale operation.
Example - Use 1746-NT8 channel data as the process variable in the
PID instruction.
1. Select scaled-for-PID as the data type in the channel
configuration word.
2. Specify the thermocouple channel data word as the process
variable for the PID instruction.
In this example, the value -32701 (8043 H) is the numeric equivalent
of configuration word N10:0 for channel 0. It is configured for a type
K thermocouple, scaled-for-PID, zero the signal for an open-circuit,
10 Hz, °C, and channel enabled.
Programming for PID Control Example
First Pass Bit
Rung 2:0
s:1
] [
15
Rung 2:1
Rung 2:2
The Rate and Offset parameters should be set per your application.
The Destination will typically be an analog output channel.
Programming Examples
Initialize NT8
Channel 0
MOV
MOVE
Source N10:0
-32701
Dest O:3.0
0
PID
PID
Control Block N11:0
Process Variable I:3.0
Control Variable N11:23
Control Block Length 23
SCL
SCALE
Source N11:23
Rate [/10000]
Offset
Dest
Publication 1746-UM022B-EN-P - January 2005
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