Interfacing To The Pid Instruction - Allen-Bradley SLC 500 1746-NR4 User Manual

Interfacing to the PID
Instruction
The RTD module was designed to interface directly to the SLC 5/02, SLC
5/03, SLC 5/04 and SLC 5/05 PID instruction without the need for an
intermediate scale operation. Use RTD channel data as the process variable
in the PID instruction.
To program this application, proceed as follows:
1. Select 100 Ω Platinum RTD, α= 0.003916, as the input type by setting bit
0 = 0, bit 1 = 0, bit 2 = 1 and bit 3 = 0 in the configuration word.
2. Select scaled–for–PID as the data type by setting bit 4 = 0 and bit 5 = 1 in
the configuration word.
ATTENTION: When using the module's scaled–for–PID data
format with the SLC PID function, ensure that the PID
!
instruction parameters Maximum Scaled S
Minimum Scaled S
maximum scaled range, in engineering units, (e.g., –200 C to
850 C) for that channel. This allows you to accurately enter the
setpoint in engineering units ( C, F)
Figure 6.7
Programming for PID Application
Rung 2:0 First Pass Bit
S:1
] [
15
Rung 2:1 Channel 0
Status
I:3.4
] [
11
Chapter 6
Ladder Programming Examples
(word 8) match the module's minimum and
min
MOV
MOVE
Source
Dest
Entering address N11:0 allocates elements N11:0 to N11:22 for required
Control Block file length of 23 words. The Process Variable is address
I:3.0, which stores the value of input data word 0 (channel 0). Output of
the PID instruction is stored at address N11:23 (Control Variable
address).
PID
PID
Control Block
Process Variable
Control Variable
Control Block Length
(word 7) and
max
Initialize NR4 Channel 0
N10:0
O:3.0
N11:0
I:3.0
N11:23
23
6–7