SNAP PID MODULE REFERENCE
18
SNAP PID Module User’s Guide
Defining a PID Control Word
To determine a hexadecimal control word for a particular combination of control settings, do the
following:
1.
In the table
“Control Word Bits” on page 18
, identify the bits that correspond to the
parameters you want to set.
2.
For each bit you select, choose the binary value that corresponds to the control setting you
want.
3.
Convert the binary values to hexadecimal to determine the PID control word.
For example, read the table below from top to bottom and right to left to see how you
might figure out a control word that sets the PID mode to Auto (that is, by setting bit 7 to 1).
Note that the leading zeros do not need to be entered; in this example, entering “80” in the
Control Word field is sufficient. See
“Binary/Hexadecimal Conversion Chart” on page 25
for a
table of 4-bit binary data and equivalent hexadecimal values.
Control Word Bits
Control word bits:
7 6 5 4
3 2 1
0
7 6 5 4
3 2 1 0
Binary data for each bit: (bits 1–7 are not used)
1 0 0 0
0 0 0 0
Hexadecimal value:
8
0
Enter this control word:
8 0
Bit
Bit Name and Description
Default
To Modify,
Use Mode...
0
(not used)
n/a
n/a
1
(not used)
n/a
n/a
2
TPO Output
Sets PID output to use analog or TPO signals.
0 = Analog PID output. The analog output value is set to the Low
Output Limit.
1 = TPO PID output. The TPO output is set to the High Output
Limit.
0
(analog
output)
Manual
3
Process Variable Source
Sets an internal or external source for the process variable value.
0 = Process variable obtained from external analog source
connected to SNAP-PID-V channel 1.
1 = Process variable obtained from internal value.
0
(external
source)
Manual
