Input scaling example: pulse encoder – Watlow CPC400 User Manual
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CPC400 Series User’s Guide
Chapter 3: Operation and Setup
Doc. 0600-2900-2000
Watlow Anafaze
61
Table 3.6
Input Readings and Calculations
Table 3.7
Scaling Values
Input Scaling Example: Pulse Encoder
Situation
A pulse encoder measures the movement of a conveyor. The
encoder generates 900 pulses for every inch the conveyor
moves. You want to measure conveyor speed in feet per
minute (FPM).
Setup
The encoder input is connected to the pulse input (loop 5 on
a CPC404, loop 9 on a CPC408). On that loop, set the Input
type parameter to pulse.
Set the Input pulse sample parameter to 1 sec, because a
one-second sample time gives adequate resolution of the
conveyor speed. The resolution is 0.006 feet per
minute:
Since the resolution is in thousandths, the Disp format pa-
rameter is set to -9.999to 30.000.
To determine the settings for the Input low range and Input
high range parameters, calculate the process variable val-
ues when the input signal is 0 Hz and 2000 Hz. (You could
calculate the values at other frequencies.)
•
At 0 Hz, the process variable is 0.000 FPM.
•
At 2000 Hz, the process variable is 11.111 FPM:
Process
Variable
Displayed
Sensor
Input
Reading in
Percent of Full Scale
65 GPM
4.75 V
(4.75 V / 5.00 V) x 100% = 95%
3 GPM
0.5 V
(0.5 V / 5.00 V) x 100% = 10%
Parameter
Value
Input range high
65 GPM
Input high signal
95.0%
Input range low
3 GPM
Input low signal
10.0%
1 pulse
1 second
------------------------x
60 seconds
1 minute
-------------------------------x
1 inch
900 pulses
-----------------------------x
1 foot
12 inches
--------------------------
0.006 FPM
=