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WATLOW Series 988 User’s Manual 8.13
General Software Features, Chapter 8
General Software
Sample Application
A Series 988 controls the humidity in an environmental chamber. The rel-
ative humidity (RH) sensor provides a 4-20mA signal over a 0-100% RH
range. The sensor is very sensitive to changes caused by air flow in the
chamber. The turbulence in the chamber makes the controller display
jump two to three percent. To remove this display dithering set the filter
time constant [Ftr1] for input 1 to two seconds. This will smooth the dis-
play and provide a more realistic reading.
Figure 8.13b -
Humidity chamber
with input filtering.
TL
W
W
A
PROCESS
L1 L2 L3 L4
DEV
% OUT
DISPLAY
MODE
AUTO
MAN
SERIES 988
input 1 output 1
limit
limit
sensor
Humidity Chamber
humitidy
transmitter
heater
Display readings with input filter OFF
time
%RH
Display readings with input filter ON
time
%RH
Figure 8.13a -
Display readings
with input filtering.
C8.wc 5/14/1999 8:55 AM Page 8.13