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General software – Watlow Series 988 User Manual

Page 127

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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

TL

W

W

W

WA

A

PROCESS

L1

L2

L3

L4

DEV

% OUT

DISPLAY

MODE

AUTO

MAN

SERIES 988

input 1

output 1

limit

limit
sensor

Humidit y Cha mbe r

humitidy
transmitter

heater

Display readings with input filter OFF

time

%R

H

Display readings with input filter ON

time

%R

H

Figure 8.13a -
Display readings
with input filtering.