Watlow Series 988 - Manual (Page 131)

WATLOW Series 988 User’s Manual 8.15 General Software Features, Chapter 8
General Software
Sample Application
A waste water process engineer needs to control the flow of a solution to
be mixed with wastewater to treat it. The transmitter provides a 4-20mA
output without square root extraction. The engineer used the Series 988
with a universal signal conditioner input and a 4-20mA process output to
control the flow. The input signal was linearized using the square root
extraction feature of the 988.
The above system has a flow range of 0 to 16 gallons per minute. The
range low and range high parameters for input 1 would be set to 0 and 16
respectively. The input 1 linearization prompt
[lin1] would then be set to
square root extraction [root]. You can see from the above graph that
without square root extraction to linearize the signal it would not be use-
ful for controlling the process.
TL TL W WA
PROCESS
L1 L2 L3 L4
DEV
% OUT DISPLAY
MODE
AUTO
MAN
SERIES 988
input 1 output 1
Wa t e r Tre a t me nt P ond
flow
transmitter
Figure 8.15b -
Waste-water treat-
ment with input lin-
earization.
Figure 8.15a -
Graph of linearized
signal.
O
O
O
O
O
O
O
O
O
O
O
O
O
O O O O 0
2
4
6
8
10
12
14
16
4 6 8 10 12 14 16 18 20
linearized signal
non-linearized signal
4-20mA input signal
flow in
gallons per
minute