Watlow Optimizing Your Process System with the Series 988 Controller - Manual (Page 29)

General Software Features
3.9
Optimizing Your Process System with the WATLOW Series 988
TL
TL
W WA
PROCESS
L1 L2 L3 L4
DEV
% OUT DISPLAY
MODE
AUTO
MAN
SERIES 988
Input Linearization
Overview:
In many flow applications the output signal
from a flow transmitter represents a squared
value of the actual flow. The square root must
be extracted from the signal to make it useful
to the operator. Many flow transmitters offer
this feature in the transmitter itself, but this
can add significantly to the cost. Using the
square root extraction option in the Series 988
controller can save the operator money. The
feature is enabled simply by setting input 1
linearization
or input 2 linearization
to square root extraction .
Requirements:
The square root extraction feature is standard
on any Series 988 controller with universal
signal conditioner inputs. The linearization
prompt will appear if a process input is se-
lected via the universal signal conditioner DIP
switches.
J
J
J
J
J
J
J
J
J
J
J
J
J
J
J
J
J 0
2
4
6
8
10
12
14
16
4 6 8 10 12 14 16 18 20
input 1 output 1
Water Treatment Pond
non-linearized signal
linearized signal
Flow in gallons
per minute
flow
transmitter
4-20mA input signal
Sample Application:
A waste water process engineer needs to control the flow of a solution to be
mixed with waste water for treatment of the water. 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 extrac-
tion 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 respec-
tively. The input 1 linearization prompt
would then be set to square root
extraction . You can see from the above graph that without square root
extraction to linearize the signal it would not be useful for controlling the
process.