Precision Digital PD941 - Manual (Page 27)

ConsoliDator Multi-Channel Controller Instruction Manual
27
Exponent
Exponent mode refers to 2-point scaling with programmable exponent (programmable
root) extraction typically used in open-channel flow applications with weirs and flumes
to linearize the signal from a level transmitter and display the flow rate in engineering
units. The graph in Figure 19 shows the display response based on example
parameters and exponent of “1.5”. For this mode select [Exponent] from Function
options. To enter an exponent, select Configure Function Parameters. Press EDIT and
use arrow keys to change the value. Press SAVE when complete.
The exponent mode supports low-flow cutoff which can be used to suppress readings
below a programmed value. Below the cutoff value, the controller will display “0”. To
enter a cutoff value, select Configure Function Parameters. Press EDIT and use arrow
keys to change the value. Press SAVE when complete.
Follow Sensor Input Setup (page 29) to enter your scaling parameters.
Note: An input that goes below the Low Value parameter results in a display of “-999999”
indicating underrange condition. This can be prevented using the cutoff feature.
Process Scaling Parameters Exponent
Input
(mA)
Display
(%)
High Value: 100.00 Low Value: 0.00
1.50000
4.00 0.00 Sensor: 20.00 Sensor: 4.00
5.00 1.56
Ex pone nt Re sponse
0.00
20.00
40.00
60.00
80.00
100.00
4.00 8.00 12.00 16.00 20.00
Sensor (mA)
Display (%
)
6.00 4.42
7.00 8.12
8.00 12.50
9.00 17.47
10.00 22.96
11.00 28.94
12.00 35.36
13.00 42.19
14.00 49.41
15.00 57.00
16.00 64.95
17.00 73.24
18.00 81.85
19.00 90.77
20.00 100.00
Figure 19. Exponent Response Graph