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6/08 ST 3000 Release 300 and SFC Model STS103 User’s Manual 75
6.4 Selecting Output Form, Continued
About square root
output,
continued
Example: If you have a differential pressure transmitter with a range of
0 to 100 inches of water with an input of 49 inches of water,
substituting into the above formulas yields:
49
100
• 100 = 49%
49%
100
• 100 = 70% Flow, and
70% • 16 + 4 = 15.2 mA dc Output
Square root dropout
To avoid unstable output at readings near zero, the ST 3000 transmitter
automatically drops square root conformity and changes to linear
conformity for low differential pressure readings. As shown in Figure
28, the dropout point is between 0.4 and 0.5 % of differential pressure
input depending on direction.
Figure 28 Square Root Dropout Points.
0 0.2 0.4 0.8 10.6 1.2 1.4
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
0
Differential Pressure (% Full Scale)
Flow
(% of Span)
0utput
(mA dc)
4
4.8
5.6
6.4
Dropout Points
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