External Compensation Page; Figure 22 External Compensation Page - Michell Instruments XTP501 User Manual

OPERATION
2.7.5

External Compensation Page

A 4–20 mA sensor may be used to compensate the % reading for the effects of process
variables such as line pressure, flow, etc. The table of compensation factors may be edited for
5 points along the compensation sensor range. The values would be determined by applying
the process variable at each point and noting the effect on the %.
For example: a compensation is needed for line pressure. A 4–20 mA line pressure sensor
would be ranged over the compensation range. While the instrument reads a fixed % O
value, a table is created (see example below) while varying the pressure at 20% of range
intervals:
Pressure
0
1
2
3
4
5
The compensation factor values are then entered into the External Compensation table
(excluding the 0% point as this will always be assumed to be 1 = no effect).
Below 0% (< 4 mA), the compensation factor is fixed to 1. Above 100% the compensation
factor is extrapolated beyond the last factor.
22
Figure 22
% of
Pressure O reading
2
span
0% 20.91
20% 21.65
40% 23.56
60% 25.99
80% 29.66
100% 38.85
XTP501 & XTC501 User's Manual
External Compensation Page
Effect =
(affected value
/ non-affected
value)
20.91/20.91=1.00
21.65/20.91=1.04
1.13
1.24
1.42
1.86
Compensation
factor = 1 /
effect
1.00
0.96
0.88
0.81
0.70
0.54
99976 Issue 1.1, May 2020
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