Michell Instruments XTC501, Руководство пользователя

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XTP501 & XTC501 User’s Manual
22 99976 Issue 1.1, May 2020
OPERATION
2.7.5 External Compensation Page
Figure 22 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
2
value, a table is created (see example below) while varying the pressure at 20% of range
intervals:
Pressure
% of
Pressure
span
O
2
reading
Effect =
(affected value
/ non-affected
value)
Compensation
factor = 1 /
effect
0 0% 20.91 20.91/20.91=1.00 1.00
1 20% 21.65 21.65/20.91=1.04 0.96
2 40% 23.56 1.13 0.88
3 60% 25.99 1.24 0.81
4 80% 29.66 1.42 0.70
5 100% 38.85 1.86 0.54
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.