Michell Instruments XTP601 - External Compensation Page; Figure 22 External Compensation Page

XTP601 User’s Manual
18 97313 Issue 5, May 2018
OPERATION
2.7.6 External Compensation Page
COMP 20%
0.50-2.00
0.50-2.00
0.50-2.00
0.50-2.00
0.50-2.00
COMP 40%
COMP 60%
COMP 80%
COMP 100%
Figure 22 External Compensation Page
A 4-20 mA sensor may be used to compensate the % O
2
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
% O
2
.
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.