External Compensation Page (Standard Version Only); Figure 24 External Compensation Page - Michell Instruments XTC601 User Manual

XTC601 User's Manual
2.7.6

External Compensation Page (standard version only)

A 4-20 mA sensor may be used to compensate the % Target Gas 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
% of Target Gas.
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 % Target Gas value, a table is created (see example below) while varying the
pressure at 20% of range intervals.
At each point the compensation factor can be set between 0.5 and 2.
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.
Michell Instruments
COMP 20%
COMP 40%
COMP 60%
COMP 80%
COMP 100%
Figure 24 External Compensation page
% of
Pressure TG reading
span
0% 20.91
20% 21.65
40% 23.56
60% 25.99
80% 29.66
100% 38.85
Table 9
0.50-2.00
0.50-2.00
0.50-2.00
0.50-2.00
0.50-2.00
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
OPERATION
Compensation
factor = 1 /
effect
1.00
0.96
0.88
0.81
0.70
0.54
21