Model 4105 Gas Sensor Module (12/02)
Page: 14
Instruction Manual
Appendix A: Unity Gain Mode
The Unity magnetic control is available during CAL
MODE to allow the ZERO and SPAN adjustments to be
centered within their range. This is similar to setting a
potentiometer so the wiper terminal is exactly halfway
between the clockwise and counterclockwise terminals.
this is identified as the UNITY GAIN mode. In UNITY
GAIN the ZERO controls have a
±
15% of full scale
adjustment range. For example, in UNITY GAIN, if the
sensor's ZERO output has drifted so high that it reads
15% with ZERO gas applied, the DOWN ZERO magnetic
control could still bring the 4105-XX reading to ZERO.
However, it will be at the end of its adjustment range. If
the ZERO adjustment required is greater than
±
10% of
full scale, a BALANCE adjustment should be performed
as described in Appendix A.
In UNITY GAIN the SPAN controls have a .5 to 2 adjust-
ment range. For example, in UNITY GAIN, if a sensor's
output sensitivity has been reduced to the point where
50% SPAN gas provides only a 25% reading, the UP
SPAN magnetic control could still calibrate the reading
to the proper value of 50%. However, it will be at the end
of its adjustment range.
Appendix B: L.C.D. Readout Calibration Procedure
The 3 1/2 digit LCD meter span and decimal points
may be configured for full scale ranges such as 1-
100, 0-25, 0-10.0, 0-1000 and many others. Zero per-
cent of full-scale readings, or those corresponding
to 4mA, are always assumed to equal a reading of 0.
Holding the magnet over the CAL key for at least 5
seconds enters the LCD METER SPAN SETUP
MODE. After this, the current setting for 100% full
scale is displayed and may be modified using the UP/
DOWN SPAN keys. This sets the LCD reading dis-
played when the 4-20mA output equals 30mA. Deci-
mal points are added with the UNITY key.
Appendix C: End of Sensor Life Indication
Old sensors near the end of their service life require
higher gain settings. M4105-XX "END OF SENSOR
LIFE" (ESL) feature may be used to indicate condi-
tion. A span trip point may be entered that when ex-
ceeded, causes the LCD to flash and ESL reading for
2-seconds each 10 seconds. Holding the magnet to
the UNITY key for at least 5 seconds brings the LCD
a span value set-point reading for setting when the
ESL indication trips. CAL MODE GAIN adjustments
range between .5 and 2 and the ESL set-point is ad-
justable between 1.5 and 2.01 with 2.01 turning the
ESL feature off. The current span setting may be
viewed on the LCD during NORMAL MODE by
touching the DOWN SPAN key.
