TXP-C20_Instruction_Manual_(Rev1.0)
REV – 1.0
[34-2900-0207-5 ]
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and the 100ppm reading remains 100.0. Resolution may be limited further by setting decimal points to 0 where in
the above example, 0ppm reads 0 and 100ppm reads 100.
3.3.4.4
Turning Off Unused Channels
The
Channel Active?
menu entry asks if this channel is to be utilized. OFF causes the controller to never process
inputs applied to this channel and no alarms are tripped or data displayed. Inactive channels have a line drawn
through them on the Setup screen to indicate it is turned off.
3.3.5
CAL Setup Menu
The TXP-C20 CAL MODE feature supports pushbutton calibration of zero and span values. This feature should be
utilized only when there are no other zero/span controls within the monitoring system since it is inappropriate to
calibrate a signal at more than one point. Therefore, if calibration will be performed at another transmitter or
monitoring device, the TXP-C20 CAL MODE feature should not be used.
The CAL SETUP menu allows entering the correct Zero Gas & Span Gas set-point values needed to calibrate the
sensor. These are entered in the same engineering units as input range.
Figure 3-6 – CAL Setup Screen
3.3.6
Calibrate Input Menu
Calibration is the most important function ensuring correct operation of TXP-C20’s equipped with sensor inputs.
The CAL MODE (flow chart shown in Figure 3-7) is designed to make calibration quick, easy and error free. A
successful ZERO and SPAN calibration requires only five keystrokes. Optional 4-20mA outputs (if equipped) transmit
1.5mA during CAL MODE and 4mA during the subsequent CAL PURGE delay to prevent external alarms during
calibration. Local TXP-C20 alarm relays are inhibited during CAL MODE. Unintentional calibrations may be reset by
the Set UNITY menu item. Set UNITY resets Cal OFFSET to 0 & Cal GAIN to 1 which is useful for returning the
calibration to a known starting place. Sensor aging may be monitored by recording zero and span readings at Unity
Gain when the sensor is new, and again later when degradation may have occurred. CAL MODE automatically exits
if no keystroke is detected after 5 minutes.
Follow these TXP-C20 sensor calibration guidelines:
•
Calibration accuracy is only as good as the calibration standard accuracy. Macurco Gas Detection
recommends calibration standards with NIST (National Institute of Standards and Technology) traceable
accuracy to increase the validity of the calibration.
