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34
087-0020 REV
E
Zero Calibration
The transmitter’s zero is set by adjusting the loop output to 4 mA while the sensor is
exposed to air which is free of the gas being detected (and any interferent gases which
may be present).
Please note that the first ±3% full scale is “clipped” to 4mA/zero,
this includes both the display and analog output. Therefore confirm the
transmitter is actually in a clean environment prior to zeroing.
Zero Calibration Using Ambient Air
Ambient air may only be used for the zeroing process if it is certain to be free of both the
target gas and any possible interferants; otherwise, a zero grade air should be used
(except when zeroing an Oxygen transmitter, which uses Nitrogen for this
procedure).
Using A Permeation Tube Device
When using a permeation tube device during a calibration session, it is recommended
that constant flow of zero air be established for at least 10 minutes
before
being hooked
up to the calibration adaptor on the sensor. This ensures that any analyte gas which
may have been present from a previous span calibration is flushed from the tubing and
adaptor.
Zero Calibration Procedure
To zero the Transmitter, proceed as follows:
Step 1 –
Install the calibration adaptor or flow cell to the GasPlus
sensor
(see Figures).
Make all appropriate tubing connections
per manufacturer recommendations. Turn on the air flow
at a rate of 500 cc/min. and let circulate over the sensor for
1 to 5 minutes.
Step 2 –
Zero the transmitter by using the magnet and placing it over
the
“Z”
(ZERO) point on the transmitter body until the display reads “CAL”.
(time required is approximately four (4) seconds). Remove the magnet and
“0.0” will be displayed. (the display will vary with range 0, 0.0,or 0.00
depending upon the sensor range)
Note:
The current output will go to 4.05 mA ±.05 mA.
This offset is to prevent nuisance faults from occurring on PLC/DCS that don’t
tolerate outputs below 4.0 mA.
Figure 16 Zero
Calibration
Freedom 5000 Universal Analog Toxic Gas Detector
Instruction Manual