GASMAX/TX Operation & Maintenance Manual, Revision 1.0
Page 28
9 CALIBRATION
CALIBRATION OVERVIEW
Calibration is critically important to ensure correct operation of the GASMAX/TX. The built-in CAL MODE
function is designed to make calibration quick, easy and error free; a successful ZERO and SPAN
calibration requires only four keystrokes.
When entering CAL MODE, the GASMAX/TX automatically transmits a data packet containing a value of
300 counts (-15.6% of scale) to enable properly programmed GDS Corp controller / receivers to indicate
IN CAL for the current channel. Once CAL SPAN is complete, the GASMAX/TX transmits a data packet
containing a value of 800 counts (0% of scale). However, if an oxygen sensor is detected, then the
GASMAX/TX will transmit a data packet with a value of 3475 counts (83.6% of scale) to simulate the
typical 20.9% value found in atmospheric oxygen levels.
CAL MODE automatically exits if no keystrokes are detected after 5 minutes.
Follow these GASMAX/TX calibration guidelines:
• Calibration accuracy is only as good as the calibration gas accuracy. GDS Corp calibration gases
are traceable to NIST (National Institute of Standards and Technology).
• Never use calibration gas that has passed its expiration date.
• Check the SPAN GAS VALUE setting and make sure it matches the calibration gas. (See Fig. 6-2)
• Always use a GDS Corp calibration cup that completely surrounds the sensor head.
• Be sure to use ZERO AIR, a mixture of 21% oxygen and 79% nitrogen, as a zero reference unless
you are certain that no target gas exists in the area. Ambient gas may result in an ‘elevated zero’
condition that will cause a FAULT to occur once the ambient gas is no longer present.
• Always calibrate a new sensor before depending on the device for personnel or equipment
safety
• Calibrate on a regular schedule. GDS Corp recommends a full calibration every 3 months, with
periodic ‘bump tests’ on a more frequent basis to ensure that the sensor has not been affected
by temperature extremes or the presence of incompatible gases.
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