GASMAX EC Operation & Maintenance Manual, Revision 3.5
Page 18
5
CALIBRATION
Calibration Overview
Calibration is critically important to ensure correct operation of the GASMAX EC. 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. During CAL MODE zero and span, the sensor output is
disconnected and the GASMAX EC transmits a fixed mA value, called the CAL MARKER, to notify the
receiving device that a calibration is in progress. During the following CAL PURGE DELAY time, the
GASMAX EC transmits a fixed 4.0 mA signal to prevent external alarms during calibration. In the case of
local or remote Oxygen sensors, during CAL PURGE DELAY the output simulates a typical atmospheric
reading of 20.8%. CAL MODE automatically exits if no keystrokes are detected after 5 minutes.
Follow these GASMAX EC 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.
