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7.0 Appendix
7.1 Warranty
General Monitors warrants the Model 610A Controller to be f ree f rom def ects in
workmanship or material under normal use and service, within two (2) years from the
date of shipment. General Monitors will repair or replace, without charge, any such
def ective equipment found to be defective during the warranty period. General Monit ors’
personnel will make full determination of the nature of, and responsibi l i ty for d ef ec tive
equipment. Def ective or damaged equipment must be shipped prepaid to General
Monitors’ plant, or representative f rom which shipment was made. In all cases, this
warranty is limited to the cost of the equipment supplied by General Monitors. The
customer will assume all liability for the misuse of this equipment b y i ts em ploy ees , o r
other personnel.
All warranties are contingent upon proper use in the application for which the product was
intended. They do not cover products which have been modified, or repaired, without
General Monitors’ approval, or which have been subjected to neglect, accident, improper
installation or application, or on which the original identif ication marks have been
removed, or altered. Except for the express warranty stated above, General Monitors
disclaims all warranties with regard to the products sold, including all implied warrant ies
of merchantability and f itness. The express warranty stated herein are in lieu of all
obligations or liabilities, on the part of General Monitors for damages incl uding, but not
limited to, consequential damages arising out of /or in connection with, the use or
performance of the product.
NOTE: The Model 610A Four Channel Combustible Gas Monitor is easy to install;
however, this manual should be read and understood bef ore attempting to
operate the system.
7.2 Sensor Operating Principle
A high ef ficiency source supplies constant direct current to a Wheatstone Bridge circuit.
One leg of the bridge is formed by two bead elements in s eries , c ontained within the
sensor. These beads are heated by the direct current. The other leg, located on the
printed circuit board in the controller, is a resistive divider. With the sensor exposed to
clean air, any initial bridge imbalance is trimmed out with a zero potentiometer. When a
combustible gas/air mixture diffuses into the sensor, it oxidizes on one of the beads (the
“active” bead, which has been catalytically treated). The second (reference) b ead, inert
to combustible gases, compensates for ambient temperature, humidit y, and pres sure
variations. The oxidation at the active bead causes a temperature increase, which
produces an electrical resistance change and unbalances the Wheatstone Bridge. The
dif ference in resistance between the two beads is proportional to t he c oncent ration of
combustible gas. The signal from the bridge imbalance is amplified and conditioned by
the circuitry. The conditioned signal is then displayed in % LEL by the indiv idual d igi t al
readouts.
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