54
Ultima MOS-5 Detector
9.0 Appendix
9.1 Warranty
MSA warrants the Ultima MOS-5 Intelligent Sensor to be free from defects in workmanship or
material under normal use and service within two years from the date of shipment.
MSA will repair or replace without charge any such equipment found to be defective during the
warranty period. Full determination of the nature of, and responsibility for, defective or
damaged equipment will be made by MSA personnel.
Defective or damaged equipment must be shipped to the MSA plant or representative from
which the original shipment was made. In all cases this warranty is limited to the cost of the
equipment supplied by MSA. The customer will assume all liability for the misuse of this
equipment by its employees or other personnel.
All warranties are contingent upon proper use in the application for which the product was
intended and does not cover products which have been modified or repaired without MSA
approval, or which have been subjected to neglect, accident, improper installation or
application, or on which the original identification marks have been removed or altered.
EXCEPT FOR THE EXPRESS WARRANTY STATED ABOVE, MSA DISCLAIMS ALL
WARRANTIES WITH REGARD TO THE PRODUCTS SOLD, INCLUDING ALL IMPLIED
WARRANTIES OF MERCHANTABILITY AND FITNESS AND THE EXPRESS WARRANTIES
STATED HEREIN ARE IN LIEU OF ALL OBLIGATIONS OR LIABILITIES ON THE PART OF
MSA FOR DAMAGES INCLUDING, BUT NOT LIMITED TO, CONSEQUENTIAL DAMAGES
ARISING OUT OF, OR IN CONNECTION WITH, THE PERFORMANCE OF THE PRODUCT.
9.2 Principle of Operation
MSA uses a proprietary Metal Oxide Semiconductor (MOS) film on the sensor for detecting
hydrogen sulfide (H
2
S) gas. The MOS film is deposited onto a substrate between two
electrodes. With no gas present, the measured resistance between these two electrodes is very
high (in the mega-Ohms). As H
2
S adsorbs onto the film, the resistance between the two
electrodes decreases (to kilo-Ohms). This decrease in resistance is logarithmically proportional
to the concentration of H
2
S that is present.
The change in resistance is converted to a change in voltage, and amplified by the input circuit.
This amplified signal is fed to an Analog to Digital (A/D) Converter, converted to a digital signal
and sent to the microprocessor to be processed. The process of H
2
S adsorbing onto the MOS
film is most effective at an elevated temperature. On the outer edge of the substrate is a heater
ring. The temperature of this heater ring is measured with a thermistor, and kept constant by a
circuit located inside the body of the sensor.
As H
2
S adsorbs onto the film, electrons move more freely from one electrode to the other. This
is represented as a decrease in resistance. The process of H
2
S adsorbing onto the MOS film is
completely reversible. As the concentration of H
2
S decreases (H
2
S desorbs), the resistance
between the electrodes will increase.
