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CTS - M17

CTS - M17 SERIES COMBUSTIBLE GAS TRANSMITTER/SENSOR

The CTS-M17 Series is a microprocessor based transmitter. It uses a Catalytic Pellistor Bead gas sensor to detect methane or propane gas. Typical applications are buildings built on landfill sites to monitor methane and parking garages to monitor propane leaks. QEL Engineers, through extensive research and development, have designed the M-17 to be an industry leader in performance and application. The M17 offers good value. Standard features within the M17 can only be found as expensive options in other manufacturers' product. A digital display (LCD), 4-20 mA DC or 2-10 VDC, linear to the measured gas range, for transmission to the Building Automation System (BAS) or controller supplied by QEL or others. The signal is fully user assignable over the gas range and can be configured for rising or falling gas concentration. In addition, RS-485 communication is built in. Input voltages of 24 VDC or 24 VAC with wide tolerances are acceptable. Relay setpoints may be set as increasing or decreasing actuation simply by adjusting the deadband relationship. Set the deactuation point above the actuation setpoint and the M17 will automatically alarm on decreasing concentrations. Relay setpoints are always present even though the relays themselves are an option. Calibration is very easy - simply apply the cal gas and adjust the potentiometer to the desired reading on the display. The standard enclosure is a fire retardant Polycarbonate/ABS blend.

Gas Selection Table

Enlarge Picture

Gas Type

#

100% LEL
In % Volume

Methane CH4 10 5.0%
Propane C3H8 30 2.1%
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PRINCIPLE OF OPERATION

Sensor assemblies consist of two matched pellistor beads, each encasing a coiled platinum wire. One of the beads is coated with platinum as a catalyst. Both elements are exposed to the same environmental conditions and heated with the platinum wire. The elements are connected to two nodes of a Wheatstone Bridge on the transmitter electronics, measuring the resistance of each element. When combustible gas is introduced to the elements, the catalyst coating on one bead will cause oxidation. This reaction will in turn raise the temperature of the element thereby increasing the resistance. This oxidation cannot occur without the coating. The resultant difference in resistance is proportional to the concentration of the combustible gas. The electronics provide a null adjustment to balance the resistance of the sensor elements in clean air conditions. The resistance differential is linearized and converted to a 4 - 20 mA DC signal proportional to a 0 to 100% LEL concentration of the target combustible gas. Zero and span adjustments are provided to calibrate the transmitter for a specific combustible gas.

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Last Updated 03/18/10