C
12-17 Combustible Gas Transmitter
13
O&M Manual
Rev-D
TRANSMITTER SPAN
The span setting for a combustible gas sensor/transmitter will depend on the gas or vapor for
which the unit will be mainly used. To calibrate the system for applications where methane in the main
combustible to be expected, connect tubing from your span gas cylinder (1% Methane) to the calibration
adapter inlet. Turn on the gas flow and adjust to approximately 500 cc/min. (ATI calibration kits contain
fixed flow regulators that automatically provide 500 cc/min. flow). The reading on the DVM attached to
the transmitter test points will immediately start to increase. Allow the gas to flow to the sensor for 2-3
minutes and observe the reading on the DVM. The reading should be relatively stable ± 0.5 mv. Use the
span potentiometer to adjust the DVM to 72 mv. This adjustment assumes the use of 1% methane gas
standards, which are the equivalent of 20% LEL. If using another methane concentration, calculate the
voltage setting as follows: (v/o = Volume Percent)
V = 40 mV + [160 mV X (Span Gas Concentration in
V
/
O
÷ 5
V
/
O
)]
As an example, if your span gas cylinder is marked with a concentration of 2.5% Methane, the
calculation would be:
V = 40 mV + [160 mV X (2.5
V
/
O
÷ 5
V
/
O
)] = 120 mV
When the span has been set, turn off the span gas flow and remove the calibration adapter from
the sensor. Place the lid back on the transmitter enclosure and tighten the cover to insure the enclosure
remains watertight. If the ATI receiver alarm relays were inhibited prior to calibration, press the
A/R
switch to return the system to normal operation.
TRANSMITTER FAULT INDICATION
The C12-17 combustible gas transmitter is designed to detect certain fault conditions in the
sensor and transmitter and to indicate the fault conditions by driving the 4-20 mA output to below 2 mA.
Receiving instruments that can identify this condition and provide a visual indication of the fault will
provide added security for your gas detection system. When the C12 signal is used as an input to a PLC
or computer system, the system should be programmed to recognize a 2 mA output as a fault condition
for the transmitter.
The below 2 mA fault condition will be generated under the following conditions:
One of the sensor leads is not connected at the terminal block.
A sensor wire has broken in the interconnect wiring of a dual condulet installation.
The combustible sensing element has failed.
