A12-17 Combustible Gas Transmitter


ATI’s A12-17 Combustible Gas Transmitter with Auto-Test eliminates the need for frequent response checks. This transmitter performs an automatic gas test on the sensing element every 24 hours. The result is a combustible gas detector system with a level of reliability beyond that of any other system available. This daily sensor response verification is as close to a fail safe detection system as you can find, with the added benefit of greatly reduced manual testing.

Combustible gas detectors are used in a wide variety of industrial plants to detect gas leakage or buildup before it reaches explosive levels. These detectors rely on thermal oxidation of any combustible gas or vapor on the surface of a heated catalyst. In other words, they simply burn the gas and measure the heat released in the combustion process. While this type of sensor is generally stable and reliable, it is also subject to poisoning by silicon vapor, lead compounds, and other environmental contaminants. To detect loss of sensitivity, most users test combustible sensors either weekly or biweekly to ensure response. The procedure is simple, but requires manpower to perform the test.

Auto-Test Operation

Combustible gas sensors are made up of two matched sensing elements, one active and one passive. Both are electrically heated and form two legs of a Wheatstone bridge circuit. When combustible gas contacts the sensor, the active element catalyzes the oxidation of gas, heating the active element and changing its resistance. The passive element remains unchanged, resulting in a change in the bridge circuit that is proportional to the gas concentration. As long as the active element remains in good condition, the sensor will respond rapidly to the presence of combustible gas.

The Auto-Test sensor is actually a combination of a gas sensor and an electrochemical hydrogen gas generator integrated into an explosion proof stainless steel housing. When activated by the electric transmitter, the generator produces hydrogen that diffuses to the gas sensor through the flame arrestor protecting the sensor. If the sensor responds properly, the transmitter will show a “Pass” indication. Should the sensor not respond properly, an “Auto Test Fail” message will activate at the transmitter and the 4-20 mA output from the transmitter will drop to 3 mA, providing for remote fault indication.


  • Transmitters contain an LCD display indicating LEL values locally.
  • Magnetic transmitter controls allow adjustments without removing enclosure cover.
  • The hydrogen generator may be activated manually on command to observe sensor response, if desired.
  • The result of each Auto-Test is logged in transmitter memory Operators may review the number of passes and fails from the LCD.
  • The 4-20 mA output from the transmitter may be manually set to 3, 4, 12 or 20 mA in order to test external alarm devices.
  • Electronic transmitters are modular, plugging into a standard really base for ease of service.
  • Where installations require the sensor be located remote from transmitter electronics, sensors may be supplied with an explosion proof junction box and a remote gas feed system to facilitate calibration.


Gas Type Calibrated for methane unless otherwise ordered
Display 3 digit LCD optional
Range 0-100% LEL
Response Time T90 < 10 seconds
Accuracy Generally ±5% of value, but limited by available calibration gas accuracy
Electronic Repeatability ±1%
Electronic Linearity ±0.5%
Zero Drift Less than 2% full scale per month
Span Drift Less than 3% per month
Output Powered 4-20mA, 675 ohms max at 24 VDC
Power 12-30 VDC, 100 mA maximum
Enclosure Explosion proof, Class 1, Div 1, Groups B, C & D
Sensor Auto-Test Hydrogen gas generator integral to gas sensor housing
Sensor 316 Stainless Steel
Enclosure Explosion proof Class 1, Div 1, Groups B, C, & D
Controls 4 magnetic switches on front of transmitter
Operating Temperature -40 to 70°C
Weight 4 pounds

Ordering Information

For pricing, please call AFC International at 1-800-952-3293, 219-987-6825 or fax 219-987-6826 or email sales@afcintl.com.


A12-17 Combustible Gas Transmitter literature

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