A12 2-Wire Toxic Gas Transmitter


The A12 2-Wire Toxic Gas Transmitter handles 28 different gases, providing the most economical and flexible gas measurement system available today. Time was, monitoring multiple gases meant using different gas transmitters – each with its own maintenance problems, its own appetite for spare parts, its own installation headaches and so on.

Never again, thanks to ATI. The A12 universal 2-wire gas transmitter handles 28 different gases, providing the most economical and flexible gas measurement system available today. Combining universal electronics, bench calibration capability, automatic sensor verification, fault detection and alarming and superior sensor technology, A12 is your best transmitter choice.

The A12 is designed for ambient gas monitoring in all kinds of industrial environments: gas storage areas, gas compressor rooms, process piping galleries, rail car sidings, analyzer shacks, gas cabinets, chemical process areas and more.

In fact, the A12 transmitter can be used most anywhere that hazardous gas conditions might develop either through leakage or through natural build up.

ATI sensing modules consist of an electrochemical gas diffusion sensor and a solid state memory assembly. These sensors provide excellent response time, maximum selectivity and superior temperature stability for reliable gas sensing in a wide range of environments. The companion memory assembly stores operational information and calibration constants, along with gas sensor identification, sensing module range and software revision level. Complete sensing modules are housed in convenient snap-in packages that mate easily with A12 transmitters.

This unique combination of sensor and memory lets you calibrate sensing modules with any A12 transmitter. So instead of calibrating in the field, you can bench calibrate sensing modules with a spare transmitter; once the sensors are snapped into a field transmitter, their calibration constants upload automatically.

The A12 microcomputer controlled transmitter provides a local digital display and a 4-20 mA analog output proportional to gas concentration. It works with any ATI sensing module, configuring its own display and output range automatically based on data read from the module’s memory. Zero and calibration data is also read into memory, so the transmitter is automatically calibrated when it’s connected to a calibrated module.

Magnetic controls on the front of the transmitter allow field calibration, manual activation of the Auto-Test feature (if installed) and review of sensing module data including gas type, range and number of successful Auto-Tests. The transmitter can also act as an analog output simulator to facilitate complete loop testing. Outputs of 4.0, 12.0 and 20.0 mA are selectable via the front panel, along with a trouble signal of 3.6 mA. The transmitter is housed in a durable cast aluminum shell with an 11 pin octal base for easy installation and removal. And since UniSens transmitter are 100% interchangeable, one unit can service as a backup for every type of gas in use.


  • Interchangeable sensing modules
  • Auto-Test sensor verification
  • Non-intrusive magnetic controls
  • 28 different gases
  • Off site calibration
  • Integral LCD display
  • Output simulation
  • CSA approved
  • Intrinsically safe & explosion proof

Gases Available

Range Available
AutoTest Range
0-2,000 ppm
Acid Gases
0-10, 0-20, 0-100, 0-200 ppm
0-10, 0-20 ppm
0-500, 0-1,000, 0-2,000 ppm
0-50, 0-100, 0-200, 0-500, 0-1,000 ppm
0-50, 0-100 ppm
0-1,000 ppb
0-1, 0-2, 0-5, 0-10, 0-50, 0-100 ppm
0-1, 0-2, 0-5, 0-10 ppm
Carbon Monoxide
0-50, 0-100, 0-200, 0-500 ppm
0-50, 0-100 ppm
0-1, 0-2, 0-5, 0-10, 0-50, 0-100 ppm
0-1, 0-2, 0-5, 0-10 ppm
Chlorine Dioxide
0-1, 0-2, 0-5, 0-10, 0-50, 0-100, 0-1,000ppm
0-1, 0-2, 0-5, 0-10 ppm
0-1,000 ppb
Ethylene Oxide
0-20, 0-200 ppm
0-1, 0-2 ppm
0-1, 0-2 ppm
0-20, 0-200 ppm
0-1,000 ppb
0-1,000, 0-2,000 ppm, 0-4%, 0-10%
Hydrogen Chloride
0-10, 0-20, 0-100 ppm
0-10, 0-20 ppm
Hydrogen Cyanide
0-10, 0-20, 0-100 ppm
0-10, 0-20 ppm
Hydrogen Fluoride
0-10, 0-20, 0-100, 0-200 ppm
0-10, 0-20 ppm
Hydrogen Peroxide
0-10, 0-20, 0-50, 0-500, 0-1,000 ppm
0-10, 0-20 ppm
Hydrogen Selenide
0-1,000 ppb
Hydrogen Sulfide
0-10, 0-25, 0-50, 0-100, 0-500 ppm
0-10, 0-25, 0-50 ppm
0-1, 0-2, 0-5, 0-10, 0-50, 0-100 ppm
0-1, 0-2, 0-5 ppm
Nitrogen Dioxide
0-20, 0-200 ppm
0-20 ppm
Nitric Oxide
0-25, 0-50, 0-100, 0-200 ppm
0-25, 0-50
0-5%, 0-25%
0-1, 0-2, 0-5, 0-10, 0-50, 0-100 ppm
0-1, 0-2, 0-5, 0-10 ppm
0-1, 0-2, 0-5, 0-10, 0-100 ppm
0-1,000, 0-2,000 ppb 0-10, 0-1,000 ppm
0-10 0-20 ppm
Sulfur Dioxide
0-10, 0-20, 0-100 ppm
0-10, 0-20 ppm


Range Supplied with standard range for each gas unless otherwise specified
Display 4 1/2″ digit LCD
Accuracy Generally ±5% of value, but limited by available calibration gas accuracy
Electronic Repeatability ±1%
Electronic Linearity ±0.5%
Zero Drift Sensor dependent, but generally less than 2% of full scale per month, non-cumulative
Span Drift Application dependent, but generally less than 3% per month
Power 12-30 VDC
Output Loop powered 4-20 mA, 675 ohms maximum at 24 VDC
Loop Simulation Operator selectable outputs of 4, 12, 20 and 3.6 mA (trouble indicator)
Enclosure NEMA 4X and explosion proof cast aluminum, Class 1, Div 1, Groups B, C & D
Controls Magnetic controls activated externally through glass window
Sensor Modular plug-in unit with calibration data, gas type and range in sensor memory
Sensor Life Average greater than two years

Auto-Test – Savings & Safety

Available on many ATI sensing modules, the optional Auto-Test gas generator can cut testing costs dramatically by automatically verifying sensor response. The Auto-Test gas generator is coupled to the end of the sensor as an integral part of the sensing module. Every 24 hours, the transmitter activates the generator and monitors the sensor for response. If the sensor responds properly, the system reverts to normal operation; if it fails, output is driven to 3.6 mA to signal trouble. (During testing, the output signal is held at the pre-test value). The transmitter maintains a log of completed tests and can display the time until the next scheduled test. An operator can manually activate the Auto-Test, too.

Combustible Auto-Test Sensor

Now sensor response can be verified every 24 hours automatically. 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.

ATI’s Auto-Test Combustible Gas Transmitter 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.

Transmitter Features

  •  Transmitters contain an LCD display indicating LEL values locally.
  • Non-intrusive calibration using a magnetic transmitter controls allow adjustments without removing enclosure cover.
  • Manual Auto-Test -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 relay base for ease of service.
  • Where installations require the sensor be located remote from transmitter electronics, sensor may be supplied with an explosion-proof junction box and a remote gas feed system to facilitate calibration.

Auto-Test System 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 (patent pending) integrated into an explosion-proof stainless steel housing. When activated by the electronic 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, and “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.


Gas Type Gas Type Calibrated for methane unless otherwise specified
Range 0-100% LEL
Response Time 10 seconds
Accuracy ±5% of value, but limited by available calibration gas accuracy
Repeatability ±0.1%
Linearity ±0 0.5%
Zero Drift Less than 2% full scale per month
Span Drift Less than 3% per month
Output Powered 4-20 mA, 1,000 ohms maximum at 24 VDC
Power 12-30 VDC, 125 mA maximum
Enclosure Explosion proof, Class 1, Div 1, Groups A, B, C & D
Sensors 316 Stainless steel
Sensor Auto-Test Hydrogen gas generator integral to gas sensor housing
Control 4 magnetic switches on front of transmitter
Operating Temperature -40°C to 80°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 2-Wire Toxic Gas Transmitter literature

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