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  • Field replaceable electrochemical sensors
  • 4 year typical sensor lifespan
  • 5000 to 7500 sq ft typical coverage area
  • Field selectable outputs
    • Current & voltage (GSTA)
    • BACnet & Modbus (GSTC)
  • Invertable output via dip switch (GSTA)
  • Output ranges (GSTA)
    • CO: 0 to 50 ppm up to 0 to 500 ppm
    • NO2: 0 to 10 ppm
  • Full-scale accuracies of 2% (CO) & 3% (NO2)


The Dwyer GSTA and GSTC carbon monoxide and nitrogen dioxide gas transmitters are designed to monitor gas concentration in underground parking garages and loading docks. The CO transmitter is used to measure the exhaust of gasoline engines and the NO2 transmitter is designed for diesel engines.

GSTA models offer field selectable analog outputs (4 to 20 mA, 0 to 5 VDC & 0 to 10 VDC), while GSTC models feature NACnet or Modbus outputs, which are also field selectable. For carbon monoxide units, the GSTA can be configured for an output range from 0 to 50 ppm up to 0 to 500 ppm. Nitrogen dixoide units come with a standard range of 0 to 10 ppm. Additionally, the output can be inverted to read 20 to 4 mA or 10 or 5 to 0 VDC via internal dip switches. The GSTC is compatible with either BACnet or Modbus communication protocol, allowing the transmitter to be used with almost any building management controller, and its output is communicated over an RS-485 wire.

Using the A-449 remote LCD display (sold separately), the Dwyer GSTC CO and NO2 sensors can be field-calibrated which maximizes the accuracy of the GSTC Accuracy of the CO sensor is 2% full-scale at the time of calibration, while accuracy of the NO2 sensor is 3% full-scale. When the sensor reaches its end of life, the display will indicate that the sensor needs to be replaced.