Series-GSTC

Supported Applications

The Dwyer Series GSTC Carbon Monoxide/Nitrogen Dioxide Gas Transmitter monitors gas concentration in underground parking garages and loading docks. The carbon monoxide transmitter measures exhaust from gasoline engines, while the nitrogen dioxide transmitter measures exhaust from diesel engines.

Operating Conditions & Performance

The Series GSTC operates within an ambient temperature range of -4 to 122°F (-20 to 50°C). For best sensor life, storage is recommended at 32 to 68°F (0 to 20°C). The device functions in humidity levels from 15 to 90% RH constant and 0 to 99% RH intermittent. Accuracy specifications are CO: 2% FS and NO2: 3% FS, at the time of calibration.

Measurement ranges include CO: 0 to 500 PPM and NO2: 10 PPM. Resolution is specified as CO: 1 PPM and NO2: 0.1 PPM. Response times are <45 s to 90% for CO and <25 s to 90% for NO2.

Communication Protocols

The transmitter communicates over an RS-485 wire using BACnet MS/TP, Modbus RTU, or switch-selectable Modbus ASCII. It accounts as one-eighth of a load on the MSTP network. Supported configurations include:

• BACnet: 9600 and 19200 baud rates with 8 data bits, None parity, and 1 stop bit.
• Modbus®: Baud rates of 38400 (Even parity), 57600 (Odd parity), 76800 (None parity, 2 stop bits), and 115200 (None parity, 2 stop bits).

Configuration Options

The Series GSTC features a UV resistant glass filled polycarbonate housing with an IP64 enclosure rating. Electrical connections utilize a removable terminal block with knockouts for conduit fitting.

Sensor and Calibration Options

• Field-Replaceable Sensors: Electrochemical sensors with a typical lifespan of 4 years. Replacement parts include A-505 (CO) and A-506 (NO2).
• Calibration Interface: Field calibration is performed using the optional A-449 remote LCD display.
• DIP Switch Configuration: Includes settings for Protocol selection, Bias Resistors (A[-] and B[+]), and Terminating Resistor status.

BACnet Object Support

The device supports the following dynamically creatable objects:

• Analog Input: CO Concentration or NO2 Concentration (AI1).
• Binary Value: Zero Sensor status (BV1).
• Date Values: Calibration Date (DV1) and Replace Sensor Date (DV2).

Accessories

The series supports the following accessories:

• A-449: Remote LCD display.
• Duct mounting kit (includes air flow pitot tube, air filter with barbed connections, tubing).
• GCK-200CO-2000CO2: Calibration gas.

Key Product Differences

The Series GSTC is distinguished from the related Series GSTA by its communication output. While the Series GSTA offers switch-selectable current (4-20 mA) and voltage outputs, the Series GSTC provides BACnet MS/TP, Modbus RTU, or Modbus ASCII protocols via RS-485.

Model variations within the Series GSTC include:

• GSTC-C: Carbon Monoxide (CO) transmitter.
• GSTC-N: Nitrogen Dioxide (NO2) transmitter.

Suffixes indicate specific configurations such as duct mounting (-D), factory calibration (-FC), or inclusion of the remote LCD display (-LCD).