Transmitter model GMW84S has one SPST-NO relay (max. 50 VDC / 50 VAC, 500 mA) that is activated when the measured CO2 level rises above the setpoint. When the relay is active (contact is closed), a green LED is lit on the transmitter cover.
Relay setpoint is set using a rotary switch on the component board. Use a small flat head screwdriver to turn the switch. The switch has ten positions with predefined setpoints.
| Switch position | Setpoint in ppm CO2 |
|---|---|
| 0 | 600 ppm (default) |
| 1 | 700 ppm |
| 2 | 800 ppm |
| 3 | 900 ppm |
| 4 | 1000 ppm |
| 5 | 1200 ppm |
| 6 | 1400 ppm |
| 7 | 1600 ppm |
| 8 | 1800 ppm |
| 9 | 2000 ppm |
A hysteresis of 50 ppm is applied to prevent the relay from switching back and forth when the measured value is near the setpoint value. The relay is activated/deactivated when the measured CO2 value passes the setpoint, plus/minus 50 ppm.
| For example, consider a transmitter that has the relay setpoint set to 1000 ppm CO2. As the measured CO2 value rises, the relay is activated at 1051 ppm. The relay remains activated until the measured value falls to 949 ppm. |