Technical Guide: Installation and Wiring for Dwyer CDT-2N40 Wall Mount CO2 Sensor

Technical Guide: Installation and Wiring for Dwyer CDT-2N40 Wall Mount CO2 Sensor

The Dwyer CDT-2N40 wall mount CO2 sensor is a premier solution for monitoring indoor air quality, helping projects achieve LEED® certification through its dual-wavelength single-beam NDIR technology. This device automatically corrects for sensor aging effects, ensuring superior accuracy for 24/7 environments such as hospitals or manufacturing plants. Before starting, engineers can refer to detailed specifications in the article on Series CDT CO2 Sensors or download technical documents directly from the Series CDT Dwyer Datasheet.

1. Common Mistakes and Safety Rules for Installation

Installing a wall-mounted CO2 sensor requires caution to avoid equipment damage and measurement errors:

• Location errors: Avoid installing sensors in areas with severe shock, vibration, excessive moisture, or corrosive fumes.

• Ignoring warm-up: Upon powering, the device requires a 30-minute warm-up period to stabilize and adjust to the current CO2 concentration.

• Electrical shock: Disconnect the power supply before installation to prevent electrical shock and equipment damage.

• Static electricity: Use electrostatic discharge precautions (e.g., wrist straps) during installation and wiring to prevent damaging internal components.

• Exceeding ratings: Never exceed power requirements of 16-35 VDC or 19-28 VAC, as permanent damage not covered by warranty may result.

2. Precise Technical Wiring Instructions

According to the CDT_MANUAL_DWYER_DLK_1.pdf, the CDT series supports universal outputs for flexible connection to most BMS controllers.

Step 1: Configure Output Type (Current/Voltage)

Before wiring, you must set the configuration switches on the circuit board:

• Switch 1: Set to select the output type for CO2 concentration (Voltage or Current).

• Switch 2: Set to select the output type for Temperature/RH (Voltage or Current).

• Voltage Range: If voltage output is selected, use switches in positions 3 & 4 to select 0-10V, 2-10V, 0-5V, or 1-5V.

Step 2: Terminal Block Wiring (Use maximum 18 AWG wire)

• Terminal 1 (PWR): Connect to the positive power supply (+).

• Terminal 2 (COM): Common ground (-) for both power and output signals.

• Terminal 3 (OUT1): CO2 concentration output signal.

• Terminal 4 (OUT2): Temperature or Relative Humidity output signal (depending on model).

• Terminals 5 & 6 (RLY): SPST NO relay contacts, rated for 2A @ 30 VDC.

• Terminals 7 & 8 (SEN): Passive temperature sensor outputs (RTD or thermistor), which are not polarity sensitive.

3. Menu Settings and Barometric Pressure Calibration

To achieve the highest level of accuracy, engineers should configure parameters using the Model A-449 remote display plugged into the internal mini-connector.

• Barometric Pressure (BAR): CO2 measurements are pressure-dependent. Setting the typical barometric pressure for your specific elevation in the BAR menu provides a more accurate measurement.

• Relay Settings (RON/ROF): Set the CO2 concentration at which the optional relay energizes (RON) and de-energizes (ROF) to control exhaust fans or dampers.

• Output Scaling (COL/COH): Set the CO2 concentration for the lowest output (COL) and highest output (COH) signals.

4. Inspection and Routine Maintenance

DLK TRADING SERVICE COMPANY LIMITED – the official Dwyer distributor, advises users to note the following maintenance points:

1. Self-calibration feature: The transmitter requires exposure to normal outdoor equivalent carbon dioxide levels once every thirty days for the self-calibration feature to function correctly.

2. Troubleshooting: Upon powering, the firmware version will flash on the display. If measurements seem inaccurate, verify the barometric pressure (BAR) settings for your location.

3. Replacement/Repair: The Series CDT-2N40 is not field serviceable. If the sensor is damaged or reaches the end of its life, the unit should be returned for repair or replacement to avoid voiding the warranty.

To ensure your system operates durably and correctly, you may refer to the guide on How to Properly Calibrate Dwyer Sensors or re-download the Series CDT Dwyer Datasheet provided by DLK to cross-check detailed wiring diagrams.