Series-CDT

Supported Applications

The Dwyer Series CDT and CDTR are wall mount or duct mount transmitters designed to monitor Carbon Dioxide (CO2) concentration, temperature, and relative humidity in indoor environments. Documented applications include schools, office buildings, and other facilities aiming for LEED® certification. The series supports compliance with California Public Utilities Code 1625 (Assembly Bill 841), which requires CO2 monitoring in classrooms.

Specific configurations address school safety requirements via the DSA-compliant option (-S). This feature includes a front-facing LED that illuminates when CO2 levels exceed 1100 PPM. The transmitters are intended for use with building management controllers to monitor air quality and support energy savings strategies.

Operating Conditions & Performance

The series utilizes a single-beam dual-wavelength non-dispersive infrared (NDIR) sensor with an expected life of 15 years. Measurement ranges are available as CO2: 0 to 2000 PPM or 0 to 5000 PPM, depending on the model selected.

Performance specifications include:

• CO2 Accuracy: ±40 PPM + 3% of reading (for 2000 PPM range); ±50 PPM + 5% of reading (for 5000 PPM range).
• Temperature Accuracy: ±1°C @ 25°C.
• Relative Humidity Accuracy: ±2% for units configured with humidity output (Series CDTR), measured over a range of 0 to 85% or 10 to 95% RH depending on the specific manual reference.

The specified CO2 accuracy is guaranteed after three weeks of continuous operation in intermittently occupied environments. A warm-up period of 30 minutes is required upon powering the transmitter for it to adjust to current CO2 concentrations. The response time is documented as 2 min for a 90% step change (or 99% per some manual references). Operating temperature limits are 32 to 122°F (0 to 50°C).

Digital barometric pressure adjustment is included to improve measurement accuracy at various elevations. The series features Automated CO2 Baseline Correction (ABC) for maintenance-free operation in intermittently occupied spaces, requiring exposure to normal outdoor equivalent carbon dioxide levels once every thirty days.

Configuration Options

The Series CDT and CDTR offer configurable mounting styles, output signals, sensor elements, and display options. The series supports the following configurations:

• Housing & Mounting: North American style wall mount or Duct mount (probe insertion).
• CO2 Range Selection: 0 to 2000 PPM (-2) or 0 to 5000 PPM (-5).
• Output Signals:
  • Current: 4-20 mA (max. 500 Ω load resistance).
  • Voltage: 0-5 VDC, 0-10 VDC, or other ranges selectable via DIP switches (min. 500 Ω load for voltage outputs).
  • Relay: Optional SPST NO rated 2A @ 30 VDC with user-adjustable set points.
• Temperature Output Options:
  • None (CO2 only).
  • 4-20 mA / 0 to (5 or 10) VDC universal output for temperature.
  • Sensor elements: Pt100 Ω RTD, Pt1000 Ω RTD, 10 KΩ NTC thermistor type II/III, or 20 KΩ NTC thermistor.
• Display & Interface:
  • Integral LCD display (Model A-449) for wall mount units only.
  • Remote LCD display with buttons (Model A-449A) compatible with both wall and duct mounts via a mini USB plug connection to the housing receptor.
• School Compliance: Option -S provides DSA compliance with an external LED indicator for CO2 > 1100 PPM.
• Power Supply: 16-35 VDC or 19-28 VAC. Power consumption averages 2 W (peak 3.75 W).

The transmitters feature a terminal block with PG11 and PG16 knockouts for electrical connection, wired using maximum 18 AWG wire.

Key Product Differences

Differences between the Series CDT and CDTR are defined by measurement capability. The Series CDT measures CO2 concentration and temperature. The Series CDTR adds ambient relative humidity (RH) measurement to these parameters, with RH output available on units configured for that function.

Mounting variations distinguish between wall mount models (North American style housing dimensions: 4-1/2" height x 2-51/64" width x 1-3/32" depth) and duct mount probes. Duct mount variants feature a probe diameter of approximately 1-15/64" [31.35 mm] with an overall length of 11-49/64" [298.85 mm].

Output configuration varies by model code selection for temperature sensing, allowing engineers to choose between universal analog outputs (current/voltage) or specific sensor element types (RTD or thermistor). The optional relay output allows control of exhaust fans, windows, dampers, or signaling lights/horns based on user-adjustable set points.