Archived: Using the Veris Industries CWL Series Carbon Dioxide Sensor with NI WSN

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This document describes the use of the Veris Industries CWL Series CO2 sensor with the NI Wireless Sensor Network (WSN) system for wireless environmental CO2 monitoring. This document is one in a series of documents describing how to use specific sensor products with the NI WSN system to wirelessly enable a variety of applications, such as environmental monitoring, climate studies, resource monitoring, etc. For more information on using other sensors with the NI WSN system, please refer to the WSN Sensor Solutions document.


Veris Industries CWL Series Sensor

The Veris CWL carbon dioxide sensor is part of the CW sensor series and is designed for use in HVAC control applications. The sensor measures the amount of CO2 in a space and can help ensure that adequate ventilation is provided. The CWL sensor also provides sensors for relative humidity and temperature. Monitoring CO2, humidity, and temperature levels in a building helps to ensure tenant safety and comfort.

Figure 1: Veris CWL Series

The CWL CO2 sensor is based on the well-known principle of infrared (IR) absorption of radiation called the non-dispersive infrared (NDIR) technique. This technique relies on the fact that molecules absorb light (electromagnetic energy) at spectral regions where the radiated wavelength coincides with internal molecular energy levels. By detecting the amount of light absorbed, within just a narrow band width that coincides with the resonance wavelength of the specie selected, one gets a measure of the number of molecules, free from interference of other species. The absorption measurement is then converted to a CO2 reading.


Wireless CO2 Measurement

With NI WSN you can remotely monitor a network of sensors over large areas. By combining the CWL sensor with the WSN-3202 voltage node it is possible to monitor the CO2 in different areas of a building, all from one location. This eliminates the need for multiple monitoring systems or computers; thus, creating a control system that is ideal for regulating air quality.

System expansion is also made easy when using the NI WSN. Sensors and WSN nodes can simply be added as needed.

Connecting the CWL to NI WSN-3202 Node

The CWL sensor can output either current or voltage signals. This document discusses the use of the CWL sensor in voltage mode, with the default voltage range of 0 to 10 V. To configure the CWL sensor for voltage mode, flip the switch on the sensor to VOLT (see Figure 2 below).

Figure 2: Setting Voltage or Current Mode on CWL Sensor


The NI WSN-3202 voltage node has 4 single ended analog inputs.  Therefore, a single WSN-3202 can monitor the CO2, humidity, and temperature outputs of the CWLSHTA. The voltage node also has a 12V voltage output that is dedicated for sensor powering. However, due to the power requirements of the CWL sensor, an external 24 VAC (20 to 30 VDC) power supply is needed to power the CWL sensor.

Connect the positive terminal of the power supply to the Power input on the CWL Sensor. Connect the negative terminal of the power supply to both the Common on the CWL sensor and the AI GND of the WSN-3202 node. Connect the CO2 Output of the CWL Sensor to AI0 on the WSN-3202 node.

To use the Humidity and Temperature sensors on the CWL, connect the RH Output to AI1, and the Temp Output to AI2 on the WSN-3202 node.

Figure 3.  Connecting CWL to WSN-3202

Programming NI WSN for use with the CWL

Using LabVIEW on a host PC with the NI WSN-3202 with the CWL

LabVIEW makes the programming for CWL sensor applications very straightforward. First, the input range for WSN-3202 analog input channels needs to be set to -10 to 10 Volts to comply with the default CWL output voltage range of 0 to 10 volts. This can be set in the Data Configuration section of the NI WSN-3202 Properties window.

With the WSN properties set, the application building can begin. Each I/O variable on the WSN voltage node has an I/O variable associated with it in the LabVIEW Project. The AI variables for the CO2, RH and Temperature channels should be dragged onto the block diagram. The data from these variables are voltage values between 0 and 10 volts and the data needs to be scaled to the appropriate values.

The CO2 output of 0 to 10V linearly maps to 0 to 2000 PPM or 0 to 5000 PPM, depending on the CO2 range set on the CWL sensor. The RH output of 0 to 10V linearly maps to 0 to 100% humidity. The temperature output of 0 to 10V linearly maps to 50 to 95oF.  Therefore the linear equation will be Temp(oF) = Vout*4.5 + 50

Below is an example block diagram for the CWL application. This example gets the voltage readings from the AI variables and displays them on the front panel. It also applies the scaling for each of the voltage values and displays this information. 


Figure 4. Block Diagram for CWL with WSN

Using LabVIEW WSN Embedded Programs on the NI WSN-3202 with the CWL Sensor

With LabVIEW WSN, you can download and run LabVIEW VIs on a programmable WSN-3202 node for local data processing and control.  For example, you could perform the data scaling to engineering units locally on the node itself, before it is sent to the host computer.