1. Veris Industries HP2XVSTA Humidity Sensor
The Veris HP2XVSTA humidity sensor is part of the HP sensor series and is designed to provide high accuracy humidity monitoring. The HP2XVSTA is also able to monitor temperature and has a fully replaceable HS element. Monitoring humidity and temperature levels in a building helps to ensure comfort and improves energy savings.
Figure 1: Veris HP2XVSTA
The HP2XVSTA uses a capacitive relative humidity (RH) sensor. The capacitance of the RH sensor changes as a function of relative humidity. The change in capacitance is used in a circuit to provide an electrical output that is indicative of the relative humidity.
2. Wireless Humidity Measurement
With NI WSN you can remotely monitor a network of sensors over large areas. By combining the HP2XVSTA sensor with the WSN-3202 voltage node it is possible to monitor the humidity levels and temperature 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.
3. Connecting the HP2XVSTA to the NI WSN-3202 Node
The HP2XVSTA sensor has four outputs: the blue wire outputs 0-10V for humidity, the orange wire outputs 0-10V for temperature, the green wire outputs 0-5V for humidity, and the yellow wire outputs 0-5V for temperature. This document discusses using the 0-10V humidity and temperature wires of the HP2XVSTA sensor.
Figure 2: HP2XVSTA Wires
The NI WSN-3202 voltage node has 4 single ended analog inputs. The voltage node also has a 12V voltage output that is dedicated for sensor powering. The HP2XVSTA sensor requires 12 to 30VDC power, with a maximum current draw of 15 mA. Therefore, the WSN-3202 node can power one HP Series sensor. Connect the red wire on the HP2XVSTA sensor to SEN PWR on the WSN-3202 voltage node. Connect the black wire on the HP2XVSTA sensor to AI GND of the WSN-3202 voltage node. Connect the blue 0-10V humidity output of the HP2XVSTA Sensor to AI0 on the WSN-3202 voltage node, and connect the orange 0-10V temperature output of the HP2XVSTA Sensor to AI1 on the WSN-3202 voltage node.
Figure 3. Connecting HP2XVSTA to WSN-3202
4. Programming NI WSN for use with the HP2XVSTA
Using LabVIEW on a host PC with the NI WSN-3202 with the HP2XVSTA
LabVIEW makes the programming for HP2XVSTA 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 HP2XVSTA Blue and Orange wire output voltage range of 0 to 10 volts. This can be set in the Data Configuration section of the NI WSN-3202 Properties window. Next, the sensor powering needs to be enabled. This can be done in the Channel Attributes section of the NI WSN-3202 Properties window. Set the attribute to “Sensor Excitation” and the value to “25 ms Delay”.
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 Humidity and Temperature channels should be dragged onto the block diagram, in this case AI0 and AI1. 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 Humidity output of 0 to 10V linearly maps to 0 to 100% humidity. The temperature output of 0 to 10V linearly maps to -40 to 122oF. Therefore the linear equation for the temperature scaling will be Temp(oF) = Vout*16.2 -40
Below is an example block diagram for the HP2XVSTA 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 HP2XVSTA with WSN
5. Using LabVIEW WSN Embedded Programs on the NI WSN-3202 with the HP2XVSTA 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.