Archived: Using the Veris Industries PXU Differential Pressure Sensor with NI WSN

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This document describes the use of the Veris Industries PXU sensor with the NI Wireless Sensor Network (WSN) system for wireless differential pressure measurement. 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 PXU Differential Pressure Sensor

The Veris PXU dry media differential pressure sensor is part of the PX sensor series and is designed to monitor duct and/or static pressure in commercial buildings.

Figure 1: Veris PXU

The PX Series Differential Pressure Transducers utilize a ceramic capacitive pressure transducer with a frequency output. The PXU sensor measures the difference between two pressures introduced as inputs to the sensing unit. The sensor calculates the differences between the pressures and outputs a voltage that corresponds to the value. 

Wireless Dry Media Differential Pressure Measurement

With NI WSN you can remotely monitor a network of sensors over large areas. By combining the PXU sensor with the WSN-3202 voltage node it is possible to monitor differential pressure 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 monitoring differential pressure.  System expansion is also made easy when using the NI WSN. Sensors and WSN nodes can simply be added as needed.

Connecting the PXU to NI WSN-3202 Node

The PXU sensor can output either current or voltage signals. This document discusses the use of the PWLX04S sensor in voltage mode, with the default voltage range set to 0 to 10 V. To configure the PXU sensor for 0 to 10 voltage mode, flip the output switch to Volt, and move the Volt jumper, JP4, to the “right” position. For this application, all other jumpers should be set to the “right”.  To set the pressure range to 0 to 100 Pa, the arrow of the rotary switch must be set to face “2”.

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 PXU sensor requires 12 to 30VDC power, with a max current draw of 25mA, for this reason an external power supply is required.

Connect the positive terminal of the power supply to the Power input of the PXU, and the negative terminal of the power supply to both COM on the PXU and AI GND on the WSN-3202. Connect the Out (0-10V) output of the PXU to AI0 on the WSN-3202 node.

Figure 2.  Connecting PXU to WSN-3202

Programming NI WSN for use with the PXU

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

LabVIEW makes the programming for PXU 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 PXU 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 power for the sensor should 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”.  This will cause the sensor power output to be turned on 25 ms before the A/D conversion.

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 variable for the pressure channel should be dragged onto the block diagram, in this case AI0. This variable outputs voltage values between 0 and 10 volts and this data needs to be scaled to the appropriate values. The Pressure output of 0 to 10V linearly maps to 0 to 100 Pa.

Below is an example block diagram for the PXU application. This example gets the voltage reading from the AI variable and displays it on the front panel. It also applies the scaling and displays this information. The example program can be found at the following link: Link to EPD example program .

Figure 3. Block Diagram for PXU with WSN


Using LabVIEW WSN Embedded Programs on the NI WSN-3202 with the PXU 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.

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