Archived:Using the Ametek WV Series Watt/VAR Power Transducer with NI Wireless Sensor Networks (WSN)

The Ametek WV series Watt/VAR power transducer is used for power monitoring applications.  The WV sensors measure voltage and current and return separate analog output signals for power (W) and reactive power (VAR).  It should be noted that depending on the model and sensor configuration the output type can differ.  The voltage and current inputs are sensed by separate leads.  The transducer computes the power in watts using Joule’s Law:  and the reactive power using the following equation: .

Figure 1. Ametek WV Series Power Transducers

The Ametek WV series consists of four models to cover 1 ½ , 2, 2 ½ and 3 Element wiring configurations– WV-15, WV-20, WV-25, WV-30.  Each model has different individual specifications and can be customized for a given application.  In general it is possible to customize the voltage range (85-550V), the max current range (1-10A), analog output type (+/-10VDC, 4-20mA, etc) and powering scheme (external or self power).  Each model is used in different applications and it is important to consult with the manufacturer to determine the best model for your application.

These sensors are designed for high voltage and current applications and it is therefore important to take the necessary precautions when installing these sensors.  During installation ensure to follow the mounting instructions provided with the transducer.  Also ensure that all wires are mechanically secured near any connection points. 

Wireless power measurements now make it possible to monitor the power consumption of a given application without the need for extensive wiring systems.  For example in large building complexes there are multiple transformers that need to be monitored to accurately depict a building’s power consumption.  It is now easier than ever to install a power sensor on all of the transformers and wirelessly transmit this data back to a central computer where it can be scaled, analyzed and recorded. 

The major benefit of wireless data transfer with WSN is the ease of system expansion.  Adding monitoring points is as easy as adding a power transducer and wiring it up to a new or existing WSN node.  If it is a new node it is easily added to the system through the I/O server.  If the node is too far to communicate with the gateway directly, other nodes in the system can be used to relay the data back to the gateway using WSN mesh networking. 

The following hardware is needed to connect an Ametek WV series sensor to an NI WSN node.  The WV series sensors can have either a current output or a DC voltage output.  For ease of connectivity, the DC voltage outputs are preferable for the WSN-3202.  If a current output is used it is necessary to use a shunt resistor to convert the current output to a voltage drop.  The WV series transducers can be self-powered.  In the case of the self powered transducers no external supply is required.

1. WSN–3202 Voltage Node.
2. [Optional]Precision resistor to convert 4-20mA output to voltage, such as the SCXI Precision Resistor Kit (249Ω).  Note that this Resistor value will map the 4-20mA signal to a 1-5VDC signal. 
3. Shielded twisted pair wire Beldin 1120A or similar (length dependent on your application).

Figure 2 shows how connect the above components to properly read the voltage signal from the Ametek WV sensor with NI’s WSN-3202. It is important to not ground the shield wire to the AI GND of the WSN Node. In this case if you are experiencing noise in your signal you should connect the shield of the sensor to a suitable ground. 

Figure 2.  Connecting WV-20 to WSN-3202

The Ametek Series can be installed in a variety of configurations depending on the particular application and which model is used.  It is also possible to combine the Ametek Sensor with external current transformers and voltage transformers to be used with larger voltage and current applications. 

Using LabVIEW on a host PC with the NI WSN-3202 with the Ametek WV-20

Extracting the data from the NI WSN-3202 is fairly straightforward.  After creating a new project and adding the WSN gateway and nodes, as outlined in the Getting Started With WSN guide, it is necessary to configure the analog input channel to be used.  To do this, right click on the WSN -3202 Voltage Node and select Properties.  In the channels tab select the analog input channel that the sensor is connected to.  Select the appropriate channel range (+/- 10V range).  The sensor excitation option can be ignored because the WV-20 is self-powered.  So long as the excitation leads on the node are not connected to a load no power will be drawn from the node. 

Once the node and gateway are setup it is a simple matter of acquiring the data, scaling it and displaying it.  NI WSN uses a share variable to bring the data into LabVIEW, which can be dragged and dropped onto the block diagram from the project explorer window.  Right click on the shared variable and select Show Time Stamp.  To ensure the indicator is updated with new data only, it is important that the data’s timestamp is not equal to the timestamp from the previous iteration.  To do this, compare the timestamp from the previous iteration to the current shared variable’s timestamp.  If the timestamps differ we update the indicator, if they are the same we do not update the indicator.  In the Case of the WV-20 voltage outputs, the linear scales simply maps the +/- 10V to the minimum and maximum power reading s of the sensor.

Figure 3. LabVIEW VI Block Diagram Running on Host Computer – Acquires, Scales and Displays Data.

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

With LabVIEW WSN, it is possible to download and run LabVIEW VIs on the programmable version of the WSN-3202 node for local data processing and control.  For example, it is possible to scale the data to engineering units locally on the node, perform custom triggering or alarming, or locally control the DIO lines.

More information on NI WSN and WSN-3202

More information on Ametek WV Sensor

WSN Sensor Solutions