Archived: Using the Veris Industries H923 AC Current Transducer with NI Wireless Sensor Networks

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This document describes the use of the Veris Hawkeye H923 current transducer with the NI Wireless Sensor Networks (WSN) system for wireless AC current monitoring. This document is one in a series of documents describing how to use specific sensor products with the NI WSN system to enable a variety of applications, such as environmental monitoring, climate studies, and resource monitoring. For more information on using other sensors with the NI WSN system, please refer to the WSN Sensor Solutions document.

Contents

Veris Industries H923 Current Transducer

The Veris Industries H923 current transducer is used to monitor AC currents.  The Veris Hawkeye H923 monitors the AC current passing through a conductor.  The H923 is a self-powered current transducer consisting of a primary winding, a magnetic core and a secondary winding.  The monitored conductor is passed through the center of the laminated iron and silicon steel ring creating a single ‘turn’ primary winding.  The secondary winding consists of a smaller gauged wire wrapped hundreds of times around the ring.  The alternating current flowing in the primary winding produces a magnetic field in the core inducing a current flow in the secondary winding. The current flow in the secondary winding is accurately proportional to the current in the measured circuit.  The H923 produces a 0-10VDC output, linearly proportional to the current in the conductor.  

Figure 1. Veris Hawkeye H923 Transducer

Veris makes a few variations of the H923 (0-2/100/150A).  The H922 (0-130/60/20A), H722HC/723HC (0-50/100/150A) and H722LC/723LC (0-10/20/40A) are all self-powered current sensors that have slide-switch selectable ranges.  The H92x series are split-core sensors and the H72x series are solid core transducers.  The sensors output a 0-5VDC or a 0-10VDCsignal. 

These sensors are designed for high voltage and current applications and it is therefore important to take the necessary precautions when installing the 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 Current Monitoring

NI WSN allows for current measurements to be taken in remote locations without the need for large wiring networks connecting various sensors to a host machine.  It is now also possible for the user to wirelessly transmit the sensor’s data back to a host machine.  This can also be done on battery power thereby eliminating all wires but that connecting the sensor’s output to the WSN Node.   

Another major benefit of wireless data transfer with WSN is the ease of system expansion.  Adding monitoring points is as easy as adding a current 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 use of 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. 

Connecting the Veris H923 to NI WSN-3202 Node

The following hardware is needed to connect the Veris H923 to the NI WSN-3202 Voltage Node. 

  1. WSN – 3202 Voltage Node.
  2. Shielded twisted pair wire (length dependent on your application).

The H923 produces a 0-10VDC output, linearly proportional to the current in the conductor.  This 0-10 V signal can be measured directly by the NI WSN-3202 voltage node.   The H923 is self-powered, so no power supply is needed for the sensor.

Figure 2 shows how to connect the above components properly.  It is important to not ground the shield wire to the AIGND of the WSN Node. In this case if you are experiencing noise in your signal you should connect the shield of the Veris sensor to a suitable ground.

Figure 2.  Connecting H923 to WSN-3202

Programming NI WSN for use with the H923

Using LabVIEW on a host PC with the NI WSN-3202 with the H923

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 +/-10V as the range.  Sensor excitation can be left alone because the H923 is self-powered and if the node’s excitation leads are disconnected, 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.  In all cases the data is transferred through a shared variable.  The shared variable can be dragged and dropped onto the block diagram from the project explorer.  Once on the block diagram, right click on the shared variable and select Show Time Stamp.  If we don’t want to update the Indicator with repeated data it is important that the timestamp is not equal to the timestamp from the previous iteration.  To do this, compare the timestamp from the previous iteration to the shared variable’s timestamp.  If they are not the same we update the control, if they are the same we do not update the control.  The scaling of the data is a simple linear relation that maps the 0-10V output to a 0 to maximum current.  The maximum current is dependent on the sensor and the select range.   A front panel control is used to change the maximum current.

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 H923

With LabVIEW WSN, you can download and run LabVIEW VIs on the programmable version of the 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.  However because of the slow sampling rates needed for most current monitoring applications, this may not provide a meaningful advantage unless your specific application requirements require additional local processing or control.