Archived: Using the Veris Industries H971 DC Current Transducer with NI Wireless Sensor Networks WSN

The Veris Industries H971 current transducer is used for DC current monitoring.  The Veris Hawkeye H971 uses Pulse Reset™ technology to measure the DC current flow through a conductor.  Pulse Reset technology is extremely accurate, repeatable, and bidirectional, enabling the sensing of the direction of current flow.  The H971 uses 15-24VDC external power to produce a 4-20 mA signal linearly proportional to the current in the measured conductor.

Figure 1. Veris Hawkeye 971 Transducer

Veris makes two different DC Current sensors: the H970 and H971.  The main difference is that the H970 series produces a 0-5V or 0-10V signal.  To use the H970 series it is not necessary to use a shunt resistor, it is a simple matter of connecting the sensor output to the WSN Node. 

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

NI WSN makes taking current measurements in remote locations easier than ever. In applications such as solar panel monitoring, battery chargers or Motor armature currents, WSN eliminates the need for large wiring networks connecting various sensors to a host machine.  NI WSN now enables the user to wirelessly transmit the sensor’s data back to a host machine.  This is often very useful for remote applications such as solar panel monitoring.

Another 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 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. 

The following hardware is needed to connect the Veris H971 to the NI WSN-3202 Voltage Node. 

1. WSN – 3202 Voltage Node.
2. External Power supply capable of 15-24VDC @ 35mA (at no Load) and 55-110mA (at 200A Current)
3. 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 approximately 1-5VDC.  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 current signal from the Veris sensor with NI’s WSN-3202. 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 H971 to WSN-3202

Using LabVIEW on a host PC with the NI WSN-3202 with the H971

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 +/-5V (for the 249 Ω Resistor) as the range.  Sensor excitation can be left alone because our sensor does not to be powered and as long as the excitation leads on the node 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 indicator, if they are the same we do not update the indicator.  The scaling of the data is a simple linear relation that maps the 4-20mA output to a 0 to maximum current by reading the voltage drop across the shunt resistor.  Although the sensor returns a maximum current output of 20mA, this maximum current corresponds to a maximum current read dependent on the sensor and the selected range.   A front panel control is used to change the maximum current read by 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 H971

With LabVIEW WSN, you can download and run LabVIEW VIs on the WSN 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.

More information on NI WSN and WSN-3202

More information on Veris Industries H971 DC Current Transducer

WSN Sensor Solutions