Archived: Using the Veris Industries H908 Current Switch with NI Wireless Sensor Networks (WSN)

The H908 series current switch offers a high performance product, with a wide array of amperage range options.  These switches are most often used to detect belt loss, coupling shear or other mechanical failures on loads from 2.5A-135A (1/5 to 100HP).  It is therefore easily possible to monitor under-current situations or over-current situations.  If these conditions are detected the switch can be configured to kill power to the motor controller thereby maintaining safe operation. 

The Veris Hawkeye H908 consists of a normally open solid state relay, rated at 1.0A @30VAC/VDC controlled by the input current to a current transformer.   The H908 has an adjustable trip point that determines the current level at which the relay closes or opens.  

Figure 1. Veris Hawkeye 908 Current Switch

Veris makes a few variations of the H908 Current switch.  The H608, H708, H808 all have an adjustable trip point and status open/closed LEDs.  Depending on the model the input range can range from 0.75A – 135A.  These models also come in a split or solid core configuration. 

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 current switch.  Also ensure that all wires are mechanically secured near any connection points. 

With NI WSN it is now possible to monitor the status of a mechanical system by combining a Veris H908 current switch and a NI-3202 Voltage node remotely.  In general these current switches are used to directly kill the power to a system, but a WSN node can be used to wirelessly send status information back to a central computer. The node can also be used in conjunction with LabVIEW WSN to make intelligent decisions based on the system status.  Using NI-WSN allows for easy system expansion, easy remote monitoring, and removes the need for large wiring networks back to the central computer.

The following hardware is needed to connect the Veris H908 to the NI WSN-3202 Voltage Node:

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

Figure 2 shows how to connect the above components to properly read the current signal from the Veris sensor with NI’s WSN-3202.  In this application the H908 sensor monitors the current flow through one of the motor leads.  If the current spikes high or low with respect to the set point the relay opens/closes.  The WSN-3202 Digital inputs have an internal pull-up resistor that pulls the line high to 5V unless a load is connect to it.  Therefore if we connect the digital ground – DGND- to one side of the H908 switch and the DIO1 channel input to the other side of the switch, the DIO1 line will read 5V anytime the switch is open and 0V when the switch is closed – shorting DIO1 to DGND. 

Depending on your application this wiring diagram will be different.  For details on how to configure the H908 set point for over-current or under-current situations please see the manufacturer’s user manual.  The H908 is a self-powered current switch and therefore no external power supply is required. 

Figure 2.  Connecting H908 to WSN-3202

Using LabVIEW on a host PC with the NI WSN-3202 with the H908

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 digital input and output channels.  To do this, right click on the WSN-3202 Voltage Node and select Properties.  From the Properties window select Discrete Output  and select Tristate for DIO1.  This configures the DIO1 for digital input and pulls the value up to 5V.   

Once the node and gateway are setup, it is a simple matter of acquiring the data, processing the logic 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.  In the case of an over-current monitoring application, continuously read in on the DIO1 input channel.  The H908 relay will close if the current is greater than the set point.  As such, if a digital logic low is read on DIO1 the relay is closed and an over-current situation has occurred. 

To implement the previous example, drag and drop a shared variable node for DIO1 onto the host block diagram.  Right click on the shared variable and select change to read.  Right click on the DIO1 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.  This is the simplest of cases where all we do is update an indicator on the front panel.  It is possible however to have the host VI conduct some more complex operations with this information depending on what is required for your application.

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 H908

With LabVIEW WSN, you can download and run LabVIEW VIs on the programmable WSN-3202 node for local data processing and control.  In this case it would be possible to do some direct interpretation of the data on the node and then change certain inputs/outputs depending on the state of the DIO1 Channel. 

More information on NI WSN and WSN-3202

More information on Veris Industries H908 Current Switch

Wireless Sensor Solutions