Archived: Using the Badger Meter Series 200 Transducers with NI Wireless Sensor Networks (WSN)

The Badger Meter Series 200 transducers are used for the  volumetric flow monitoring of industrial pipe flows and irrigation systems within pipes of 2 1/2 " to over 40” in diameter.  In general these sensors can be used in both corrosive and non-corrosive fluids, it is only necessary to choose the appropriate sensor construction to be compatible with the measured flow.

Figure 1. Badger Meter Series 200 Transducer

The Badger Meter Series 200 transducers consist of a forward swept six-bladed impeller and a non-magnetic pick up.  Once the sensor is inserted into the flow, the fluid forces the impeller to rotate at a given frequency directly proportional to the volumetric flow rate of the fluid.  The non-magnetic pick up generates a 0-12V square wave proportional to the rate at which the impeller is rotating. 

The 200 series consists of two main types of sensors.  The 220 is a general purpose flow sensor that can be constructed of a variety of materials: brass, stainless steel, or PVC.  The 220 must be installed when the pipe is depressurized and therefore may cause downtime for the plant.  On the other hand, the 225 and 226 sensors are hot-tap sensors allowing the insertion of the transducer into the flow without shutting down the pipe.

Wireless flow measurements now make it possible to monitor the volumetric flow rate of a large network of pipes without the need of complex wiring harnesses.  It is now easier than ever to install a flow sensor and wirelessly transmit the volumetric flow rate of each pipe section 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 flow sensor 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. 

To use a series 200 sensor with WSN a WSN-3202 voltage node is required.  Figure 2 shows how to connect the 200 sensor to the WSN-3202 voltage node.   The Badger Meter Series 200 requires external excitation, which can be sourced by the sensor power (SEN PWR) terminal.  It is important to use a current limiting resistor of approximately 10 kΩ or greater to connect power to the sensor.  This limits the current drawn from the node and extends the battery life of the node.  It is also important to connect the shield to the digital ground of the node to reduce the noise in the signal.

Figure 2.  Connecting Badger Meter 200 Transducer to WSN-3202

In general, whenever the impeller is stationary, the WSN node reads 12V – a digital high.  When the impeller rotates the non-magnetic pick up shorts the high lead wire to ground for 5ms - a digital low.  The most effective way to detect this very small pulse width with the WSN-3202 is to use DIO Notifications and LabVIEW Wireless Sensor Network (WSN) Module to detect the rising edges of the pulse and then calculate the frequency of the signal.   With LabVIEW WSN , you can add intelligence to NI wireless sensor nodes using the same graphical programming approach that has become the industry standard for developing applications that acquire and process data .

When combining a digital input task with LabVIEW for Wireless Sensor Networks it is possible to reach sampling rates near 1kHz.  Although there are different ways of coding this application, the approach in this example uses DIO notifications to record a tick count in milliseconds every time a rising edge is detected.  The two most recent tick counts are stored in shift registers.  We then configure the sample case to iterate every 2 seconds.  When the sample case executes the time difference between the two stored tick counts is calculated and inverted giving the instantaneous frequency of the signal.  This frequency is written to the network published AI0 shared variable which can be read by the host.  From the signal frequency the host can easily calculate the volumetric flow rate of the system.

Figure 3.   LabVIEW for WSN Program Start Case

Figure 4.   LabVIEW for WSN Program DIO Notification Case

Figure 5.   LabVIEW for WSN Program Sample Case

More information on NI WSN and WSN-3202

More information on Badger Meter Series 200 Flow Sensor 

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