1. Honeywell FP2000 Amplified Pressure Transducer
The Honeywell FP2000 series is a configurable pressure transducer, available in ranges from 0.5 psi to 10,000 psi, with gage, absolute, barometric, or vacuum reference. The FP2000 can be ordered with a variety of options for accuracies, pressure ports, connector types, pressure ranges, and electrical interfaces.
Figure 1. Honeywell FP2000 Pressure Transducer
For example, the pressure transducer tested with the NI WSN product is the model FPG (gage transducer) with pressure range of 0-150 ps, configured with the internal amplifier Option 2d. This internal amplifier outputs a 0-5 VDC signal and requires a power supply of 9-28 VDC with a current draw of 10 mA. Other options are available for 4-20mA outputs and different power supply ranges.
2. Wireless Pressure Monitoring and Test
By combining the Honeywell FP2000 Pressure Transducer with NI WSN, you can easily deploy a wireless sensor system for wireless test and measurement applications. In applications with multiple pressure measurement points, particularly over a wide area, WSN eliminates the need for long runs of sensor cabling to bring the signal and data back to a central location. Additionally, the wireless test system is easily expandable. You can easily add WSN pressure transducer nodes, as well as other sensor types, to grow the wireless sensor network. Additionally, the mesh networking feature of NI WSN allows you to grow and expand the network beyond the capabilities of point-to-point wireless links.
3. Connecting the FP2000 Pressure Transducer to the NI WSN-3202 Node
The amplified versions of the FP2000 pressure transducer outputs a high level voltage or current signal, allowing it to be easily used with the WSN-3202 analog input node. In this example, we will illustrate how an FP2000 transducer configured with an internal amplifier and 0-5 VDC outputs (model option 2d), connects directly to the WSN-3202 node.
As shown in Figure 2, the output pins of the amplified pressure transducer are connected directly one AI input channel (single-ended) of the WSN-3202. The FP2000 pressure transducer used in this example is configured with the internal amplifier option 2d, which requires a 9 – 28 VDC power supply, with a current draw of up to 10 mA. The WSN-3202 node can source up to 20 mA at 12 VDC on the SEN PWR pin. Therefore, a single WSN-3202 can power up to two FP2000 pressure transducers configured with the Option 2d internal amplifier. Alternatively, you can use an external power supply to power the FP2000 pressure transducer.
Figure 2. Connecting FP2000 Amplified Pressure Transducer to the WSN-3202
4. Programming NI WSN for use with the FP2000
Using LabVIEW on a host PC with the NI WSN-3202 with the FP2000
Configuring a LabVIEW program to work with the FP2000 and NI WSN system is very straightforward. First, since the amplified pressure transducer used in this example outputs a 0-5 VDC signal, we should configure the input range of the WSN-3202 to an input range of ±5V. This can be set in the Data Configuration section of the NI WSN-3202 Properties window, accessed by right-clicking on the node in the LabVIEW Project.
With the WSN properties set, the application building can begin. Each I/O channel on the WSN voltage node has a shared variable associated with it in the LabVIEW Project. This shared variable returns the unscaled voltage reading returned form the pressure transducer. The 0-5 VDC output of the pressure transducer corresponds to a pressure range of 0 – 150 psi. Therefore, we can use a scaling factor of 30 psi/V, which we calculate on the block diagram from the maximum pressure and output. This allows easy modification for other model options for using calibrated factors for more precise scaling.
Below is a very simple example block diagram for the wireless pressure transducer application. This example acquires the voltage from the node, scales the voltage to engineering units (psi), and displays the pressure value on the front panel. In order to only perform the scaling and displaying when the shared variable returns new data, the VI checks the time stamp of the shared variable for a change of value. In order to access the time stamp, you must right click on the shared variable (AI0) in the LabVIEW project, select Properties, and then check the box next to Enable Timestamping. After dragging the shared variable onto the block diagram, right-click on the shared variable in the block diagram and select Show Time Stamp.
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 FP2000
With LabVIEW WSN and programmable version of the WSN-3202 node, 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, filter the data, program a customized triggering or event detection algorithm, or perform local alarming in the node itself