Archived: Using Applied Geomechanics Model 801 Tiltmeters with NI Wireless Sensor Networks (WSN)

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This document describes the use of Applied Geomechanics tilt sensors with the NI Wireless Sensor Networks (WSN) system for wireless measurements of angular displacement. 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.

Applied Geomechanics Model 801 Tuff Tilt Uniaxial Tiltmeter

All tiltmeters utilize some type of tilt transducer that generates an electric signal that corresponds to the level of displacement that the sensor experiences.   While most tiltmeters use an accelerometer or pendulum to sense the incident force of gravity, the Applied Geomechanics Model 801 Tuff Tilt Uniaxial Tiltmeter utilizes an electrolytic solution to sense the amount of tilt experienced by the sensor.   Electrolytic tilt sensors offer very high performance and have no mechanical moving parts to break or wear out.

Figure 1.  Applied Geomechanics Model 801 Tuff Tilt

Although tilt sensors are used in a large variety of applications, the 801 Tuff Tilt is typically used in more rugged environments to monitor anything from land movement, to structure and bridge activity.

Wireless Tilt Measurement

Whether they are deployed in small or large quantities, rugged tilt sensors are often placed in areas where it can be difficult, not to mention expensive, to lay the conduit and wiring required in order to bring tilt measurements into any kind of intelligent control or data logging system.  For situations like this, you can easily combine the NI WSN system with the Model 801 Tuff Tilt to deploy a distributed, wireless tilt monitoring system.

Connecting the Model 801 Tuff Tilt to the WSN-3202 Node

The ±5 V analog output of the Tuff Tilt connect directly to an analog input channel of the WSN-3202.  The Tuff Tilt requires a power supply of 8-18 VDC with an operating current draw of 8 mA.  Even though this is within the specification of the sensor supply output (SEN PWR) of the WSN-3202 node, the inrush current of the Tuff Tilt at power-on exceeds the 20 mA limit of the SEN PWR output.  Therefore, you should power the Tuff Tilt sensor with an external power supply or 12V battery.  


Figure 2.  Connecting the Model 801 Tuff Tilt Sensor to WSN-3202

Programming NI WSN for use with the Model 801 Tuff Tilt

Using LabVIEW on a host PC with the NI WSN-3202 with the Mode 801 Tuff Tilt

Configuring a LabVIEW program to work with the 801 Tuff Tilt and NI WSN system is very straightforward.  First, you 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.

When programming in LabVIEW, you read the input on an analog input of the WSN-3202 node via a LabVIEW shared variable.   This shared variable returns an unscaled voltage value, which must be scaled to the appropriate tilt angle in degrees.  The scaling factor used depends on what model of the 801 Tuff Tilt you are using, and whether you are reading the input as single-ended or differential.  If using the 801-H model for instance, the scaling factor is 0.1 degrees/Volt in single-ended mode.   An example block diagram of a LabVIEW program that takes a reading, scales the reading to degrees, and displays the value on the front panel, is show in Figure 3.  Consult your 801 Tuff Tilt user manual for more information on what scaling factor you should use for your specific tiltmeter.



Figure 3.  LabVIEW block diagram to acquire, scale and display reading with Model 801 Tuff Tilt

Using LabVIEW WSN Embedded Programs on the NI WSN-3202 with the FP2000

With LabVIEW WSN and the programmable version of the WSN-320s 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