Using MEMS Sensors in Inclinometers

Inclinometers, which are otherwise referred to as tilt sensors, typically utilize electrolytic, mercury, pendulum or gas bubble-in-liquid technologies to convert the angular changes of one axis, or more, into relational electrical signals.

To further advance this technology, Micro-Electro-Mechanical-Systems (MEMS), chips which consist of micro-mechanical structures that form double capacities, have become available. When these chips are exposed to terrestrial acceleration, a change of the capacity values occurs that converts the signal to a g * sin(α)-signal.

A complex range of micro-controlled stages comprised of filters, temperature compensation, calibration, coordinate mapping, as well as both in- and output connections that function to update algorithms, result in an angular value output. The I/O circuit can take the form of either a CANopen or an analog current or voltage interface for a direct link to a receiving monitoring or control unit.

Newly Developed Inclinometers by TWK-ELEKTRONIK

The newly developed NKN and NBN series of inclinometers are equipped with either one or two sensor channels that are capable of detecting the angular movements within one or two axis, selected from one of the three degrees of freedom (x,y,z).

Both sensor channels have identical output interfaces that can be directly connected to the CANopen bus; however, the two-channel version is a redundant system that contains both nodes 1, which sends data, and node 2, which sends the bit inverted data. Figure 1 demonstrates how this system’s guarantees the utmost accuracy of the transmission by matching both signals.

Block diagram of inclinometer with redundant CANopen layout

Figure 1. Block diagram of inclinometer with redundant CANopen layout

The protocol conforms to the CANopen Application Layer and Communication Profile, CiA Draft Standard 301, Version 4.1, as well as to the CiA Draft Standard 410, Version 1.2 fo Device Profile for Inclinometers. By applying the CANopen Safety protocol to CiA DS 304 Version 1.0.1, the device will meet Safety Integrated Level 2 (SIL2) IEC 51508, required for many engineering equipment applications.

Two mechanical configurations of the inclinometer are currently available. Firstly, the Model NKN is a square shaped PCB whose dimensions are 55 mm by 55 mm, allowing for its easy integration into devices that have space restriction requirements. Solder pins are also provided for the electrical connections and mounting holes that are used for mechanical fixing purposes, as shown in Figure 2.

Inclinometer NKN on PCB.

Figure 2. Inclinometer NKN on PCB.

The second mechanical configuration is the Model NBN, which is a transducer unit enclosed in a robust aluminum or stainless-steel case, and contains one or two connectors to allow for its serial connection with other CANopen devices. The mounting flange has proportions of 65 mm by 65 mm, with an overall height of 42 mm. The Model NBN transducer complies with protection grade IP65, and with optional potting, to IP69K, as demonstrated in Figure 3.

Transducer unit of the NBN series.

Figure 3. Transducer unit of the NBN series.

Product Details

  • Measurement span of both novel inclinometers is ± 90° maximum; however, these devices can also be programmed to unsymmetrical deflections, such as +30°/-90°.
  • Resolution is as low as 0.005°
  • Repeatability of 0.045°
  • Working temperature range is -40 °C up to +85 °C.
  • Voltage supply in the range of 11 to 36 VDC is required (Figure 4).

Example of output diagram.

Figure 4. Example of output diagram.

Inclinometers are applied for a wide range of applications, most of which are involved in both mobile and stationary engineering equipment that require the observation of safety relevant operation conditions. Some examples of these specific applications include cranes and other lifting machinery, harvest vehicles, theatre controls and a number of types of platforms.

The inclinometers above deliver the feedback and surveillance signals in a highly efficient manner to ensure the appropriate setting of such mechanical equipment, as well as for the ultimate protection of all workers and the environment.

This information has been sourced, reviewed and adapted from materials provided by TWK-ELEKTRONIK GmbH.

For more information on this source, please visit TWK-ELEKTRONIK GmbH.

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