ACCELENS inclinometers (ACS) sense and measure the angle of tilt (Inclination/ Slope/ Elevation) of an object with respect to the force of gravity. In general, absolute inclinometers identify all points of a movement by means of an unambiguous output signal. This signal can be analog or digital. Due to their ability to assign unique values to all inclination positions, inclinometers have become one of the interesting alternatives to singleturn absolute encoders.
Measurement Principle of ACCELENS Inclinometers
The basic principle behind ACCELENS (ACS) inclinometers is a Micro-Electro-Mechanical Systems (MEMS) sensor cell that is embedded to a fully molded ASIC. The function can be explained easily based on a simplified model with only two electrodes: one is fixed, and the other is flexible (connected with spring elements). When the inclinometer is in a horizontal position, a corresponding capacitance is measured. If the sensor is tilted, the flexible electrode will change its position relative to the fixed electrode. This results in a change of the capacitance between the two electrodes which is measured by the sensor cell. The change of the capacitance is converted to a corresponding inclination value. The MEMS sensor cell in the ACS consists of a micromechanical structure with an array of electrodes for better accuracy. Under the influence of gravity, the distance between some electrodes changes and this distance can be detected by measuring the capacitance between the electrodes, as explained above. This technology is available in different grades, with lower grades entering mass markets like mobile phones or tablet computers. The ACS series of inclinometers is available in two variants. First, a single axis measurement variant with a range of 0-360° (either clockwise or anti-clockwise) and the other variant, a dual axis measurement capable ACS model with a range of ±80°.
Data Processing
A microcontroller is reading and processing the output signals of the MEMS sensor. One readout cycle takes less than 5 ms. In a first step these „raw data“ are filtered with a moving average filter or more advanced filters. The number of raw data that are considered for the filtering can be configured according to the requirements of the application. In case that 20 subsequent raw data are considered for every calculation, the output value of the ACS will be based on position data from a time period of about 100 ms. A smaller amount of raw data will make the sensor more dynamic to follow fast movements, but also more sensitive to vibrations. A larger amount of raw data will make the output signal of the ACS very stable, but the output will also take more time to follow faster movements. In a second step of data processing, non-linearities will be compensated for in the output signal of the MEMS sensor. For this purpose, all ACS sensors are calibrated during production. During the calibration process raw data from the MEMS sensor will be compared to a high precision reference sensor while the ACS is moved within the full measurement range. In this way, non-linear characteristics of the MEMS sensor will be detected and considered for a linearization software routine. In a third step, measurement data will be corrected with regard to the influence of ambient temperature. The ACS includes a temperature sensor and its output is used for active temperature compensation. Further steps of data processing include an offset correction (Preset) and a scaling function in case of analog output signals. After the data procesing is finished, the final digital result will be provided to the electrical output that can either be analog (Voltage or Current) or digital (SSI, CANopen or DeviceNet).
Sensor System
The electronics of the ACS are fully molded in a plasic material (Thermelt) that protects the system against humidity, water and dust. The system is connected with a robust industrial M12 connector and a protection calss of IP69K is reached if a proper counter-connector and cable is used. ACS inclinometers are fixed on a machine using 3 screws. The bottom side of the ACS is raised around these screw positions to prepare the ACS for installation on slightly uneven surfaces.
Benefits and Limitations
+ fast settling time
+ small size
+ cost efficient
+ High Protection Grade
- High Accuracy (For applications involving even higher accuracy visit ANGUSENS Technology)
- High Resoltion (For applications involving even higher resolution visit ANGUSENS Technology)
