Electronic Design

Tiny Dual-Axis MEMS Inclinometer Simplifies Industrial Measurements

This very small and highly accurate device provides a fully compensated direct-angle digital output with less than 0.1°linear inclination error.

Targeting industrial applications, Analog Devices’ ADIS16209 dual-axis inclinometer and accelerometer breaks new ground in price, performance, size, and ease of use. The company claims this highly integrated device is the industry’s most accurate and easy-touse tilt sensor. It’s also 100 times smaller than other available devices.

The ADIS16209 offers a fully compensated direct digital output with less than 0.1° of linear inclination error. That makes it about three times as accurate as competitive tilt sensors, according to ADI. To boot, the company says that it has one-tenth the price tag of functionally equivalent competitive units.

The ADIS16209’s core is based on ADI’s dual-axis ADXL203 MEMS accelerometer. Its dimensions are a mere 9.2 by 9.2 by 3.9 mm, available in a laminate-based land-grid array (LGA) package (Fig. 1). Many alternative tilt sensors make use of bulky fluid-filled electrolytic sensors, which can require special board mounting.

“While there are other inclinometers available that are fully calibrated, these are much larger in size. There are also many other small-size units, but these require extensive calibration procedures,” explained Bob Scannell, iSensor Business Development Manager for Analog Devices.

The ADIS16209’s small size enables users to place the device right at the point of applications, simplifying its use. It features dual-mode operation either as a dual-axis inclinometer with a ±30° range (operable to within ±90°) or a single-axis vertical mode within a ±180° range. It operates from a single 3.3-V power supply and typically dissipates 11 mA. The product is designed to withstand 3500-g shocks as well.

An embedded controller
The ADIS16209’s serial peripheral interface (SPI) enables simple integration into most industrial system designs. Thanks to an embedded controller, the chip is fully compensated for variances in bias, sensitivity, power-supply levels, cross-axis sensitivities, axial misalignment, non-linearity, and temperature drift (Fig. 2).

Unlike other units on the market, which typically feature an analog acceleration signal output, there’s no need for users to perform sometimes extensive calibrations and adjustments. The tunable 14-bit digital sensor output data provides access to inclination (within 0.025° resolution) and acceleration (within 0.244-mg resolution). A simple internal register structure handles all output data and configuration features.

Other features include typical low accelerometer noise of 1.7 mg rms and typical noise density of 0.17 mg/vHz rms. Offset error is rated within ±4 least-significant bits (LSB), and gain error is within ±2 LSB. Figure 3 shows a plot of the unit’s inclination accuracy as a function of acceleration accuracy.

Additional features include typical alignment error (X sensor to Y sensor) of ±0.2°, an acceleration frequency bandwidth of 50 Hz, and a resonant frequency of 5.5 kHz. The ADIS16209 is rated for operation over the –40°C to 85°C temperature range. The accelerometer’s output in the self-test mode ranges from a minimum of 706 LSBs to a maximum of 1973 LSBs at 25°.

“The ADIS16209 provides an accurate and simple bits-out angle in a standard semiconductor format. This is a big departure from both electrolytic and less integrated MEMS-based sensors,” said Andy Garner, product line director for Analog Devices’ iSensor intelligent sensor products.

“The on-chip dynamic compensation of the ADIS16209 is important for two reasons. It allows our customers to confidently absorb mid-stream system design changes without losing their time-to-market advantage, and it provides end users with equipment that delivers accurate sensing data that is resistant to in-field environmental changes that can often result in costly, cumbersome recalibration,” Garner added.

One important feature is its programmable condition monitoring. Configurable operating parameters include sampling rate, power management, digital filtering, auxiliary analog digital outputs, offset/null adjustments, and selftesting for the integrity of the sensor’s mechanical structure.

The inclinometer’s combination of features makes it a natural for a host of industrial applications. These include surveying equipment, factory machine tools, satellite-antenna stabilization systems, robotics, motion-safety monitors for medical and security systems, and automotive wheel alignment.

Samples of the ADIS16209 sensor are available now at a price of $34.40 each in 1000-unit quantities. A complete evaluation board, the ADIS16209EVAL, is available for about $175. It includes a board-mounted sensor, interface hardware, and evaluation software. Volume production quantities are expected sometime this month.

Analog Devices

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