Tilt sensor (slope sensor, inclinometer)

01

Build the accuracy budget from offset, drift and resolution

Murata's SCL3300-D01 datasheet shows how a MEMS inclinometer works and what limits it. It is a three-axis sensor that computes each angle from the acceleration components, for example ANG_X = atan2(accx / √(accy² + accz²)), giving a ±90° range in its inclination modes, with selectable sensitivities of 3,000, 6,000 or 12,000 LSB/g and low-pass filters of 70, 40 or 10 Hz, angle output resolution of 0.0055°/LSB and noise density of 0.001 °/√Hz, on a 3.0–3.6 V supply from −40 to +125 °C. [1]

Its error terms are stated in both mg and degrees: offset error up to ±20 mg (1.15°) on the X and Z channels, offset temperature dependency up to ±10 mg (0.57°) on X and Y over −40 to +125 °C, and offset lifetime drift of ±4 mg (0.23°) (typ.) with limits of ±8 mg (0.46°) on X and Z [1]. Sensitivity near level is 105 LSB per degree in its 6,000 LSB/g mode. [1]

Editorial calculation: an offset of 20 mg corresponds to asin(0.020) ≈ 1.15°, matching the datasheet. In the 6,000 LSB/g mode a 1° tilt changes the reading by 6,000 × sin 1° ≈ 105 LSB, again as listed. At the end of a 10 m boom, a ±0.10° angle accuracy corresponds to about 10,000 × tan 0.1° ≈ 17 mm. Ask whether a packaged sensor's stated accuracy includes temperature drift and ageing, or whether it is calibrated at room temperature only.

Packaged sensors state the budget in degrees. Axiomatic's preliminary data sheet for its AX060851 triaxial CANopen inclinometer gives pitch and roll over ±180°, an effective resolution of 0.35° at the default 5 Hz cut-off (selectable 1–50 Hz, 0.2 s settling), initial accuracy of ±3° maximum at 25 °C, temperature drift of ±3.5° maximum over −40 to +85 °C, nonlinearity of ±0.7% and cross-axis sensitivity of ±3.5%. It runs on 9–36 V DC at 20–30 mA, is rated IP67 with MIL connectors (IP65 with strain reliefs), was vibration-tested to MIL-STD-202G at 10 g peak sinusoidal and 7.68 Grms random from 5 to 2,000 Hz for 8 h per axis and shock-tested at 50 g half-sine for 9 ms, and measures 75 × 80 × 52 mm. [3]

Editorial calculation: adding Axiomatic's ±3° initial and ±3.5° temperature terms gives a worst case of ±6.5° over temperature, against POSITAL's ±0.10° accuracy figure, a factor of 65; ask each supplier for total error over your temperature range, not resolution. [3] [2]

Give the supplier the measuring range and axes (single, dual, 360°), required accuracy over your temperature range, resolution, mounting orientation (horizontal or vertical), machine motion, shock and vibration, update rate and filtering, output (4–20 mA, 0–10 V, CANopen, J1939, SSI, Modbus RTU), supply voltage, ingress protection and any ATEX or functional-safety needs.

02

Choose a static or dynamic sensor for the machine duty

POSITAL, an inclinometer maker, separates static inclinometers for monitoring tilt in mobile machines, platform levelling, solar trackers, scissor lifts and aerial work platforms from dynamic inclinometers that combine an accelerometer and gyroscope to filter accelerations, shocks and vibration and give a clean signal on cranes, construction, mining and agricultural machines. It lists static sensors with up to 360° single-axis or ±180° dual-axis range and analog, CANopen, J1939, SSI or Modbus RTU outputs, and heavy-duty and compact versions with 0.01° resolution and ±0.10° accuracy, up to IP69K or IP67, with ATEX versions available. It notes the sensor may be mounted horizontally to measure two axes or vertically to measure one. [2]

Editorial note: if the sensor sits on a boom or chassis that accelerates, brakes or vibrates, ask whether a dynamic sensor is needed and how the filter settings affect response time.

03

Inclinometer ranges listed: static, dynamic, wireless and MEMS inertial

Listings include static and dynamic industrial inclinometers, wireless inclinometers and attitude sensors, MEMS inertial products, and dual-axis inclinometers from a sensor maker. Ask each for range, accuracy over temperature, output, protection class and test data.

04

Ask how drift and ageing are removed after installation

Researchers at Warsaw University of Technology (Sensors, 2022) name the main MEMS accelerometer errors as misaligned sensitive axes, thermal and long-term drift, imprecise factory calibration and ageing. They built a two-axis tilt sensor around an ADXL 327 triaxial accelerometer in a cubic housing that is recalibrated on a levelled surface by recording the output in six orientations, one per face, and aligned its axes to the housing within about ±0.03°, 16 times lower than the ±0.5° minimum they cite for axes relative to the package. [4]

At constant ambient temperature, long-term drift changed offset and scale factor by up to 0.2% (3 mV) within 48 h, an acceleration error of ca. 0.7% that they convert to a tilt error of about 0.43°; for a 1.5% ageing error over 4.5 years from earlier tests of the same accelerometer they derive about 0.86°. Recalibration eliminated the thermal and long-term drift in their tests. [4]

Editorial note: ask the supplier whether the stated accuracy holds over the service life, and how the installed sensor can be re-zeroed or recalibrated.

05

MEMS accelerometer, gyroscope, signal processing, output, housing and mounting

Murata's datasheet covers the sensing element and angle computation; POSITAL's product pages cover the gyro-aided dynamic types, outputs, sealing and mounting.

06

Component versus packaged-sensor figures: range, accuracy, supply and ruggedness

Component values (Murata SCL3300) and packaged-sensor values (POSITAL, Axiomatic) sit side by side here; compare packaged figures with packaged figures.

07

Send the range, accuracy and duty data together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Range: [axes; degrees]
Accuracy: [over temperature; resolution]
Duty: [static or moving machine; shock; vibration]
Output: [analog; bus protocol]
Power: [supply]
Environment: [temperature; IP; ATEX]
Mounting: [orientation; bracket]

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