Verifying MEMS Accelerometer Accuracy Without a Lab

Calibrating a MEMS accelerometer does not require lab-grade equipment or outsourced metrology services. For users of Silicon Designs MEMS DC accelerometers, accuracy can be verified with only a voltmeter and the force of gravity.

This guide outlines a static calibration process that can be performed either in the field or on a benchtop.

The Importance of Calibration

Even sensors that are stable and low-drift may benefit from periodic checks. Over time, small shifts resulting from handling, mounting, or temperature changes can introduce measurement errors. By utilizing gravity as a known reference, performance can be quickly verified to ensure that the data remains accurate and actionable.

Required Equipment

The following tools are necessary to complete the calibration process:

• A Silicon Designs test and measurement module or surface-mount accelerometer
• A DC power source within the range of +8V to +32V
• A voltmeter or multimeter
• Optional: SDI G-Logger 3330 or 3340, paired with EB-L or EB-J analog test kits
• For surface-mount devices, the appropriate EB kit for connectivity is required

Manual Calibration Using Gravity

1. Connect Power
   Follow the Quick Start Guide for wiring instructions. Most SDI accelerometer modules operate within the +8V to +32V DC range. Ensure clean and consistent power to the sensor before taking measurements.
2. Measure +1G and -1G Positions
   Position the sensor flat with the lid or sensitive axis facing upwards to measure the +1G output. Record the voltage. Then, rotate the sensor so that the sensitive axis faces downward (or invert it) to measure the -1G output, and record that voltage. Correct positioning of the sensitive axis is essential for accurate calibration.
3. Calculate Sensor Output Parameters
   The following formulas can be used to verify performance:Zero-G Bias 0.5 × (+1G voltage + -1G voltage)
   Scale Factor 0.5 × (+1G voltage – -1G voltage)
   Sensitivity (mV/G) (|+1G| + |-1G|) × 1000 / 2
4.  Example Calculation
   Measured voltages:
   +1G = 0.199 V
   -1G = -0.124 V
5. Using the formulas
   Zero-G Bias = 0.5 × (0.199 + -0.124) = 0.5 × 0.075 = 0.0375 V
   Scale Factor = 0.5 × (0.199 – -0.124) = 0.5 × 0.323 = 0.1615 V
   Sensitivity = (|0.199| + |-0.124|) × 500 = (0.199 + 0.124) × 500 = 161.5 mV/G
6. These calculations confirm the accelerometer’s proper operation and provide a reliable basis for interpreting subsequent output voltages in applications.

Estimating Sensitivity Without Calibration Data

For selecting a sensor or estimating performance without recorded calibration values, sensitivity can be roughly approximated:

1. Take the sensor’s output span in millivolts.
   For example, a ±4V differential output corresponds to a 4000 mV total span.
2. Divide the output span by the sensor’s G range.
   For a sensor with a ±25G range:
   4000 mV ÷ 25 G = 160 mV/G

This provides an estimated sensitivity based on the sensor’s configuration. For more accurate measurements, the gravity-based calibration process should be followed.

These steps ensure that the sensor responds correctly to gravitational input. For triaxial accelerometers, the process should be repeated for each axis.

Auto-Calibration with the G-Logger

For faster calibration, the SDI G-Logger Models 3330 and 3340 can automate the process. When paired with the EB-L or EB-J kits, the G-Logger powers the sensor, logs data, and calculates calibration values for up to three input channels. This streamlines the calibration process, improves repeatability, and minimizes human error, whether in the lab or field environment. The G-Logger is especially beneficial when multiple axis measurements or repeated calibrations are required.

Practical Field Calibration

This calibration method is compatible with all Silicon Designs test modules and surface-mount accelerometers, regardless of model. It provides engineers and technicians with a fast, reliable method for verifying sensor performance without the need to return devices for factory calibration or rely on third-party services. This approach ensures consistency and reliability in both field and lab settings.