CALIBRATE YOUR SDI ACCELEROMETER

All Silicon Designs DC accelerometers use MEMS capacitive sensing technology and respond to the Earth’s gravity.  This makes it very easy to verify the calibration because they will show approximately 1G of input when stationary and laid flat.  It’s possible to use this capability to do a static calibration of the device.  The following instructions pertain to calibrations performed in DIFFERENTIAL mode.

AUTO-CALIBRATING USING SDI'S 3330 or 3340 G-LOGGER

In addition to live and recorded data review and FFT analysis, SDI's G-Logger® Models 3330 and 3340 include an auto-calibrate function that will perform all the calculations below for up to three input channels.  The G-Loggers simplify the calibration process even more by supplying all necessary power and eliminating the need for an external power supply.  Both the 3330 and 3340 G-Loggers can perform auto-calibrations on SDI's Industrial Test & Measurement modules, as well as its Industrial Surface Mount Accelerometers, when wired to the SDI Model EB-L or EB-J Test Kits.  

RECOMMENDED EQUIPMENT

This example uses a Silicon Designs 2260-025, however these instructions will work for all Silicon Designs Industrial Test & Measurement modules.  A triaxial module would repeat the process below for each axis. Calibration of SDI’s surface mount accelerometers is possible in a similar manner by using SDI’s EBL or EBJ Analog Test Kits.

Recommended equipment for calibrating SDI accelerometers
positive and negative voltage readings

HOW TO CALIBRATE

Connect your accelerometer wiring according to the instructions in the Quick Start Guide. In this example
we are using a 9 Volt DC battery, which falls within the +8 to +32 Volt DC range supported by the 2260.


Place the module in the +1G position (lid up) and check the output voltage (Figure A).


Place the module in the -1G position (lid down) and check the output voltage (Figure B).

CALIBRATION FORMULAS

Calculate the 0G Bias
½ x (+1G reading + -1G reading)
This 2260 measures ½ x (.199 + -.124) = .0375


Calculate the Scale Factor
½ x ([+1G reading] - [-1G reading])
This 2260 measures ½ x (.199 - -.124) = .1615


Calculate the Sensitivity
(absolute value of +1G reading) + (absolute value of -1G reading) x 1000/2  = mV/G
In this example, the readings were .199 and -.124.
This 2260 measures |.199| + |-.124| x 1000/2 = 161.5mV/G

The math for figuring out approximate sensitivity without the above data is simple. Take the accelerometer’s output span, for example in SDI’s differential ±4V output it would be 4V, and convert to mV, in this case 4000 mV. Divide that mV number by your sensor’s g range, in this example 25g, so 4000/25 = 160mV, which equals 160 mV per 1G of acceleration.