Joined: 11 April 2008
Location: US
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I am querying a MLX90609 via the spi/adc interface. With the device taped to a table I am reading 2428 - 2444 mV which would translate to 2.7 d/sec - 2.1 d/sec counterclockwise rotation. I would like to be able to calibrate the device but am not sure exactly how to go about it, I was wondering if you could give some suggestions?

Joined: 28 November 2007
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Hello Dennison,
Calibration and temperature compensation of the MLX90609 is done at the Melexis' factory to guarantee the accuracy put into the MLX90609 datasheet. According to the datasheet the Zero Rate Temperature drift is limited by the value +/-5% of the typical FSout = 4V that means: Voutar = 2.5V +/- 200mV = 2.3V...2.7V for VDD=5V and full temperature range (-40C...+85C).
For the MLX90609EEA-N2 (FSin=75deg/sec that is your case) the +/-200mV inaccuracy can be estimated by the angular rate velocity: +/-200 / 26.67 = +/-7.5 deg/sec
Here I'd mention that all silicon gyros have quite big ZRO inaccuracy. That is why they usually need some algorithm fixing real zero value and/or providing autocalibration. The choice of the algorithm strongly depends on the type of the application. There are some examples:
- If your device is not rotated you can fix zero level at that moment. Good accuracy is important there, so averaging is recommended.
- For some applications the low angular rate is applied with high angular rate acceleration only. It makes possible to recognize the ZRO drift (low angular rate and low angular rate acceleration) and to remove it continuously.
- Some applications have GPS that can be used for autocalibration from time to time.
Regards,
Nikolay

Joined: 30 July 2008
Location: US
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I would like to know if I can reduce the Zero Rate Temperature Drift by measuring the temperature of the Gyro and applying an offset correction value from a look-up-table or equation. If so, can you tell me the correction versus temperature function?

Joined: 28 November 2007
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Hello Ron,
Indeed, in order to improve ZRO accuracy of the factory calibration you can use a look-up-table generated for the particular MLX90609. The EEPROM of the MLX90609 includes the look-up-table (3 temperature points only). But this approach is not still validated and hence we can not officially recommend it for the public use.
Nevertheless, you can characterize chips you have on your own in order to create the look-up-tables for each of them. Pay attention, the look-up-table should include ZROs versus TEMPOUT values (the absolute temperatures is not needed in the table). And please wait a settling time of the TEMPOUT before measuring of each temperature point. It's important. By the way, we can discuss possible algorithms directly through E-Mail.
Regards,
Nikolay