Memsic Accelerometer Running at 98 Hz instead of 100 Hz...
grahamreitz
Posts: 56
I was checking the period of the Memsic Accelerometer and noticed on the scope trace, attached (yellow trace), that it's really running at ~98 Hz, a ~10.2 ms period.
The input voltage (blue trace) is clean and at 3.3V.
Most of the conversion equations use 100 Hz as a constant.
I have two questions:
1) Is a 2% delta in the period within spec.? I might have missed it but didn't see it in the data sheet.
2) Will the 2% delta contribute much to the tilt error, when converted to degrees for angular measurements?
Thanks in advance for any advice and etc.
graham
The input voltage (blue trace) is clean and at 3.3V.
Most of the conversion equations use 100 Hz as a constant.
I have two questions:
1) Is a 2% delta in the period within spec.? I might have missed it but didn't see it in the data sheet.
2) Will the 2% delta contribute much to the tilt error, when converted to degrees for angular measurements?
Thanks in advance for any advice and etc.
graham
Comments
Each axis has a 100 Hz PWM duty cycle output in which acceleration is proportional to the ratio tHx/Tx. In practice, we have found that Tx is consistent so reliable results can be achieved by measuring only the duration of tHx.
The MXD2125G&M(.pdf) datasheet indicates a Minimum frequency of 95Hz, Typical frequency of 100Hz, and a Max frequency of 105Hz.
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Beau Schwabe
IC Layout Engineer
Parallax, Inc.
Tx is definitely consistent. I think I understand why it won't matter.
If the ratio of tHx/Tx is consistent I should still get the same result regardless of the measured delta from the ideal 100 Hz (10 ms)
When at 0 degrees the duty cycle is 50% of the ideal 100 Hz (10 ms) the device should read a a ratio of 5 ms/10 ms or 0.5.
In the case when its 98 Hz (10.2 ms) the device should read a ratio of 5.1 ms/10.2 ms or 0.5. The same as above for 0 degrees @ 100 Hz.
Thanks,
graham