Duty cycle - Another Math dilemma

[Ramius]

Hi Henrik!
Thank you and I finally got that the duty cycle is a "fixed" number assumed to be at 50%. According to the information about the device, each device can have a zero duty cycle of from 48.7% to 51.3%. My experience has been that at a room temperature of about 72 degrees F, my device has a measured duty cycle of 49.93%. However as the room temperature increase or decrease so does the zero point duty cycle! So if the submarine is sitting on a table at the park with an air temperature of 72 degrees F then 4993 works. Put the sub in water where the water temperature is 65 degrees F and 4993 is no longer valid. Originally the thinking was to measure and calculate the duty cycle however this method does not work as you first must be at an known zero degrees of tilt.

Best Wishes, Ed

[HenrikOlsson]

Hi Ed,
Is the dutycycle at various temperatures repeatable? I mean, you say that 0° at 72F is 4993 and 0° at 65F it's xxxx, are those numbers repeatable from time to time or is 4993 one time and 5006 another?
If they are repeatable then all you need is a temperature sensor (which I suspect you have anyway) and a bit of more math....

Mount the tempsensor in very close proximity to the accelerometer, set the accelerometer exactly level and leave it there. Then, using a hairdryer or whatever measure and plot the dutycycle vs temperature over the range you expect to use it and see what comes out. If you're lucky you'll get a linear realationship between temp and dutycycle which is very easy to compensate for in software. If it's not a linear relationship that too can be compensated for - not as easily though.

If you're very amibitious repeat the test at 30° tilt and see if the relationship is the same.

/Henrik.

[Ramius]

Hi Henrik!
Just an update, it turned out I had a bad sensor! Got a new one and it seems to work fine!