DC42, thank you, I understand I can calibrate out in one position. Here is more information from a post I made over at Pololu.
Is there any type of shielding product available or that can be described to magnetically shield the ACS series of current sensors?
I've read online that the toroid style sensors (with the feed through sensed wire) can be shielded via adding a coil, to eliminate external magnetic fields.
(see 2/3rds of the way down this page http://www.answers.com/topic/hall-effect
where it shows adding a ferrite ring;
For example, a Hall sensor integrated into a ferrite ring (as shown) can reduce the detection of stray fields by a factor of 100 or better
(as the external magnetic fields cancel across the ring, giving no residualmagnetic flux). This configuration also provides an improvement
in signal-to-noise ratio and drift effects of over 20 times that of a bare Hall device.
What can be done to shield this Pololu board style sensor?
Does anyone know if these are used in any significant volume by any manufacturer? Who I might be able to contact for information on how they shielded the sensor?
The only feedback I've had on the internet so far is just to calibrate it out at one position. While that can work for the bench, I have other concerns described below.
My testing shows that the orientation of the part as delivered by Pololu appears to be sensitive (affected by) the earth's magnetic field. I believe I've ruled out any other source except perhaps body capacitance, but even for that I varied the orientation of the part to my body.
However it was moved the values read vary consistently (ie, 100% reproducible) with orientation to the earth.
The connecting cable, the processor board, and the surrounding environment (ie positional aspects about each) were varied and have no effect on the values read.
The value drifts about 14 counts when the board is rotated with respect to earth/ground in the following manner. board is level, chip side up. rotate on an axis through the center of the chip along its length (ie, raise VGO connector end while lowering sense wire end), or more loosely in a larger arc/loop. Or rotate about the orthogonal axis in the board plane. When the chip is facing down the counts are the lowest, when facing up, the highest. Rotating the board in the board plane varies the output by only a few counts.
My intended application is in an electric snowblower, and of course there is a relatively large rotating mass about 2 feet away, with small variation in speed when in operation, and a motor controller and motor nearby. I haven't yet tested it in that environment. I will be using a 30A unit in that application, I'm currently testing with the 5A on the bench.
Thank you in advance for any advice.