0
\$\begingroup\$

I have a A1308KUATN-9-T Hall Effect sensor with the following sensitivity (from the data sheet): enter image description here

As you can see, the sensitivity comes to about 9mV per Gauss on average.

My calculations (see below if you think this sounds wrong) come out to a flux density of 1.36 Gauss when I'm 3 inches above the magnet.

So that means I can expect a reading of 12.6 mV on my sensor's output... My goal here is to try to boost this to something closer to say 3V or so. Using an op-amp is the direction I'm assuming I should be taking, but if there's a better way I'm open to that.

Additionally, I'm really worried about noise affecting this. In other applications I'd say noise on a signal of +/- 10mV is fine but here it'd be terrible. If I put a decoupling capacitor on the 5v rail going to the hall effect, would that help clean up my noise? Should I do something between my sensor's output and op-amp's input?

So finally, to summarise: I'm expecting a ~12mV analogue response from a sensor that general outputs 0-5V. So I'd like to boost it the best I can and filter out any noise that could give a false reading (since the expected signal is so low to begin with).

For those interested,

Explanation for Flux density calculation: enter image description here

The cylinder magnet I'm trying to detect will be approximately 3 inches below my sensor and given a diameter of 12mm and a height of 2.6mm with the assumption the residual magnetism of my magnet will be ~1.3 T.

Values used + answer (B)

\$\endgroup\$
1
  • \$\begingroup\$ What kind of measurement are you taking? Is it DC or a time-varying signal? \$\endgroup\$
    – Platytude
    Feb 7, 2019 at 22:16

1 Answer 1

Reset to default
1
\$\begingroup\$

Yes, an op-amp is the way to go. Properly bypassing power to the sensor will help. You're trying to use such a small portion of its range, though -- that's usually a plea to the Electronics Gods to "please smite me".

So proceed, but see if the sensor has a noise specification. Also carefully check the sensor's rated offset voltage, and the degree to which that offset voltage is expected to change with temperature. My intuition tells me that you can pretty much count on having to adjust for offset, and that it would be a very good idea to breadboard a prototype, and test it over your anticipated temperature range.

\$\endgroup\$
2
  • \$\begingroup\$ He could also add a low-pass filter (either passive or active) to the amplifier to try and help with the noise. Of course, that will slow response time proportionally. \$\endgroup\$
    – rdtsc
    Feb 7, 2019 at 22:29
  • \$\begingroup\$ I wouldn't want to assume what the magnetic field actually is. The OP writes what they think it should be. But a NIST traceable commercial instrument and sensor would provide some assurances. Otherwise, who knows what the cylinder magnet is actually producing at some given distance and relative position? (Unless the magnet itself comes with a NIST traceable calibration paper.) I suppose a compass could technically be used to get a reasoned approximation, if and only if a good figure for the local geomagnetic field can be found somewhere (and since this is moving 30+ miles/yr, may not be easy.) \$\endgroup\$
    – jonk
    Feb 8, 2019 at 0:24

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.