I'm experiencing problems with a Hall speed sensor that we have mounted on our turbine engine.
It came with the FADEC (engine control unit for the turbine) so I don't exactly now what's inside but it does look like a classical hall sensor/switch in a TO92-like enclosure. It's fed by a 5Vcc and ground and has a third "Output" pin.
It is supposed to measure speeds up to 120000RPM (2kHz, there's a magnet at the end spinning and thus changing polarity once per turn).
Now the problem is that it is very noisy and the FADEC reading regularly jumps up and puts itself in security mode thus cutting injection... not good...
This problems mostly happens at low speed and when I have a small spark generator (automotive ignition coil + MOSFET cutting it @20Hz) on.
Also, there's a R/C Brushless motor ESC closeby which I suspect is not helping on the EMI front.
What can I do to make the reading more robust?
I had thought of two things :
Shielding the cable (it's now a classic three wire R/C unshielded cable) but the shielding is not gonna be very easy to do especially as it's R/C servo types (3pins) plugs.
Putting a 3V zener between signal and ground so it only gives "significant" readings. Ok so this one is a long shot, I thought of it but have no idea if it's really possible or not...
Yes, shielding the cable is the first thing to do. Connect the outer cable shield to ground at the controller end and not at the sensor end, use the GND signal inside the cable for the GND of the sensor..
Add ferrite cable clamps at both ends of the cable.
You can also add 100nF at GND and 5V near the sensor.
It would help a lot if you know what kind of hall sensor it is. Perhaps you can lower the value of the pullup resistor to lower the impedance. What value is your pullup resistor now ?
Do you have a (storage) oscilloscope ? To measure the difference between the hall output and the electrical noise ?
The 3V zener is not a good idea. You could try a RC filter, but that should be done after the pullup resistor.
This problems mostly happens at low speed and when I have a small spark generator (automotive ignition coil + MOSFET cutting it @20Hz) on.
Also, there's a R/C Brushless motor ESC closeby which I suspect is not helping on the EMI front.
If other suggestions here don't work, you could try using an opto-isolator to interface the hall sensor to the MCU. Another thing might be to put the electronics into an EMI/RFI enclosure, or devise your own barrier/shielding for the electronics and use EMI/RFI conductive coating spray.