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[on:]

This sensor is fixed to the frame just next to the pulley and pulley has a small round magnet fixed to it.  Is it some kind of hall effect sensor? And what are the chances that it may go bad?  It controls the speed of the motor and the problem I am facing is the speed fluctuation.  Not sure if this sensor is the contributor to the problem or something else.  Any help is greatly appreciated and thanks in advance.

[Reply #1 on:]

A sensor that has a magnet moving past almost certainly is a hall effect sensor.  I would think that they are very reliable and would be looking for loose connections rather than questioning the sensor.  Or you can hook a batter powered Arduino to it and take readings and see what it looks like.  If this is a car part, a messed up sensor would be easy enough to fix as the part is certainly available.  I bet it isn't that easy.

[Reply #2 on:]

And its easy to check if its a magnet on the wheel, just test with a steel screwdriver (while its stationary!!!)

There might be loose connections, the sensor-wheel spacing might have increased, magnet got weaker, water got into the sensor body (or it could easily be something else not related to the sensor).  Good luck.

[Reply #3 on:]

I take it that the unit is a running machine.  Chances are that the sensor is a simple reed switch.

[Reply #4 on:]

Yes, Its a treadmill and sensor has only two wires.  Is it a reed switch?

[Reply #5 on:]

Generally speaking, 2 wires = reed switch, 3 wires = hall effect.

There are 2 wire hall effect devices out there but all that I have seen require some type of amplifier (opamp) to sense the current flowing through the hall device.

Looking at the circuit where the sensor connects may provide a clue.

[Reply #6 on:]

  If the treadmill has seen lots of use, the brushes in the motor could be worn out. Generally, I would say that only treadmills at gyms where they see lots of use, get worn out brushes.

[Reply #7 on:]

Thanks for your input  .  I have tested it with multimeter and confirm its a reed switch.  If the magnet is near to it, I can see the continuity in the multimeter.  Now the question is, are there any chances that it may go defective or malfunction at higher speeds?   

[Reply #8 on:]

Now the question is, are there any chances that it may go defective or malfunction at higher speeds?   

Reed switches can fail in a few ways, mostly by becoming magnetized (usually not enough for a measurable magnetic field outside the reed switch, but enough to cause false positives/negatives), additionally forcing too much current the switch will either melt the thin metal "reed" closed or even vaporize enough of it to cause an open.  The first failure mode can happen either through short term exposure to an excessively strong magnetic field or occasionally over a long period of time during normal use.  If this happens it's sometimes possible to use demagnetizer tools to fix the switch, but often it's easier to replace them and not that much more expensive.  The second failure mode is usually avoided through proper design practices (i.e. limiting the current going through the sensor and taking steps to prevent shorts or large induced currents), but if and when it does happen the reed switch is basically ruined.

So to answer your specific question... Yes there is a possibility that it can malfunction at higher speeds especially if the switch has been part of a device that has previously been used a lot, due to a low level of magnetization that might have developed in the switch.  On the other hand, it's by no means certain to happen and the probability really depends on the confluence of factors specific to the switch and application. 

[Reply #9 on:]

Thanks for your input  .  I have tested it with multimeter and confirm its a reed switch.  If the magnet is near to it, I can see the continuity in the multimeter.  Now the question is, are there any chances that it may go defective or malfunction at higher speeds?   

Not likely, if good at static test then should be fine at some speed. However keep in mind that all electro-mechanical relays suffer from some duration of 'contact bounce' so there is always going to be an upper limit to how fast one can control a relay and still have proper reliable contact response. Reed relays are however among the fastest of all electro-mechanical relays and should have contact bounce of only some microseconds.

Lefty

[Reply #10 on:]

Thank you all for your responses and suggestions!!!  I will replace the reed switch with a new one and check.