Reed switches vs Hall Effect sensor for speed measurement

Thread Starter

Xavier Pacheco Paulino

Joined Oct 21, 2015
728
Hello,

I want to measure the speed of a treadmill. I have seen some treadmills that use reed switches as sensor. They place a magnet in the pulley, so I guess the measure the times that the reed switch detects the magnet. However, I've heard that reed switches are not reliable, and that's why I want to replace the reed switch with a hall effect sensor. I think the concept remains: the detection of the magnet. The US5881 is a non-latching Hall effect sensor quite used, so I think it could do the job. What do you think?

Also, if we are going to detect a pulse per revolution, I think that resolution is really poor. What are yout suggestions?
 

MaxHeadRoom

Joined Jul 18, 2013
22,340
The ones I have seen fitted use a slot opto and multi-shuttered wheel, ~50 slots/rev.
You can also use a retro-reflective type such as the QRE1113 etc.
You can use a hall effect, it would need to be the ferrous metal detect type, rather than magnet sensor.
Although if you already have a magent, it will be low resolution count.
However these tend to be a little larger physically than the opto versions.
Max.
 

theodoravain

Joined Mar 21, 2018
34
Hello,

I want to measure the speed of a treadmill. I have seen some treadmills that use reed switches as sensor. They place a magnet in the pulley, so I guess the measure the times that the reed switch detects the magnet. However, I've heard that reed switches are not reliable, and that's why I want to replace the reed switch with a hall effect sensor. I think the concept remains: the detection of the magnet. The US5881 is a non-latching Hall effect sensor quite used, so I think it could do the job. What do you think?

Also, if we are going to detect a pulse per revolution, I think that resolution is really poor. What are yout suggestions?
Do you really need a Hall effect sensor? A tiny iron core magnetic pickup coil driving a single transistor class E amp into sat will do as well minus the agro of abrupt threshold and slow recovery.
Hall effect sensors really come into their own detecting static and very slowly changing fields. Otherwise they're usually more work with no advantage.
 
Last edited:

MrAl

Joined Jun 17, 2014
7,959
Hi,

Here are the differences...

1. Reed switch: Easy to install, no power supply line needed. Reliability can be questionable as some last long others not so long.
2. Coil of wire: Have to make or buy a coil with a metal core. Signal strength depends on speed of movement.
3. Hall Effect Sensor, linear sensor: Modern design. Reliable.
4. Hall effect sensor, switch action sensor: modern design used in a lot of things. Very reliable.

Out of all of these i would go with the hall effect switch sensor. Very reliable and provides an output that does not depend on speed of the object being sensed which is important for slow moving things. Also fairly cheap price wise. Will work with a ceramic magnet but of course a rare earth magnet makes it even better. In fact a rare earth magnet makes any of those above better.

I have personal experience with all of those above. The metal core in the coil of wire solution helps increase signal strength by a large factor, and a metal focusing core works great for the linear HE sensor too.
#2 was used on very expensive mailing equipment back in the 1970's to detect revolutions of a shaft but other types of sensors were not as common back then as they are now, and i am sure if they had HE devices back then that work as good as they do today they would have used one instead of the metal core coil.
 
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