Wednesday, 30 April 2014

speed sensor for treadmill | Error E1, Error E2 on Treadmills and bikes

How does a speed sensor works and what is the effect of its location on bikes

As you exercise on a fitness trainer, you set the drive mechanism in motion by pedaling. This pedaling sets a drive pulley in motion and this motions drives a flywheel by the help of a drive belt. Mostly the drive pulley is much bigger as the pulley on the flywheel (the flywheel is the driven wheel)  
This difference is diameter can also be seen as a gear and thus will the flywheel spin much faster compared to the rotation speed of the drive pulley. This gives a comfortable feeling as the flywheel helps you keeping the machine in motion with the help of the rotating mass.


If the drive pulley is 32 cm in diameter and the pulley on the flywheel only 4 cm in diameter

Than the gear will be 1:8
This because 32/ 4 = 8

In this example the flywheel will rotate 8 times in each drive pulley revolution. 

As we want to know the RPM (Rotations Per Minute)  while we pedal we need to put our speed sensor in place where the motion is. You can image by the example shown above that it is a huge difference in where to put the magnet. Do we want one or 8 revolution counts for each rotation the drive pulley makes.  Thus do you measure the real motions or the high speed generated motion of the flywheel. 

Magnet on the drive pulley: 

This is the most simple way of measuring, and is accurate enough for permanent magnet break systems.   Each sensor pulse is one revolution and as long as the sensor is not idle for more than 3 seconds there is no problem. ( 60 seconds / 3 seconds = 20 RPM. as a minimum to keep on working ) 
The break level does not need the speed to adjust the tension level. It is adjusted only on the users behalf or in a program*  when a certain time or distance has been achieved. ( * Servo systems only ) 
When the machine is an Ergo meter* and can function in Watt controlled mode than it does need the speed sensor but only with a time interval of 3 seconds.

Magnet on the flywheel:
This is a high speed measurement in where the trainer do need the sensor to make the machine operate. Mostly this is used in combination with a EMS ( Electronic Break System ). An EMS is a combination of induction magnet coil and a control board. 
In this way of measurement the reaction time really as it should process 8 times the amount of signals in the same time. This is needed to make the display react fast enough to make the training feel smooth.

Correct speed sensor location for bikes
In every high speed magnetic speed sensor system the sensor is not allowed to be  positioned in a 90° angle. Best position would be a 180° or a 80° position. This would avoid the sensor from being charged in static way. The reason for this is, that the sensor will not be triggered with full magnet power, and is therefore easier to release the inner sensor switch. Best distance between speed sensor and magnet should be set between 3 and 5 mm.

Correct speed sensor location on treadmill to avoid E1 and E2 errors
The standard distance between the active sensor and the magnet should be as less as possible (2-3 mm).

Some sensor is provided with double sensor housing.  Therefore the active sensor print comes to far from the front roller pulley magnet. 
You can easily cut of a part of the sensor housing without creating an open environment for the
sensor electronics. Please try to modify the sensor housing to make sure this is not the problem for
the problem you are facing before you report an error. Proceed as below. 

Cut of the front sensor housing wall from the lower sensor cover. Lower sensor cover is indicated
with a B in the first picture.

After modifying the sensor housing you can re-assemble the sensor again. And Check if this solved
your speed sensor readout problem.

Need a new speed sensor? Buy it here: speed sensor for treadmills / speed sensor for bikes

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