C1XX Wheel speed Hall effect glitch at low speed

[FrankL]

Hi,

I am logging wheel speed using a Hall effect sensor on a speed input configure for a Hall effect.

When I stop the vehicle, the speed from the Hall sensor seem to get stuck at a steady low speed for a few seconds before going to down to zero. See attachment image

It seem this glitch is produce by the calculation mode of the dash (C187) itself. I have monitor the channel using the trace graph utility of the dash and I still have the same issue.

?? Any body know how to fix this issue without creating a Math channel ??

Extra info
My trigger wheel have 20 steel teeth and I am reading each tooth, I am logging the channel at 100Hz. I have tried to change threshold.

Thanks, Frank

[David Ferguson]

What is the "sample teeth" value set to in the input pin calibration window? Do you have the "Timout: override' ticked (normally this is not needed)?

Is the Hall Voltage Threshold set to something between 1 & 2 volts (Spd Levels... button)?

What is the channel default value (settings... button)

[FrankL]

Pulse Per Revolution = 20
Sample Teeth = 1
Timeout = Not checked
Hall Voltage Threshold = 1.498V -- I tried other values, but it did not solve the issue
Channel Default = 0.0 km/h

[David Ferguson]

That is odd. What you show is exactly what happens when the Sample Teeth is set too high (which slows the update rate), and you stop the wheel very suddenly.

My suggestions -- be sure this really happens in the logged data, not just with the monitor channels graph utility (it may be different, as I believe it updates much slower).

Try turning on the Timeout override -- it's interesting that your delay is 2 seconds, and appears to be the default value. Basically this sets the slowest speed that can be detected. With 20 triggers/rev, you may be able to tolerate a much shorter timeout (like 0.1 sec)

[FrankL]

Thanks David,

Effectively the strange speed values were linked to the Timeout default value of 2 sec, even if the Timeout check box is uncheck.

Thanks for the cue, I lowered the Timeout value and it fixed the glitch.

I thought that a uncheck box would not apply any Timeout value, I am wrong?
What does the Timeout exactly do?

Frank

[David Ferguson]

I think of the Timeout as "how long between pulses before the speed should be reported as zero". In other words it sets the minimum speed that can be measured. If you know the distance traveled between pulses you can calculate what that would be.