Magnetic Pickup output signal problem

[lissy6098]

I am observing the voltage output of a magnetic pickup transducer.
When I maintain a constant rpm (speed) it seems that the signal shows
that the voltage varies alot in between peak points. Is there a reason
for a voltage in the signal and how can I solve this problem.

 

[Eeyore]

I am observing the voltage output of a magnetic pickup transducer.
When I maintain a constant rpm (speed) it seems that the signal shows
that the voltage varies alot in between peak points. Is there a reason
for a voltage in the signal and how can I solve this problem.

I though that's what they're supposed to do.

Did you expect a constant DC voltage ?

Graham

 

[Michael A. Terrell]

I am observing the voltage output of a magnetic pickup transducer.
When I maintain a constant rpm (speed) it seems that the signal shows
that the voltage varies alot in between peak points. Is there a reason
for a voltage in the signal and how can I solve this problem.

This question really belongs in or
http://groups.google.com/group/sci.electronics.basic?hl=en for google
group users.


How are you reading the voltage? If it is with a digital meter, the
sample rate will cause the meter to read at different points of the
waveform generated by the sensor. You need a scope to see what the
waveform looks like, and to compare the waveform. Also, what are you
sensing? a single point, or gear teeth/multiple points?

--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[[email protected]]

I am observing the voltage output of a magnetic pickup transducer.
When I maintain a constant rpm (speed) it seems that the signal shows
that the voltage varies alot in between peak points. Is there a reason
for a voltage in the signal and how can I solve this problem.

The most common reason for mag pickup signal amplitude variation is
run out in the speed wheel (tone wheel excitation ring etc.) This
effectively changes the gap which is relatively proportional to the
signal amplitude. If you look at the signal on a scope set with the
sweep equal to one revolution, you can see the signal amplitude
variation for one revolution. Other physical factors can cause
amplitude variation, like inconsistant tooth profile, damaged or
missing teeth. Usually the rotation speed is determined by frquency
to voltage converter measuring the time between signal zero crossing,
or averaging of fixed size pulses, derived from each cycle of the
signal.

 

[Stanislaw Flatto]

I am observing the voltage output of a magnetic pickup transducer.
When I maintain a constant rpm (speed) it seems that the signal shows
that the voltage varies alot in between peak points. Is there a reason
for a voltage in the signal and how can I solve this problem.

"A lot" means what? How precise IS the mechanical distance from pickup
to 'points'?
BTW what did you expect, and what setup you provided?

When "testing" it is very good to rely on known AND steady settings.

HTH

Stanislaw.

 

[John Popelish]

I am observing the voltage output of a magnetic pickup transducer.
When I maintain a constant rpm (speed) it seems that the signal shows
that the voltage varies alot in between peak points. Is there a reason
for a voltage in the signal and how can I solve this problem.

The gear teeth (or other objects being sensed by the pickup)
are not well centered. Some are passing closer to the
sensor than others are.

 

[Glenn Gundlach]

"A lot" means what? How precise IS the mechanical distance from pickup
to 'points'?
BTW what did you expect, and what setup you provided?

When "testing" it is very good to rely on known AND steady settings.

HTH

Stanislaw.

I work on Sony analog Betacam tape machines that use Hall sensors to
read the tape reel rotation info. When operating properly, the
variations are less than 10% but as the reel tables age and the
adhesive that hold the magnet onto the wheel shift a bit, the
variations can get up to 50%. Replacing the reel turntable corrects
this. Output is a pair of quadrature sines that get squared up in
comparators.

GG

 

[lissy6098]

This question really belongs in orhttp://groups.google.com/group/sci.electronics.basic?hl=enfor google
group users.

How are you reading the voltage? If it is with a digital meter, the
sample rate will cause the meter to read at different points of the
waveform generated by the sensor. You need a scope to see what the
waveform looks like, and to compare the waveform. Also, what are you
sensing? a single point, or gear teeth/multiple points?

--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

The voltage output goes directly into a Labview DAS. Once we have the
data in the computer, the data is plotted using Matlab. Where sensing
the voltage vs time at a constant rpm. Every time one of the teeth
passes the pickup a pulse is outputted, and it should be a sinusoidal
waveform but instead of a perfect sinusoid we get one that in between
peaks there are a variety of different peaks. Is there anyway to
insert a picture of the waveform, this is my first time on here

 

[Michael A. Terrell]

The voltage output goes directly into a Labview DAS. Once we have the
data in the computer, the data is plotted using Matlab. Where sensing
the voltage vs time at a constant rpm. Every time one of the teeth
passes the pickup a pulse is outputted, and it should be a sinusoidal
waveform but instead of a perfect sinusoid we get one that in between
peaks there are a variety of different peaks. Is there anyway to
insert a picture of the waveform, this is my first time on here

Like I said, you need to look at it with a (Preferably a triggered
analog) scope to see the real waveform. I doubt that the shape of the
tooth will allow a clean sine wave. The precision of the machining of
both the teeth and of the sensor will affect the amplitude and waveform,
but unless you have a very high sampling rate, you can't really see the
true waveform. You will have aliasing unless the rate is high enough.


Pictures are not allowed on this newsgroup. We use a binaries
newsgroup, that you can't access through Google. Put it on a website
and post the link.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[[email protected]]

The voltage output goes directly into a Labview DAS. Once we have the
data in the computer, the data is plotted using Matlab. Where sensing
the voltage vs time at a constant rpm. Every time one of the teeth
passes the pickup a pulse is outputted, and it should be a sinusoidal
waveform but instead of a perfect sinusoid we get one that in between
peaks there are a variety of different peaks. Is there anyway to
insert a picture of the waveform, this is my first time on here- Hide quoted text -

- Show quoted text -

You would need a proper tooth profile to approch a sinusoidal
waveform. In most cases the output is quasi sinusoidal, with all
kinds of distortions due to tooth profile and other factors. If your
DAS is sampling fast enough, you maybe able to determine zero crossing
with enough resolution to measure signal crossing intervals or
crossings per time. With the crossing interval method, a rolling
average of succesive intervals will stablize the reading and provide
more acurracy. Counting crossings per time is good when the speed is
stable and you can count for 1 to many seconds.

BobS

 

[neon]

magntics lines follow the law of thr the square of the distance