# Magnetic pickup speed sensor

I am looking at a magnetic pickup sensor datasheet.

This graph shows the output voltage against the surface speed.

However, there are 3 curves, that changes the output voltage range changes.

What could be the meaning of "8P", "10P" and "16P"? Are these the poles of the reluctor?

There are no other information in the datasheet except mechanical drawings.

Edit: I don't have the datasheet file right now, here is the best datasheet I found on google about this sensor... it's the same one except the graph.

• Where's the datasheet link for context? Edit it into your question rather than in the comments. Commented Oct 23, 2020 at 16:51
• How about a link to the datasheet? Commented Oct 23, 2020 at 16:51
• I'll tell you if you can tell me what "23M" means in a data sheet I read the other day. Commented Oct 23, 2020 at 16:55
• My guess is that P means poles or pulses.
– user80875
Commented Oct 23, 2020 at 17:21
• I added a link to the datasheet. Aha andy, I know this is hard to answer, I tried to explain the context best I could. Like I said, the datasheet has poor information. Commented Oct 23, 2020 at 19:13

What could be the meaning of "8P", "10P" and "16P"? Are these the poles of the reluctor?

Standard spur gears are used as 'reluctors' with variable reluctance pickups, in order to generate sinusoidal output signals.

8P, 10P, 16P are not the number of poles of the reluctor. They signify its Diametral Pitch (the number of teeth per inch of its pitch circle diameter). Diametral Pitch is a measure of the size of its teeth (smaller the number, greater the size).

The graphs, for a pickup having a specific sensing diameter, show a drastic increase in output voltage with an increase in tooth size from 16P to 8P.

The unit of 'Surface Speed' of the reluctor, on the X-axis, is 'inches per second' (IPS).

• It makes sense, thanks you for the correction ! Commented Oct 24, 2020 at 16:52
• Anytime, Ultra67! Commented Oct 24, 2020 at 17:09

With more P, poles per rev or per linear distance, the voltage per unit distance of flux change of induced flux change is reduced.

• the relationship may not be quite inverse with more gaps thus 16P is slightly less than half V/ips of 8P.

Similarity Magnetic pickups like motors generate voltage according to the rate of flux change or RPM or surface speed and for motors are rated in kV/RPM for DC motors

Thus the fastest RPM for the same voltage or lowest kV/RPM will be 2 pole and slowest with more torque will have more poles.

• Wheel Speed Sensors (WSS) for automotive ABS often use 96 poles /rev with 3 Hall sensors detecting magnetic teeth for fine velocity sensing for slip control at any speed > 0.5Hz per pole.
• the voltage drops out below this threshold due to the air gap and low flux change rate.
• Thank you for your answer. I wasn't sure. Do we agree that the frequency of the output signal of the sensor increases as well with more RPM? Commented Oct 23, 2020 at 19:11
• Not only same frequency, it must synchronous and proper phase Commented Nov 10, 2020 at 18:53