A Better Gear Tooth sensor

[Tim Skloss]

Originally Posted by Alan Anderson

According to the 2008 Sensor Manual, the KOP gear tooth sensors give a pulse every time a tooth comes by. Where are you finding information saying they only give rate information? And what do you mean by "hard to use"? We used the ones in the 2006 kit with substantially the same software you suggest for the Honeywell parts.

Well, it says the output is a "PWM" signal with a period of 45 us. When I read that I imagine a train of pulses that flows regardless of gear motion. Add to that description the statement of "duty cycle varies from 41-61 percent" and you have a good description of a classic PWM rate-type signal.

Now that I have read the Allegro data sheet I find that you are correct and the sensor manual to be misleading. The sensor manual should say: "Each time a gear tooth passes the sensor a 45 (nominal) microsecond pulse will be transmitted on the S output with no indication of the direction of rotation." Saying it is a PWM signal, when it isn't (no width modulation) only leads to confusion. The variation in pulse width comes from the distance between the sensor and the gear, according to the data sheet.

Thanks for pointing that out. We will try them this year on the gearboxes and save the Honeywell sensors for other sensing jobs. The Honeywell sensors are easier to mount and extremely durable, that much is for sure. Plus you only need 3 wires.