About speed change detect

Hello everyone,

I have a problem to detect speed change in my program.
I use a sensor to detect a feeder roller speed change. When some strap was feeding into the roller, the speed will go fast. I check the sensor timer to determine whether the speed was changed. The problem is sometime there is a mechenical vibration happen, then cause the sensor off shortly, I will get wrong signal. Because speed change only between two cycle, very fast, so I get wrong signal.

Does anyone has some good idea to check speed change in PLC program?

Thanks a lot.

By the way, I use AB controllogix.


Regards,
shanna

You can:

a. Use a better sensor.
b. Average out the counts.
c. Set variation limits in order to reject some readings.
d. Relocate the sensor where the vibration least effects it.
d. Include these real variations caused by vibrations into you algorythm.
e. Slow down your PID

How often do you need to update your speed change detection scheme?

We use a quad encoder on our products that feeds back direction, position, and SPEED. Speed is caluclated by counting how many counts per second.

You will need to store two counter values from your counter.

Use a one second clock cycle bit to trap, and store the current count value, and compaire it to the last stored count value. any differance in count value will be a change in speed. You didnt mention the differential threshold tolarance that you need to detect, but I imagaine your looking for more than incremental differences?

Mike.

Thanks for all your reply.

Actually I want to use encoder before, but my boss thought it was expensive. So I use sensor to detect speed.

Yes, I do use two Timer to record the speed, every cyle finish, I capture a value from Timer to my register Array. I can get the dat successfully, the only thing is to screen some noise signal according to my monitor.

Anyway, right now I solve the problem by judge more than 1 valve in register array (3 or 4). It work. I hope maybe some better logic to do it.

Thanks!

Shanna

Shanna,

Your boss is cheap. You can buy a good encoder for as little as $120.00 US from AutomationDirect.com. Typical Prox sensors arn't really that much less expensive.

Just my opinion.

Thanks Mike for your information.

Shanna