Optical encoder to reading motor rpm

[splendid]

Hi all,

Anyone can tutor me that how to write the formula for encoder to read the motor RPM(Omron PLC).

Thanks in advance

 

[jvdcande]

I doubt it can be done with an encoder and a PLC, except with very low RPM and a very low number of pulses per RPM. What frequency will the pulses be and what type of input are you using? So, in the end: more information is needed to help.

BTW the formula is very simple: count the pulses during a set time period. Divide the number of pulses by the number of pulses per revolution and the set time period which gives you the RPS (revolutions per second). Multiply by 60 and you get the RPM. The accuracy is dependent on the accuracy of the set time period, the accuracy with which you can count (how much pulses did you fail to see) and the accuracy of the calculation.

 

[splendid]

I doubt it can be done with an encoder and a PLC, except with very low RPM and a very low number of pulses per RPM. What frequency will the pulses be and what type of input are you using? So, in the end: more information is needed to help.

BTW the formula is very simple: count the pulses during a set time period. Divide the number of pulses by the number of pulses per revolution and the set time period which gives you the RPS (revolutions per second). Multiply by 60 and you get the RPM. The accuracy is dependent on the accuracy of the set time period, the accuracy with which you can count (how much pulses did you fail to see) and the accuracy of the calculation.

Hi jvdcanda,

My encoder is 600 pulse/rev and to use A phase input to PLC 0000.
The motor max rpm is 3000.

 

[Steve Bailey]

PLC 0000 had better be a high speed counter input. At 3000 RPM and 600 PPR the PLC receives pulses at the rate of 30000 per second.

 

[splendid]

I see!

So how to write in ladder diagram?

Btw, I'm confusing that encoder PPR meaning.
Is it encoder rotate a cycle(360 degree)?

 

[Steve Bailey]

PPR = Pulses Per Revolution

Before you write the first line of code you have to sure of your hardware. Can the input you plan to use be configured to accept a 30 kHz pulse train? If it can, you may find that the work has already been done for you. I say that because a typical use for high speed counter inputs is to measure rotational speed. In the process of configuring the input you may also define an address or tag that will show the pulse frequency.
The previous paragraph is speculation on my part. I'm not all that familiar with Omron PLCs in general and you haven't specified which model. I suggest you read the manual.