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# Rotary Encoders

## 6 posts in this topic

Hello Mr. Anthony and hello all: I am wondering what the difference is between counts and hertz of an incremental encoder. In terms of what the plc can see. I have two catalogs in front of me. One is for the CPM2A and one is for the C200HAlpha. The CPM2A says it can handle up to 5 khz from the encoder while the C200HAlpha says it can handle 50 kcps. Now how is the conversion between Hertz and Kilo counts per second? I would like to know which is faster, how much faster, and more importantly how the answer was derived. The reason I ask this is because a coworker and I are working on a spindle that will index to three different positions (0,90,180). It will have to be able to keep track of where the spindle is at, at all times even when the spindle is running at a maximum of 1700 RPM. Thanks again for helping me a while back on the indexer and comparison table problem Jay. It is finally working. But the air actuated cylinders are lacking on repeatability and speed. I am still trying to pick up PLC's so please bare with me. Thank you for your time.

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By 'hertz' and 'count' they mean same thing, which is number of pulses per second. In your case 50 kcps = 50kHz or 10x higher for C200HAlpha than for CPM2A. panic mode

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As panic_mode mentioned above Khz and kcps are the same. CPS=Counts per Second Hertz= Cycles per Second Therefore: Khz=Kcps 360 ppr encoder: 1700 RPM x 360 ppr(pulses per revolution = 612000 pulses per minute / 60 seconds = 10200 cps or 10.2khz(kcps) 200 ppr encoder: 1700 RPM x 200 ppr(pulses per revolution = 340000 pulses per minute / 60 seconds = 5666.667 cps or 5.67khz(kcps) 100 ppr encoder: 1700 RPM x 100 ppr(pulses per revolution = 170000 pulses per minute / 60 seconds = 2833.333 cps or 2.83khz(kcps)

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Things you need to know What is the coupling ratio between spindle & encoder? i.e. how many revs of the encoder for one rev of the spindle? How many lines on the encoder? What is the counting mode? I'm not familiar with Omron, but other devices can operate in different modes: 1X - count on leading edge of phase A 2X - count on leading edges of phase A and phase B 4X - count on leading and trailing edges of phase A and phase B In your case, I presume you would have a 360-line encoder coupled at 1:1. 1700 RPM = 28.33 rev/sec in 1X mode, that gives 10,200 hz or cps in 2X mode, 20,400 hz in 4X mode, 40,800 hz Clearly the 5Khz unit is inadequate.

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Good point Gerry! The Omron CPM2A encoder input can be used in two modes: Differential (quadrature) - 4x PPR - Advantage - Reversible count Incremental (single phase) - 1x PPR - Disadvantage - Counts only in one direction

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Thanks guys! Your really cleared that up for me. I appreciate the effort. Baden