High speed counter with Compobus?

[fredal 0]

Hi everyone, I'm not coming here very often, and maybe it is only my second question since one year, but when I come here, I always find what I'm needing (some people had the same problems before me ;)). Anyway, here is my question: I have a CJ1M-CPU11 PLC with 1 16-inputs and 1 16-outputs modules. Now, I need a high speed communication with a part of the mill who is located 110 feet from the PLC. I need high speed reception time from the PLC to take quick decisions so I decided to make a Compobus network. I bought a CJ1W-SRM21 Master module, a SRT2-ID16-1 input module and a SRT2-OD08 output module. I'm only using 2 or 3 inputs for now, balance is for future development. But today, we decided to change a part of a system located 3 feet from the SRT2 Modules (I didn't get them actually, they were B.O.) and I will need to put an encoder wheel to measure lenght. The encoder I'd like to use is a Hohner 1002-0110-1000 . I search on the Internet but there is no Compobus remote module for a high speed counter. Maybe I don't need that?? The system works like that. There is densified logs that are coming down a cooling line. We cut a log every 10 inches because it comes as 1 long simgle log in the line. 10'' = 0.83 foot. In one hour, there is approx. 1200 logs coming out, so approx. 1000 feet long in one hour = 16,6 feet in 1 minute = 0.27 foot in 1 sec. (3.24 inch in 1 sec.). I give that information because maybe I don't need a High speed counter.. Anyway, what is the best way to do? I seen about CPM2C with a counter integrated (I only activate one output when the lenght is OK) but can I link it to a CJ1 with compobus? Will I need to buy another CJ1 PLC or should I just put a long cable through all that distance??... I think I gave all the informations needed... Thank you very much! Steven

[Aart Rietveld 0]

Hi Steven, I've used Compobus S in High Speed-mode for counting the revolutions of a 2950 rpm motor using a inductive proximity-switch. I found out that the Compobus was faster than the cycle-time of my CJ-cpu.... I've also used a CPM2A as a slave on the Compobus, only disadvantage is the small amount of bits (8 input and 8 output) the slave can handle. If your CJ1-plc can count the pulses using a standard digital input you can do the same with Compobus-S. Edited 27 Nov 2008 by Aart Rietveld

[fredal 0]

Thank you very much Aart! The encoder I have here is 1000 pulses per revolution. That is way too fast for a normal digital input. I looked with one of my distributors, and he has one encoder 50 pulses per revolution. With a 3 1/8'' wheel that will turn on the logs, I get 1 pulse per 0,05 second at the maximum speed. 50ms is slower than all my PLC ( I calculated 16ms Tmax) so i'll be able to handle it. It only gives 1,2 KHz but I think it will be OK. I'll have a precision +-5mm, that is better than my +-25mm (that is in real +-50mm) I have now.. Maybe I can check for smaller wheel to be more precise... Maybe I forgot something important too..

[fredal 0]

Hi again everyone, My system is installed and works, but sometimes, the cut logs are not always the same lenght. I know I can have some differences because I doN't saw the logs, I cut it with a kind of finger rolling on an hydraulic cylinder. The time the finger goes into the log can vary a bit I think. But I want to be sure my programmation can handle the best of the encoder. It is 50 pulses/revolution with a 3'' wheel at the end, I have two (2) channels A and B, wired to one digital input each. Maximum speed is 240''/minute, minimum 150''/minute. I tried a few things before getting that, but I really don't know if my program is the most precise one. Maybe I just complicated myself, but anyway, I send the part of the program so you may help me! Thank you very much! encoder_program.cxp