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manav

RPM measurement.

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I have 2 encoders giving me output around 1Khz. Can I read 2 High Speed Inputs in MicroLogix1100? I have read 2 HSI using the 2 HSC in ML1500. In ML1100 there is only 1 HSC available. Can I use the same HSC for 2 different inputs? How many onboard inputs on ML1100 can count high speed inputs? The other option is to use 2 pulse to mA/V converters from the encoders and use the onboard AI. What is the i/p range of the ML1100 AI? What is the data format for the same? I read in an article in here that there are limitations to these. Any one done this before? Urgent help required on this issue.

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HSC Function file in ML1100 you can program upto only one counter it is not possible to read as you stated. You do with simple Counter instruction in RSL500. First four on board inputs will do the High speed. The other option is to use 2 pulse to mA/V converters from the encoders and use the onboard AI. What is the i/p range of the ML1100 AI? I hope this not possible unless you use of absolute encoder it can give data in devicenet, grey code or BCD or many comm type

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How can I read a 1KHz frequency thru simple counter in RSL500? Would I not need a scan time of 1ms to do so? I can convert the frequency into 4-20 mA or 0-10V. Would I be able to read this signal in onboard I/O of ML1100?

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Really your application requires 1 Khz frequency what type of encoder you are using if Incremantal then what the PPR

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Maybe I wrongly quoted encoder. I am basically a software guy with working knowledge of electrical stuff. Basically I am getting a high speed pulse input from the machine. This is of 10000RPM. 6 pulse per rev. This I calculate at about 1KHz frequency. I have earlier used a ML1500 using 2 of the onboard HSI and 2 HSC using a 1 sec STI to read the acc value and move to buffer before clearing the acc of the HSC. Scaling the moved value gives me the RPM for the 2 signals. I have successfully deployed this application 1 yr back using ML1500. Can I do the same with ML1100? Since the ML1100 has 1 HSC I can calculate the RPM for 1 signal. For the other can I use a simple counter? Not sure if it will be possible. Can I use the same STI and HSC to alternately calculate RPM for 2 signals. Again not sure if possible. For the 2nd signal I can use a pulse to 4-20 mA / 0-10V converter and try to read this from onboard I/O. I have been informed by our electrical guys that such a converter exists even though I have never used it before. Any ideas on this?

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60,000 pulses per minute i.e 1000 pulses per sec,I hope this not possible with out HSC you can try with simple counter but it misses pulses during scanning & same condition with analog I/O it has its delay for conversion in the external device & analog A/D convertor. Simple counter is better then Analog input

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One way that comes to mind is to use a 1 ms STI. XIC the HSI every scan and add 1 on true. Clear and reset after 1000 counts of STI. For this the scan time of the STI would need to be less than 1 ms. Again I do not know if this will be posible. What would the scan of this STI be approximately if anyone has tried this earlier? Problem is that I will be able to only de-bug aplication in field or with 1KHz simulated signal which I dont have. I have to validate the system right now for this. The RPM variation is not very fast. Say from 9000RPM to 8000RPM in 2-3 secs. So instantaneous values are not important. How would the delay with the pulse to mA converter be? Would it be greater than 1 sec? Has anyone tried to read a 1Khz signal using normal counter or STI in RSL500? Any experience on this would be helpful.

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It is not possible to have the STI to 1ms this will overload the processor & cause delay on remaining codes it is also not recommended

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I understand. My basic application is to compare RPM of 2 motors and calculate differential error between the 2. It is fairly straightforward. Only reason to migrate to ML1100 from ML1500 is that this time client wants ethernet. With NET-ENI cost goes up. But if this app is not possible in 1100 then 1500 + ENI would be OK too. Thanks.

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then you have use same method of measurement to eliminate errors & delays

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That is why I wanted to go with 2 pulse to mA converters because they would have the same delay in ML1100. Question is how much delay would they have. If less than 1 sec then it might be acceptable to client. Unfortunately I do not have much knowledge of Non RA items and rely on our electrical / instrumentation guys for it. Any ideas?

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Unable find such convertor they non standard you can try with Omron make,

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Use the EII and calculate your RPM off of a timebase. You still need to lower the resolution of your feedback system significantly. 20kHz is the absolute max

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Chances are you have the wrong tool for the job. You should have two hardware counters. The time you waste will fighting this will cost more than a more appropriate solution. I could say more but we haven't been told what the final goal is except to match RPM. Does that mean you don't care about phase? Why do you care about matching RPM? What are you going to do about it they don't match? If the RPMs must match then how closely? TWControls, the counts come in at 1 khz which is in range of one counter. This is a easy with a decent motion controller. If you are trying to match speeds then the encoder resolution should be higher.

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I agree. The ML1100 really is not appropriate for what you are trying to do. Either use a ML1500, or step up to a CompactLogix if you are married to a PLC. Personally, I would recommend the CompactLogix based on the information you have provided.

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Right again Peter. It is the wrong device for the job

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No, phase measurement is not part of the application. 2 motors are running coupled to each other thru a mechanical contraption (no clue what that actually is). Its part of an energy saving methodology. There is slip between the 2 motors measured as the difference % of the 2 RPMs. If this slip exceeds a setpoint then the system has to shut down thru DO. Some other monitoring of parameters is there like V,A,Temp etc. The app logic is simple enough. I have already implemented this system last yr thru ML1500 + IF4 module + microview. System working fine till date. Only prob is that this time client wants ENet. So ML1100 came to mind. But looks like will have to go with ML1500 + NetENI on this one. Thanks for all the help guys!!

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isn't cost of ML1100 less than what they ask for ENI?

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Yep. The ML1500 + Net-ENI versus ML1100 + 2 pulse to mA converters = 40% higher cost Also I need the ethernet to connect to RSView32 HMI at distance of about 900 metres. Will it work fine on NET-ENI at that distance. Max I have gone with Enet is about 200 metres so I do not know about any extra hardware I need to include in BOM for 900 metres. Anyone networked ENET with NET-ENI upto 900 metres or above?

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Are you referring to Cat5 copper going 200 meters? The spec for Cat5 Copper is 100 meters or 300 feet. See this link or google for others. If you need 900 meters I'd go fiber. You'll need a switch/router/hub at each end which can do fiber to copper. This option from blackbox claims to support 2 kilometers between switches and cost about $400 per switch. OF course you'll need the fiber and a conduit to protest it would be how I'd do it althought not needed if plenum grade fiber. This guy might also work and others willr ecommend better.

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Thanks mate.

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