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| 12/18/2014 10:20 PM | |
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Posts: 5225 Rating:
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[Late note] @Toeternietoe: Nice design for code you shared with us. My notes in the block above does not apply to what you have done. If the pulse rate is too high the code might run into trouble.. this can become tricky. Encouragement: Any more ideas? My ideas for this design (brainstorming exercise) * using the threshold trigger instruction * using your 2nd idea but have I1 replaced with I1 > COUNTER > {original}. The new counter has a target (example 10). So the sample now has a divider. A faster pulse can be handled. * A type of phase-locked loop. Using the analog ramp function to adapt the time of the pulse generator instruction. The time changes until the pulse generator is running at the same pulse rate as the incoming signal. Is this useful? |
Last edited by: William B. at: 12/18/2014 10:29 PMadd variation image |
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| 12/19/2014 10:11 AM | |
Joined: 12/27/2006 Last visit: 8/18/2024 Posts: 1197 Rating:
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In the LOGO 0BA8 tere is a Blok Average. Thats missing i the 0BA6 But you can make it. In the attachment, i have make a average of 3 measures. If you want, you can make more measures. Note: The value my NEVER exeed the 32767 (or les - 32766) In a mathematical block (inten) this valuwe may never exeed 65400! This programm is made for slow actions of input 1 No shorter time than 2 sec between the pulsen of I1 Have the TopicStarter (stewpid) say there is only 1 revolution in about 3 sec? If its a litte quicker you have to make some settings differend. Z.B make longer pulses by B001 or make schange multiply of V3 in B004 315 to 31 If you want a quicker program, zb interval of I1 < 1 sec then there is a better solution to work with the LOGO Then you must counts the inputs of I1 per minute (ore someting else) Then you have direktly the revolutions per minute. For slow working its better to measure the time between the input, so i have make in this programm. AttachmentCircuit Diagram4.zip (362 Downloads) |
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| 12/19/2014 6:50 PM | |
Joined: 10/15/2014 Last visit: 11/7/2024 Posts: 80 Rating:
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Guys, thanks so much for the help. i'm sorry I haven't replied earlier but i've been busy today. Toeternitoe, you are correct in that i am trying to measure the speed of a slow moving shaft. (if it had been a fast pulse on the proximity I would have just counted the pulses for a fixed time as you say, and i wouldn't have had a problem. it was trying to measure the gap between pulses as a speed measurement that had me stumped) William, sorry I haven't contributed much to this problem, my excuse is it is the first program i have attempted to write and i don't want to look too stupid! I am happy with this solution to the problem, but I thought you might be interested in the bigger picture, and maybe you have some insights that are helpful to me. I have a laminator/sheeter/cutter machine that first laminates a sheet of dough then passes it through a series of gauge rollers and webs to form a dough sheet of a precise thickness, before a cutter roller cuts pieces out of the sheet and feeds them into an oven. there are five gauge rollers and a cutter roller plus 10 webs.as the dough passes through each gauge roller it gets thinner and so theweb after it must run faster to take the dough sheet forward without it stretching or wrinkling. thespeed relationships between allthe webs and rollers is critical and must stay proportional as the line speed goes up or dowm.at present each web or roller has an inverter which has it's speed controlled by a line speed 10 turn pot which is cascaded from the oven back through every web and roller backto the laminator via 714 op amps,so that all the motors speed up and down together.each inverter also has a 10 turn trim pot. each trim pot speeds up or slows down its own inverter plus everything upstream in the cascade but not downstream. there is no feedback of the actual speed to the inverters or any speed display on the machine, only the frequency on the inverters. my plan is to replace the potentiometers on the machinewith logo!'s, one for each inverter. the logo!'s will measure the line speedusing the method discussed in this thread, then display it on the TD and either feed itback to the inverter or maybe use the Logo! forbetter control. Also the logo!s will replace the pots and op amps and will be used to control the speed cascade. the inverters are all IMO jaguar VXR's and I was planning to use 0-10v from a LOGO! analog output module to send the speed signal to the appropriate terminal on the inverter, however I have been reading about PWM on the LOGO! and i was wondering if I could use that instead. I realise this could be done other ways (using a central S7 plc and remote touchpanels etc) but for various reasons it is going to be done with Logo!s. Any suggestions about which model Logo! i should use or whether i need to network them or programming suggestions would be much appreciated. I have (with your help) written a first draft of the program for one unit which i will post when i get a chance. |
Last edited by: stewpid1 at: 12/19/2014 7:03 PM |
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| 12/19/2014 10:06 PM | |
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Joined: 12/27/2006 Last visit: 8/18/2024 Posts: 1197 Rating:
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Fun challenge I think. I think you will succeed with a LOGO. Personally, I would prefer to use an output signal of 4-20 mA to the frequency inverters. This signal is much less susceptible to interference. I would give this task will also make use of the new LOGO! 0BA8 series. This also has more analog outputs than 0BA6. An HMI may be linked to that you can use again to set your speed. Then comes more precise than with a potentiometer. But you can practice first with a potentiometer. Want one frequency converter control, each frequency converter in the following cascade control, or want to send any frequency inverter directly? |
Last edited by: Toeternietoe at: 12/19/2014 10:07 PM |
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| 12/19/2014 10:17 PM | |
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Posts: 5225 Rating:
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Hey.. do not worry friend, we understand. There is no shame in starting something new and needing some help - we all have to start somewhere. You loose me a bit in the detail, but I do understand you have a speed cascade puzzle to resolve. I agree that getting rid of the potensiometers is a good idea. How well do you know the variable speed drives that is used on this line. I would recommend strongly that you study what functionality you have available. Especially concentrate on the possible analog inputs and analog outputs. There is a very high possibility that you can control the drive's speed via an analog setpoint (sometimes the potnsiometer is connected there). Also there probably is the ability to feed an analog output from the drive too. (EXAMPLE) In my case the drives could be adjusted to have non zero speed when the analog is 0V and full speed for 10V (bias and gain settings but also minimum and maximum adjustable speed). For another case I had a pulsing encoder signal. The drive I had could actually read the frequency of the pulse (up to 10kHz) and adjust speed to follow. My point?.... study the user's manual of the drives you have on the line. Put your attention to what digital and analog I/O you have available and what it can be set to do. You already have a type of PLC functionality (better than LOGO in some respects) at your finger tips that can help you solve your problem. I hope this opens some doors for you. w |
| 12/22/2014 10:41 AM | |
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Joined: 10/15/2014 Last visit: 11/7/2024 Posts: 80 Rating:
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here is a block diagram showing how the potentiometers and inverters cascade at present
Attachmentcascade diagram.zip (359 Downloads) |
| 12/22/2014 10:46 AM | |
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Joined: 10/15/2014 Last visit: 11/7/2024 Posts: 80 Rating:
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this is a picture of a similar machine |
| 12/22/2014 10:47 AM | |
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Joined: 10/15/2014 Last visit: 11/7/2024 Posts: 80 Rating:
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and another |
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