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Application Example - RPM Measurement by Proximity Sensor

Created by: MicroMan at: 1/20/2017 11:29 AM (10 Replies)

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1/20/2017 11:29 AM	Rate (0)
MicroMan Platinum Member Joined: 11/29/2011 Last visit: 12/6/2019 Posts: 1317 Rating: (214)	Hi, I am looking for an application example for RPM measurement done by a proximity switch! Cheers
	- What you read here, please check with manuals and your requirements. - Do not forget to Test, Test and Test... - If the post is helpful, please RATE it! MicroMan
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1/20/2017 1:07 PM	Rate (1)
Duris_I Platinum Member Joined: 4/28/2015 Last visit: 12/6/2019 Posts: 6020 Rating: (444)	Hello, as I see you as experienced user, only (hope it can be also helpful to you) this standard document is good, also with some know-how. As there are some clear infos (hope I was good understand that), via simple pulse catch it can be probably solved. http://www.opto22.com/documents/1784_rpm_measurement_techniques_technical_note.pdf
	With kind regards... Duris_I
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1/20/2017 3:14 PM	Rate (2)
Piotr.M Platinum Expert Joined: 6/24/2013 Last visit: 11/7/2019 Posts: 1303 Rating: (294)	First you need answer some questions: 1. what is min and max period (in seconds) between measurements (are you measuring at the motor or after the gearbox where each rev takes a long time i.e. more than a second 2. based on 1. will you use a fast counter input? 3. for 2. calculate for max frequency what would be better: measure period (time between pulses) or frequency (pulses in given time). Error will depend on mode and max frequency, If max frequency is low period mode is better then calculate in the PLC. if you are using the sensor input without a counter card: use TON timer: I used it for S7-300 project and it worked well [it does measure spool revolution time which is 5+seconds) NW1: Capture measured time when new edge appears (before timer resets in NW2) Sensor Sensor_Pulse ------------\|P\|-------------------()----------------\|TON Timer\|---- FP_Sensor \| \|---Measured_Time NW2: Measure Time - trigger timer on every raising edge at the sensor input ----------------------------------------------------\|TON_Timer\|--- Sensor_Pulse \| \| --------------------------\|\\|------------------------\|IN \| T#21D-\| \| from measured time in ms you can calculate RPM: RPM:=60000/Measured_Time NOTE: Corrected error - pulse should have been inverted so timer counts time between pulses.
	Last edited by: Piotr.M at: 1/23/2017 10:08:21 AM Last edited by: Piotr.M at: 1/23/2017 10:11:39 AM
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1/20/2017 3:15 PM	Rate (1)
William_B Posts: 5225 Rating: (1068)	MicroMan Hi, I am looking for an application example for RPM measurement done by a proximity switch! Cheers To further the conversation... I have not searched for such application example - but some detail would be instrumental in what will work. Which PLC and extension cards do you have for this project? Or are you able to specify them still? In what range (kHz) do you think the sensor would pulse at? How accurate do you need? External devices can do this job and give a value per communication or analog feedback. If you want something a little more accurate and the PLC is not "strong" enough, then this is a good option. I prefer using an S7-200 or S7-1200 even more than CPU31xC as to avoid needing special cards to read the input quickly enough. Cheers.
William_B Posts: 5225 Rating: (1068)
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1/20/2017 3:18 PM	Rate (0)
William_B Posts: 5225 Rating: (1068)	Piotr.M if you are using the sensor input without a counter card: use TON timer: I used it for S7-300 project and it worked well [it does measure spool revolution time which is 5+seconds) I would go for hardware interrupt.. if available. Then capture the PLC system time at each interrupt. Trouble is... hardware interrupts are not always available.
William_B Posts: 5225 Rating: (1068)
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1/20/2017 9:25 PM	Rate (0)
MicroMan Platinum Member Joined: 11/29/2011 Last visit: 12/6/2019 Posts: 1317 Rating: (214)	Hi, Thank you for your responses. I was after an application example issued by Siemens. To cut it short: I am working on a validated system. I needed to close a deviation: code have a control module for DI, the Scada have requirement for display in RPM. My validation people offered me this easy way out, that why I was desperate to have a "valid" source. Thank you anyways!
	- What you read here, please check with manuals and your requirements. - Do not forget to Test, Test and Test... - If the post is helpful, please RATE it! MicroMan
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1/23/2017 10:14 AM	Rate (0)
Piotr.M Platinum Expert Joined: 6/24/2013 Last visit: 11/7/2019 Posts: 1303 Rating: (294)	Hi What do You mean by validated example? The Siemens examples do came with condition 'use at your own risk' i.e. Siemens is not responsible for any bugs in their examples and final engineering of the solution is the developers' responsibility.

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1/23/2017 10:22 AM	Rate (0)
William_B Posts: 5225 Rating: (1068)	Piotr.M Hi What do You mean by validated example? The Siemens examples do came with condition 'use at your own risk' i.e. Siemens is not responsible for any bugs in their examples and final engineering of the solution is the developers' responsibility. [CONVERSATION] A valid argument you are making. But I think the real point is to have some mechanism that can be verify the work already done. The idea is to get something from a 3rd party and not from the original designer of the 'thing' that needs verification. If code from Siemens (or other independent 3rd party) gives the same result.. then the verification is made. (naughty smile) Maybe get Omron rep to demonstrate their RPM counter device at the clients' plant <hint hint>. w
William_B Posts: 5225 Rating: (1068)
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1/23/2017 4:23 PM	Rate (0)
MicroMan Platinum Member Joined: 11/29/2011 Last visit: 12/6/2019 Posts: 1317 Rating: (214)	Yes, that is also a good point. Anyways my validation folks accept it, and I am trying to make them happy. Of course there is a Test Procedure on place to verify the functionality.
	Last edited by: MicroMan at: 1/23/2017 4:36:53 PM - What you read here, please check with manuals and your requirements. - Do not forget to Test, Test and Test... - If the post is helpful, please RATE it! MicroMan
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10/15/2019 6:57 PM	Rate (0)
mightymannan Regular Member Joined: 11/12/2018 Last visit: 10/30/2019 Posts: 8 Rating: (0)	I'm also looking for that. Can you share the application example for that? Thanks in advance.

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