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Reading RPM from encoder

Created by: adrian_botez at: 6/27/2014 1:34 PM (23 Replies)

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6/28/2014 10:11 PM	Rate (0)
William_B Posts: 5225 Rating: (1204)	Marcjan ... This is a public forum, if you have information that can help, share it. ... okay, password removed.
William_B Posts: 5225 Rating: (1204)
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6/29/2014 7:20 PM	Rate (0)
adrian_botez Posts: 185 Rating: (9)	Thanks you for the documets in the PDF. Very useful. I´ve made the program some sort of this. But I don´t understand how you will calculate the RPM. If I don´t want to use frequency , how do I do it? Attachment encoder.zip (1187 Downloads)
adrian_botez Posts: 185 Rating: (9)
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6/29/2014 8:48 PM	Rate (0)
William_B Posts: 5225 Rating: (1204)	adrian_botez Thanks you for the documets in the PDF. Very useful. I´ve made the program some sort of this. But I don´t understand how you will calculate the RPM. If I don´t want to use frequency , how do I do it? ¡hola amigo! Gracias por sus comentarios. The file your sent is a good starting point. In my next message I will answer your question. Please expect that soon. It is very important that we get the baseline set. With the attached ZIP, I am trying to close the gaps left by the previous files I left you. Please make that part of your project. I'll talk to you agin in a few minutes. w Attachment A001.zip (1026 Downloads)
William_B Posts: 5225 Rating: (1204)
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6/29/2014 9:10 PM	Rate (0)
adrian_botez Posts: 185 Rating: (9)	Thanks you. But if I read the value in my normal OB1 scan, I will not get real values, I have to read it with :P. That is right?
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6/29/2014 9:24 PM	Rate (0)
William_B Posts: 5225 Rating: (1204)	adrian_botez Thanks you for the documets in the PDF. Very useful. I´ve made the program some sort of this. But I don´t understand how you will calculate the RPM. If I don´t want to use frequency , how do I do it? Adrian, I should mention that what we are doing here will (probably) solve the question you started wit for this theme. I have no guarantee that it will help you with your actual application problem. The frequency measurement that the HSC can provide is actually very helpful for working out the RPM. We will attempt another approach however. [background] The HSC you created is a continuous counter. Each pulse the encoder gives, the HSC will count. If your program does not interfere, the value will continue growing. Some encoders have a zero mark signal. You can register this signal into the hardware definition which will cause the HSC to zero at each revolution. Careful: The A/B pulse encoder set up will give x4 the value of your encoder for each encoder revolution. So if the encoder is rated 2,500 the HSC will increase by 10,000 counts for every encoder revolution. [program addition] In the next step we will add a cyclic interrupt OB30. OB30 will grab the value of the HSC at regular precise intervals. You have to decide for yourself how long this period is. The longer the period, the more accurate the measurement but also slower the reaction. Hints on creating OB30 is given in the JPEG. For argument we keep it at 100ms time. Also create three global variables from memory: BUFFER1, BUFFER2 and DIFFERENCE of type DINT. Now you can create code inside OB30 to do the following tasks: 1. %ID1000 -> BUFFER2 1. BUFFER2 - BUFFER1 -> DIFFERENCE 2. BUFFER2 -> BUFFER1 DIFFERENCE is the count of encoder pulses that was counted by HSC1 within 100ms. We now know that there are 10,000 pulses for each encoder revolution (2,500 x 4). Then also 1min = 60sec = 60,000ms or 600 x 100ms. So you can create this code inside your normal program.. RPM_ENCODER = 600 x DIFFERENCE / 10,000. Remember.. * the "600" depend on what you set the update time for in OB30. * 10,000 depends on what encoder you use and what you set it for * RPM_ENCODER is a REAL number. You may need to convert DIFFERENCE to a REAL number. Finally.. RPM_ENCODER is the RPM of the encoder. RPM of the motor depends on where you mount the encoder in relation to the motor.. in other words.. how many revolutions of the motor is how many revolutions if the encoder. If you give us more info on how the encoder is mounted we can help there. --- Please look at the previous post about the creation of the HSC. Then create the coding as listed above. Then please publish your project for me, or another member to make comments. Please ask questions after you have done this exercise. Greetings. w
William_B Posts: 5225 Rating: (1204)
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6/29/2014 9:33 PM	Rate (0)
William_B Posts: 5225 Rating: (1204)	adrian_botez Thanks you. But if I read the value in my normal OB1 scan, I will not get real values, I have to read it with :P. That is right? Yes you are right. BUT.. The scan of OB1 is so "slow" when comparing with HSC, that reading ID1000 as is, is better. Within one scan of OB1 you do not want the inputs to change.. this can cause problems for your coding. Each time you use the :P, the value would have changed. Using %ID1000:P inside the interrupt is okay. This is not a fixed rule however.. this is my technical opinion. Also never try to do.. %ID1000:P ----\| = \|----- "value" your code will have a possibility of missing the "equal to" position. Better to use a compare within two limits.. the two limits does not have to be far apart. w
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6/30/2014 3:03 PM	Rate (0)
adrian_botez Posts: 185 Rating: (9)	OK. This week I will try it and the resut will be posted here.
adrian_botez Posts: 185 Rating: (9)
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7/25/2014 2:02 PM	Rate (0)
adrian_botez Posts: 185 Rating: (9)	I have done all this configuracion, but I dont have any response from the encedor. If I move the encoder slowly I get values incrementing one by one. Bt if I do it fast, I don´t have any answer. It doesn´t count. What can I do?
adrian_botez Posts: 185 Rating: (9)
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7/25/2014 2:20 PM	Rate (0)
William_B Posts: 5225 Rating: (1204)	adrian_botez I have done all this configuracion, but I dont have any response from the encedor. If I move the encoder slowly I get values incrementing one by one. Bt if I do it fast, I don´t have any answer. It doesn´t count. What can I do? Welcome back. Please check the filter timing of your digital inputs. These are set to a too high value. See the JPEG. Do let us know the result. Greetings. w Attachment Visual clue_Where to find filtering times for inputs.jpg (1093 Downloads)
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7/28/2014 9:31 PM	Rate (0)
adrian_botez Posts: 185 Rating: (9)	Great. That was the issue. Thx!
adrian_botez Posts: 185 Rating: (9)	Last edited by: adrian_botez at: 7/28/2014 9:31 PM
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This contribution was helpful to 1 thankful Users William_B