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set pulses of PWM function

Created by: engco at: 7/14/2016 8:46 AM (6 Replies)

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7/14/2016 8:46 AM	Rate (0)
engco Bronze Member Joined: 2/2/2016 Last visit: 2/1/2023 Posts: 220 Rating: (2)	how to set the number of pulses in PWM function that is required to be generated?

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7/14/2016 9:33 AM	Rate (0)
William_B Posts: 5225 Rating: (1160)	OFF TOPIC engco, My apologies in advance. I would desperately not wish to sound cruel, but unhappily I will have to be the pig. It is doubtful any one else will come forward with this. I for one, can not just say nothing - I want to see you helped. I had a look at your program left in another post (thanks). It is a chaotic mess. = though not the worse that I have seen from 'professionals' = Not only in style and lack of commentary - also in technical usage issues when comes to the code and tech objects. I am also having difficulty to have you understand how to use the PWM.. it is not used as a PTO. I will not write the code for you. IMO - You need to spend some face-to-face time with a tutor. This Forum can not do what a tutor can. Speak to the nearest Siemens Office and enquire what they can do for you. I will take no offence if you ignore this note. Sorry for letting you down. - William B.
William_B Posts: 5225 Rating: (1160)
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7/14/2016 2:31 PM	Rate (0)
Marko Bursic Platinum Member Joined: 9/8/2009 Last visit: 1/20/2023 Posts: 1410 Rating: (146)	engco how to set the number of pulses in PWM function that is required to be generated? PWM stands for Pulse Width Modulation, number of pulses has nothing to do with it. PTO stands for Pulse Train Output, you get number of pulses with 50% duty ratio. These are two totaly different things. Nobody needs PWM with certain amount of pulses, so even you don't need it.

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This contribution was helpful to 1 thankful Users William_B

7/14/2016 7:00 PM	Rate (0)
engco Bronze Member Joined: 2/2/2016 Last visit: 2/1/2023 Posts: 220 Rating: (2)	Marko Bursic engco how to set the number of pulses in PWM function that is required to be generated? PWM stands for Pulse Width Modulation, number of pulses has nothing to do with it. PTO stands for Pulse Train Output, you get number of pulses with 50% duty ratio. These are two totaly different things. Nobody needs PWM with certain amount of pulses, so even you don't need it. the load have gear ratio and i don't know this gear ratio so i am planning to count pulses using PWM and calibrate it with motor revolution(angle) so i need the amount of pulses. if you have another solution please go ahead

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7/14/2016 7:42 PM	Rate (0)
grrrrrroooo Platinum Member Joined: 3/16/2015 Last visit: 10/10/2021 Posts: 1250 Rating: (164)	engco Marko Bursic engco how to set the number of pulses in PWM function that is required to be generated? PWM stands for Pulse Width Modulation, number of pulses has nothing to do with it. PTO stands for Pulse Train Output, you get number of pulses with 50% duty ratio. These are two totaly different things. Nobody needs PWM with certain amount of pulses, so even you don't need it. the load have gear ratio and i don't know this gear ratio so i am planning to count pulses using PWM and calibrate it with motor revolution(angle) so i need the amount of pulses. if you have another solution please go ahead A bit of refresher from previous discussions. Your motor is not a stepper/servo motor so there's not set relation between step/rotation angle and pulses. Your drive simply sends the pulses from the PLC output to the motor and what the motor sees is an "effective voltage". When you change the duty cycle or frequency of pulses you're changing the effective voltage which has effect on speed and torque. The rotational angle is something you derive loosely by experimenting with different settings and it is unlikely to be replicated with a great degree of accuracy every time. So it is advisable to keep in mind that though your project is interesting and good way to learn the reality is your motor is a not designed for the kind of motion control you're trying to attain no matter how geared down it is. Specially if you attach a load to it. everything will go right out of wack.

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This contribution was helpful to 1 thankful Users William_B

7/14/2016 9:36 PM	Rate (0)
Jav Pinz Posts: 108 Rating: (27)	Hello Engco, As far as I know, to control a induction motor (suppousing that this is the class of motor taking a look in the other posts), you need an encoder to control the position of the motor. To avoid a high desviation or error, the motor needs to go to a slow speed (may be a frecuency inverter or a really good gear relation) thats is to avoid free rotation of the rotor. PWM is use to control step and servos as KaI.A says. if you use PWM to control an induction motor, you will only control its speed (what a frequency inverter does) varying the amout of voltage applying in the coil. What i recommend you is to make or buy a encoder that allows you measure 1° or the sensibility that you need. Regards, Javier
Jav Pinz Posts: 108 Rating: (27)
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7/14/2016 11:07 PM	Rate (1)
William_B Posts: 5225 Rating: (1160)	Hand drawn pictures attached as PDF. Attachment PWM usage.pdf (89 Downloads)
William_B Posts: 5225 Rating: (1160)
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This contribution was helpful to 1 thankful Users Gordon Shumway

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