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Analogue Speed exact scaling

Created by: chrisymorganuk at: 5/29/2013 9:54 AM (4 Replies)

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5/29/2013 9:54 AM	Rate (0)
chrisymorganuk Posts: 11 Rating: (0)	Hello everyone I am currently trying to set up a analogue speed for a hydraulic driven drum. Its using a proportional valve driven by a solenoid via my analogue output. In my logic that I currently have, see attached zip, the operator uses a bit on the HMI to enter their speed in meters per minute and I can get the drum to spin at different speeds but not getting the desired voltage on my analogue output to my solenoid. I would like to have it perfectly scaled so 1VDC output = 10 meters per minute, 2VDC = 20 meters per minute etc up to 10VDC = 100 meters per minute. Thanks for the time guys! Attachment A_speed.zip (128 Downloads)
chrisymorganuk Posts: 11 Rating: (0)
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5/29/2013 2:07 PM	Rate (0)
BryanG2001 Posts: 113 Rating: (22)	I think you are aiming for an unnecessary target. Unless you can guarantee that the two hydraulic valves act perfectly linearly and that at 1V you get 10metres/min and at 10V you get 100metres/min it is a target you will never achieve. Plus unless the proportional valve is full pressure compensated then changes in back pressure will affect the flow rate. The important thing is that the system runs at the speed set by the operator, I would think that you would need a feedback mechanism and probably a PI (out of PID) control system.
BryanG2001 Posts: 113 Rating: (22)
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5/29/2013 3:36 PM	Rate (0)
Marcjan Platinum Member Joined: 4/22/2010 Last visit: 12/15/2022 Posts: 5697 Rating: (702)	Hello, Besides the technical problems you could have. To unscale use: [code] L MD10 // load frequency 0.0 to 100.0 L 1.000000e+002 // load 100.0 /R // Divide L 2.764800e+004 // load max analog value *R // multiply RND //round T "analog_output" // transfer to output PQWxxx[/code] If your value is an int convert to real first. Regards, Marcjan
	Last edited by: Marcjan at: 5/29/2013 3:38 PM Problem solved? Please let us know! Please no technical questions by PM, use the forum sections for your questions.
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5/29/2013 4:19 PM	Rate (0)
chrisymorganuk Posts: 11 Rating: (0)	Thanks for the replies guys. Firstly the machine is a gravure so speed is critical. I have no feedback on my proportional valve, just a analogue 0-10v output to the solenoid ontop of the proportional valve. I basically want when the Operator selects 40metres/min for example when I put my taco on it reads 40metres/min. At the Moment when I use the attached new logic it reads 30metres/min and then when I select 50metres/min the taco reads 75 metres/min. But what is puzzling me is that when I have 50metres/min selected the output word I get is 13824 which is correct?! Attachment A-speed1.zip (94 Downloads)
chrisymorganuk Posts: 11 Rating: (0)
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5/29/2013 5:17 PM	Rate (0)
BryanG2001 Posts: 113 Rating: (22)	I didn't know what a 'gravure' was so I put it in to Google, either you are doing something with printing, or it involves young Asian women not wearing much. I will guess that it is the first option. If speed is critical then you need a closed loop system, you can't rely on hydraulic valves to give a consistent speed. You would need something measuring the speed of the roller, then you feed that back to your control system so that it adjusts the speed to match the Set Point.
BryanG2001 Posts: 113 Rating: (22)
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