solenoid valve control linked to motor control - what is needed?

Discussion in 'The Projects Forum' started by spencermauro, May 24, 2016.

  1. spencermauro

    Thread Starter New Member

    Mar 2, 2016
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    I have four NC valves (work) and two NO valves (exhaust - labelled "a" and "b") with everything else the same. 24VDC direct acting solenoids. Each of the four NC valves will have its own tactile momentary switch to open the valve. The motor is a Micronel U71HL with integrated electronics; also 24VDC (datasheet attached). When powered up, the motor will produce 1 CFM and all output will go through the two NO valves. When one of the NC valves is energized, one of the NO valves needs to be closed; no change in motor. When two of the NC valves are open, both NO valves need to be closed; no change in motor. When three NC valves are open, both NO valves remain closed; motor RPMs increase to yield 0.5 CFM increase in flow (1.5 CFM total now). When all four NC valves are open, both NO valves remain closed; motor RPMs increase to yield 0.5 CFM increase in flow (2 CFM total now). The system needs to work the same whether the two open valves are 1 and 3 or 2 and 4 or whatever combination. The easiest way to think about it is that there needs to be 1 CFM minimum at all times, either being used (one or more of the NC valves opened) or exhausted (through one or both of the NO valves).

    My questions are whether this can be done fairly simply (if 0, then RPM 3000; if 1, then RPM 3000; if 2 then RPM 3000; if 3, then RPM 4500; if 4, then RPM 6000) or something similar? What would need to be in place to deal with the NO/NC operation? Could it be as simple as (if 0 NC, NOa and NOb open; if 1 NC open, NOa open and NOb closed; if 2 NC open, NOa and NOb closed; ...etc.)

    This is part of a larger project, but I think I have the temperature control part figured out. I just need to know what is possible (and if there is a better/easier/cheaper way to accomplish that above) and how I can design a simple control system. I will have to hire someone to design the PCB and then deal with manufacturing, but at this point, I don't even know what to ask the perspective designer to design.

    Thank you for any help/advice you can give me.
     
  2. spencermauro

    Thread Starter New Member

    Mar 2, 2016
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    Also, I have been told that a BLDC motor may be above and beyond what is needed for this project. However, I need a blower that can maintain continual use and have a long MTTF. I am just not sure if the cost of the blower with integrated electronics is worth the added expense (each motor is ~$200) based on the limited variability of the flow needed. Could I get away with a lesser motor and still have the necessary control?

    Thank you,
    Spencer
     
  3. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Off the shelf BLDC/ECM motor is not bad for $200.00 a cheaper alternative with rpm control would most likely require a custom drive of some kind, also a max of 6000rpm is limiting the type of motor..
    Max.
     
  4. spencermauro

    Thread Starter New Member

    Mar 2, 2016
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    Just for clarification, the RPMs noted are only to represent the increase steps, not actual values. Better to think in terms of X, 1.5X and 2X where X = RPMs needed to generate 1 CFM. Once we get the system up and running, we can determine the actual RPMs needed to generate that flow, but I wanted to stay away from using pressure differences to trigger the motor to increase/decrease speeds. I thought altering RPMs would be sufficient since all downstream pressures should be fairly equal. Thank you for replying. Do you think the alternative you spoke of with a custom driver would be cheaper than going off the shelf for the motor? I have a feeling it might be cheaper, but I am concerned about up front development cost as well. This whole thing is bootstrapped, so cost is a huge concern.
     
  5. MaxHeadRoom

    Expert

    Jul 18, 2013
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    The most rpm you would get out of a P.M. DC brushed motor would be around 3krpm tops.
    A BLDC would give you the 6krpm.
    What type of controller do you envisage? A custom micro based or off the shelf?
    Max.
     
  6. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Another option is a 3ph motor ran off of a VFD if 240v single phase is available.
    These have a 6 to 8 preset rpm inputs, parameter selectable.
    Max.
     
  7. spencermauro

    Thread Starter New Member

    Mar 2, 2016
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    The best way to control is the question. The BLDC motor I've chosen (see attachment to first post above) has integrated drivers already, I just need to control the input to get the output I want. That shouldn't be too difficult, based on what I have read thus far. The real control question is how do I adjust the power to the motor based on the number of valves in active operation? I need something that would sense the solenoid activity and adjust the voltage to the motor. So really, I have two control issues. One to control the NO valves (close one NO valve when one NC valve is open and close both NO valves when two or more NC valves are open) and another to determine output to the motor based on the number of NC valves open.
     
  8. spencermauro

    Thread Starter New Member

    Mar 2, 2016
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    I looked at VFD drivers and 3 hp motors and it looks like there would be little to no cost savings and a slight loss in longevity.
     
  9. MaxHeadRoom

    Expert

    Jul 18, 2013
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    It seems that either way some kind of logic controller is needed, the controller would obviously know when the valves are energized and set the motor speed accordingly.
    There is the Micropressor option or a smart relay or PLC to incorporate all of the control in.
    It all depends on your amount of expertise and how much is needed to farm out.
    More info would be needed on the motor chosen as to the present method of control using its control board.
    Max.
     
  10. spencermauro

    Thread Starter New Member

    Mar 2, 2016
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    What other information about the motor would be needed that isn't in the datasheet? My expertise is virtually nil, and although I am a quick learner, electronics has never been a strong suit. The purpose of the questions and thread is to help me understand what I need for when I farm it out. Without a little knowledge, you have to have complete trust in your contractor and that isn't a strong suit for me either. I need to understand what I am asking for. Can I get away with using Raspberry Pi and having someone program it, or would I need a more robust system? Could I use Arduino and have one run the valves and the second control the motor? What would be the easiest, cheapest way to do this project?
     
  11. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Maybe just me, but that data sheet seems really vague!
    If that could be pinned down to something simple then a SmartRelay may be able to do it.
    If not maybe a micro, I have used Microchip but am not familiar with Raspberry Pi or Arduino but I would assume they are capable, again depends on more info on the motor control.
    Seems to be some kind of analogue control?
    Max.
     
  12. KeepItSimpleStupid

    Well-Known Member

    Mar 4, 2014
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    The TS made the specs a little too hard to understand. Probably because of terminology. The NC valve instead of A, B and C or A0 for a normally open valve and A1 for a normally closed one. The "integrator" doesn't have to know, but the designations have meaning to you.

    Two common ways of determining if a valve is open or closed is to monitor that they have power,the have current or the valve itself has a position switch on it or you just assume a state based on how you have commanded it.

    Now, the motor has a tach signal and a 0 to 100% speed input, but I would not assume that 50% input is 50% of the max speed.

    A "smart relay" is a mini-PLC with essentially limited I/O. If this is integrated into something larger, it's possible to have MODBUS communication.
     
  13. spencermauro

    Thread Starter New Member

    Mar 2, 2016
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    So I could use a smart relay to control the valves and the motor? I was looking at Zelio and it looks like it could work. What would be the cheapest smart relay you would recommend? I would prefer to stay away from off-the-shelf as this will be integrated into a product and I will have to remove the case, inputs, etc. anyway.
     
  14. MaxHeadRoom

    Expert

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    The clincher is if you need to monitor the tach and provide a analogue output to this controller, a Smart relay may not be enough.
    I would like to see more information other than the limited detail in the motor link.
    IOW what is already configured and what, if any custom work has to be done.
    BTW, many are one manuf. and just re-labeled.
    Max.
     
  15. spencermauro

    Thread Starter New Member

    Mar 2, 2016
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    I'll check with the rep. These are medical grade CPAP blowers, so I'm sure they have plenty of documentation available. As for output, I don't anticipate the need. I will have a flow sensor to kill the heater if the motor fails. If the motor goes ape @&$&) and maxes out, the sensor will kill the heater and motor. As long as it is running, it shouldn't need active monitoring.
     
  16. KeepItSimpleStupid

    Well-Known Member

    Mar 4, 2014
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    There are some "naked" PLC's I just found this one: http://velocio.net

    Here: is sort of another: http://www.comfiletech.com/

    No experience with either of them. Search for "Board based plc"

    DIN rail is the "industrial erector set" but may not be appropriate for what you need to do.
     
  17. MaxHeadRoom

    Expert

    Jul 18, 2013
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    But in your OP you have spelt out a conditional logic as to when the motor runs and at what rpm based on the energizing of valves, according to the way I read the motor instructions for powering and control the digital feedback signal is used in conjunction with an analogue signal input which would indicate some kind of feedback controller is used externally and possibly provided by the system integrator?
    Max.
     
  18. spencermauro

    Thread Starter New Member

    Mar 2, 2016
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    I believe the frequency generator (yellow wire) is available for RPM monitoring, but I don't think it will be necessary once we pass the prototype stage (alarm output maybe). If we know that 2.1 VDC to the green line gives us our base flow rate and 2.8 gives us 1.5x flow, we would just need to program "if x valves open, supply y voltage"... Correct? I am trying to learn as I go here, so I apologize if any of this is blatantly wrong.
     
  19. MaxHeadRoom

    Expert

    Jul 18, 2013
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    That would basically be open loop control and would be trusting that the conditions on the motor are absolutely constant in order to maintain rpm.
    Max.
     
  20. spencermauro

    Thread Starter New Member

    Mar 2, 2016
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    True. Again, I would be happy to use a non-integrated controller, but most off-the-shelf controllers put the price point well above what this project can justify. Also, the true measure is flow, not RPMs. Flow is being constantly monitored and any adverse change in the motor would be reflected in these values. The system wouldn't be able to automatically fix the issue by altering the RPMs to compensate for discrepancies, but it would be able to alarm when out of parameters so the unit can be investigated. I would love to have 100% oversight and control, but cost limits us on a perfect system.
     
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