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  1. #46
    BobL is offline Member: Blue and white apron brigade
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    We have coffee!

    Today I assembled everything inside the cupboard under the coffee machine and connected the stuff inside the cupboard through the 50 mm hole in the bench top to the machine.
    There are 6 connections
    Input water from pump to machine
    Output waste water from machine to drain
    Solenoid control
    VFD power
    VFD control
    Pump pressure sensor

    Had to drill out and seal/paint a 24mm hole in the base of the machine so the woven SS water cable end fittings could get water into the machine itself
    No leaks - that was good.
    And it all worked as it should!
    30s later a connection on the thermocouple broke - repeated overhanding most likely.

    Here's what it looks like inside the cupboard.
    You can just see the front of the the coffee machine on the bench above e (green light)
    You can see it does not take up a lot of space
    Still have to try up the cables etc.
    ALLIN.JPG

    Close up
    S = Solenoid that opens only when the pump activates
    PRV is the pressure reducing valve - dropping the pressure gives the pump better control at low speed.
    The gauge on the PVR tells me what I have dropped the pressure to
    V = VFD - its a little Telemechanique 1/2HP - I got it for the price of postatge from a Woodie forum member
    PS is the Pressure sensor.
    That power plug in the picture has nothing to do with the pump gear - its for the dishwasher in an adjacent cupboard.
    CLoseup.JPG

    Best thing is it's very quiet.
    With ambient noise levels @ about 40dB, with the pump running it was about 55 dB versus >85dB for the vibe pump.
    Now I need to do something about coffee grinder noise and fix that thermocouple!

  2. #47
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    Very cool. Curious to see your flow sensing solution and how that works out in terms of closed-loop operation.

  3. #48
    BobL is offline Member: Blue and white apron brigade
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    Thanks. No flow sensing happening yet it’s just pump substitution at this stage. The strain gauge to sense fluid mass arrived but I managed to break off one of the fine wires and had a devil of a time reattaching it. I managed also to get hold of an actual flow sensor but I think it will be too coarse for what I need.

  4. #49
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    Measuring the very low flow of a coffee shot at decent sample rate sounds tricky. I have collection of paddle wheel and axial impeller flow sensors from 1/2" to 2" and even with decent flows, they're tricky to get repeatable readings from, particularly when you start to factor in turbulent flow whose effect on readings changes with flow rate. Filtering helps, but you sacrifice responsiveness.

    That said, I'll have to go Google fluid mass sensing. Sounds like it might be more appropriate for the application

  5. #50
    BobL is offline Member: Blue and white apron brigade
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    Quote Originally Posted by RustyArc View Post
    Measuring the very low flow of a coffee shot at decent sample rate sounds tricky. I have collection of paddle wheel and axial impeller flow sensors from 1/2" to 2" and even with decent flows, they're tricky to get repeatable readings from, particularly when you start to factor in turbulent flow whose effect on readings changes with flow rate. Filtering helps, but you sacrifice responsiveness.

    That said, I'll have to go Google fluid mass sensing. Sounds like it might be more appropriate for the application
    I agree, I doubt a conventional impeller or paddle wheel sensor will be sensitive enough. The best tech for low flow is ultrasonics as used in medical devices but these are out of my price range. I've been looking on eBay but they typically start at US$500 for used gear and over a grand US for new stuff. That's why I'm looking at using mass rather than volume.

    Meanwhile it turns out the thermocouple was not broken. Like my dust collector pressure/temp sensors the Thermocouple is upset by the VFD, there's noise from the VFD sneaking through somewhere. I thought it was via the PS but there's a bunch of other ways it could be sneaking in. For example the speed controller is connected to Arduino analog and earth ports.

    I suspect it might be radiated noise. With a right PITA. Gunna have to get out my filtering hat.

  6. #51
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    Hi Bob,

    Sounds like you need some ferrite rings or beads. If its any help the lump in a cable near the end is a ferrite tube and they are easily salvageable. If you want any I've got hundreds of various ones. From 3 mm diameter with a 1.5 mm bore right up to 3" inches and a 2" bore.
    Best Regards:
    Baron J.

  7. #52
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    Hi Bob,

    Wow what people will do for the perfect brew! Good job and it's "cheaper than golf" lol

    How are you getting the frequency from the VSD? an RS-485 port?

  8. #53
    BobL is offline Member: Blue and white apron brigade
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    Quote Originally Posted by Stustoys View Post
    Hi Bob,

    Wow what people will do for the perfect brew! Good job and it's "cheaper than golf" lol
    I know it sounds ridiculous, but it really has cost me very little in hard $ and providers hours of fun and many hours of frustration

    How are you getting the frequency from the VSD? an RS-485 port?
    I have no idea,

    There's only a problem when the VFD is switched on ie motor not even running, with motor on problem is worse.

    Some possibilities
    The VFD control lines are connected to the Microcontroller through an unshielded Cat5 cable - need to move to earthed shielded cable (eg cat 6)
    I have put a ferrite ring on this cable but it makes no difference

    The TC is connected to the coffee machine through a twisted teflon insulated wired pair. This thing seems to act like an aerial - move it away from the machine and it works OK, the closer I move the wire to the machine the weirder the temps become. when the insulated wire itself touches any metal part of the machine that's when its at its worst. I need to use a shield cable here too

    The Press sensor is also connected between the pump and microcontroller - this works fine and I doubt is a source of the problem.

    The 240V mains into the VFD has a Ferrite core on it - no difference. I need to put a ferrite on the VFD output.

    The main issue seems to be around the presence of AC on the output of the TC op amp.

    Theres <0.01mA of AC on the TC input signal going into the op amp (DC is ~1mV)
    Out of the OP amp is ~1.5V DC BUT between 500 and 200 mV AC!

    Interestingly my meter says this AC is 100Hz.
    Have tried various input and output filters with no luck.
    When I remove the TC from the coffee machine back to a position on the bench where it was reading normally and turn off the VFD the temp reading is not back to normal until I turn the microcontroller off and then back on.

  9. #54
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    Hi Bob,

    I would check the power supply to the micro. 100 Hz suspiciously like line hum !
    Best Regards:
    Baron J.

  10. #55
    BobL is offline Member: Blue and white apron brigade
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    OK - we have significant progress.

    Firstly I put a large ferrite ring on the VFD output phases to the motor.
    EMfilter2.JPG
    WHALLA!
    This immediately dropped the AC on the TC Opamp output from ~500mV to <5 mV.
    In terms of what it did to the temperature reading by the TC was it moved it from a constant -13ºC to something between ~8ºC when the motor is off and +4 ºC when the motor is on.

    Next I added a snap on ferrite ring to the TC lead.
    One loop made only a marginal difference but the more I looped it the lower the AC volts on the OPamp

    EMfilter1.JPG
    5 turns of the TC lead around the ferrite dropped the Opamp AC out to <0.01mV with the VFD on and motor of , and a transient of max ~ 0.5mV AC when the motor starts dropping to ~0.02mV.
    The reading of the TC with the VFD and motor running is nominally now within 2º of what it should be.
    I could just recalibrate the TC to take this difference into account but now I have a lead I will chase this further ie try more winds onto the ferrite, more/different size ferrite rings etc.
    Also try shielding.

    Interestingly just after I did all this I found an excellent practical website on reducing EMI from VFDs (https://kebblog.com/7-steps-to-reducing-emi-with-vfds/) and it said

    A relatively inexpensive option to reduce common mode noise is to install correctly sized ferrite rings at the output of the VFD. Common mode noise is a result of the interaction of pulse width modulation and parasitic capacitances of the cable and motor. Common mode noise produced by PWM travels throughout the motor to ground.
    So I reckon this has been a very useful pursuit of a tricky problem. Thanks to BaronJ for the tip on the Ferrites - just needed to work out how and where to place them

  11. #56
    BobL is offline Member: Blue and white apron brigade
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    Quote Originally Posted by BaronJ View Post
    Hi Bob,
    I would check the power supply to the micro. 100 Hz suspiciously like line hum !
    Thanks I thought that too and have spent a lot of time looking at power supplies.
    If it was this then it shouldshould show up all the time but there was only a problem when the VFD was on and worse still with the motor running.
    The AC on the 5V DC out of the Arduino is <0.01mV.
    As I described above the noise seems to be the VFD-motor-ground and anything else that connects with ground..

  12. #57
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    I was always told that the VFD output should be shielded cable to reduce noise. Is yours?

    Michael

  13. #58
    BobL is offline Member: Blue and white apron brigade
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    Quote Originally Posted by Michael G View Post
    I was always told that the VFD output should be shielded cable to reduce noise. Is yours?

    Michael
    Nope - but it soon will be.

  14. #59
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    Quote Originally Posted by BobL View Post
    I have no idea,
    Oops sorry. I saw your display, then read "MF is the VFD/motor frequency " in your post, but missed the very next line "Both ET and MF are working on the test bench with dummy inputs but as I don't yet have the new pump connected they are not working on the machine"
    I was asking as I'm working on a project that will use an Arduino to control fan speed via a VSD, but I wont mess up your thread further with that.

  15. #60
    BobL is offline Member: Blue and white apron brigade
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    Quote Originally Posted by Stustoys View Post
    Oops sorry. I saw your display, then read "MF is the VFD/motor frequency " in your post, but missed the very next line "Both ET and MF are working on the test bench with dummy inputs but as I don't yet have the new pump connected they are not working on the machine"
    I was asking as I'm working on a project that will use an Arduino to control fan speed via a VSD, but I wont mess up your thread further with that.
    Sorry, I misread your post. I thought you were asking about noise.

    The VFD speed is set on the Arduino box using an external potentiometer.
    I'm adjusting the speed using a pair of pots [one for coarse and one for fine adjustment) in what is known as an H-pattern but that's not part of your question.

    The connection to the Arduino itself is as follows.
    1) Ardunio Ground to the VFD Analog COM or ground.
    2) Since the the max V of the pot wiper is 10V and the max analog input of the Arduino is 5V I've set up a simple Voltage divider using a pair of 100k resistors between the pot wiper and ground, an Arduino analog port is connected to the midpoint of the divider so the analog port never sees more than 5V.

    I'm using a max VFD frequency of 100Hz and the Ardunio analog port has a max ADC value of 1024 bits, if I divide just divide any ADC value by 10.24 and that gives me Hz.

    Depending on the VFD you can get the frequency from the VFD in other ways - I just thought of doing it this way as I already have the speed control lines for the external speed pots in the arduino box.

    The VFD and the Arduino display the same frequency to within 0.1Hz.

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