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Monitoring electric motors — Parallax Forums

Monitoring electric motors

John BondJohn Bond Posts: 369
edited 2005-02-21 08:56 in General Discussion
Hi Guys
·
What IC or device can I place alongside an electric motor to sense when it is running?
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·I am making a portable, non-intrusive data logger to monitor production machines. The idea is to carry the logger to the machine you want to monitor, place the sensors next to the various motors and servos in the machine and record how efficiently it runs. I’ve tried using a Hall Effect Switch UGN 3140 but the motors do not appear to have enough of a magnetic field.
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I know it can be done because I saw a similar device some six years ago.
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Kind regards from Kwa Dukuza
·
John Bond
·

Comments

  • Jon WilliamsJon Williams Posts: 6,491
    edited 2005-02-17 12:13
    You could use an opto-isolator; the input side would match the motor voltage, the output side would be monitored by your datalogger.

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    Jon Williams
    Applications Engineer, Parallax
    Dallas, TX· USA
  • John BondJohn Bond Posts: 369
    edited 2005-02-17 13:42
    Thanks for your quick response Jon.

    The problem is I want to be able to send non-technical staff to set up these devices. I don't want the staff touching the electrical power. The data logger must not be electrically connected to the 380 Volt machines. Once a machine's performance has been logged for a shift, the staff remove the logger, plug the RS232 into a PC with StampPlot and download the results. We want to be able to monitor any machine in the factory.

    Makes it a little more complex

    Kind regards from Kwa Dukuza

    John Bond
    ps. Does Jon Williams ever sleep?
  • steve_bsteve_b Posts: 1,563
    edited 2005-02-17 16:44
    Hmmm....interesting.

    Depends on what exactly you want to know!!

    What happens when you motors become inefficient....do they overheat?· Then you could use a thermistor or some temp sensing device.

    If the shaft is exposed, then you could put a little reflector on the shaft and place an IR sensor and determine RPM's from that...not sure if that could help you equate efficiency.

    You could put a small (large wattage) resistor inline and run some 'pigtails' out to a plug connector that the users could walk up to and plug in.· You might want this isolated in some way (depending on variation in current draw on motor; more current draw the large the voltage at the end of this pigtail).

    A simple clamp-on-meter running in to an A/D maybe?!· You could measure 'symptoms' of an inefficent system....but you'd need to know your load characteristics (if it's a conveyor, then if it slows down but the current draw goes up....inefficent?! dunno).



    Just ideas....I'm light headed and I've still got 15minutes til lunch!

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    ·

    Steve
    http://members.rogers.com/steve.brady
    "Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."
  • Paul BakerPaul Baker Posts: 6,351
    edited 2005-02-17 17:07
    Steve hit on the point I was going to make, there are clamps which can measure current draw on a line indirectly, but they might only work on AC lines (never used one), but you didnt specify if its AC or DC power. Coupling the current measure with an RPM measure can give you an indication of effieciency.
  • NateNate Posts: 154
    edited 2005-02-17 17:52
    I'm not sure what you mean by "place the sensors next to the various motors and servos in the machine and record how efficiently it runs".· Do you mean how efficient the motors and servos are, or is efficiency of the machine determined by the timing of when certain servos and motors turn on and off?·

    If you simply want to·log when motors and servos are turning on and off, try placing the hall effect sensors next to the wires carrying the supply currents.· I believe these would have more of a magnetic field than the motors themselves (motors are designed to leak as little magmetic flux as·possible to maintian high efficiency).· Don't know what the specs of your hall effect sensor are, but you may need top get one that is more sensitive.· You will also need to take into account whether the motors are AC or DC when interpreting the data from the hall sensor.

    Nate
  • steve_bsteve_b Posts: 1,563
    edited 2005-02-17 18:52
    Paul, you can buy the AC/DC (not the rock band) probes to measure both.

    Amprobe makes a nice DMM model.· It's a clamp device but has plugs for measuring voltage like anormal DMM.· Costs a few $ for the added DC current clamp feature.

    So, you must be able to measure DC current with those 'add-on' style of clamps.



    Nate, I think if the wires aren't shielded, you'll be able to measure 'indication' of current flow.· Not sure how well a hall affect would work in telling you how much current is flowing...I thought a hall sensor was just a flux switch....maybe not, as I think and type!

    If you were able to get a hall sensor inside the motor casing you might measure more flux.

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    ·

    Steve
    http://members.rogers.com/steve.brady
    "Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."
  • NateNate Posts: 154
    edited 2005-02-17 19:28
    A linear hall-effect sensor outputs a voltage proportional to the magnetic field sensed by it.

    You could use a hall effect sensor near the motor current supply line.· It would take some experimentation to determine exactly what sensor you would need, and how close to the wire to mount it.·A non-linear type hall effect switch·certainly could·be used to determine 'on' or 'off' status of the motor, and I believe with experimentation a linear type hall-effect sensor could enable you to determine the current being supplied to a DC motor

    If the motor was AC, I still believe it could be done, but would require some interpretation of the data sent by the hall sensor· (I use the SX with assembly, so this bit level manipulation is the normal grind for me).

    With either AC or DC you would have to be careful in that the hot and neutral lines were·seperated somewhat so their fields don't cancel each other.

    Nate

    Post Edited (Nate) : 2/17/2005 8:09:11 PM GMT
  • steve_bsteve_b Posts: 1,563
    edited 2005-02-17 21:07
    Here's a link to an article that I received today.

    It's not directly stamp compatible...but a little bit of reading might give you some ideas!

    http://www.edn.com/article/CA502423.html?spacedesc=designideas&nid=2431&rid=2033975798

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    ·

    Steve
    http://members.rogers.com/steve.brady
    "Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."
  • achilles03achilles03 Posts: 247
    edited 2005-02-17 21:08
    Honeywell makes some magnetic sensors that are more sensitive than Hall Effect sensors. Look up the datasheet for HMC1001. +/- 2 Guass! A lot of rocketeers use them to sense apogee, as the magnetic field's orientation switches quickly at tipover (they're that sensitive).

    Having said that, I suspect there might be a better way than with magnetic sensors, but in case you do go that route....


    Dave
  • John BondJohn Bond Posts: 369
    edited 2005-02-21 08:56
    Thanks for your advice guys

    More sensitive Hall Effect seems to be the way. I only wanted to see if the motor was running or off. I’ve ordered a linear Hall Effect to play round with.

    The current clamp is also an intriguing solution. You could calculate the power the motor is using.

    Kind regards from Kwa Dukuza

    John Bond
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