VFD Remote Motor Frequency Meter
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  1. #1
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    Default VFD Remote Motor Frequency Meter

    I would like to have the VFD motor frequency displayed on my remote control box. The manual for my Hitachi WJ200 VFD indicates that a remote meter can be wired as shown. My question is what type of meter do I need?

    Something like this? 0Hz-300Hz AC/DC Red LED Frequency Panel Meter Sine Square Triangle Wave | eBay

    wj200-meter.jpg

    wj200-meter.jpg

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    you need a 0-10 volt volt meter, 2ma max


    a number of the cheap lcd digital meters from china such as the one you linked are very hard to read, but not always, you may want a standard analog meter, print your own rpm chart.

    page 4-90 covers how to program the vfd for the meter. there is no reason specifically why you need a 0-10v meter, a 0-5 volt or a 1ma or 2mA amp meter (will likely need a resistor in series) can work as well.

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    To put it another way, do not waste your money on buying a frequency meter. The VFD puts out a dc signal
    that is an analog of the driving frequency.

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    I've used the analog out into one of the FactoryMation PML Meters before and liked it.

    PML Series Panel Meters

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    Quote Originally Posted by johansen View Post
    page 4-90 covers how to program the vfd for the meter. there is no reason specifically why you need a 0-10v meter, a 0-5 volt or a 1ma or 2mA amp meter (will likely need a resistor in series) can work as well.
    Thank you for looking that up! That helps a lot.

    Quote Originally Posted by jim rozen View Post
    To put it another way, do not waste your money on buying a frequency meter. The VFD puts out a dc signal that is an analog of the driving frequency.
    I only have very basic knowledge of electronics and was pretty confused by the use of analog and a volt meter in this situation. That makes it more understandable. Or at least as much as I'm ever going to understand it. Thanks.

    And too late on the frequency meter! I ordered one in the link. It was a way for me to get around not knowing how to do it with the VFD. It dawned on me while it was in transit from China that it probably wouldn't work on a PWM created wave. And it didn't. But it also didn't work when I tried on 240V single phase either. So I'm not sure it works at all.

    AC Combo Meter 100A digital Voltmeter Ammeter Frequency 600V 110V 220v 380V | eBay

    Quote Originally Posted by rbent View Post
    I've used the analog out into one of the FactoryMation PML Meters before and liked it.

    PML Series Panel Meters
    Those are very cool! But it looks like the scale only goes up to 65Hz. I reduced the motor pulley size and I'm running the motor from 40 to 120Hz. I have step pulleys on my lathe and this allows me to rum from about 200 to 800 RPM without changing belts and without losing any torque. I think I actually gain torque through most of the range. I can still get lower or higher RPM ranges with back gear or step pulley changes if I need to.

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    I find a tacho on the spindle more useful than a frequency meter on the drive - they're pretty cheap form the gents in China and can be used with optical (slotted disc or reflective), magnetic or inductive pickups - I had to hack the tacho (actually frequency counter) to allow for a 70-tooth spindle gear by changing the onboard quartz crystal - with a 60-tooth its Hz display would have read RPM straight out of the jiffy bag.
    A gear tooth sensor like the ATS667LSGTN is very cheap and the size of pea plus the leads, can be mounted anywhere near the gear you're reading.

    What is helpful is a meter for motor current (if your drive provides it), that gives a good idea of how hard (i.e. how profitably!) the machine's working.

    Dave H. (the other one)

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    I did get a digital tach for the spindle. I kinda would like to know the motor speed since I'm over speeding it by double. It dawned on me while reading your post that I can also put a tach on the motor and be done with it. Which is what I think I'll do.

    And because it sunk in (I think it had been mentioned) that the analog readout shows voltage not actual cycle. So 60 cycles will read 10, not 60. Or in my case 120 cycles would read 10. Maybe I have that wrong. Please let me know if I do.

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    So there are a number of things to consider, the VFD display can be used to show motor RPM, or for that matter spindle RPM providing the drive ratio doesn't change. If you change the drive ratio then everything changes. Since you are dealing with an analogue output from the VFD you can use a scalable output voltmeter and you can make it display whatever value you want at full scale. My mill uses this type of digital meter with two independent voltage inputs, one is used for setting the high speed which is set to 5000 RPM and the other is for back gear which is 500 RPM. There is a small switch on the back gear which sets the meter input and thus the scaling. It is accurate enough. You could also use an analogue meter and change the scale or sensitivity.

    They also sell programmable meters which can be setup for any scale and display characteristics.
    PML Series Panel Meters

    Another approach is to use a small hall sensor and magnet ring on the spindle for a direct spindle RPM readout. Don't really care about the motor RPM, this is set by the programmable parameters and the speed is proportional to the linear pot setting.

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    Agree with Hopefuldave with an exception. Use a optical sensor with a little piece of plastic epoxied to a spindle pulley. The sensor stays in a fixed position and the piece of plastic (or whatever) passes through the slot of the sensor. The setup produces a digital signal every revolution. I played around with this a little as the picture shows. For me it was just one of those let's see if I can make this work and is it useful. I made it work easily but it was not that useful.


    dsc_0865.jpg

    Internal Error

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    Thanks for the suggestions. I've been mulling them over for days and decided cheap hall effect LED tachs do everything I need to do and 2 of them including sensors is less than $25 shipped. Easy to install as well. So I ordered some last night. Enough for my lathe and my mill.


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