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Agitation Speed Query

  • 23-03-2017 10:30pm
    #1
    James 007
    Registered Users Posts: 962 ✭✭✭


    All, I would like to check something here:

    We have an agitator to run at 20rpm. During an FAT the rpm was visually measured for 1 min to confirm this. A tachmeter was not used at the time.

    We have a digital read out in Hz and prior to completing the FAT it was found that 40.3 Hz was equivalent to 20rpm.

    However during PV one panel was set a 40.2Hz and a reading was taken to give 40.2Hz.

    QA have now queried this reading, and the equivalence of Hz to rpm in the FAT. How can we address this.


Comments

  • #2
    CatFromHue
    Moderators, Science, Health & Environment Moderators Posts: 18,239 Mod ✭✭✭✭CatFromHue


    how did you calculate that 20rpm = 40.3Hz?

    I just looked here ( https://en.wikipedia.org/wiki/Revolutions_per_minute ) and it's different than how you calculated your number.


  • #3
    James 007
    Registered Users Posts: 962 ✭✭✭James 007


    CatFromHue wrote: »
    how did you calculate that 20rpm = 40.3Hz?

    I just looked here ( https://en.wikipedia.org/wiki/Revolutions_per_minute ) and it's different than how you calculated your number.

    I know, and this is exactly what QA are asking, they are checking google too. I am perplexed as I do not have an understanding of the conversion, or if it can be converted.

    The agitation is definitely 20rpm as we measured it visually, but the display has always been displaying 40.3Hz, is this an error, or is there something else at play here. I don't have an electrical background.


  • #4
    CatFromHue
    Moderators, Science, Health & Environment Moderators Posts: 18,239 Mod ✭✭✭✭CatFromHue


    There should be a manual knocking about somewhere so I'd start with that and then, if needed, I'd check with the manufacturer of the device giving you the 40.3Hz and see how it's calculating that number?


    I'd also check/re-check to make sure the device is fitted correctly.


  • #5
    James 007
    Registered Users Posts: 962 ✭✭✭James 007


    CatFromHue wrote: »
    There should be a manual knocking about somewhere so I'd start with that and then, if needed, I'd check with the manufacturer of the device giving you the 40.3Hz and see how it's calculating that number?


    I'd also check/re-check to make sure the device is fitted correctly.

    I have the manuals, I will check this, this morning. Hope your right on shedding light in this direction.

    Fitting correctly, I don't believe this is an issue. We have 2 control panels and each panel has 2 VSDs. How this came to light was 3 of the VSDs were set to 40.3 Hz and one was set at 40.2Hz.


  • #6
    Peregrinus
    Registered Users, Registered Users 2 Posts: 26,846 ✭✭✭✭Peregrinus


    40.2 or 40.3 Hz would normally suggest something rotating very fast indeed - a bit more than 40 times a second (obviously). Whatever the 40.3 Hz setting is referring to, it's definitely not referring to the component that you observe to be rotating once per second.

    What kind of agitator is this, and can you describe its action? Does it include a gearing mechanism which steps down rotary motion from a motor, so that the observed component rotates more slowly than the motor? Something of that kind?


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  • #7
    James 007
    Registered Users Posts: 962 ✭✭✭James 007


    Peregrinus wrote: »
    40.2 or 40.3 Hz would normally suggest something rotating very fast indeed - a bit more than 40 times a second (obviously). Whatever the 40.3 Hz setting is referring to, it's definitely not referring to the component that you observe to be rotating once per second.

    What kind of agitator is this, and can you describe its action? Does it include a gearing mechanism which steps down rotary motion from a motor, so that the observed component rotates more slowly than the motor? Something of that kind?

    Peregrinus, the agitator is a vertical shaft with an impeller at the end. It sits into a mobile vessel. The motor is vertically mounted on top of the vessel. I think you have hit the nail on the head. Is there some sort of 'reducer' mechanism that would reduce the speed of the shaft. I can only take a guess that there is a gear mechanism within this motor, I need to check this this morning.


  • #8
    OldMrBrennan83
    Closed Accounts Posts: 26,658 ✭✭✭✭OldMrBrennan83


    This post has been deleted.


  • #9
    James 007
    Registered Users Posts: 962 ✭✭✭James 007


    Patww79 wrote: »
    This post has been deleted.

    Patww79 do you have any good link, even from google that could demonstrate this. QA are looking for an answer on this. Do you have a link showing how a 'reducer' if there is such a thing would reduce the speed.


  • #10
    OldMrBrennan83
    Closed Accounts Posts: 26,658 ✭✭✭✭OldMrBrennan83


    This post has been deleted.


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