come on you clever folks help me out!

Discussion in 'Off-Topic Chat' started by super_sop, Sep 7, 2004.

  1. super_sop

    super_sop Supporting Member

    I know there are some clever chaps and chapeses on here, and i hope you can help me out!

    does anybody know anything about hysteresis??

    i could do with knowing how to work it out correctly when dealling with pressure
  2. Naomi McFadyen

    Naomi McFadyen New Member

  3. WoodenFlugel

    WoodenFlugel Moderator Staff Member

    What exactly are you up to mate? Can't find any calcs for that in the textbooks I have here but I might be looking for the wrong thing.

    Disclaimer: my repling to this thread is in no way an admission of being clever:p
  4. TheMusicMan

    TheMusicMan tMP Founder Staff Member

    Craig - have used this site here many times when looking for certain 'physics' information.
  5. Di

    Di Active Member

    Wow, i looked it up on google and

    :hammer :hammer :hammer
  6. super_sop

    super_sop Supporting Member

    cheers dude!

    here goes.

    i'm calibrating some presure gauges for bristow helicopters, giving results for rising and falling pressure across the gauges range. (still awake everybody?)the british standard says that the hysteresis for the gauge should fall within the specification of the gauge.
    i dont know how to work it out. the guy thays worked on pressure here before seems to be doing it wrong so im trying to make sure that i do it right.
    last thing i wont is an helicoptyer falling outa the sky cose i didnt check a gauge properly!!!:oops:
    thanks for the help so far guys (John ill register on that physics forum when i get home and try them also)
  7. WoodenFlugel

    WoodenFlugel Moderator Staff Member

    Sorry mate - gonna have to wuss out of this - it's getting well out of my field of knowledge (I say "field of knowledge" but it's more akin to half an acre of wasteground:p ).

    My knowledge of hysteresis is more to do with magnetic fields and such like. The only fluid stuff I get involved in is in large hydraulic systems (rarely) and they ever look marginal enough for hysteresis to become a factor we just whack a bigger pump in the line;)

    BTW good link John! Thanks mate - I'll be adding that one to my favourites:)

    ..who said "BOC"
    Last edited: Sep 7, 2004
  8. jus followed the link to the puzzle....... too difficult. but i am blonde so that could be a reason!!
  9. TheMusicMan

    TheMusicMan tMP Founder Staff Member

    Yeah, that link has been very worthwhile on several occasions. Not sure how I found it intitially though...

    Hysteresis: one way to describe this is 'slack' i.e. the amount you could say, move the first cog in a set of a few connected gears, before the final cog actually moved. There is usually some small movement in the first cog and an amount of slack in the chain of cogs before the final cog will move. The engineering term for this slack is hysteresis.
  10. stephen2001

    stephen2001 Member

    In simple terms, hysteresis is a cycle of the stretching and unstretching of an object which in turn creates head.

    Think of a car tyre, pick a point on it and imagine it going around and around. When it is in contact with the road, that point of the tyre is fully compressed because it is taking the weight of the car. When the point is directly above the road, it is fully uncompressed because there is no weight on it.

    So as the car moves, the tyre is constantly stretching and unstreching and this process creates heat which gradually builds and warms the tyres up. If you watch motorsport on the telly, you will constantly hear the commentators going on about getting the car's tyres warmed up and this is why it happens.

    I think in Craig's case, it is important that the rate of change of pressure across gague is not too quick as this will create too much heat in whatever system it is measuring, leading to failure. As for any equations or such like, I'm afraid I can't help off-hand, but will have a look at some of my uni books tonight to see if I can find anything which could be of any use.
  11. Jan H

    Jan H Moderator Staff Member

    I'm guessing that a "pressure gauge" is a device to measure the pressure? (sorry for my limited English vocabulary) In that case I think that the problem has more to do with the accuracy of the measuring device.

    Maybe it could be this: when the pressure rises, the needle of the pressure gauge goes up, let's say from 0 bar to 0.5 bar. When the pressure is released, the needle should go down again from 0.5 bar to 0 bar. But because of some internal friction in the moving parts of the gauge, the needle doesn't go back to 0 bar but only to 0.05 bar. When the pressure is going up and down all of the time (let's say between -0.5 and +0.5 bar), the relation between the actual pressure and the position of the needle will not be completely linear: when the pressure is falling, the indication is a little bit too high; when the pressure is rising, the indication is a little bit too low. If I remember correctly from my physics courses, this effect is called the "hysteresis-effect" of a transducer. Of course this effect should be as small as possible, to ensure a correct measurement of the pressure.

    So when the Brittish standard says that "the hysteresis for the gauge should fall within the specification of the gauge", it probably means that you should check this hysteresis effect and see whether it isn't bigger then the value that is mentioned in the specifications of the gauge (as declared by the supplier)

    I'm not garanteeing that this is the correct explanation, it's just my interpretation of what's been said here. If you wish, I could check my "measurement techniques" text book from university this evening. There should be a chapter on "pressure measurements" in it...
  12. stephen2001

    stephen2001 Member

    Just to give me and others some idea of what you are looking for, can you give us the British Standard for the hysteresis of the gauge and what it is measured in (ie %, psi or Newtons).

    Cheers :)
  13. super_sop

    super_sop Supporting Member

    WOW Dude! thast about the sum of it as i understand it!
    if you wouldnt mind having a look at your text book for me, that would br great

    It's been a hectic afternoon, at work, and we think we have the problem solved.

    thanks to everybody who posted on here.:metal:
  14. super_sop

    super_sop Supporting Member

    cheers dude ill do that for ya in a bit, have to go out side for a bit(helping Abigail to ride her bike!:()
  15. stephen2001

    stephen2001 Member

    Dosen't matter if you've got it sorted mate. Just glad to have been part of the assistance! :)

    TIMBONE Active Member

    Well, I know nothing about 'hysteresis', (which I thought was a medical condition), but I do know how to spell 'chapesses' lol
  17. HBB

    HBB Active Member

    Always helpful Tim ...
  18. Jan H

    Jan H Moderator Staff Member

    I'm sorry, but I forgot about the rehearsal thing that I had this evening. if it's still needed, I could look for the book tomorrow... (it'sprobably buried somewhere under layers of dust :) )
  19. BoBo

    BoBo Member

    I didn't realise tMP required such intellectual capacity, what a clever lot we are.

    Lots of opinions here about hysteresis but for my 2p worth....

    Hysteresis is when a gauge (in this case) gives a different reading on the way up than it does on the way down, if you plot its response on a graph, you end up with a characteristic curvy parallelogram thing. Its due as suggested above by slack in the mechanics. So what the specification is calling for here is that the difference in readings for rising pressure and falling pressure are within the specified accuracy of the gauge.

    Clear as mud? Try an example...

    Say your reference (test) pressure is 10barg, on the rise the gauge might read 9.9 barg, on the fall it might read 10.1barg, the difference is 0.2 barg or 2%. If the accuracy of your gauge is 1% you are in trouble, if it is 5% you are OK.

    I would have thought that for something like this that the company would have a validated procedure.

    Congrats to all tMPers who are still awake at this point, just as well we don't have to calibrate our instruments.