PH meters.

Discussion in 'Supporting Chemistry' started by Igor, Feb 9, 2016.

  1. We have a set of Hanna "PHep" PH meters, that I've inherited from my predecessor.

    They are an arse. Plain and simple. For some insane reason, it's always been "the way" that the kids calibrate the things, with the screwdrivers. This has led to some being marked "f", and some "g" - presumably "fooked" and "good" or similar.

    Now, when I come to use them, they're uncalibratable - the heads on the polythene cermet pots are shredded, due to kids. Some just go insane - I was trying to calibrate some for A-level, and in PH4 buffer they'd refuse to go low enough, while in PH10 I'd get readings flickering between 4.0 and 13.5.

    They're expensive, they're mostly knackered, and the students calibrating them is to my mind insane..can anyone think of any reason this may be necessary?

    Also, what do you all use?

    I'd be happier if the meters were made with decent trimmers with brass pots, but I suppose that's cost. If I could solder well, I'd refurbish the damn things..
     
    GeorgetheScienceTech likes this.
  2. Yes this has been a problem.. I would suggest that you never let the students calibrate these. Also the ones that do work it is well worth calibrating them at the very last minute as they can drift considerably.
     
  3. I've just purchased as an eval. unit, one almost direct clone of the PHep from gearbest.com. £6. If it's even close to being as accurate, I'll put a case in for going for these - I baulk at paying £45+ for something made in such a disposable manner. £6, I'll do. Hell, I could replace our fleet of knackers with these china knockoffs for the cost of 2 hannas, almost.

    It'll take a while to arrive..but I can live with that. If it's gash, I'll use it at home and not lose any sleep..heh.
     
    GeorgetheScienceTech and Karis like this.
  4. Hi Igor. I'd be interested in hearing what you have to say about your pH meter when you put it through its paces.
     
  5. Use to having a long discussion abt pH meters & probes with my old HOC. Used to think we could get them out of store and use them straight away - nah, need to look after them, clean the probes then paired up a probe with a meter - then calibrated. Usually held ok for abt 2 weeks.
     
  6. I bought a class set of the Hanna ones a few years ago and I can count on one hand how many times they have been out. We calibrate them each time they go out, which can be a bit of a pain, but teachers seem to prefer UI.
     
  7. Igor, has the pH meter turned up yet? We are very interested in whether or not they are adequate. The Hannas are so expensive ant the pupils only trash them!
     
  8. not yet..they were (it was, correction) coming from far flung china..got a mail last week to say it was shipping..so, awaiting with interest!

    Agreed though - the Hanna's are flipping expensive considering the materials used..plastic trimmers are NOT what I'd expect for my money..that really limits the lifespan of them. Plus, none of ours have replaceable heads..they're soldered on, not screwed..Hanna must have revised the spec at some point.

    To be quite fair, I also favour UI...heh. I like pretty colours!
     
    Sar H likes this.
  9. gearbest looks like an excellent site, but I've Googled for reviews and found there are quite a few dissatisfied customers out there. Some report that the site was fine for a small order (perhaps a single item), but then it went wrong when they ordered a second time and a larger quantity.
     
  10. Do you have a method to calibrate the PH meters, I thought I have seen one, but can`t find it. Thank you
     
    GeorgetheScienceTech likes this.
  11. I do indeed May! Depending on what type of pH meter you have you can do a 2 point or 3 point calibration (using pH 4.00 and 7.00 and pH4.00, 7.00, 9.20 Buffers respectively). The line if extrapolated, should pass through zero.:);)

    3 point calibration.png
     
  12. Thank you, I have the Hanna Red one, but they seem not working well, If I buy new one, which one you recommend? any tips to maintenance.
     
  13. Hello again May. We have Hanna as you can see from the pic. My top tip is to maintain them dry so no bacterial film forms (which will have a real change in pH) then,say 2 days before they are required, they are left to condition in 3M KCl then calibrated in pH 4 and pH 7 Buffer. We also number them and we note which student has which. It is the student's responsibility to report to us any problems which the pH probe. I believe that the new Hanna probes are self calibrating. Hope this is of help.:);)

    [​IMG]
     
    May Aziz likes this.
  14. JFKtech

    JFKtech and then there were two - now JFK Techs :)

    Did your chinese pH meter ever arrive Igor, and did it meet expectations ? I want to buy some cheap ones for KS3/4 use but HOD won't let me in case they're rubbish, so I'm looking for ammunition to back up my case !
     
  15. we use the ones on amazon for less gbp 10, they work fine.
     
  16. Thank you very much, really helpful