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Poor Choice of TDS Meter :(

AverageWhiteBloke

AverageWhiteBloke

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Joined
27 Oct 2009
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Location
Cumbria
Just bought a TDS/PH/Temp meter off Ebay. Firstly, thought I'd calibrate it before using it just in case it's been sat about in some warehouse for a long time only to find the instructions say to calibrate using 6440ppm standard fluid. I assumed that it made no difference what fluid you calibrated the meter with as long as its accurate.
So, tried the 240ppm fluid I have which gave a higher reading and couldn't get the trimmer to go down low enough, it screwed in so far then starting clicking. Tried again with the 1382ppm I had which to be fair has probably been sat about a bit and again the reading was high and I can't trim it down any further.

Now I'm in a bit of a dilemma, getting hold of 6440ppm standard is the proverbial rocking horse excrement, the only place I could find was wanting nearly £30 inc delivery for 500ml which seems a bit mad saying the meter itself cost less than that.

My other dilemma is that the meter may be faulty and I have no way of knowing without having a calibration fluid to test it to. You would assume though that you should be able to keep adjusting it down regardless of which you have. Anyone know if this is the case or where I could get hold of some 6440 fluid a bit cheaper?
 
can you provide a link to what you purchased or perhaps just name & model
:)
 
Hi all,
AverageWhiteBloke said:
I'd calibrate it before using it just in case it's been sat about in some warehouse for a long time only to find the instructions say to calibrate using 6440ppm standard fluid.
Click to expand...
Bad luck, it is a "high range meter", which means that I'm pretty sure it will never be of any use to you.

I'll assume the conversion from microS to ppm TDS is 0.64, but it may be 0.5 (it should say on the meter). If you search for "6.44 ppt calibration fluid" you should find some cheaper options.

If you want to make your own up you can (using potassium chloride (KCl)).

35ppt salinity is ~53,000 microS, (which is approx. 33,900 ppm TDS) and 32.4 grams of KCl (made up to one litre with RO) is ~35 ppt, salinity, 6.44/32.4 ~20% and 20% of 32.4 ~5g.

So 5g of KCl in one litre should give you your "6.44ppt" calibration fluid

cheers Darrel
 
Hmm, not the reply I was hoping for if I'm honest, this is the meter I bought. So if it's only high range will it be less accurate at lower readings I guess? Also can't really see any UK suppliers of the calibration fluid when searching.
 
Then you start looking at ones for £3ish and wondering whether it's worth messing. Getting the KCI I would would have to assume the RO water I was mixing it with had a TDS of Zero to get accurate results and ironically I have no way of checking this with a......:D
 
alto said:
I'd just return the meter & start again
Click to expand...

I don't think that's fair on the seller though, My mistake really plus the ph and temp side of the meter work fine. What's the deal with these £4 TDS meters, are they all just as good as each other or false economy?
Came across some KCI on ebay but they appear to be slightly chemically different..this and this.
 
I'm not sure why this would hurt the seller - you still give positive feedback, I assume you pay any shipping fees rather than the seller etc
Or just keep the TDS for another day :)

AverageWhiteBloke said:
are they all just as good as each other
Click to expand...
No
Hanna Instruments would be my go to (it's been discussed here before - try Hanna as the search term)
It depends on what you want in terms of accuracy/precision, an "electronic calibration" is easy/cheap but doesn't actually "test" the meter
 
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