Probe Placement for an In-Line Dual TDS Meter
- Thread starter cdeakle
- Start date
I'd put one probe after the RO membrane and the other one after the DI cartridge. That way you can tell when both are going bad. No point in really testing what the TDS of your incoming water is as it really doesn't matter in relation to when to change filters or membranes.
Shane
Shane
I like this idea. With this placement I would know the effectiveness of my RO membrane and the effectiveness of my DI cartridge and wether either of them needs to be changed out. I agree, I don't really care about the incoming TDS as long as the end result is 0 TDS!
This comment has me thinking twice about the above statement. Which one of these would you guys recommend??
420puff, until some other people post about the readings of the dual meter against another TDS meter, or until I have time to do a calibration (need to order new solution), don't take the reading of the meter with too much confidence. Again, the relative reading seems to be fine, since it is 30% higher consistently for the meter I got. See your thread for detail.
One thing to keep in mind is that TDS meter should have temperature compensation, and a simple two-pronge probe in this and other comon TDS meters used in this hobby just barely cut it for RO and tap water monitoring. I had been warning the use of TDS meter for DI water application, but so far, no one had came forward and admit that I am right about the misapplication.
One thing to keep in mind is that TDS meter should have temperature compensation, and a simple two-pronge probe in this and other comon TDS meters used in this hobby just barely cut it for RO and tap water monitoring. I had been warning the use of TDS meter for DI water application, but so far, no one had came forward and admit that I am right about the misapplication.
A little too good to be true !
Tangir, what is your concern about using TDS meters to check DI water ? I suspect that you need one which can be calibrated to this end of the scale, and I would prefer just a simple conductivity reading (since the conversion from conductivity to TDS will be quite bogus in this application). But otherwise, should be okay I would have thought.
I tried to follow yor link but it's a little ....umm...weird !
kim
Tangir, what is your concern about using TDS meters to check DI water ? I suspect that you need one which can be calibrated to this end of the scale, and I would prefer just a simple conductivity reading (since the conversion from conductivity to TDS will be quite bogus in this application). But otherwise, should be okay I would have thought.
I tried to follow yor link but it's a little ....umm...weird !
kim
kim:
Thanx for the heads up. The post was updated, and the link is http://reefs.org/phpBB2/viewtopic.php?p=485268#485268.
My concern for TDS meter for DI is that is will often give you a "0" reading due to underranging. Regular TDS meter is not designed to monitor low conductivity fluid like DI water. Another issue is the accuracy. At 2% of the scale (typical accuracy for hobby meters), the TDS reading can be off as much as 20 ppm.
I am not particularly antigostic toward the use of TDS meter for DI water, but just want everyone to be aware of the issue if they decide to do it, and not spread the misuse/abuse without caveat.
Thanx for the heads up. The post was updated, and the link is http://reefs.org/phpBB2/viewtopic.php?p=485268#485268.
My concern for TDS meter for DI is that is will often give you a "0" reading due to underranging. Regular TDS meter is not designed to monitor low conductivity fluid like DI water. Another issue is the accuracy. At 2% of the scale (typical accuracy for hobby meters), the TDS reading can be off as much as 20 ppm.
I am not particularly antigostic toward the use of TDS meter for DI water, but just want everyone to be aware of the issue if they decide to do it, and not spread the misuse/abuse without caveat.
Absolutely agreed. When I'm using my probe for freshwater I calibrate to 84 and 1,413 microS/cm, which seems a reasonable range when I want to measure tap, RO and DI. Also easily obtained (Hanna make these) - I have found low range calibration fluids but minimum order on these is a few litres.....
But even then, I am sure that the DI reading can be out. I do tend to watch for changes rather than the absolute value.
kim
But even then, I am sure that the DI reading can be out. I do tend to watch for changes rather than the absolute value.
kim
The reason that people usually buy large volumn of low range fluids is that you really need to use the calibration fluid to risen and clean the probe very, very well before you do the calibration. Even a slight amount of contaminant can increase the conductivity a lot.
For low conductivity fluid (DI water), I use resisitivity meter instead of conductivity meter. Even the CO2 in air can affect the DI resistivity/conductivity a lot.
For low conductivity fluid (DI water), I use resisitivity meter instead of conductivity meter. Even the CO2 in air can affect the DI resistivity/conductivity a lot.
Oh oh.....I get very confused about resistivity meters..
Conductivity is just the reciprocal of resistivity, so the difference should just be a display issue (in the same way as a TDS and conductivity meter really do the same thing, but the TDS meter does a conversion).
Perhaps in the "world of testing" there's some kind of concensus that a different technique is used when referring to one or another, but since that isn't made explicit I am lost. And I keep asking the question !
What is the material difference in technique/theory (ie not referring to the choice of display) ?
kim
Conductivity is just the reciprocal of resistivity, so the difference should just be a display issue (in the same way as a TDS and conductivity meter really do the same thing, but the TDS meter does a conversion).
Perhaps in the "world of testing" there's some kind of concensus that a different technique is used when referring to one or another, but since that isn't made explicit I am lost. And I keep asking the question !
What is the material difference in technique/theory (ie not referring to the choice of display) ?
kim
>... but since that isn't made explicit I am lost. And I keep asking the question ! ...
In one of my former lifes, I thought I already iron out the issues between resistivity and conductivity with you in private, kim. :?
Anyway, as I mentioned before, the main difference are the way temperature compensation is done, the choice of solution standard(resistivity use NaCl, TDS people use 442, and conductivity people use KCl), and the way the temp. comp'ed conductivity is convert into the appropriate unit (uS, ohm, or tds)
In one of my former lifes, I thought I already iron out the issues between resistivity and conductivity with you in private, kim. :?
Anyway, as I mentioned before, the main difference are the way temperature compensation is done, the choice of solution standard(resistivity use NaCl, TDS people use 442, and conductivity people use KCl), and the way the temp. comp'ed conductivity is convert into the appropriate unit (uS, ohm, or tds)
I put one prior to the whole unit
and the other after the DI
I have 50 going in, and 0 coming out
I'm going to move the 2nd one before the DI and see if I get any reading there
Trouble is, I really dont care if there's a reading prior to the DI, I just want to know when the DI needs replacing.
and the other after the DI
I have 50 going in, and 0 coming out
I'm going to move the 2nd one before the DI and see if I get any reading there
Trouble is, I really dont care if there's a reading prior to the DI, I just want to know when the DI needs replacing.
>... I really dont care if there's a reading prior to the DI,
I hope they have a three electrode model (which you can DIY, BTW), ...the problem is that if the membrane got ruined, you want to be able to notice it ASAP. With the DI right behind it, you going to get good water until the resin is ruined, and you will ended up wonder why a cartidge of it that used to last half a year now only good for one or two water changes....
I hope they have a three electrode model (which you can DIY, BTW), ...the problem is that if the membrane got ruined, you want to be able to notice it ASAP. With the DI right behind it, you going to get good water until the resin is ruined, and you will ended up wonder why a cartidge of it that used to last half a year now only good for one or two water changes....
Sponsor Reefs
We're a FREE website, and we exist because of hobbyists like YOU who help us run this community.
Click here to sponsor $10:
