My system included a DM-1 Dual TDS meter & I haven't calibrated it in the over 3 years the system's been running. These aren't lab grade instruments, although I think the DM-1 accuracy is +-2% which is actually pretty good. Not sure how a +-2% shift in accuracy relates to the displayed TDS, but I would guess the meter read out isn't going to move until there are a few more % at work. We're making up water for a hobby here, not for medical purposes. Some folks still use treated tap water. It took 3 years until TDS out of my DI stage finally showed 1 instead of 0. Why would I attempt a calibration at this point & possibly risk messing it up? TDS meter is likely nothing more than a simple ohmeter calibrated to measure electrical current flow through water between 2 metal probes. If you don't mess with the probes, it's unlikely the calibration is going to change significantly. I've just read the calibration instructions for the DM-1 after finding a copy online & the word "may" is used with respect to the need for periodic calibration.
I can also attest to the fact that the colour changing DI media is a poor indicator of whether it's exhausted & pretty much a waste of money. You're better off paying less for the non colour changing DI media & putting the $$s towards a TDS meter if you don't have one. In addition to using TDS readings to monitor when DI media and/or RO membrane needs replacement, like gregzz, I use two pressure gauges to monitor when the pre filters need replacement. Not trying to say that calibration is never required, simply that it's best to know your own system, monitor the readings & if things are consistent, don't worry, be happy. If there's a spike or unusually low reading at a sample point where you expect some consistency, then it's an indication to investigate further & possibly look into calibrating. Calibration on some sort of calendar based schedule is of little value IMO.
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01-03-2013, 09:31 PM
http://www.canreef.com/vbulletin/showthread.php?t=82206
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