Help comparing TDS meters?

[jlinzmaier]

I'm interested in the comparison of TDS meters. Which would be more accurate and precise:

a com 100 TDS meter that can read down to 0.1PPM TDS and it's accuracy can be confirmed with a control solution??

or

an in-line meter which has no calibration capability and only reads by whole numbers??

The answer seems pretty obvious to me, but I just need a chemists perspective.

Thanks.

Jeremy

[MavG]

As far as i understand it, TDS (and salinity for that matter) when tested with electronic monitors is not as accurate as testing with a conductivity meter.

Because TDS and salinity are calculated from conductivity they require the use of a conversion factor, and this is where some inaccuracy in readings can occur.

Because conductivity is a "raw" reading and is a direct reading of the probe being used it is a "what you see is what you get" reading, and so using conductivity to measure salinity is much more accurate.

From memory the conductivity of seawater is 53mS, or there about's depending on what salinity/specific gravity u are targeting.

Just make sure u get a monitor that is Automatically temperature compensated. other feature after that, such as resolution and accuracy, as well as various monitor feature are dependent on your budget and preferences.

MavG

[jlinzmaier]

Thanks.

This meter will be used for measuring the purity of RO/DI water and both meters compensate for temp.

Standard in-line meter
http://www.bulkreefsupply.com/store/products/reverse-osmosis-filters-and-systems/ro-di-accessories/dual-inline-tds-meter-dm-1-hm-digital.html

COM -100 TDS meter (first hand held shown)
http://www.spectrapure.com/St_quality_p5.htm

Which would be better for getting more accurate and precise results?


Jeremy

[bertoni]

The inline meters are fine for monitoring trends, which is important for judging when DI cartridges have become exhausted. The COM meter is likely a lot more accurate, but the accuracy might not be needed.

[MavG]

ok so its for inline monitoring.

In that case a TDS meter will be fine, as you are wanting to monitor if there are ANY dissolved solids in the water, and monitor its build up over time, to determine when cartridges/membranes are exhausted.

conductivity is still a more accurate option, but because you are not looking for an accurate reading in order to keep livestock in your aquarium it is not at all necessary IMO.

MavG

[bertoni]

All devices that measure TDS with a probe are measuring conductivity. I'm not sure what distinction you're trying to make, but all the monitors function in about the same way: they use a waveform to analyze the conductivity of the water.