Tunze 7032/2 Conductivity Meter

[kbd]

Roger,

I ordered a Tunze Conductivity Meter 7032_000/M and rec'd, I now realise, something called 7032/2. It has the same range as the model I requested but has different coloration (looking at the website). Is it new, old or a collector's edition ?

The information brochure also refers to Temperature Controller 7028/3 - I can't find a mention of this anywhere else.

If I may, I'd also like to mention that the box has a conversion of mS/cm to density. I'm surprised that (i) the conversion isn't made to salinity, (ii) the scale only extends as far as 50 ms/cm, which is effectively 32.8 ppt salinity, less than that for which many of us strive, and (iii) finally....is it really density as stated in the information manual ? I've checked against authoritative data - I don't have the exact same "data points" (so resort to interpolation) but something looks odd.

Many thanks,

kim

 

[rvitko]

The book Aquarium Ecology by Tunze includes salinity conversion as well. These are rough conversions because no exact conversion exists, it would vary with brand of salt mix. Conductivity is technically more correct it is a measure of ion content. Density would include sugars and any molecules dissolved in the water as well. It is just for the sake of reference and not to be used literally. The meter does read higher than 50mS this is just the calibration point. Last month the new meters were released and these replaced the old units. Outside of the housing the circuitry is designed to extend the life of the electrode. Otherwise not much is different.

 

[kbd]

Many thanks,

The point about salinity is that it is independant of temperature, so we don't need to target different numbers depending upon other parameters. It is therefore more "fundamental".

Certainly using a conductivity meter to measure salinity introduces an approximation, but using it to measure density or specific gravity introduces additional uncertainties.

Particularly given the myriad of definitions of SG (I know of four so far).

The conversion points on the case of the instrument (density or SG) do not include extend as far as NSW, which is a pity for many reefers. This scale is therefore of little help to those seeking to emulate NSW when measuring our tank conditions.

I admit that they would help if we purchased our calibration fluids according to density or SG in order to calibrate to conductivity.



It'll work for me, but it doesn't try very hard to help, does it !

kim

 

[rvitko]

While I can't find my copy right now see if you can't borrow a copy of Aquarium Ecology, it has a chart of the conditions in the Maldives over a month period including conductivity, further it correlates this to Specific Gravity and Salinity at 25C in much greater detail. If I find my book I will try to post the data.

 

[rvitko]

OK, found it! At Eriyadoo on the Maldive Islands in November of 1985.

17/11/85 50.2mS 28.5C
27/11/85 49.3mS 27.8C

These were the high and low points.

50mS corresponds at 25C to 32.7 Salinity and 1.0244 Density

"The different ionic compositions of various salt mixes are the cause..." In reference to the widely varying tables given for correlation.

In general a value between 48 and 51mS is appropriate for most marine aquaria. For a Red Sea aquarium values as high as 53mS may be appropriate. Stability is the key factor rather than any ideal level. Conductivity is the most sensitive measure and thus can very accurately indicate change.