TDS Sensor for measure brix

[Clinkis]

I am repurposing a water purification RO for sap. It has a TDS sensor (total dissolved solids) incorporated into the controller and display. Just curious if these will give an accurate representation of sugar content? Anyone have any expertise using these? If not then I will just remove it but thought it might be handy.

[Bricklayer]

It doesn't give you a Brix reading but if it's installed on your permeate line it will give you an idea if your passing sugar. I check my permeate from time to time to make sure it reads 0.00 ppm. It reads total dissolved solids.
I'm sure there's more science to it but if your permeate is at 0.0 then your not passing sugar and your RO is functioning.
If it's there then leave it on. Why not.

[Clinkis]

After posting this thread I did a little research. From what I've read sugar will not measure on a conductive style TDS sensor which is what this sensor is I believe. They work by passing a small current through the liquid and measuring its conductivity. Dissolved solids will increase its conductivity but there is exceptions and sugar is one of them. Apparently sugar does not effect a liquids conductivity so this style of sensor will not work effectively. I have to replumb the whole RO so not sure if it's worth the extra parts to reincorporate the TDS sensors. I guess one could argue that if it starts detecting other solids then you could assume sugar is there as well.

[DrTimPerkins]

Conductivity (or resistivity or TDS) can be used indirectly to look for sugar passage. Although the sensor will not pick up the sugar itself, it will detect minerals dissolved in sap. Typically in permeate, the mineral concentration is quite low (most minerals are retained on the concentrate side along with the sugar). If it goes up, it indicates some leakage either through the membrane itself (very bad) or through seals (often fixable). If that occurs, then sugar is also likely being lost. A conductivity sensor is a few tens to few hundred $ (depending upon how sophisticated you want the unit). Inline refractometers for sugar measurement start in the thousands of $.

[Clinkis]

Thanks good info. So one should expect a proportionate increase in sugar to TDS. There are 2 TDS sensors on this RO. I will plumb one into the permeate line and one into the concentrate line. Sounds like it should give me a good indication of what’s happening. I can then use my hydrometer to verify.

[Bricklayer]

If it was me I wouldn't worry about a tds meter on the concentrate line. I'd spent the time send money and plumbing parts on a temp gauge on incoming sap line to the RO. I put one on mine and it's nice to know the temp of the sap. Also plumbed in a high temp shut off also.

[Clinkis]

The TDS is already there and configured to the controller and display so just a matter of a few fittings to plumb it in. To add a temp sensor would require more significant changes to the wiring and controller. Although I agree it would be helpful, If i decide to incorporate that it will be significantly more work and a different discussion altogether.

[BigPine]

My first year with R/O. I bought 'The R/o Bucket'. I know the TDS sensor is to confirm that all the sugar and minerals are being filtered out.
My question is, Can the TDS be used to measure brix? If so, is there a conversion chart of PPM = Brix? If there is no 'exact' conversion, is there a standard for "average mineral contant sap"?

[carls47807]

The TDS only measures ionic dissolved solids. Sugar is a covalent compound and therefore won’t show up in a conductivity tester. Luckily, membranes tend to pass ionic content long before they pass the larger sugar molecules.


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[DapperTapper]

Not sure if this is useful or not, but I successfully used a TDS meter as a guide for sugar % - My Sap (Birch) sat around 360ppm fresh, and around 580ppm after one pass.
It kept relatively steady until the membranes slowly clogged, I've recorded numerous TDS and Brix to see if there's any correlation, but as it's not measuring sugar, I guess it's only a loose guide at best.

Oh, for a dip-and-read Brix-o-meter..