Total Dissolved Solids Meter

Author

Mark Yaney

Probe/Sensor

Conductivity meter to find Total dissolved salts

One of my students and I were really interested in desalination, and how to best accomplish that. I ended up making an earth science lab of it, and incorporated the use of a solar still, and a way to check how effective the desalination/distillation was. Thanks be to Amazon, once again, as the solution came in a box, or blister pack in this case. This little blue doohickey measures the dissolved solid in the water by the water's electrical conductivity. Pure water has no IONs, but salty/mineral water does. Any water with 002 parts per million (ppm) would be essentially pure.

However, the meter does NOT measure biological impurities, nor VOCs (volatile organic compounds) such as Benzene, so it's only pure of dissolved SOLIDS.

This TDS meter is an inexpensive and convenient digital tool to instantly check your overall water quality. TDS = Total Dissolved Solids, which is any salt, metal or mineral in the water. With the push of a button, the TDS-EZ can tell you your overall water purity level, which will be displayed on the screen in ppm (parts per million). The lower the TDS level, the purer the water, with 0 ppm being pure H2O (description from Amazon).

Highly efficient and accurate due to its advanced microprocessor technology.

Hold Function: saves measurements for convenient reading and recording.

Auto-off function: the meter shuts off automatically after 10 minutes of non-use to conserve batteries. Display: large and easy-to-read LCD screen.

Measurement Range: 0-9990 ppm. From 0-999 ppm, the resolution is in increments of 1ppm. From 1000 to 9990 ppm, the resolution is in increments of 10ppm, indicated by a blinking 'x10' image. Fun, translucent blue housing that's very strong and durable.

TDS-EZ meters are calibrated with a 342 ppm NaCl solution. Meters can be recalibrated with a mini-screwdriver. Includes a TDS chart sticker on the back of the meter that explains TDS values.

Sample Investigation

I did a lab to calculate the energy required to desalinate water. We distilled small amounts of saltwater using cut off 2 liter soda bottles with their bottom curled under, cups containing a measured amount of water and dissolved salts, and sunshine. We measured the volume of the distillate, and its salinity to see how pure it was. It was a little advanced, and many of the stills we created blew over. To calculate salinity before and after, we used this handy tool.

Independent Variable: Energy of sunshine

Dependent Variable: Salinity of water to start

Controlled Group: None, but next time I will leave some of the bottles in a darkened classroom.

Sample Data & Analysis and Interpretation

Unfortunately, the data were lost. Also, because 8 of the 10 stills blew over, no distilled water was recovered. We began with 200 mL of 1000ppm salt water, and I simply gave the students a fixed outcome to with which to calculate. Below, this is what the graph might have looked like if we began with sea water.

In the video below, the man with the English accent test the TDS Meter out on a fish tank. I was only able to get Brita water to 250 ppm. Maybe it's my pitchers.