You see advertisements beaming on TV that sings the virtues of water purifiers. They say things like RO + UV + UF + TDS Controller/Modulator, etc.
What exactly do you mean by the words, TDS Controller? Let us see the concept in brief.
The principal job of the RO water purifier is to purify the source water by eliminating all kinds of impurities that include TDS.
Normally, the RO process ensures the removal of 90% of TDS. Hence, if the TDS levels of input source water are around 1500 ppm, the TDS levels of pure water after RO purification comes to around 150 ppm.
Water with TDS levels below 150 ppm does not have a good taste because of the elimination of essential minerals like sodium, magnesium, and calcium. Therefore, the water has a lower pH level and hence tastes bitter.
You require a special mechanism known as the TDS controller/modulator to rectify this anomaly. There is a need to bring the TDS levels of water in the range of 300 ppm to 400 ppm. Let us see how the TDS controller works.
The basic system is such that the water that goes into the RO process is split into two parts. One part goes through the RO membrane and the output you have is pure RO water.
As discussed earlier, this water has a lower level of TDS. The other part of the water does not go through the RO membrane.
Instead, it passes through the UF membrane or a UV chamber depending on the configuration of the water purifier. This output will also be pure water but with the same levels of TDS as input source water.
Now, comes the interesting part. The system ensures the mixing of both these water outputs. There is a valve that controls the flow of water from the Part 2 assembly.
This effectively controls the TDS. If you notice the configuration of the water purifiers you will find that the TDS controller is always paired along with the UV chamber or the UF membrane.
Related: TDS Controller vs Mineralizer
The resultant water contains optimum levels of TDS. This is very useful in case the source water has low levels of TDS. Understand that water with low levels of TDS does not constitute that the water is pure. This is why you need to purify water with low TDS levels by passing it through the UF membrane or the UV chamber.
You can also refer to the TDS controller as a TDS modulator because it controls as well as modulates the amount of TDS in the water.