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.
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 500 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.
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.
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.