In a solar panel plant, a temperature sensor installed in a chemical bath has to do more than read accurately. It must survive years of immersion in acid or alkaline solution while releasing no contaminants into it. Many wet process problems start with the wrong choice of protective material for the sensor.
The biggest challenge usually comes from hydrofluoric acid (HF), used for etching and removing oxide layers from wafers. HF reacts with glass and quartz, so sensors with glass sheaths cannot be used in these baths. A mixture of HF and HNO3 also quickly attacks most metals, including stainless steel, especially as the solution temperature rises.
For baths containing HF or strong acid mixtures, the common choice is a sensor with a fluoropolymer sheath or coating such as PTFE or PFA. These materials resist nearly every chemical in the wet process and do not release metal ions into the solution. The trade-off is a slightly slower response than a metal-sheathed sensor, since plastic conducts heat more slowly, so this should be accounted for when tuning the bath temperature controller.
Alkaline texturing baths with hot KOH or NaOH behave differently. Stainless steel 316 does hold up better against alkalis than against HF, but solar cell lines have another concern: cleanliness. Even tiny amounts of metal ions such as iron or nickel can settle on the wafer surface and reduce cell efficiency. That is why many plants still choose fluoropolymer sheaths for baths in direct contact with wafers.
Ultrapure water systems call for a similar approach. Water with resistivity close to 18.2 MΩ·cm is very easily contaminated, so any sensor part in contact with the water must be made of a material that does not release ions. For cooling water and utility lines that never touch the product, on the other hand, stainless steel 316 is usually sufficient and more economical.
The right material also needs the right installation. Cables and sensor heads above the bath are still exposed to acid vapor, so enclosures and cable glands should be corrosion-resistant and well sealed. If the signal goes to a PLC through a 4–20 mA temperature transmitter, place the transmitter outside the vapor zone or inside a protected panel.
Before ordering sensors for wet processes, prepare a list of chemicals and their concentrations, the bath temperature range, the solution depth, and how the sensor will be mounted in the bath. This data helps determine the most suitable material, probe length, and configuration.
CV. Rach Tekindo Makmur supplies Temperature Sensors & Temperature Transmitters for a wide range of industrial instrumentation needs. If you need sensors, transmitters, or consultation on configuration and installation for your temperature system, contact us on WhatsApp at 0877-8620-5656 to discuss your technical requirements and request a quotation tailored to your application.
