A cost effective method for temperature measurement in HV system using fiber optic cable

Plasma based systems are playing a dominating role in numerous industrial applications such as surface treatment, RCB etching, thin film deposition, water treatment, sterilization of medical instruments, plasma polymerization and treatment of fabrics (enables improved wetability, wickability, printability of polymer fabrics and wool) etc. During plasma process there is need of precise control over temperature. This is a very important parameter in plasma-based reactors used for industrial applications. Here conventional temperature monitoring and control system behaves abnormally because plasmas are conductive, respond to electric and magnetic fields and also it can be efficient sources of radiation. In some of the cases the object (substrate) itself is biased at few thousands volts. Therefore, the only option is to opt for pyrometer, which is neither in contact of plasma nor to the substrate. But pyrometer is not a cost effective way for industrial purpose. It is a very costly instrument for higher temperatures measurement; also it requires a special quartz window and need very precise focusing. To overcome such problem, FCIPT has developed an indigenous fiber optic based temperature measurement and control system. For e.g. in PSII (plasma source ion implantation) reactor the plasma is created with 100 watts RF power and 20 KV fast pulses are applied to an object to increase its surface hardness or modify its surface properties. To measure the temperature of this component a K type thermocouple is directly connected to the object (substrate) and its temperature can be anywhere between 25/spl deg/C to 900/spl deg/C. The output of thermocouple (few mV) is processed and this signal is transmitted through a fiber optic cable. This technique improves the signal integrity before processing. Finally the actual value of temperature is displayed at panel. This is an efficient, cheap and accurate method to measure the temperature of all those devices and components, which are in direct contacts with high voltage and working under EMI atmosphere. In this paper the topology of complete systems, its functioning, problem observed and obtained results are discussed. This technique would be very much helpful for all the industrial and research applications where there is need to measure of such substrates, which are in directly exposed to the plasma and are at very high voltage.