Chemically Deposited Optical Fiber Humidity Sensor

Humidity measurement in industries is a critical factor, since it may affect the business cost of the product, end product quality, optimal functioning of equipment, and the health and safety of the personnel. Hence, humidity sensing is becoming very important, especially in the control systems for industrial processes. Since humidity is expressed in different ways, it is very difficult to come up with a reliable, consistent, and repeatable humidity measurement approach. In contrast to other sensors employed for measuring other parameters like temperature and pressure, a humidity sensor has to be in contact with the process environment and hence is difficult to implement. This research was initiated at the Diagnostic Instrumentation and Analysis Laboratory (DIAL) for the requirement from the DOE to monitor the moisture in the soil at the nuclear waste storage facility. The idea was to monitor the leakage, if any, in the storage cylinders to avoid any hazard that may come up. The humidity sensor in this case had to be able to transmit the measurement over a distance far away from the actual measurement site. Keeping all these factors in mind, a chemically deposited optical fiber humidity sensor was developed. It was based on the evanescent tail absorption of light passing through an optical fiber due to hygroscopic material deposited on it. The hygroscopic material used was an aqueous solution of Poly-vinyl-acetate (PVA) and Cobalt Chloride (COCl2). The sensor yielded a consistent humidity measurement from 75% to 95%. Based on the above research, research is currently in progress to bring up a commercial prototype of the sensor