7. An Instrumentation System for Smart Monitoring of Surface Temperature

The authors of this paper are a part of a team tasked with developing a low-cost and easily deployable advanced sensing system for monitoring the levels of identified close proxies such as surface temperature and surface moisture on the sewer concrete surface. In this regard, to estimate the influence of surface temperature causing corrosion, it is necessary to develop an innovative sensing system for monitoring surface temperature variations in sewer condition that will perhaps facilitate the present sewer monitoring capabilities. It is to be noted that the proposed system is aimed to be deployed inside the harsh conditions of sewers having daily average relative humidity over 90% and higher levels of H2S concentration [8]. Thus, the design of proposed system should be capable of withstanding the harsh environmental conditions of the sewer.

A concrete wall was used as the surface of interest for evaluating the sensing performance of the infrared radiometer sensor that performs non-contact surface temperature measurements. The measurements were taken at different distances such as 10 cm, 20 cm, 30 cm, 40 cm and 50 cm from the surface of interest. Also, the measurements were taken by keeping the infrared radiometer sensor at different angles such as 50, 70, 90, 110 and 130, focusing the targeted surface. Further, the temperature measurements were taken in two different lighting conditions; a bright room and a dark room. The sensing enclosure window is presently equipped with hardened glass. In order to replace that window, another germanium optical window sensitive to 8-14μm was mounted in front of the temperature sensor. All the infrared radiometer measurements were taken with temporal logging interval of 30 seconds.

A thermistor (THERM-EP Epoxy, Apogee Instruments) with an accuracy of ±0.05ºC was used in the experimentation as a reference measure of surface temperature data. This thermistor was affixed on the concrete surface region, where the infrared radiometer is pointed to perform measurements. Another thermistor was used to monitor the ambient temperature conditions while monitoring the surface temperature measurements. The signals from different sensors are transmitted to a stand-alone logging instrument (TSM1, ICT International). This instrument also logs data to the on-board memory card. For evaluating the performance of the custom-made data logger, it was connected to the signal processing ports of the TSM-1 to read signals coming from the infrared radiometer.

In this work, an instrumentation system has been developed and characterized for monitoring the surface temperature variations of the concrete. Experimental evaluation demonstrated that for all undertaken measurements, the surface temperature values were slightly higher than the ambient temperature values. Also, the surface temperature measurements obtained from the infrared radiometer and the reference measure showed a similar pattern. Statistical error analysis was performed to study the sensing performance of the infrared radiometer by positioning the temperature sensor at different distance and angles from the surface of interest. For measurements taken in bright and dark rooms, it was observed that from 10 cm to 50 cm the RMSE was below 0.16ºC, and for angles from 50 to 110 the RMSE was below 0.19ºC.

Overall, the sensing performance of the proposed instrumentation system was deemed satisfactory.