Windscreen Heat Monitoring

Once considered a luxury, rear windscreen heating is almost standard equipment for any car produced today. This ingenious component has a simple mechanism: heat is provided by small resistance wires inside each glass. However, the wires are so small that short circuits are not visible to the naked eye. This means that car manufacturers face a challenge in the identification of defects in their windscreen heating systems.

While short circuits may not be visible to the naked eye, they are easily recognizable with a WIC thermal imaging camera. This is because the short circuit produces a large amount of heat. If automotive companies are to meet consumer demand for highly reliable, error-free products, they must monitor these miniscule defects. That’s where Workswell’s line of thermal imaging cameras comes in.

Our Assignment

One of Workswell’s clients, who will remain unnamed, is a world leader in flat glass production. They required a monitoring solution to achieve their goal of fully homogeneous windscreen heating. We provide a WIC thermal imaging camera to help our client identify tiny defects in the resistance wires. This is a technically challenging task. Since there is not sufficient space for extensive glass heating during the client’s production process, glass is heated by ±5° C. However, the initial glass temperature may vary by up to 20° C during the year due to changes in ambient temperature. Therefore, the client requires a detailed evaluation of measured temperature in relation to the initial temperature of the windscreen. Since they produce more than one type of windscreen, they also require automatic adjustments to the system settings for each type of windscreen.

The Workswell Solution

We decided to deploy the ThermoInspector thermal imaging system for this assignment. ThermoInspector is primarily designed to monitor production processes. This includes monitoring temperature stability and homogeneity throughout complex processes, as well as tracking input – output temperature. Up to 4 WIC thermal imaging cameras may be connected simultaneously in ThermoInspector.

Because of the size of the client’s windscreen, we decided to use a single WIC 640x512px thermal imaging camera, which we connected to the ThermoInspector control computer via Ethernet cable. The thermal imaging camera sits on a static holder perpendicular to the monitored windscreen. Because glass is a very reflective material, we position the camera in a black, homogeneous chamber, without surrounding heat sources. The system is configured to the Fixed Time Measurement Mode, which means that the camera monitors areas in the image (ROI) for a fixed number of pictures – in this case, one picture – after the trigger signal. The trigger signal is transmitted to Thermoinspector from the control PLC, and it activates when the glass heats to the desired temperature. If the temperature limit on one of the ROI is not met, an alarm displays on the screen to inform the operator and save the appropriate record to the control computer. In addition, the system has digital outputs that inform the control PLC of the detected short circuit in the windscreen heating. It also communicates with the PLC via Ethernet cable using TCP/IP protocol. Before each measurement, the PLC always sends information about the windscreen type and temperature to the ThermoInspector. The system itself then sets the ROI based on the information without the need for operator intervention. ThermoInspector sets the desired temperature limits and manual pallet temperature range for easier visual monitoring by the operator.

Optionally adjustable ROI are used to check the temperature of the windscreen, in which the camera evaluates the measured data in real time. Polygons covering the most problematic parts of the windscreen are chosen as the optimal ROI. In these areas, the maximum measured values/temperatures are monitored in real time and compared with the set limits. The visualization of the entire process is then displayed on the ThermoInspector touch control computer for operator use.

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