High Temperature Capacitance Probes Monitor and Control Windshield Manufacturing Processs - MTI Instruments - #1

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MTI Instruments, Inc. 325 Washington Avenue Extension Albany, NY 12205 PH: +1-518-218-2550 OR USA TOLL FREE: 1-800-342-2203 FX: +1-518-218-2506 sales@mtiinstruments.com www.mtiinstruments.com APPLICATION NOTE High Temperature Capacitance Probes Monitor and Control Windshield Manufacturing Process Introduction Remember the days when windshields were made of fl at sheet glass? Not anymore. The complex shapes and designs of today’s windows complicate the manufacturing process and signifi cantly increase quality control measures. Maintaining a constant shape and thickness is required to reduce the possibility of failure from stress induced during the quenching process. The Problem In order to maintain proper profi le and thickness within a glass furnace the extrusion plate spacing must be maintained at a predetermined gap. Unfortunately, due to process changes and temperature swings this gap can fl uctuate signifi cantly in short periods of time. This variation causes the glass thickness to change, producing uneven temperature gradients and creating potentially weak glass panels. To control this critical parameter the manufacturing process requires automated active feedback control sensors installed into a very harsh environment. The Solution Limited space, extreme temperatures and excessive vibration had to be considered in the solution design. After careful analysis, MTII Engineers designed a custom, passive capacitance probe capable of operating at temperatures exceeding 500oC. The probes featured “fail-safe” construction, eliminating the possibility of catastrophic failure should the probe cement be compromised from excessive vibration. The passive design removed all active elements from the measurement area allowing for stable control of the extrusion gap. MTII selected the AccumeasureTM 1500 capacitance system, which allowed multiple measurement and control points. The high frequency response and minimum phase delay made it the ideal choice for closed loop control. The Results The fi nal probe confi guration was a custom ASP-100-CTA sensor with a 0.5” (12.5mm) measurement range. Although the gap only fl uctuated by +/-0.005” (125 ìm) the large measurement range allowed for an increased probe operating distance and reduced the probability of probe damage. At 500 Hz frequency response the Accumeasure 1500 resolved measurements to less than 50 ìin (1.25 ìm) and provided continuous monitoring and real-time feedback control. This signifi cantly improved product quality and virtually eliminated any scrap, saving $1000’s in the fi rst month alone. MTII appnote: windshieldglass.pdf - Page 1 of 1