High Temperature Pressure Sensor Based on Thin Film Strain Gauges on Stainless Steel for Continuous Cylinder Pressure Control

This paper describes the design and performance of imes long-life high-temperature thin film strain gauge pressure sensors that have been specifically developed for monitoring of reciprocating compressors, natural gas or diesel engines, and high-pressure fuel systems. In a robust, durable, and low-cost design imes pressure sensors utilize the principle of thin film layers. Basis is a thin film cell which forms a metal substrate. This is overlaid by insulation layers which form an electrical barrier to the metal. TION (Titanium oxi-nitride, patented) and nickel for the functional layers of the measuring cell , with the result that the substrate can be designed thicker, which in turn has a significant effect on the longevity of the sensor. Finally, the measuring cells are thermally aged at high temperature. Altogether the sensor is no bigger than a spark-plug. The most important measured value describing the operation of a diesel or gas engine is cylinder pressure. By constant monitoring of this pressure, as enabled by the imes system, malfunctions and wear can be recognized immediately. Permanent monitoring and control of cylinder pressure is of growing importance. The test results are reported here obtained in marine diesel engines and natural gas engines . In the longest application to date, hundreds of combustion pressure sensors have demonstrated over 10,000 hours or 500-Million pressure-cycle lifetime. Dynamic pressure sensors for compressor monitoring have already demon-strated the lifetime of 1 billion cycles and target 5 billions. In compressor applications the sensor demonstrates typical +/-0.5% accuracy while combustion pressure sensor accuracy is typically +/-1%. For almost two years tens of indicator valve-mounted combustion sensors have been monitored for calibration stability demonstrating better than +/-0.1% performance over a 6-month period. INTRODUCTION: