As the process pressure moves a diaphragm sensor, which in turn lifts a vane in front of an infrared light beam, the amount of light affected on the measuring diode varies. A reference diode is also provided to compensate for the aging of the light source (LED) or for dirt buildup on the optics. This transducer is insensitive to temperature variations, as such variations affect the measuring and reference diodes in the same way. Because the amount of movement in the sensor is very small (0.5 mm), both the hysteresis and the repeatability errors are negligible.
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Instrumentation Basics 