The FCX-OHS/OHSLIGHT: Measurement of humidity at high temperatures

The high process temperature has a decisive influence on the selection of the humidity sensor. This is because not many sensors still offer sufficient measurement accuracy at such high temperatures. Pewatron has developed the highly accurate (+/-2 %Vol H2O), reliable and durable FCX-OHS/OHSLIGHT sensor, a product for a wide variety of industrial applications and operating temperatures ranging from 100 °C to 300 °C. The FCX-OHS/OHSLIGHT single sensor is used in a wide range of applications to control humidity in all areas of large industrial ovens and has thus established itself as an important process optimization element for maximizing the yield and quality of baked goods. The FCX-OHSLIGHT transmitter is used for high-throughput smaller ovens such as rotary rack ovens, where an integrated PLC is often used to control the signal output via the transmitter.

The measurement principle of the sensor used in the FCX-OHS and FCX-OHSLIGHT is based on the oxygen displacement of the measured gas compared to dry air with an oxygen content of 20.95%. With increasing humidity in the atmosphere, the oxygen concentration decreases, in case of complete humidity saturation and at temperatures above 100 °C down to 0 %Vol H2O. At temperatures above 100 °C, the transmitter generates an output signal that varies in proportion to the humidity from 0 to 100 % between 4 and 20 mA (FCX-OHS) or between 20 and 4 mA (FCX-OHSLIGHT).

The stainless steel probe (M22 x 1.5) with its moisture sensor integrated in the tube is ideal for wall mounting with a removable flange, but can also be mounted in other positions on smaller furnaces (for example, horizontally). The length of the probe is freely selectable between 30 cm and 2500 cm. The sensor and the materials used for the probe (metal parts, wires and connectors) can withstand temperatures above 300 °C and pressure up to 20 bar. With the help of a four-pole high-temperature cable, the probes are connected to the electronics of the transmitter. The sensor element can be equipped with a dust and particle protection filter.