Cooled Mirror Instruments Why use Cooled Mirror Sensing Technology? Applications

Michell Instruments manufactures hygrometers suitable for almost any application. So why choose one of our cooled mirror instruments rather than an impedance product or a process analyser? Below are some answers to consider.

Applications

Sensitivity – Michell’s cooled mirror products detectminute changes in moisture down to the ppb range. Accuracy – Cooled mirror technology is accurate to 0.1°C(S8000 and S4000 model). Drift free – A cooled mirror sensor will measure consistentlyevery time. Calibration – The S8000, S4000 and Optidew can be usedto calibrate relative humidity and dew point instruments. All Michell’s products offer traceability to the major national and international standards laboratories. Rugged – Michell’s cooled mirror products are designed towithstand industrial use. Fundamental – The optical condensation principle of dewpoint measurement has been established for centuries as the most fundamental method of determining the moisture content of a gas.

The Technology

In Michell’s cooled mirror sensors, a miniature polished metal mirror is cooled by a solid state Peltier thermoelectric heat pump until it reaches the dew point of the gas under test. When this temperature has been reached, condensation will begin to form on the mirror surface. An electro-optical loop, comprising a visible red light-emittingdiode and a high gain photo-detector, detects that condensation is forming. A reduction in the intensity of light reflected from the mirror surface is used as a feed input into the instrument control electronics to modulate the cooling power applied to the Peltier.The mirror surface is then controlled in an equilibrium state,whereby evaporation and condensation are occurring at the same rate. In this condition, the temperature of the mirror (measured by a platinum resistance thermometer) is equal to the dew point temperature of the gas. •Air dryers •Environmental chambers •Power Generation •Natural Gas •Pure Gases •Metrology Laboratories
DetectorLight SourceMirrorPRTSupplyHeat Pump •Plastics •Aerospace •Food / Beverage Processes •Chemical •Metallurgy / Heat Treating •Petrochemical •Automotive

Contamination Correction

•Drying Processes
All Michell’s cooled mirror instruments incorporate anautomatic compensation system that periodically re-balancesthe sensor optics to compensate for any reduction in light intensity caused by contamination. •… and many more