New Twist on Moisture Measurement Technology
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German sensor specialist BARTEC is heading to Sensor + Test 2007 (May 22-24 in Nuremberg, Germany) with a new twist on existing technology. The company’s innovative twist on cooled mirror dew point sensors makes it possible to precisely measure the moisture content of gases for dew points between -40° and +80° Celsius (relative humidity between <2% to 100%). The new sensor was awarded the coveted SENSOR Innovations Prize 2006 by Germany’s respected AMA Fachverband für Sensorik e.V.
Conventional methods of measuring moisture content and humidity are based on capacitance, changes in resistance or thermal conductivity, have tolerances that are too high for many applications. Measurements using cooled mirror sensors are accurate but involve technology that is too bulky and expensive for widespread use. By miniaturizing and tweaking cooled mirror technology, BARTEC has created a cost-effective alternative that still permits ultra-precise measurements.
In one sense, BARTEC’s Hygrophil DT 1500 sensor relies on the proven and widely used cooled mirror principle. In this sensor design, light is reflected from a mirror and captured by a photo diode. As soon as moisture condenses on the mirror as the result of cooling, there is a change in the intensity of the light captured by the diode. The dew point is measured by recording the temperature at this point.
The Hygrophil DT 1500 introduces an innovative twist on this technology that leverages the advantages of the cooled mirror sensor while reducing its disadvantages. The BARTEC sensor uses the principle described above with the exception of one important detail: the light beam no longer passes through the gas stream. Instead, light from the LED light source is no longer directed at the top of the mirror’s surface, but is instead coupled into the glass from below and then internally reflected and finally guided to a photo detector.
When the glass is cooled using a Peltier element, the light that has been coupled in is then coupled out by the condensate and the light is no longer guided to the photo detector. The temperature at which this phenomenon takes place is measured using a platinum sensor and this temperature is, in effect, the dew point temperature.
The Hygrophil DT 1500 offers a number of significant advantages over conventional sensor designs. Topping the list is the fact that dust and other particulates in the gas no longer affect the measurement results. This is because the smaller water particles condense directly onto the glass surface of the sensor. In addition, the BARTEC design dramatically reduces the size of the mirror, which allows the miniaturized sensor to be used in many industrial processes.
The suitability of the sensor for industrial applications is definitely new. Despite their high level of accuracy, conventional cooled mirror sensors were previously restricted to use in calibration applications and research, primarily because of their size, complexity and cost. Its small size and superior technology – the Hygrophil DT 1500 delivers drift free measurements and requires no cyclical recalibration of the sensor – make the DT 1500 perfect for a wide range of industrial applications. The Hygrophil DT 1500 can be used wherever precision measurements and exceptional long-term measurement stability are required. Examples include medical technology, industrial processes, bio-gas plants, coating plants and climate chambers.
One good application example is the compressed air industry, where the humidity of compressed air must be continuously monitored to protect downstream processes from the unwanted effects of excessive moisture. Because of this, the compressed air must be dried in a process where imprecise sensor data can dramatically boost the cost of the drying process. With the Hygrophil DT 1500, the process industry can perform ultra-precise monitoring of humidity levels with a sensor that is completely unaffected by contaminants such as dust and nearly unaffected by oil. This, in turn, allows for ultra-precise control of the drying process and can result in very significant savings for the operator
Press release
Gotteszell, Germany
March 2007