Humidity measurement is key to process control

Cooled mirror instruments use a fundamental humidity measurement technique that is ideal for the accurate measurement of humidity in process control applications.

Coating processes are widely used in the pharmaceutical and confectionary industries for tablets, pills and sweets.

Michell Instruments' cooled mirror range of instruments uses a fundamental humidity measurement technique, making their products the ideal solution for the accurate measurement of humidity in process control applications.

Most tablets consist of a product core and a coated cover.

The coating can be a variety of proprietary compounds or various forms of sugar.

Coating of the product core is used for several reasons including, preventing discolouration of the core, to counteract an unpleasant or bitter taste and to prevent the core from degrading when exposed to the ambient atmosphere.

There are two aspects to tablet coating.

The generation of inlet air of a known humidity and the monitoring of the drying process itself.

In order to ensure a high quality product is maintained it is important that the humidity of the air fed to the drier is validated.

The fundamental cooled mirror principle, in products like Michell's Optidew provide the control signal for the generation of an inlet air with known humidity.

This is passed over the product during the spray coating process to guarantee that the tablets, or sweets have a consistent, smooth, high finish outer coating.

The monitoring of the drying process avoids excessive or under drying of the product.

Excessive drying will incur additional costs and time in manufacturing, as well as possibly causing negative effects to the product itself.

Equally under-drying will result in product spoiling and poor aesthetic qualities.

Therefore, determining the 'ideal' drying cycle is the key to this application.

Cooled mirror dew point sensors are used in the coating process to measure the dew point or absolute humidity of the inlet and exhaust of the drier.

This type of humidity sensor, such as the one used in the Optidew, is typically used because of the fundamental nature of the measurement and its drift free characteristics.

The high performance optical dew point transmitter works on the proven dew point measurement principle offering the user unmatched performance, ease of maintenance and zero drift.

This has led to a number of world leaders in the manufacturing of pharmaceutical and confectionary products moving over to this technology.

The Optidew offers a wide measurement range from the equivalent of below 0.5 to 100% relative humidity at ambient temperatures and from -40 to +90C.

The Cooled Mirror instrument also provides two linear 4-20mA outputs in addition to serial communications, allowing set-up and monitoring by a suitable computer or PLC system via specific Optidew logging software.

An adjustable volt-free contact alarm means Optidew can be used for direct process control.

An optional high definition alphanumeric display provides local indication of the measured humidity.

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