Dew-point sensors and transmitters are standard devices in industrial, process and laboratory applications around the world. They are compact, robust, reliable and use proven technologies to make measurements under a wide range of demanding environmental conditions.
In common with all sensing devices, dew point sensors need to be recalibrated at regular intervals; depending on the operating conditions, this is typically once a year, although it may need to be more frequent in critical applications.
For many customers with a relatively small number of dew-point sensors or transmitters, it makes sense to return each instrument to the manufacturer for recalibration, or to use a service such as our Sensor Exchange Service Program, where a calibrated sensor is supplied to the customer for installation before the old sensor is returned for recycling. This minimizes downtime for the customer and ensures that the quality and performance of their process or production operation is maintained.
For customers with large numbers of dew-point sensors, such as major pharmaceutical production operations or energy generating plants, the most efficient option is to carry out sensor calibration on site.
This requires a specialized system, comprising:
Compressed air is first pre-treated to remove liquid water and particulates before being passed through a high-performance pressure swing dryer. The dryer provides a constant source of dry air for the dew-point generator.
Michell’s latest dew-point generator, the ADG400 is based on the volumetric mixing of dry and wet gases. This gives the fastest response when changing between set points, compared to other dew-point generation technologies (such as two-temperature, two-pressure or the combination of both).
Dried compressed air is fed to the generator from the pressure swing dryer and split into two streams. One stream is bubbled through liquid water via a sintered glass nozzle, ensuring it is completely saturated with water vapor, while the other stream remains dry. The two gas streams are then mixed in a single or multi-stage process to generate the target dew-point level. The generator has an output range of -80 to +20 °C dew point. The entire enclosure is insulated and temperature controlled, ensuring the saturation, and therefore the output, is stable and repeatable.
The first mixing stage in the ADG400 uses a parallel configuration of high-precision mass-flow controllers to precisely control dry and saturated air flow rates. This stage enables dew points from +20 °C to -30 °C to be produced. The second mixing stage uses a further two mass-flow controllers to dilute the output of the first stage with additional air from the dryer. This allows the generation of dew points from -40 °C to -80 °C.
The output calibration air from the generator is then fed into a sensor calibration manifold holding the units under test, and to a chilled mirror reference instrument for precise and accurate measurement of the generated dew point.
This complete system can be supplied in a rack-mount format as the Michell DCS80. Michell calibration systems such as the DCS80 are used daily in our own calibration labs, at leading manufacturers, independent calibration laboratories, and national standards institutes around the world.
The ADG400 features a full-color touch screen, making set-up and operation quick and simple. The main screen shows status and diagnostic information, and allows users to select Manual, Profile or Remote modes and change set points at the touch of a button. There are eleven factory-programmed set points at 10 °C intervals, which enable standard calibrations to be carried out quickly and easily, and the thirteen user-customizable set points mean intermediate points can be generated based on specific calibration requirements. The built-in set-point editor gives the user complete control over the output.
In Profile mode, unattended calibrations are made possible when the ADG400 is used in conjunction with a Michell S8000 RS or S8000 - 100 reference chilled mirror hygrometer. A built-in profile editor allows timings to be customized, and set points from either the factory or user tables to be selected as desired. The time and cost-saving benefits are obvious when calibrations can be run overnight or during the day without user intervention.
Remote mode allows the ADG400 to accept serial commands over the USB port to change set points, allowing the dew-point generator to be completely integrated with a customer’s own software calibration system. Further to this, the HMI can be mirrored on a PC via the USB port which gives another flexible option for remote operation, for instance over a remote desktop connection.
The ADG400 replaces Michell’s long-serving DG4 Dew-Point Generator, bringing significant advances in functionality, performance and flexibility. The new system is available now for all customers who regularly need to calibrate dew-point sensors on site, with the assurance that, subsequently, each sensor will function precisely to specification.
With almost 50 years’ experience in the development of innovative precision sensors, analyzers and calibration systems, Michell are the application experts in dew-point and moisture measurements for industrial, process and laboratory applications. If you would like to discuss your requirements, please contact our team today.
Click here to explore our full range of calibration systems.
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