Humidity detection boosts process efficiency

Paul Boughton
Michell Instruments has released a new edition of its moisture and humidity product catalogue which contains comprehensive information on the company's range of relative humidity transmitters and sensors, dew point transmitters and humidity calibration instruments.

As well as information on new products such as the MDM300 portable dew-point hygrometer and PC62 relative humidity probe, the catalogue also contains a handy guide to the measurement of humidity, which explains common equations as well as terms and conventions used in the industry.

The company's latest addition is the S8000 Integrale cooled mirror hygrometer which provides highly reliable, drift-free dew-point measurements in vacuums as low as 0.05mbar. It is particularly aimed at applications that involve vacuum pumping, such as oil refilling of transformers (Fig 1).

Many high voltage transformers, especially those switching many thousands of kVA (such as the types found in power plant sub-stations), are filled completely with a refined mineral oil. This serves several purposes: most importantly the oil must act as a main part of the transformer's insulation, although it also serves to cool the transformer.

Moisture inside transformers adversely affects the dielectric and insulating properties of the oil. Vacuum pumping the transformer enclosure is a common practice in the industry, with the sole purpose of minimising the total moisture content prior to oil filling.

Optimal dryness is desirable at this critical stage and a reliable, accurate dew point measurement enables users to monitor the process and ensure that moisture is eliminated as much as possible.

Together with its low-pressure capability, the S8000 can measure dew-points as low as -60°C with 0.1°C accuracy. Its fundamental chilled-mirror technology is drift-free so measurements are reliable over time.

The design of the sensor head allows for excellent sealing both in high-pressure as well as in low-pressure and vacuum applications, making it a highly versatile instrument.

New from Rotonic is the HygroGen self-contained transportable humidity and temperature calibrator. This enables users and calibration engineers to accurately and rapidly calibrate any type of humidity instrument (Fig. 2). According to the company, the launch of the second generation Airchip3000-based calibrator takes transportable humidity calibration to a new level of performance and ease of use.

Stabilisation of relative humidity (RH) set-points within the HygroGen's test chamber is typically achieved within five minutes. This means a three point RH calibration can easily be performed within 30 minutes, which is at least 75 per cent faster than other typical systems. Temperature control of +/-0.05°C and embedded AirChip3000 technology means that extremely precise and stable conditions are assured throughout the calibration test.

HygroGen takes the calibration laboratory to the instrument or transmitter so that full system validation may be performed without the need to remove equipment from operation. The touch screen user interface allows rapid set-point change and display of actual conditions in both a numeric and graphic format.

Thanks to the significant calibration time-saving possibilities, the HygroGen delivers a rapid return on investment. Embedded PC technology means a simple upgrade path for additional functionality and performance enhancements.

The OMEGA iTHX-SD transmitter lets users monitor and record temperature, RH and dew point over an Ethernet network or the Internet with no special software except a Web browser.

It serves active Web pages to display real time readings, display charts of temperature and humidity, or log data in standard data formats for use in a spreadsheet or data acquisition program such as Excel or Visual Basic.

The virtual chart viewed on the web page is a JAVA Applet that records a chart over the LAN or Internet in real time. With the OMEGA iTHX-SD, there is no need to invest time and money learning a proprietary software program to log or chart the data.

E+E Elektronik's latest focus is on its EE33 series that is designed for fast and reliable measurement of relative humidity, dew point temperature and absolute humidity under the most demanding process conditions. Neither condensation nor heavy chemical pollutions will affect prompt and reliable measurements. Process pressures as high as 100 bar (1450 psi) and continuous high humidity are also no problem for the EE33 series.

Testo's new 6781 transmitter is capable of robust and durable performance and is extremely resistant to condensation formation and offers an accuracy of +/-3.0°Ctd at a dewpoint of -90°Ctpd. With these extremely low, measurable dewpoints, the Testo 6781 fulfils the two highest ISO quality classes regarding the requirements of, for example, modern semi-conductor production (class 1: -70°Ctd) or granulate drying processes (class 2: -40 °Ctd). As a comparison: the absolute humidity corresponds in class 1 = 0.003 and in class 2 = 0.12 g of water vapour per m3.

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