PURA QUALITY FROM MICHELL INSTRUMENTS

Michell instruments has developed a rugged, self contained hygrometer designed specifically for the measurement of trace moisture content in high purity gases.

The PURA Pure Gas Dew-Point Transmitter represents a landmark in moisture transmitter design, giving high accuracy, stability and repeatability in a specialised application, offered at a highly competitive price.

The PURA has been developed for and tested by the semiconductor industry, to measure trace moisture in the high purity gases used in the processing of silicon wafers in a semiconductor fabrication plant. Historically trace moisture measurement has been a difficult exercise, demanding the use of complex moisture analysers or expensive analytical techniques. The PURA provides on-line measurement of dew-point temperatures down to -100 °C, (equivalent to less than 15 parts per billion), and provides indication down even lower to -120 °C (less than 0.2 parts per billion). The PURA is suitable for large-scale integration into a semiconductor fabrication plant or high purity gas line.

PURA is deceptively simple. Its self-contained transmitter module has been designed to fit seamlessly into pure gas processes and give continuous and reliable measurement thereafter. Installation is also simple. The ¼ inch male VCR gas connection ports are set at a pitch of 120mm to fit into a standard MFC footprint. The whole unit is only 152 mm in height and weighs less than 500g. PURA provides ultimate flexibility in operation and is powered by any regulated 12 to 28V dc source.

PURA's sensor housing is fabricated from stainless steel with an internal 0.25 micron electro-polished finish for minimal moisture adsorption. The ¼" male VCR gas connection ports are supplied capped for cleanliness. PURA can be delivered clean and double bagged to the class 100 clean room standard, if specified. Furthermore, PURA is delivered fully calibrated and ready to use. The 4-20mA output can be connected to a process indicator or centralized control system, or the RS485 text output can be used to connect directly into a suitable computer system.

Internal volumes have been designed to a minimum. This ensures the fastest possible response speed in commissioning and also when a moisture event occurs.

The sensor body seal is rated to 10-9 torr whilst the whole system will handle pressure right up to the VCR coupling rated maximum of 24 MPa.

Whilst PURA is shipped ready to use, calibrated precisely at thirteen points across its measurement range against transfer standards traceable to NIST and NPL, it is also user-customisable. The 4-20 mA output can user set over any part of the 140 oC dew point range, with a minimum output span of 1 oC. Also, the factory pre-set alarm signals, providing over-range, under-range and sensor fault conditions, can also be easily re-set to suit your own application and system needs. Adjustment of all these parameters is achieved through a simple PC-based user interface, supplied free of charge with every PURA on request.