IOP Groups

Measurement of Pressure in Vacuum Systems

Held at the Institute of Physics, London - 26 November 2003

This meeting took the form of a series of tutorial/workshop sessions conducted by leading practitioners in the field of vacuum measurements. The meeting was aimed primarily at new post-graduate students, but was equally of interest to research workers and technicians starting to work in areas where vacuum measurements are important and for those wishing to brush up their skills. The leaders did not seek to cover the details of the physics of various types of pressure measurement instruments which can be gleaned from any textbook on the subject. Instead, they concentrated on discussing how instruments are used in practice in real vacuum systems, how the instrument readings relate to real pressure and pointed out some of the common pitfalls and misconceptions around the subject.

Participants were invited to bring along questions to ask the Panel in the discussion session.

There was a small table-top exhibition by the main suppliers of vacuum instrumentation and participants received a copy of a Guide to the Measurement of Pressure and Vacuum published by the Institute of Measurement and Control.

For those attending the meeting, there was a free prize draw for a 2nd edition copy of the textbook Modern Vacuum Practice by Nigel Harris (see http://www.modernvacuumpractice.com). Voted editors choice - Semiconductor International, Spring 2001, and recommended vacuum technology entry level book by R&D Magazine, March 2002.

Abstracts

Measurement of Pressure in the Low and Medium Vacuum Regions
Dr John Greenwood., National Physical Laboboratory

Topics to be covered will include:

• Uncertainty and Traceability - Ask yourself why are you making a measurement of the pressure? What is important?
• A brief external look at some gauges - It looks like a black box, does it behave like one - no, so find out what it is doing. Useful web sources of information.
• The use of calibration data and pitfalls - How to invalidate your calibration and measurements eg temperature, drift, location with respect to the vessel, vibration, etc
• Some brief safety pointers, overpressure, unexpected high voltage (eg several kV switched up from 10V dc)

Pressure Measurement in Industrial Systems
Dr Keith Vanner, Silson Ltd

Industrial systems require consistent measurement of pressure. Absolute measurement is not always essential, but repeatable, drift free measurements are required for process control. It is also necessary to be able to transfer successful processes to other equipment with a minimum of process re-centring.

This talk will cover some of the practical aspects of pressure measurement in industrial systems such as coaters and plasma etchers.

The selection of suitable gauges for process control, diagnostics and fault finding will be discussed, and attention will be given to the use of simple pressure measurement systems during maintenance and repair of vacuum systems.

The main part of the presentation will cover the requirements for pressure measurement in plasma systems, which often use mixtures of reactive gases, and where process durations can range from a few seconds to several hours. In such equipment good process control is essential, and the pressure gauge plays a crucial role in achieving this.

Total and Partial Pressure Measurements in High and Ultra High Vacuum
Dr Ron Reid, Daresbury Laboratory

In high and ultra high vacuum systems, particular care must be taken to ensure that the gauge does not affect (or indeed dominate) the measured pressure. This is true for both total and partial pressure measurements. This session will discuss the steps taken to minimise such effects and will attempt to answer the question "Can I really believe what the gauge is telling me?"

A CD of the presentations is available on request, contact the chairman j.i.b.wilson@hw.ac.uk for details.

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