Test Instruments

The measurement of microwave power flux density requires the use of a specialist professional instrument, accurately calibrated using equipment traceable to the UK National Standard.

There are a number of such instruments readily available to perform this safety critical task, a number of which have been approved for use by leading oven manufacturers.

During the early nineties, following the significant increase in use of the microwave oven in the UK, oven manufacturers were keen to promote the safety of their ovens in the face of concerns expressed by the general public.

The oven manufacturers adopted a pro-active approach in which the supply of technical support, service information and spare parts was restricted to those engineers in possession of a suitable instrument and an “in-date” calibration certificate. This approach was successful in ensuring the use of suitable, calibrated instruments.

However, in recent years this approach has been relaxed and we have witnessed the appearance and use of instruments claiming to hold specification that, on examination, they fail to meet.

The need for an accurate, calibrated instrument is recognised by the NPL and set out on page 2 of their publication “A guide to power flux density and field strength measurement” published in 2004. ISBN 0 904457 39 7

“Neither an exacting specification nor an accurate instrument is a substitute for a regular calibration routine, as without calibration at suitable intervals the instrument is unlikely to remain accurate or perform to its intended specification. Furthermore, where measurements are intended for RF hazard purposes, the integrity of the measurement is paramount to ensure the safety of public and personnel.”

While expensive and sophisticated instruments may be purchased for the purpose, users may consider that instruments of this type are not cost effective when compared to the number of times a test may be carried out.

However, there are a number of relatively inexpensive instruments available with a specification sufficient to meet the needs of technicians engaged in the maintenance of microwave ovens.

Below is a list of the specifications to be considered when choosing instruments generally used for the purpose of microwave leakage testing.

Instrument Specification.

  1. Dimensions and weight
  2. Power source and current consumption
  3. Incorporated 5cm spacer
  4. Calibration accuracy
  5. Response to step input
  6. RF Power range
  7. Overload capability
  8. Sensor type
  9. Display type and resolution
  10. Nominal operating frequency (Frequency at which calibrated)
  11. Calibration stability

The above give an indication of fitness-for-purpose of a given instrument. However, many of the later models now available offer additional benefits that may make the task of the user easier. These benefits usually come at an extra cost.

If we consider the above list, items 1 to 3 are self-explanatory and are not considered further. Please click an the item above, for more detailed information