As the name suggests our microwave leakage instruments are designed to detect the presence of microwave energy; specifically in this case at a frequency of 2.45 GHz, the frequency chosen in the UK for domestic and commercial microwave heating equipment.
Digital Microwave Tester
In earlier years this instrument type, known as a “microwave monitorâ€, “microwave testerâ€, “microwave meterâ€, or sometimes by its more accurate title of, “microwave power flux density survey instrumentâ€, was of the analogue type. i.e, a moving coil meter provided the display arrangement. However, in recent years there has been a move towards the use of digital displays to visualize the microwave power level. These displays offer significant advantages over their analogue counterparts; in particular, a clear and unambiguous representation of power level without the potential of parallax error. The digital microwave instrument incorporate microcontrollers, used to convert the analogue sensor signal into a digital format for the display.
These micro-controllers allow the introduction of increase sophistication, including, battery state indication, audible indication of leakage, sensor/electronics integrity monitoring, temperature stability, and robust calibration data storage.
Calibration
This last point is a particular advantage since it reduces one of the causes of calibration “drift†and inaccuracy over time. Potentiometers, used in analogue instruments to set the calibration data have a tendency to produce drift over time, as a result of wear, shock or misuse. The prospect of storing the calibration data within an EEPROM in the micro-controller offers a more stable arrangement, less prone to “drift”.
Calibration accuracy is important since without it there can be no guarantee that the displayed value is a true representation of the actual microwave power present.
There are of course “low-cost” instruments available, in which the manufacturer claims such great accuracy that no calibration is required. This is of course incorrect. Calibration is essential, particularly in the case of a safety instrument, where protection of the user and customer is paramount. Accurate calibration requires the use of external equipment to provide a reference source and the term “self-calibrating†refers only to a check that the basic electronic circuitry is functional and does not test the accuracy of the sensor to represent the true microwave power being received.
When considering the purchase of a microwave instrument it is as well to consider which instrument offers the most cost effective option and to avoid instruments that may present problems associated with inaccuracy.
With this in mind I would advise anyone considering a purchase to review a recent study commissioned in the USA by the “International Microwave Power Institute†and presented by Robert F. Schiffmann and Rupert Steiner.
Details may be found by pasting the URL shown below into your browser:
http://www.jmpee.org/jmpee_site/Vol_46%283%29/JMPEE46-3-128Shiffmann.pdf