|
|
|
A free electronic newsletter covering news and other topics for those interested in RF safety issues.
LIVE, Web-Based RF Safety Training
|
Contents
Accuracy of Survey InstrumentsThe accuracy of a survey instrument is almost entirely driven by the accuracy of the sensors. Many sensor specifications are expressed in the logarithmic ratio of dB. A parameter that has a 1.0 dB tolerance means the value could be off by 26%. In contrast, even a simple meter should be accurate within a maximum of 5%.
Richard Strickland filed comments to the FCC on Measurement Uncertainty in response to their Notice of Proposed Rulemaking. These comments provide an overview of much of the discussions in this section on equipment accuracy and frames them in the context of typical measurement environments. Read the Comments on Measurement Uncertainty. Defining AccuracyIt is almost impossible to define the “overall accuracy” of a survey instrument because accuracy depends not only the instrument but also what is being measured and the techniques that are used to make the measurements. The best that one can do is to estimate the overall measurement “uncertainty” for a particular set of conditions and qualify that the uncertainty is valid providing that the equipment is used properly. There are several parameters that you should look at when attempting to establish the level of measurement uncertainty. The parameters are listed in order of importance, i.e. the parameters that can result in the greatest uncertainty are listed first. The list assumes that the probe is well designed and appropriate for the measurement task. See Specifications and What They Mean for descriptions of each parameter and information on acceptable specifications for each parameter.
What the Specifications MeanThere are several factors to consider when you attempt to understand both the overall specifications of a survey instrument and the specifications of specific parameters. For specifications that are given by the manufacturer look at:
What the Specifications Do Not Tell You Many important specifications are often shown by manufacturers. Often this is because they do not know how the equipment will perform under certain conditions. Sometimes specifications are purposely omitted or presented in a confusing manner so that the average person will not figure out exactly how big a problem there might be. Some important parameters that are often not specified include:
See Measurement Artifacts for additional information. Accuracy of RF Personal Monitors The specifications for RF personal monitors are similar to those for RF survey instruments. A personal monitor includes a sensor and a metering circuit. In addition, a personal monitor includes one or more alarm devices. All personal monitors include at least one audible alarm. Some personal monitors include multiple audible alarms, a vibratory alarm, and visual indicators. The visual indicators are usually LEDs but LCD displays are used in some models. The major difference between an RF personal monitor and a survey instrument is that the RF personal monitor must accurately measure RF fields while it is attached to a human body! In general, you cannot measure RF fields through the body. Therefore, an isotropic (omni-directional) sensor is neither needed nor desired. In fact, the biggest technical challenge in designing a good RF personal monitor lies in making the monitor function properly while on the body. This involves making the monitor immune to reflections off the body. Therefore, check the specifications carefully! |
Send mail to
web@rfsafetysolutions.com with
questions or comments about this web site.
|
Measurement
Uncertainty