8.6 RF MEASUREMENT INSTRUMENTS
An RF measurement result is produced by a complete measurement system. The system includes a sensor, probe, or antenna that couples to the field; a detector or receiver that converts the response into a usable signal; and processing and display functions that calculate and present the measured quantity. The indicated unit alone does not establish that the system is suitable for a particular assessment.
Selection begins with the assessment objective and the applicable measurement method. Relevant factors include the quantity to be determined, operating frequency, field region, expected field level, spatial variation, modulation and time variation, required frequency selectivity, and acceptable measurement uncertainty. The probe dimensions and response must also be appropriate for the spatial and temporal averaging required by the applicable exposure standard.
RF safety measurements commonly use three broad classes of equipment. Broadband field meters provide a rapid indication of the combined field within a specified frequency range. Frequency-selective systems identify and quantify individual frequency components. Current-measurement systems determine RF currents in limbs, conductors, or standardized contact-current arrangements. These systems answer different questions and are often used in combination.
The instrument, sensor, cables, accessories, and software settings should be treated as one measurement system. Calibration must be current, traceable, and applicable to the frequency range, field-strength range, and configuration being used. Any corrections, limitations, and uncertainty contributions must be carried through to the reported result.