8.6.4 Selecting The Measurement System

The measurement system should be selected from the assessment question, not from the equipment that happens to be available. The assessor should first identify the applicable exposure quantity and averaging condition, then establish the source frequencies and operating states, field region, expected level and variability, required spatial resolution, and whether individual transmitters must be distinguished.

A practical assessment may begin with a broadband survey, proceed to frequency-selective measurements where source attribution or frequency-dependent summation is required, and add current measurements where conductive structures or contact-current pathways are relevant. Strongly nonuniform fields, close-body sources, or comparison with basic restrictions may instead require a standardized laboratory method or computational assessment.

Table 8.2 provides a preliminary guide to common RF assessment objectives, quantities, and methods. The final selection must be confirmed against the applicable assessment standard and the documented capabilities of the complete measurement or computational system.

Table 8.2. Typical selection of RF assessment methods.

Assessment Objective	Principal Quantity	Typical Method and Qualification
Rapid Broadband Screening	Total electric- or magnetic-field strength	Suitable broadband field meter; valid only when its frequency response, dynamic range, and comparison method cover the contributing sources.
Identify Individual Sources or Assess Combined Exposure	Source-specific E, H, or S contributions	Frequency-selective measurement system; apply the frequency-dependent limits and required summation.
Reactive Near-field Assessment	Electric- and magnetic-field strengths, or a relevant dosimetric quantity	Separate E- and H-field measurements, or a validated laboratory or computational method; do not use plane-wave conversion.
Radiating Near-field or Large-aperture Assessment	E, H, S, or a relevant dosimetric quantity	Source-specific spatial measurement or computation; field nonuniformity and method validity must be addressed.
Far-Field Assessment	Electric field, magnetic field, or power density	Suitable broadband meter or calibrated antenna system; one quantity may suffice when far-field conditions are established and the applicable standard permits. RPS S-1 requires both E and H from 100 kHz to 30 MHz.
Induced Limb-current Assessment	Induced limb current	Measurement arrangement specified by the applicable standard; conductor current is not automatically limb current.
Contact-current Assessment	Contact current	Risk-management assessment using a suitable contact-current arrangement where useful. RPS S-1 provides guidance rather than a numerical contact-current restriction; superseded RPS3 limits are not current compliance criteria.
Diagnose Currents in Conductors or Structures	Conductor current	Clamp-on RF current probe; useful for investigation and control design, but not automatically an exposure quantity.
Close-body or Basic-restriction Assessment	Induced electric field, SAR, or absorbed power density	Standardized phantom measurement or validated computational model; an external field meter alone is insufficient.
Supplementary Worker Warning	General RF field indication	Personal RF monitor; useful as a warning or control device, but not normally a substitute for a documented compliance assessment.

Personal RF monitors can provide useful warning or exposure-management functions for workers, but their alarm response, wearing position, body shielding, frequency response, and calibration must be understood. Unless the applicable method expressly permits it, a personal monitor should not be treated as a substitute for a documented compliance survey.

No single instrument is suitable for every RF safety assessment. A defensible result depends on matching the complete system to the quantity, frequency, field region, source behavior, environmental conditions, and uncertainty required by the assessment.