Objective To understand the configuration, calibration, and performance of power frequency electric field measuring in struments in Guangdong occupational hygiene technical service agencies by inter-laboratory comparison.
Methods Forty power frequency electric field measuring instruments were selected from 40 occupational hygiene technical service agencies in Guangdong Province, and calibration certificates were examined. Using a transformer as standard source, measurements were conducted at 1.0 m distance from the transformer at different time periods, and homogeneity was evaluated by one-way ANOVA. Spot measurements were then conducted at 1.5 m and 2.0 m distance from the standard source by surveyors from each agency using respective measuring instrument, and the measurement results were analyzed by z-score.
Results Homogeneity analysis results showed that there was no statistical difference in electric field intensity among three selected time periods(209.52±0.38), (209.96±0.51), and (209.74±0.60) V/m for afternoon of the first day, morning of the second day, and afternoon of the second day, respectively, P > 0.05, indicating that the standard source was qualified for inter-laboratory comparison in terms of stability. One measuring instrument was unable to provide calibration certificate, calibration certificates of two instruments were expired, and one instrument's calibration result was not within tolerance range. The inter-laboratory z-score (zB) of 40 measuring instruments ranged from -1.16 to 13.41, while the intra-laboratory z-score (zW) ranged from -1.29 to 25.26. Both|zB|and|zW|of two instruments were above 3.00, and the|zB|of another instrument was above 3.00, indicating outliers; the|zB|or|zW|of four instruments were above 2.00, indicating problematic results. In light of those results, three instruments were unqualified.
Conclusion It is feasible that a transformer could be applied as standard source in inter-laboratory comparison of power frequency electric field measuring instruments. There are still problems in the use of power frequency electric field measuring in struments in Guangdong occupational hygiene technical service agencies.
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