Exposure duration: 12 trials of 25 s each
SIAM adaptive procedure
Exposure duration: 100 consecutive trials of 25 s each
SDT rating procedure
|Exposure room||Experimental chamber was located in a high voltage laboratory in the center of a shielded test room with three high electrodes located in the ceiling. High voltage power sources were located outside the chamber.|
|Setup||Attempts were made to eliminate equipment sound and corona noises as well as a recording of audible noises from an actual high voltage DC transmission line was played in the chamber during the experiment.|
|Additional info||SIAM (single interval adjustment matrix) adaptive procedure was a yes-no single interval procedure in which half of the trials were signal trial and the other half no-signal. During the signal trials, fields and ions were presented at a certain intensity and depending on the answer the intensities and ions were either increased or decreased in 2 kV/m steps in the next trials. Fields and ions of positive polarity were generated. Fields were presented either alone in combination with ions.|
|Additional info||Specific combination of DC fields and ion currents were presented in the signal trials and no fields or ions were presented on the non signal trials. Both of these trials were presented equally. In SDT trials, the subjects were suppose to tell if the signal was 1) surely present, 2) rather certain about the presence, 3) unsure 4) rather certain about absence and 5) certain about the absence. Half of the signals were presented at high field intensity (40 or 47.5 kV/m) and the other half at low field intensity (17.5 or 25 kV/m) along with either 0, 60 and 120 nA/m² ion current. 120 nA/m² was not presented with 47.5 kV/m and 17.5 kV/m.|
|electric field strength||17.5 kV/m||-||calibration||-||lower intensity|
|electric field strength||25 kV/m||-||calibration||-||lower intensity|
|electric field strength||40 kV/m||-||calibration||-||higher intensity|
|electric field strength||47.5 kV/m||-||calibration||-||higher intensity|
Subjects were significantly more likely to detect direct current fields as the intensity increased. They were able to detect the presence of direct current fields alone, but only at high intensities; the average threshold was 45 kV/m. The simultaneous presence of ions facilitated the perception of direct current fields, but only at relatively high concentrations or current densities (i.e. 120 nA/m²). Data analysis also revealed large variations in perceptual thresholds among the subjects.
These data can form the basis for environmental guidelines relating to the design of high voltage direct current transmission lines.