System for detecting human presence in hazardous situations

Details System for detecting human presence in hazardous situations System for detecting human presence in hazardous situations

1993-05-13

1995-07-25

Peng, John K.

Communications: electrical

Condition responsive indicating system

Specific condition

340904, 324666, 324663, 395 90, 395 88, 395 97, 395124, G08B 2300

Patent

active

054366135

ABSTRACT:
The disclosure relates to a system for the detection of human presence in hazardous situations near moving machinery; appropriately shaped electrodes are placed in an area to be safeguarded and a radio-frequency signal of appropriate frequency and voltage is applied on the electrodes creating an alternating electric field around them. A bridge circuit is used to measure the capacitive impedance created by the electrodes and a dissipation factor is calculated from the real and imaginary parts of the impedance. If a foreign object is introduced into the electric field, the characteristics of the dielectric are modified creating a change of the value of the dissipation factor. The dissipation of energy in the high frequency region is much greater if this foreign object is a biological tissue as compared to other types of materials, such as conductors or insulators. Thus, the system detects human presence by noting the increase of the dissipation factor above a threshold value, and the movement of the appropriate machine part can then be stopped, thereby eliminating the danger of injury to the person.

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ND 1618-126-87 Institute National de Recheche et de Secutete 30, rue Olivier-Noyer 75680 Paris Cedex 14, France.

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