| 摘要 |
<p>Apparatus for sensing the presence of an article. One end of a very high impedance resistor is held at a fixed voltage. The other end of the resistor is connected to a sensing element. When an article is placed close enough to the sensing element, a form of capacitive coupling to ground is created which causes a minute current flow through the resistor. This causes a small voltage drop across the resistor. The current and voltage difference are presented to a voltage follower which effectively amplifies the current. Sample and hold circuits furnish a signal which indicates the actual voltage level. A minimum level detector measures the voltage level with no article present. This level is compared with the sample and hold signal, and an article present signal is generated if the sample and hold signal is a pre-selected amount greater than the minimum level.</p> |
