Proximity detector
A circuit for generating an indicative signal regarding the approach of an object to an observation area has a send electrode device, a generator circuit for supplying alternating voltage to the send electrode device, a receive electrode device which extends in or along the observation area, and an output circuit for generating an output signal correlating with the field at the receive electrode device. A compensation circuit is provided to add a compensation current i 2 to a signal current i 1 flowing from the receive electrode device.
1. A circuit for generating a signal indicating the approach of an object to an observation area, the circuit comprising:
a send electrode immediately adjacent the observation area;
a generator for supplying alternating voltage to the send electrode to create adjacent the send electrode in the observation area an alternating electrical field;
a receive electrode extending in or along the observation area for outputting an alternating electrical signal current i 1 that varies as the object enters the area,
a compensator for adding to the outputted signal current i 1 of the receive electrode an alternating compensation signal current i 2 having a phase offset by 180° to the signal current i 1 , and
an output circuit for receiving the added signals i 1 and i 2 and generating an output signal correlating with the field at the receive electrode.
2. The circuit in accordance with claim 1 wherein the compensation current is triggered via the generator voltage.
3. The circuit in accordance with claim 1 wherein the amplitude of the compensation current is adapted in accordance with the output signal.
4. The circuit in accordance with claim 1 wherein the output circuit is in the form of an i/u converter.
5. The circuit in accordance with claim 1 wherein the compensation circuit is a microcontroller.
6. A method of generating a signal indicating the approach of an object to an observation area, the method comprising the steps of:
feeding to a send electrode immediately juxtaposed with the observation area an alternating current to form in the area an alternating electrical field,
detecting the field with a receive electrode extending in or along the observation area and outputting a signal current, and
adding to the outputted signal current i 1 of the receive electrode an alternating compensation signal current i 2 having a phase offset by 180° to the signal current i 1 , and
generating with an output circuit an output signal correlating with the field at the receive electrode.
7. The method in accordance with claim 6 wherein the output signal is generated using a converter coupled with the receive electrode device.
8. The method in accordance with claim 6 wherein the output signal is suspended in the area of the compensation circuit.