Electrical transmission or interconnection systems – Capacitor
Reexamination Certificate
1999-03-25
2001-05-01
Jackson, Stephen W. (Department: 2836)
Electrical transmission or interconnection systems
Capacitor
C307S125000, C307S129000
Reexamination Certificate
active
06225710
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a process for operating a capacitive switch, the switch having an oscillator which delivers a measurement signal, a capacitive sensor consisting of at least one sending electrode and one measurement electrode, and an evaluation circuit. In addition, the invention relates to the circuit of a capacitive switch, with an oscillator, with a gauge length and an evaluation circuit, the oscillator delivering a measurement signal and the gauge length having at least one sensor with a sending electrode and a measurement electrode.
2. Description of the Related Art
Switches, especially inductive and capacitive switches, are used in a host of very different applications in industrial engineering. They can be both switches which operate without contact, i.e. those in which the actuation object simply approaches the active surface of the switch, which are then usually called proximity switches, and also contact switches, i.e. those in which the actuation object touches the active surface of the switch. It is common to these switches that they are so-called open electronic systems, i.e. the active sensors are not entirely shielded and thus release electromagnetic radiation and signals into their vicinity and vice versa pick up electromagnetic radiation and signals from the vicinity. This circumstance can on the one hand lead to noise emissions of the switch, on the other hand to incident noise into the switch.
The aforementioned problem has been addressed in switches by on the one hand the active sensors being at least partially shielded, on the other hand by the voltage on the sensors being reduced. The two however lead automatically to a lower maximum possible object acquisition distance—generally called the operating distance—and/or to a poorer ratio of the useful signal to the noise signal.
Due to the increasing popularity of devices which emit electromagnetic radiation and signals, such as mobile telephones or remote controls, and due to increased use of switches also in the vicinity of these electromagnetic signal-emitting devices, malfunctions of switches and/or electronic devices by noise emissions and incident noise can occur to an increasing degree. One example is the use of capacitive switches in the door handles of motor vehicles, which on the one hand are disrupted by the emitted signals of a car phone and on the other hand can interfere with the car phone itself.
SUMMARY OF THE INVENTION
Thus the object of this invention is to make available a process for operating a switch or a circuit of a switch in which noise emission or sensitivity to incident noise is reduced.
The aforementioned object is achieved according to a first teaching of the invention in the initially described process by the measurement signal being frequency-spread by a noise signal delivered by a noise source, by the frequency-spread measurement signal on the one hand being sent preferably via a matching network to the first input of a correlator and on the other being emitted by the sending electrode of the capacitive sensor, by the received signal picked up by the measurement electrode of the sensor being sent to the second input of the correlator and by the output signal of the correlator being sent to the evaluation circuit. According to a second teaching of the invention the aforementioned object in the initially described process is achieved by a second oscillator generating an auxiliary signal which has the same or a slightly different frequency from the measurement signal, by the measurement signal and the auxiliary signal being frequency spread by a noise signal delivered by the noise source, by the frequency-spread measurement signal being emitted by the sending electrode of the capacitive sensor, by the frequency spread auxiliary signal—preferably via a matching network—being sent to the first input of a correlator, by the received signal picked up by the measurement electrode of the sensor being sent to the second input of the correlator and by the output signal of the correlator being sent to the evaluation circuit.
The frequency spreading of the measurement signal which takes place by means of a noise signal according to both the first and second teaching of the invention increases the bandwidth and thus reduces the spectral energy density of the measurement signal without the need to reduce the voltage on the sensor. In this way, on the one hand the amplitude of the emitted noise signals is reduced, on the other hand the maximum allowable amplitude of a noise signal emitted into the switch is increased. Thus both the interference of the switch with other devices and also the sensitivity of the switch to noise by other devices are reduced.
It is therefore critical for the teaching of the invention that the measurement signal not be of a single frequency or be narrowband, but that it be located within a broadband frequency spectrum.
According to a first advantageous embodiment of both the first and second teaching of the invention the frequency spreading of the measurement signal or the auxiliary signal is produced by frequency modulation of the measurement signal or the auxiliary signal with the noise signal. For frequency modulation a transistor is advantageously used which is used at the same time as a noise amplifier. In this process it is especially advantageous that only very few components are needed and overall power consumption is very low. This process is especially suited for noncritical sensor applications, i.e. in those sensors which do not require a large operating distance. One possible application of this process is use in a capacitive motor vehicle door handle in which it is important that the switch consumes only very little power so that the battery is not discharged when the motor vehicle is idle for a longer time.
According to one alternative advantageous embodiment of the process according to the first or the second teaching of the invention the frequency spreading of the measurement signal or the auxiliary signal is produced by phase shift keying of the measurement signal or the auxiliary signal. In phase shift keying which takes place preferably using a binary random signal obtained from the noise signal, very high noise immunity can be achieved by 0/180° phase shift keying. In this process then a correlation is possible when a permanent electrical connection between the transmitter and the receiver is not possible or not wanted. In this case the correlation code would then have to be stored and transmitted.
Within the framework of the invention a measurement signal as such can be abandoned, therefore the noise signal can be used as the measurement signal. Then of course it is not possible using the second correlator from the broadband receive signal to generate one which is of a single frequency or which is narrowband.
The object of the invention in the initially mentioned circuit of a switch is achieved in that there are a noise source and two correlators, that in the first correlator frequency spreading of the measurement signal takes place by a noise source, that the frequency-spread measurement signal on the one hand is connected to the first input of the second correlator and on the other to the sending electrode and that the measurement electrode is connected to the second input of the second correlator. With this circuit the process according to the first teaching of the invention can be used to special advantage. The circuit is thus made especially simple and power-saving by using the emitter diode of a transistor as the noise source in breakdown operation. In the sense of a circuit which requires only a few parts it is advantageous if as the first correlator there is a second transistor which is used both as a noise amplifier and which also accomplishes frequency modulation of the measurement signal with the noise signal.
A correlator in the sense of this patent application is defined as an electronic component with which averaging of products (correlation) is done. Here the product co
Palata Jaromir
Schulz Jorg
i f m Electronic GmbH
Jackson Stephen W.
Nixon & Peabody LLP
Polk Sharon
Safran David S.
LandOfFree
Process for operating a capacitive switch and a circuit of a... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process for operating a capacitive switch and a circuit of a..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for operating a capacitive switch and a circuit of a... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2519666