Communications: electrical – Condition responsive indicating system – Specific condition
Reexamination Certificate
1999-04-26
2002-06-11
Tong, Nina (Department: 2632)
Communications: electrical
Condition responsive indicating system
Specific condition
C340S573100, C340S573400, C340S568100, C340S010100, C340S870030, C340S870030
Reexamination Certificate
active
06404338
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention concerns a measuring and/or security system of the type given in the precharacterizing clause of Claim
1
.
2. Description of Related Art
Measuring and security systems are needed today in a multiplicity of types for the most varied of applications. One of these is the protection of objects against theft.
A system of this type is known, for example, from the German published patent application DE 36 18 416 A1, and consists essentially of two transmitting/receiving devices, one of which is installed on the object to be protected, while the other is arranged in fixed fashion in a monitoring unit. During operation, the two transmitting/receiving devices communicate with each other, with the one transmitting/receiving device generating a control signal, to which the other transmitting/receiving device answers with an acknowledgment signal. After receipt of the acknowledgment signal, the transmitting/receiving device that radiates the control signal measures the time difference between the sending out of the control signal and the receipt of the acknowledgment signal, and upon exceeding a prescribed signal transit time triggers an alarm.
In the case of the previously-known measuring and/or security system, however, it is disadvantageous that the transmitting power required for a certain transmission of data between the two transmitting/receiving devices is relatively high.
For one thing, this limits the operating time of the security system, since the transmitting/receiving device installed on the object to be protected is battery operated. For another thing, because of the relatively high transmitting power, it can result in interference with other communication systems, in particular other security systems.
Therefore, the task underlying the invention is to obtain a measuring and/or security system of the initially-mentioned type having a reduced transmitting power.
This task, starting out from a measuring and/or security system based on the pre-characterizing clause of Claim
1
, is resolved by the characterizing features of Claim
1
.
SUMMARY OF THE INVENTION
The invention includes the technical teaching of generating on the transmitter side, as control and/or acknowledgment signals, pulses that shift in frequency over the duration time of the pulse, and of compressing these pulses on the receiver side by means of dispersion filters.
A dispersion filter of this type is, in principle, actually known from the European patent application EP 0 223 554 A2, without more detailed application instructions having been given.
The invention starts out from the knowledge that the pulses transmitted as control and/or acknowledgment signals, for achieving a high precision when measuring distance, may display only a slight temporal imprecision. On the other hand, in order to be able to transmit these types of short pulses, a relatively wide bandwidth is required.
With the invention a measuring and/or security system for measuring distance is created that is based on a measurement of the signal transit time, and that, even with a low transmitting power in signal-interference surroundings, nevertheless can operate with a minimum temporal imprecision of the emitted signal.
In the case of the measuring and/or security system in accordance with the invention, chirp signals are radiated for determination of transit time, said chirp signals being compressed in time in the receiver by a suitable dispersion filter, in order to achieve a low temporal imprecision as a presupposition for an exact distance measurement, and furthermore to raise the amplitude on the receiver side.
In addition to this, at least one of the transmission systems displays on the transmitting side a signal source that generates, as a measurement signal, pulses—also designated as chirp signals—having a frequency that falls or rises monotonically during the duration of the pulse and that corresponds to a prescribed, preferably linear, modulation characteristic curve. However, it is not necessary that the modulation characteristic curve be linear. It is critical merely that the frequency, in each instance, rise or fall monotonically, in the mathematical sense, over the duration of the pulse.
On the other hand, the receiving transmission system displays for pulse compression a dispersion filter having a frequency-dependent signal transit time corresponding to a prescribed filter characteristic curve. It is important here that the filter characteristic curve be matched to the proposed modulation on the transmitter side such that the signal portions of the modulated pulses corresponding to this modulation characteristic curve, because of the different frequency-dependent signal transit time through the dispersion filter, appear at its output essentially coincidentally, and subsequently with lesser temporal imprecision.
In one variant of the invention, as an approximation, a Dirac pulse is first generated and fed to a low-pass filter whose filter characteristic displays a peaking shortly before reaching the limit frequency, and therewith transforms the Dirac pulse into a sinc pulse, whose form is described by the known sinc function sinc (x)=
sin x
/
x
. The sinc-form output signal of the low-pass filter is next passed over to an amplitude modulator, which impresses on the carrier oscillation a sinc-form envelope. If the signal generated in this fashion is fed to a dispersion filter, then appearing at the output is a frequency modulated pulse. In this variant of the invention, therefore, there first follows on the transmitter side an expansion of the relatively sharp sinc-pulse through the dispersion filter into a frequency modulated pulse, which in comparison to the sinc-pulse is lengthened, and displays a correspondingly lower amplitude.
According to another variant of the invention, generation of the frequency modulated pulse, on the other hand, is accomplished by means of a PLL-loop (PLL: Phase Locked Loop) and a Voltage Controlled Oscillator (VCO). For this purpose, a square pulse is first converted into a sawtooth shaped pulse. The pulse generated in this fashion is then used for control of the VCO, such that the frequency of an output pulse increases or decreases linearly during the duration of the pulse.
In another variant of the invention, generation of the frequency modulated pulse is accomplished in the digital signal processing unit, which advantageously enables realization of random modulation characteristic curves.
The previously mentioned dispersion filters are preferably realized as Surface Acoustic Wave (SAW) filters, since these types of filters can be produced with a high degree of precision and stability. Moreover, these types of surface acoustic wave filters offer the advantage that amplitude response and phase response can be dimensioned independently of one another, which opens up the possibility of realizing, in a single structural element, the narrow band bandpass filter and the dispersion filter required in each receiver.
According to the invention, distance measurement between two previously described transmission systems is accomplished with one transmission system preferably being installed on or in the object of measurement, and with the other transmission system preferably being arranged in fixed fashion.
For distance measurement, the first transmission system generates, by means of a transmitter, a measuring signal that is radiated to the second transmission system and there detected by a receiver. Measurement of the signal transit time is accomplished by a time measuring device that is connected on the input side with the receiver of the second transmission system.
Interval determination is accomplished by determining the time duration of signal travel, to and return, between two transmitter and receiver pairs. Distance measurement is introduced herewith by the transmitter of the second transmission system emitting a measuring signal—also designated in the following as a control signal—to the receiver of the first transmission sy
Altera Law Group LLC
Nanotron Gesellschaft fur Mikrootechnik mbH
Tong Nina
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