Communications: electrical – Continuously variable indicating – Plural circuits – each for particular magnitude
Reexamination Certificate
1999-08-20
2002-08-06
Edwards, Timothy (Department: 2635)
Communications: electrical
Continuously variable indicating
Plural circuits, each for particular magnitude
C340S870110, C340S853200
Reexamination Certificate
active
06429786
ABSTRACT:
TECHNICAL AREA
The invention relates to a sensor and evaluation system for acquiring data at a measuring point, especially for double sensors for detecting final positions and limit values, consisting of at least two sensors that are connected via a control circuit to a remotely located switching amplifier with a current source or voltage source, whereby a connection wire leads from the current source or voltage source to the sensor and another connection wire leads from the sensor to an evaluation unit, and the sensor signal of each sensor normally consists of a change in the current flow as compared to the current flow in the quiescent state of the sensor and said sensor signal is transmitted via the control circuit to the switching amplifier in order to be evaluated there in an evaluation unit and to be output at an output stage in the form of signals (e.g. binary ZERO, ONE) as a function of the sensor and of the time, according to the generic part of claim
1
.
STATE OF THE ART
Sensors are normally connected by two connection cables or by a two-core connecting line to a switching amplifier which supplies the sensors with direct current or direct voltage. The sensor signal consists in a change in the strength of the direct current flowing through the sensor to the evaluation unit as compared to the current flow in the quiescent state of the sensor. For example, an oscillator that is integrated into the sensor vibrates when the current circuit is closed and, in the quiescent state, i.e. without an object to be measured, it consumes a certain current, which is measured as the quiescent signal. If an object to be measured is brought closer to the active surface of the sensor, then the current consumption of the sensor changes, for example, as a result of eddy-current losses in the object to be measured, and thus the current flow in the evaluation unit also changes. The sensor signal is measured and amplified in the evaluation unit, and an output stage—depending on the signal level, e.g. when the value exceeds or falls below a certain switching threshold—generates a switching signal, e.g. binary “zero” or “one”. The switching signal informs the user whether a certain state of the object to be measured is present, for instance, a certain spatial position or a certain pressure.
For many applications, it has to be determined whether the state of the object to be measured lies within certain tolerance limits. Therefore, in order to ascertain these two limit values, two sensors, i.e. a double sensor consisting of a sensor pair, with four connection wires are needed. This calls for quite complex wiring, which is disadvantageous for many applications. In particular in the realm of chemistry, electric lines should be reduced to a minimum. For this purpose, it is known to combine the two control circuits for double sensors on one side, thereby reducing the four connection wires to three. However, when work is done with inherently safe control circuits corresponding to DIN 19234 NAMUR), this has the drawback that the resultant sum current has to be taken into account in the verification of the inherent safety since, with NAMUR which provides that each of two sensors is a two-wire direct current sensor that operates at 8.2 V with switch points operating between 1.2 to 2.1 mA systems, failures such as line breaks or short circuits are checked via the current in the interface between the sensor and the switching amplifier.
Moreover, for numerous applications, more than two states of the object to be measured are to be detected with one system consisting of several sensors. Here as well, two connection wires per sensor or, if applicable, three per sensor pair constitutes quite complicated wiring and there is a need for subsequent electronic devices that are capable of receiving the connection cables and processing the corresponding signals. This is complex in terms of assembly and documentation, and entails potential sources of error.
Another disadvantage of the state of the art is that inductive sensors cannot be mounted at a location too close to a sensor system since they influence each other if they are in operation at the same time, thereby distorting the measured result.
DE 40 33 053 C1 describes a measured value acquisition and transmission device, consisting of a pick-up unit and a detection unit, which can be coupled together inductively for purposes of measured value transmission. The measured value acquisition and transmission device is supposed to prepare and transmit measured data in such a way that, first of all, environmental influences are eliminated to the greatest extent possible and secondly, the measured data can be transmitted interference-free and contact-free, even over long transmission distances. The elimination of environmental influences, for example, high temperatures, is achieved in that the pick-up unit—in addition to a measuring oscillator circuit—also comprises a reference circuit. The oscillation frequency of the measuring oscillator circuit changes primarily as a result of changes in the measured quantity to be monitored, for example, the pressure, but it is also influenced and distorted by environmental influences such as, for example, temperature changes. The reference circuit mimics the measuring oscillator circuit, but it is not capable of reacting to changes in the measured quantity. Its frequency changes only with the environmental influences. Therefore, interfering environmental influences should be eliminated by forming the quotient of the output signal of the measuring oscillator circuit and the output signal of the reference circuit. The quotient is formed in an electronic computing circuit.
The output signal of the electronic computing circuit is transmitted inductively from the pick-up unit to a detection unit. The computing circuit supplies a quasi digital signal that can be transmitted inductively without being very interference-prone. The information on the state of the object to be measured is contained in the frequency of this signal or in the number of counting pulses per unit of time.
TECHNICAL OBJECTIVE
The invention is based on the objective of creating a sensor and evaluation system of the type described above, in which the configuration of the individual sensors to form a system is simplified and the wiring effort between the sensors and the switching amplifier is reduced, and which allows an individual monitoring of the operating state of the individual sensor, a close spatial configuration of adjacent sensors without influencing each other and a compact design of the switching amplifier.
DISCLOSURE OF THE INVENTION AND ITS ADVANTAGES
With a sensor and evaluation system for acquiring data at a measuring point, especially for double sensors for detecting final positions and limit values, of the type described above, the achievement of the objective is characterized by the following features: a) two sensors—a sensor pair—are associated together with each of the two connection wires to form the control circuit; b) an alternating current or alternating voltage interface is associated with each sensor pair, and said interface is located in the vicinity of the sensors and is capable of transmitting positive signals to and from one sensor as well as negative signals to and from the other sensor of the sensor pair, whereby the two sensors of the sensor pair are connected together antiparallel and are always operated alternately with respect to each other; c) on the basis of the polarity of the signals, the switching amplifier establishes the association of the sensor signals of a sensor pair that are transmitted via the same connection wires to the sensor in question; d) the current source or voltage source is a current source or voltage source with an alternating polarity.
In another advantageous embodiment of the invention, in order to form the alternating current or alternating voltage interface of the connection wires that establish the connection to the switching amplifier, a short connection wire with a series-connected diode branches
Bansemir Werner
Jung Gerhard
Edwards Timothy
Kasper Horst M.
Pepperl + Fuchs GmbH
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