Electrical transmission or interconnection systems – Wave form or wave shape determinative or pulse-producing...
Patent
1994-05-26
1996-04-02
Wong, Peter S.
Electrical transmission or interconnection systems
Wave form or wave shape determinative or pulse-producing...
327 77, 327 18, H03K 522
Patent
active
055043801
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention relates to a method of controlling a current generator, which generator has two voltage inputs and a current output connected to a load, and generates a current on the output that is proportional to the difference voltage of the voltages on the inputs. The invention also relates to an apparatus for use with the method.
BACKGROUND OF THE INVENTION
In many devices in the field of control engineering, e.g. regulators, actuators and sensors for proportional control, output values, i.e. desired values and actual values for e.g. valve positions and temperatures, are generally represented by the voltage of an analogue signal that can range between e.g. 0 and 10 volts. In many other devices receiving these analogue signals, these values are expected to be in the form of a current signal, e.g. 0 to 20 mA.
This constitutes a problem, as not all devices will interact, when the output of one device does not correspond to the expected input of another device. In certain devices the mode of operation, i.e. current control or voltage control, can be switched by means of a jumper, e.g., but this switch means one more installation step and it can also lead to an incorrect installation. Also, two separate solutions, one for current control and one for voltage control, lead to a higher cost for electronic circuitry.
OBJECT OF THE INVENTION
Accordingly, the main object of the present invention is to achieve such a method of controlling the output of a current generator that this output is automatically adapted to the preferred mode of operation of a receiving device. The invention also relates to an apparatus for implementation of this method.
SUMMARY
The present invention is based on the realization that the abovementioned object can be achieved using the fact that a current controlled input has a much lower input impedance than a voltage controlled input.
According to the invention, this object is achieved by a method of controlling a current generator having two voltage inputs and an output connected to a load, which generator generates on the output a current proportional to the difference voltage of the voltages on the inputs, so that, if the impedance of the load is lower than a predetermined first lower limiting value, the current generator is controlled in a non-feedback way to generate a signal on the output of the generator, the current value of which signal is determined by said input voltage, and that, if the impedance of the load is higher than a predetermined second limiting value larger than said first limiting value, the output signal of the current generator is negatively fed back to generate an output signal on the output of the generator, the voltage value of which signal is determined by said input voltage.
The invention also relates to an apparatus using the method according to the invention.
The invention provides a technique that eliminates the abovementioned problems connected with adaption of the modes of operation of interconnected devices.
BRIEF DESCRIPTION OF THE DRAWING
The invention will be further described by means of an example with reference to the accompanying drawing, in which:
FIG. 1 is a general diagram of an apparatus according to the present invention,
FIG. 1b shows the characteristics of an amplifier incorporated in FIG. 1, and
FIG. 2 is a circuit diagram of an embodiment of an apparatus according to the present invention.
EXAMPLE OF AN EMBODIMENT
The device according to FIG. 1 comprises, besides a current generator 1, a high gain amplifier 3 with essentially infinite input impedance, which amplifier has ground and a voltage +V as power supplies. The output signal V.sub.out of the current generator is supplied to the positive input 11 of the amplifier 3, and an input V.sub.in is supplied to the negative input 12 of the amplifier from a voltage input 2, which input signal can represent e.g. a desired or an actual value. The output of the amplifier is connected to the negative input 10 of the current generator. The characteristics of the ampl
REFERENCES:
patent: 4417151 (1983-11-01), Klein et al.
patent: 4603299 (1986-07-01), Monett
patent: 4665327 (1987-05-01), Bacrania et al.
patent: 4926140 (1990-05-01), Schenberg
Krishnan Aditya
Landis & Gyr Building Control AB
Wong Peter S.
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