Communications: electrical – Continuously variable indicating – With particular transmitter
Patent
1994-08-24
1997-04-15
Mullen, Thomas
Communications: electrical
Continuously variable indicating
With particular transmitter
324660, 7351432, G08C 1910
Patent
active
056213999
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention deals with a circuit arrangement according to the preamble of the first patent claim.
BACKGROUND OF THE INVENTION
Various circuit arrangements such as for instance bridge- and charge amplification circuits are known for analyzing sensor signals. These types of circuits require mostly more extensive technical resources for proper signal editing by microcomputers and are therefore not very cost effective. Sensor circuits operated in a LC-oscillatory circuit are also known, which provide a frequency signal, which can indeed be directly analyzed in a downstream located microprocessor for the ensuing signal processing; however they have the disadvantage that these oscillatory circuit arrangements are greatly affected by temperature changes, so that a temperature compensation located downstream is required in most application cases.
SUMMARY OF THE INVENTION
The subject of the present application is meant to use a novel method for process-equitable editing of sensor signals, which is particularly suitable for transducer applications in motor vehicles. Here the expression transducer means a device, which as a component contains the sensor element proper as well as a first electronic circuit arrangement analyzing the signal measured by the sensor, in order to provide a measured signal at the transducer output, which is suitable to be conveyed meaning to be transferred also across long distances. The special motor vehicle relevancy deals with the rough environment in which the transducer is to be operated, as for instance extreme temperature differences, as well as also with the requirement for being suitable for an economical mass production.
Therefore the invention is based upon the task, of creating a simple and thus economical analysis circuit for sensor signals from a capacitive transducer, which circuit itself compensates for temperature effects, where the sensor element can have a very small capacitance and where the circuit produces at its output an electrical signal able to be transported, which can be analyzed by a microprocessor without any additional signal conversion.
This task is solved by the characteristic features of the first and second patent claim.
The circuitry in the invention can be built up extremely economically with the simplest means. The PWM (pulse width modulated) output signal can be transmitted also across large distances without impairing the information content. The output signal is digital, thus a A/D (analog/digital) converter is not required. The pulse duration containing the information content of the magnitude measured by the sensor can be analyzed in the simplest way in the microprocessor. For instance the analysis can occur in such a way, that the duration of pulse and pause for one period can be determined by two counters of the processor. Subsequently the processor forms in a simple computational step the divisional ratio as a measure for the excursion of the mobile central electrode configured as a flexural resonator. If necessary the output signal can be converted by a simple RC (resistance capacitance) low pass filter into an analog voltage signal.
Depending upon the type of the differential transducer a trimmable very slight non-linearity is achievable by this circuit. Pertinent subsequently measured signal corrections need not be performed for many applications. The differential capacitance principle acts in a self-compensating manner in case of environmental interferences, so that for instance the temperature drift is extremely low. The circuit structure permits, due to the principle on which it is based, to achieve in actual practice a very high temperature stability and a very high resolution of the measured signal without any additional measures. This circuit has a very low inherent current consumption and also requires only a unipolar voltage source (VCC), which when CMOS (complementary metal oxide semi-conductor) structural elements are used, permits a wide voltage supply range. Since the circuit is defined so as
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Edwards, Jr. Timothy
Mannesmann Kienzle GmbH
Mullen Thomas
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