Thermal measuring and testing – Temperature measurement – By electrical or magnetic heat sensor
Patent
1995-06-07
1997-03-18
Fulton, Christopher W.
Thermal measuring and testing
Temperature measurement
By electrical or magnetic heat sensor
374142, 364557, 36443103, G01K 702, F02D 4124
Patent
active
056116241
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to a method and a device for digitally measuring an analog voltage that varies over a predetermined voltage range, and more particularly to the use of such a device for measuring a temperature.
In automotive electronics, it is often necessary to measure the temperature of certain fluids, oil or coolant, or devices such as a catalytic converter for oxide reduction of the exhaust gases from a motor vehicle, or an oxygen sensor used in a device for regulating the air and fuel mixture supplied to the engine of such a vehicle. Currently, a suitable temperature pickup furnishes an analog electrical signal to an analog/digital converter, which furnishes a digital expression of the temperature measurement that can be used by a computer that forms part of an open- or closed-loop control unit provided in the vehicle.
The signal output by the pickup is normally an electrical voltage. When the temperature monitored becomes the subject of closed-loop control, this control keeps the signal within a predetermined voltage range. Thus oxygen sensors are known that are associated with a heating resistor actuated in such a way as to maintain the sensor temperature within a very narrow temperature range, for example 650.degree. to 750.degree. C., in which range the signal output by the sensor can be used. If the sensor temperature is evaluated on the basis of the temperature of the heating resistor, whose resistance is a function of that temperature, then the voltage picked up at its terminals to do so also varies within a range whose values are fixed by the limits of the aforementioned temperature range.
It has also been desirable for the temperature of the catalytic converter, around an optimal operating temperature of 850.degree. C., for example, to be known by a computer with a fixed precision of several percent. If a thermocouple is used to do so, then its output voltage varies in a corresponding manner within a predetermined voltage range.
The problem then arises of the precision of the digital measurement of the image voltage of the temperature observed. This precision is a function of the reference voltage V.sub.ref of the converter and of the number of bits n of the measurement N that it furnishes. In the aforementioned applications, measuring the voltage is of interest only within a predetermined voltage range, which a priori does not correspond to the dynamics of the digital measurement chain used, which depends on parameters (V.sub.ref, n) that are independent of this range.
SUMMARY OF THE INVENTION
Accordingly, the object of the present invention is to furnish a method of digital measurement of a voltage that varies within a predetermined range, with the aid of a measurement chain including an analog/digital converter, with which method a maximum measurement precision within this range can be attained.
Another object of the present invention is to furnish such a method that is suitable for measuring an analog voltage affected by the voltage furnished by an electrical power source, which may possibly fluctuate, as is the case of the voltage furnished by the battery of a motor vehicle, by which method a digital measurement freed of any influence of the fluctuations of the voltage can be obtained.
Furthermore, an object of the invention is to use a device for implementing this method that can be used particularly in a temperature measurement chain.
These objects of the invention as well as others that will become apparent in the ensuing description, are attained with a method by which ratio between the reference voltage of the analog/digital converter used and the length of said voltage range; between the lower value of the voltage range to the breadth of this voltage range; and between the thus-amplified voltages.
As will be noted in further detail hereinafter, this method makes it possible to adapt the converter dynamics to the length of the voltage range, so as to advantageously maximize the precision of the measurement furnis
REFERENCES:
patent: 3826983 (1974-07-01), Garratt et al.
patent: 4211113 (1980-07-01), Harrison
patent: 4223549 (1980-09-01), Kitzinger
patent: 4924399 (1990-05-01), Kaiser et al.
Fulton Christopher W.
Greenberg Laurence A.
Lerner Herbert L.
Siemens Aktiengesellschaft
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