Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – With auxiliary means to condition stimulus/response signals
Reexamination Certificate
2001-01-08
2003-06-17
Le, N. (Department: 2858)
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
With auxiliary means to condition stimulus/response signals
Reexamination Certificate
active
06580277
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Inventiuon
The invention relates to a device for the rationmetric measurement of sensor signals.
The demands on the measurement accuracy of sensors in motor vehicle electronics are becoming ever higher. Many measured values are transmitted from the sensor to the processing microcontroller as analog DC voltages Vme&bgr; (0 . . . 5V+0 . . . 100%). The microcontroller digitizes them using an analog/digital converter ADC (e.g. 10 bit ADC: 0 . . . 5V+0 . . . 1023 steps). In an analog/digital converter, the measured voltage Vme&bgr; to be converted is set in relation to a reference value VAref, which is supplied to the analog/digital converter ADC as an analog reference voltage. To convert the analog value to a digital value as accurately as possible, it is therefore desirable for the sensor S and the analog/digital converter ADC to use the same reference voltage.
In motor vehicle electronics, this is generally not possible because the reference voltage VAref used for the analog/digital converter ADC integrated in the microcontroller &mgr;C is the supply voltage V
5
int for the microcontroller &mgr;C (VAref=V
5
int). Since, however, in the event of a short circuit between the sensor reference voltage V
5
ext and ground or the battery, the microcontroller and hence the engine/transmission control unit need to remain operational, the supply voltage V
5
int must not be routed to the vehicle wiring harness.
In this context, the notation V
5
int signifies the internal 5 volt supply voltage for the microcontroller &mgr;C, while V
5
ext signifies the 5 volt reference voltage for the sensor or sensors S arranged outside of the motor control unit ST. The supply voltage for microcontroller and sensors is usually 5 V.
A voltage controller SR having a plurality of mutually independent outputs—V
5
int, V
5
ext—and a common reference Ref is generally used, see FIG.
1
. The mutual discrepancy (tracking error of the controller) which is possible in this context is typically V
5
int−V
5
ext=±50 . . . 100 mV. In sensors such as air mass flowmeters, this error (1 . . . 2%) is already an essential proportion of the total error budget.
SUMMARY OF THE INVENTION
It is therefore the object of the invention to provide a device for measuring sensor signals which can be used to eliminate or minimize this tracking error.
In the device according to the invention, the reference voltage VAref for the analog/digital converter ADC is isolated from the supply voltage V
5
int for the microcontroller &mgr;C. It follows—in a certain range around the supply voltage V
5
int—the sensor reference voltage V
5
ext, so that the tracking error is largely eliminated in this range. This range is defined by the maximum permissible difference between the reference voltage VAref for the analog/digital converter ADC and the supply voltage V
5
int for the microcontroller &mgr;C; in a typical microcontroller used in automobile electronics, it is ±100 V, for example.
An illustrative embodiment in accordance with the invention is explained in more detail below with the aid of a schematic drawing, in which:
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patent: 5028874 (1991-07-01), Parle
patent: 5515048 (1996-05-01), Honda et al.
patent: 5579247 (1996-11-01), Kerth et al.
patent: 5684407 (1997-11-01), Zdanys, Jr. et al.
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patent: 196 36 838 (1998-01-01), None
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patent: 63-57851 (1988-03-01), None
patent: 06 318 138 (1994-11-01), None
patent: WO 92/00504 (1992-01-01), None
Greenberg Laurence A.
He Amy
Le N.
Mayback Gregory L.
Siemens Aktiengesellschaft
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