Examination circuit for a sensor

Details Examination circuit for a sensor Examination circuit for a sensor

1993-01-19

1994-03-15

Wieder, Kenneth A.

Electricity: measuring and testing

Fault detecting in electric circuits and of electric components

Of individual circuit component or element

324718, 340650, 340652, 340514, 374142, 204401, G01R 3102

Patent

active

052948900

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The invention relates to a circuit for checking the operating state or status of a sensor. The sensor can either be operational or can transmit an erroneous signal which is caused in particular by a short circuit to ground, a short circuit to the supply voltage or by an interruption.
In the following, the expression "electron receiving electrode" is employed in connection with transistors, etc. This refers to the drain or collector in transistors with n-type conduction and to the source or emitter in transistors with p-type conduction.
Automatic status detection is particularly important for sensors which can only be observed and monitored at longer intervals of time or which supply their signals to fully-automated processing devices. In such cases it is standard to monitor operating parameters continuously and to generate binary status signals.
When checking the operation of a sensor it is desirable to be able to detect different operating states in the simplest manner possible. Accordingly, the problem arises of providing a testing or monitoring circuit for a sensor which makes it possible to distinguish between different operating states in a simple manner.


SUMMARY OF THE INVENTION

The monitoring circuit according to the invention for a sensor is characterized by: potential is lower (low-potential line) than that of the other line (high-potential line) and which supplies the low-potential line with an offset voltage relative to ground which is higher than the minimum voltage at the control electrode of a transistor so as to control the latter (minimum control voltage of transistor); one hand and to ground on the other hand; high-potential line via a resistor arrangement and which blocks when the potential on the high-potential line falls below the minimum control voltage of the transistor, which occurs either because of a short circuit of the sensor to ground or due to the pulldown resistor during an interruption; low-potential line via a resistor arrangement and which blocks when the low-potential line is grounded, which occurs during a short circuit to ground; the output of a p-type transistor whose control electrode is connected with one of the two sensor lines and which is connected in such a way that it blocks when the lines have a potential which corresponds at least to the potential of the electron receiving electrode with respect to the minimum control voltage, whereupon the third testing transistor also blocks; indicates the operating state of the sensor, that is distinguishes between operational, short circuit to ground, short circuit to supply voltage and interruption.
As a result of the aforementioned combinations of switching states of the three testing transistors, four sensor function states can be checked with only three transistor signals. The evaluation is even simpler when two or three testing transistors are connected in series according to a particularly preferred embodiment form. Even in this case the respective operating state of the sensor follows in a definite manner from the combinations of the switching states of the transistor series connection and the remaining testing transistor. If the blocking state of a transistor is designated by "1" and the switch-through state (connection to ground) is designated by "0", the four states can be distinguished from one another as 2-bit signals "00", "01", "10" and "11".


BRIEF DESCRIPTION OF THE DRAWINGS

The objects, features and advantages of the present invention will now be illustrated in more detail by the following detailed description, reference being made to the accompanying drawing, in which: circuit for a sensor according to the invention which detects a total of four operating states of the sensor with the aid of two test signals each of which is in one of two states; and the first testing transistor and the combination of the second and third testing transistors and operating states of the sensor.


DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a monitoring circuit 10 to which is conn

REFERENCES:
patent: 3883753 (1975-05-01), Harrison
patent: 3973184 (1976-08-01), Raber
patent: 4103299 (1978-07-01), Swinehart
patent: 4647920 (1987-03-01), Corso
patent: 5079506 (1972-01-01), Choi

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