U.S. patent application number 11/416813 was filed with the patent office on 2006-12-14 for touch-sensitive momentary-contact switch.
This patent application is currently assigned to Diehl AKO Stiftung & Co. KG. Invention is credited to Georg Arnold.
Application Number | 20060282070 11/416813 |
Document ID | / |
Family ID | 36951576 |
Filed Date | 2006-12-14 |
United States Patent
Application |
20060282070 |
Kind Code |
A1 |
Arnold; Georg |
December 14, 2006 |
Touch-sensitive momentary-contact switch
Abstract
A touch-sensitive momentary-contact switch has an optical
sensor, particularly an infrared sensor, and an evaluation circuit.
The evaluation circuit is able to identify a malfunction in the
optical sensor, so that the momentary-contact switch can be
switched off, for example, for safety reasons. Therefore, it is
possible to identify a malfunction in the optical sensor.
Inventors: |
Arnold; Georg; (Schwabach,
DE) |
Correspondence
Address: |
LERNER GREENBERG STEMER LLP
P O BOX 2480
HOLLYWOOD
FL
33022-2480
US
|
Assignee: |
Diehl AKO Stiftung & Co.
KG
|
Family ID: |
36951576 |
Appl. No.: |
11/416813 |
Filed: |
May 3, 2006 |
Current U.S.
Class: |
606/38 |
Current CPC
Class: |
D06F 34/32 20200201;
H05B 3/746 20130101; H03K 2217/94116 20130101; H03K 17/9636
20130101; D06F 34/28 20200201 |
Class at
Publication: |
606/038 |
International
Class: |
A61B 18/18 20060101
A61B018/18 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 4, 2005 |
DE |
10 2005 025 782.8 |
Claims
1. A touch-sensitive momentary-contact switch, comprising: a cover
being at least partially permeable to electromagnetic radiation; an
optical sensor having a transmitter emitting the electromagnetic
radiation and a receiver for receiving the electromagnetic
radiation and disposed downstream of said cover; an evaluation
circuit for evaluating a measurement signal generated by said
receiver and producing an evaluation signal; a device for routing a
portion of the electromagnetic radiation emitted by said
transmitter to said receiver even when the momentary-contact switch
is not operated; and said evaluation circuit takes a detected basic
level of the evaluation signal as a basis for assessing that there
is a malfunction in said optical sensor if no change in a level of
the evaluation signal in said evaluation circuit is detected during
a transmission cycle by said transmitter.
2. The touch-sensitive momentary-contact switch according to claim
1, wherein said device includes a masking frame and a partition
with an at least partially permeable feed-through opening formed
therein, said partition disposed in said masking frame between said
transmitter and said receiver.
3. The touch-sensitive momentary-contact switch according to claim
1, wherein said cover has a front surface and a back surface and
reflects a portion of the electromagnetic radiation emitted by said
transmitter by said front surface and/or said back surface in a
direction of said receiver.
4. A touch-sensitive momentary-contact switch, comprising: a cover
being at least partially permeable to electromagnetic radiation; an
optical sensor having a transmitter emitting the electromagnetic
radiation and a receiver for receiving the electromagnetic
radiation and disposed downstream of said cover; and an evaluation
circuit for evaluating a measurement signal produced by said
receiver and generating an evaluation signal, said evaluation
circuit having a device for changing over a measurement range for
the evaluation signal, said evaluation circuit taking a detected
basic level of the evaluation signal as a basis for assessing that
there is a malfunction in said optical sensor if no change in a
level of the evaluation signal in said evaluation circuit is
detected during a changeover cycle for changing the level of the
evaluation signal.
5. The touch-sensitive momentary-contact switch according to claim
4, wherein: said evaluation circuit has a voltage divider circuit
formed of a first resistor and a first transistor, said first
transistor being controlled by the measurement signal from said
receiver, the evaluation signal in said evaluation circuit being
tapped off between said first resistor and said first transistor;
and said device is a device for altering a voltage divider ratio of
said voltage divider circuit.
6. The touch-sensitive momentary-contact switch according to claim
5, wherein: said device has a series circuit containing a second
transistor and a second resistor, said series circuit connected in
parallel with said first resistor, said second transistor being
turned on during the changeover cycle.
7. The touch-sensitive momentary-contact switch according to claim
6, further comprising a third resistor connected in parallel with
said first transistor.
8. A touch-sensitive momentary-contact switch, comprising: a cover
being is at least partially permeable to electromagnetic radiation;
an optical sensor having a transmitter emitting the electromagnetic
radiation and a receiver for receiving the electromagnetic
radiation and disposed downstream of said cover; an evaluation
circuit for evaluating a measurement signal produced by said
receiver in said optical sensor and generating an evaluation
signal; said evaluation circuit having a first device for changing
over a measurement range of the evaluation signal, said evaluation
circuit taking a detected basic level of the evaluation signal as a
basis for assessing that there is a malfunction in said optical
sensor if no change in a level of the evaluation signal in said
evaluation circuit is detected during a transmission cycle of said
transmitter and/or during a changeover cycle for changing the level
of the evaluation signal; and a second device for routing a portion
of the electromagnetic radiation emitted by said transmitter to
said receiver even when the momentary-contact switch is not
operated.
9. The touch-sensitive momentary-contact switch according to claim
8, wherein said second device includes a masking frame and a
partition with an at least partially permeable feed-through opening
formed therein, said partition disposed in said masking frame
between said transmitter and said receiver.
10. The touch-sensitive momentary-contact switch according to claim
8, wherein said cover has a front surface and a back surface and
reflects a portion of the electromagnetic radiation emitted by said
transmitter by said front surface and/or said back surface in a
direction of said receiver.
11. The touch-sensitive momentary-contact switch according to claim
8, wherein: said evaluation circuit has a voltage divider circuit
formed of a first resistor and a first transistor, said first
transistor being controlled by the measurement signal from said
receiver, the evaluation signal being tapped off between said first
resistor and said first transistor; and said first device provided
for altering a voltage divider ratio of said voltage divider
circuit.
12. The touch-sensitive momentary-contact switch according to claim
11, wherein: said first device has a series circuit containing a
second transistor and a second resistor, said series circuit
connected in parallel with said first resistor, and said second
transistor being turned on during the changeover cycle.
13. The touch-sensitive momentary-contact switch according to claim
8, wherein the electromagnetic radiation is infrared radiation.
Description
BACKGROUND OF THE INVENTION
[0001] Field of the Invention
[0002] The present invention relates to a touch-sensitive
momentary-contact switch and particularly to such a
momentary-contact switch for use in a control device for a
household appliance.
[0003] The basic design and the basic principle of such a
touch-sensitive momentary-contact switch are known from published,
non-prosecuted German patent application DE 40 07 971 A1, for
example. The touch-sensitive momentary-contact switch has a
transmitter emitting electromagnetic radiation and a receiver
receiving electromagnetic radiation, which are disposed downstream
of a cover which is at least partially permeable to the
electromagnetic radiation. In addition, an evaluation circuit for
evaluating a measurement signal produced by the receiver and
producing an evaluation signal for further processing is generally
provided. One advantageous application of such touch-sensitive
momentary-contact switches is their use in control devices for
household appliances, for example, such as cookers, glass ceramic
hobs, microwave ovens and the like, in which the momentary-contact
switch is accommodated behind a cover, such as a glass plate or
glass ceramic plate, for simple operation and cleaning.
[0004] One problem of conventional momentary-contact switches of
this type is that it is not possible to identify whether the
optical sensor, i.e. particularly the transmitter and/or the
receiver, in the momentary-contact switch is faulty. This is also a
safety risk, for example if the momentary-contact switch becomes
faulty only after being successfully switched on and therefore
cannot be switched off again. There is therefore a need for a
touch-sensitive momentary-contact switch of the type mentioned in
the introduction in which it is possible to identify a malfunction
in the optical sensor, so that an appropriate reaction to an
identified malfunction of this type is finally possible if
appropriate.
SUMMARY OF THE INVENTION
[0005] It is accordingly an object of the invention to provide a
touch-sensitive momentary-contact switch which overcomes the
above-mentioned disadvantages of the prior art devices of this
general type, in which it is possible to identify a malfunction in
its optical sensor.
[0006] With the foregoing and other objects in view there is
provided, in accordance with the invention, a touch-sensitive
momentary-contact switch. The momentary-contact switch contains a
cover being at least partially permeable to electromagnetic
radiation, an optical sensor having a transmitter emitting the
electromagnetic radiation and a receiver for receiving the
electromagnetic radiation and disposed downstream of the cover, and
an evaluation circuit for evaluating a measurement signal generated
by the receiver and producing an evaluation signal. A device is
provided for routing a portion of the electromagnetic radiation
emitted by the transmitter to the receiver even when the
momentary-contact switch is not operated. The evaluation circuit
takes a detected basic level of the evaluation signal as a basis
for assessing that there is a malfunction in the optical sensor if
no change in a level of the evaluation signal in the evaluation
circuit is detected during a transmission cycle by the
transmitter.
[0007] The inventive momentary-contact switch is distinguished in
that a device is provided for routing a portion of the
electromagnetic radiation emitted by the transmitter to the
receiver even when the momentary-contact switch is not operated.
The evaluation circuit takes a detected basic level of the
evaluation signal as a basis for assessing that there is a
malfunction in the optical sensor if no change in the evaluation
signal level in the evaluation circuit is detected during a
transmission cycle initiated by the transmitter.
[0008] The effect achieved by the above configuration of the
momentary-contact switch is that the receiver receives a small
amount of radiation and thus produces an appropriate measurement
signal even when the momentary-contact switch is not operated. If
the measurement signal is not produced, the evaluation circuit can
infer that the optical sensor has malfunctioned. In this case, it
is also necessary to take account of the basic level of the
evaluation signal, however, since in the case of a flare, for
example, it is not possible to detect a change in the evaluation
signal level (when the momentary-contact switch is or is not
operated) even when the optical sensor is working.
[0009] In one refinement of the invention, the device has an at
least partially permeable feed-through opening in a partition in a
masking frame between the transmitter and the receiver, so that
regardless of the momentary-contact switch being operated a portion
of the radiation emitted by the transmitter always arrives at the
receiver directly through the feed-through opening.
[0010] In one alternative refinement of the invention, the device
has the cover, which is configured such that a portion of the
radiation emitted by the transmitter is reflected on the front
and/or the back surface of the cover in the direction of the
receiver. This can be achieved, by way of example, by choosing a
specific refractive index for the material of the cover, by a
specific nature of the surfaces or by a specific coating for the
surfaces of the cover.
[0011] The inventive momentary-contact switch is distinguished in
that the evaluation circuit additionally has a device for changing
over a measurement range for the evaluation signal. The evaluation
circuit takes a detected basic level of the evaluation signal as a
basis for assessing that there is a malfunction in the optical
sensor if the basic level of the evaluation signal detects no
change in the evaluation signal level in the evaluation circuit
during a changeover cycle in the measurement range.
[0012] The above configuration of the evaluation circuit makes it
possible to change over a measurement range for the purpose of
measuring the saturation voltage of the receiver, which causes a
voltage step change in the evaluation signal. If this voltage step
change is not produced, the evaluation circuit can infer that the
optical sensor has malfunctioned. Such a voltage step change cannot
be produced, in principle, if the receiver is incorrectly at the
level of the supply voltage or if the receiver is shorted, for
example.
[0013] In one refinement of the invention, the evaluation circuit
has a voltage divider circuit which is formed from a first resistor
and a first transistor, with the first transistor being controlled
by the measurement signal from the receiver, and the evaluation
signal in the evaluation circuit being tapped off between the first
resistor and the first transistor. In this case, the device is a
device for altering the voltage divider ratio.
[0014] In a further refinement of the invention, the device has a
series circuit containing a second transistor and a second resistor
which is connected in parallel with the first resistor, the second
transistor being turned on during the changeover cycle. In
addition, a third resistor is connected in parallel with the first
transistor in the evaluation circuit.
[0015] In line with a third aspect of the invention, the
aforementioned object can naturally also be achieved by a
combination of the first and second aspects. In this case, the
momentary-contact switch contains a device for routing a portion of
the electromagnetic radiation emitted by the transmitter to the
receiver even when the momentary-contact switch is not operated,
and the evaluation circuit additionally has a device for changing
over a measurement range for the evaluation signal, so that the
evaluation circuit can take a detected basic level of the
evaluation signal as a basis for assessing that there is a
malfunction in the optical sensor if no change in the evaluation
signal level in the evaluation circuit is detected during a
transmission cycle in the transmitter and/or during a changeover
cycle in the measurement range of the evaluation signal.
[0016] Other features which are considered as characteristic for
the invention are set forth in the appended claims.
[0017] Although the invention is illustrated and described herein
as embodied in a touch-sensitive momentary-contact switch, it is
nevertheless not intended to be limited to the details shown, since
various modifications and structural changes may be made therein
without departing from the spirit of the invention and within the
scope and range of equivalents of the claims.
[0018] The construction and method of operation of the invention,
however, together with additional objects and advantages thereof
will be best understood from the following description of specific
embodiments when read in connection with the accompanying
drawings.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0019] FIG. 1 is a diagrammatic, sectional view of a
touch-sensitive momentary-contact switch in line with a preferred
exemplary embodiment according to the invention;
[0020] FIG. 2 is a simplified circuit diagram of a conventional
evaluation circuit;
[0021] FIG. 3 is a simplified circuit diagram of an evaluation
circuit for the touch-sensitive momentary-contact switch based on a
preferred exemplary embodiment of the present invention;
[0022] FIGS. 4 and 5 are schematic signal graphs to explain a
signal profile of an evaluation signal in the evaluation circuit
from FIG. 3 based on the present invention when the optical sensor
in the touch-sensitive momentary-contact switch is operable;
and
[0023] FIGS. 6 to 8 are schematic signal graphs to explain the
signal profile of the evaluation signal in the evaluation circuit
from FIG. 3 based on the present invention when the optical sensor
in the touch-sensitive momentary-contact switch is faulty.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0024] Referring now to the figures of the drawing in detail and
first, particularly, to FIG. 1 thereof, there is shown a mechanical
configuration of a touch-sensitive momentary-contact switch 10
according to the invention. The touch-sensitive momentary-contact
switch from the invention is an infrared momentary-contact switch
for a household appliance, for example, such as a cooker, a
microwave oven, a hob, a washing machine, a washer-dryer, a
dishwasher or the like, without the invention being limited to
electromagnetic radiation in this wavelength range or to these
specific applications.
[0025] The touch-sensitive momentary-contact switch 10 has an
infrared transmitter 14 and an infrared receiver 16 on a printed
circuit board 12. The transmitter 14 and the receiver 16 are
surrounded by a masking frame 18 which has two openings 20 and 22
on its top 19. The masking frame 18, formed from an
infrared-impermeable material, has feet 24 inserted through holes
in the printed circuit board 12 and is mounted on the latter in
this way.
[0026] The transmitter 14 and the receiver 16 are positioned in the
masking frame 18 such that they are disposed within respective
cavities 26 and 28 below the masking openings 20 and 22. In this
case, the two cavities 26 and 28 are separated from one another by
an infrared-impermeable partition 30. Lying directly on the top 19
of the masking frame 18 is a cover 32 made of a material which is
at least partially permeable to infrared, for example a glass
ceramic plate on a household cooker.
[0027] The radiation emitted by the transmitter 14 arrives at the
top 34 of the cover 32 via an optical path 36. When the
touch-sensitive momentary-contact switch 10 is operated by a finger
37 placed onto the surface of the cover 32, the radiation from the
transmitter 14 is reflected diffusely and a plurality of times, so
that sufficient scattered radiation is reflected to the receiver 16
and the latter sends an appropriate measurement signal V.sub.E to
an evaluation circuit 40 in order to trigger an appropriate
switching function.
[0028] In the case of a conventional evaluation circuit 40', as
illustrated in FIG. 2, the measurement signal V.sub.E would switch
a first transistor Q1 in a voltage divider circuit which is
constructed from a first resistor R1 and the first transistor Q1
and to which a supply voltage V.sub.dd is applied. In this case,
the transistor Q1 acts as a receiver. An evaluation signal V.sub.IN
is tapped off between the first resistor R1 and the first
transistor Q1 and is supplied to a microprocessor 42' for further
processing. In the case of an operable momentary-contact switch 10,
the first transistor Q1 has a high impedance when the
momentary-contact switch 10 is not operated, which results in that
the evaluation signal V.sub.IN has a high signal level. When the
momentary-contact switch 10 is operated, the first transistor 10 is
switched to low impedance by the measurement signal V.sub.E from
the receiver 16, so that the signal level of the evaluation signal
V.sub.IN drops accordingly, which the microprocessor 42' interprets
as the momentary-contact switch 10 being operated.
[0029] If there is a fault in the optical sensor 14, 16 or in the
resistor R1 or in other components of the momentary-contact switch
10, the microprocessor 42' is no longer able to identify when the
momentary-contact switch 10 is operated. In addition, the
conventional evaluation circuit 40' does not allow such a fault in
the optical sensor 14, 16 to be identified and reacted to in
appropriate fashion, which in some cases can be a safety risk, for
example when a hotplate can no longer be switched off.
[0030] To increase the operational reliability of the
touch-sensitive momentary-contact switch 10, the following measures
are therefore taken in line with the present invention.
[0031] As FIG. 1 shows, the partition 30 in the masking frame 18
has a feed-through opening 38 which is at least partially permeable
to the electromagnetic radiation emitted by the transmitter 14. In
addition or alternatively, a top 34 and/or a underside 35 of the
cover 32 may be of a nature or coated such that at least one
portion of the electromagnetic radiation from the transmitter 14 is
reflected in the direction of the receiver 16. In this way, the
first measure achieved is that the receiver 16 receives a certain
amount of radiation from the transmitter 14 and produces an
appropriate measurement signal V.sub.E for the evaluation circuit
40 even when the momentary-contact switch 10 is not operated.
[0032] As a second measure, a measurement range changeover is
introduced, which modifies the evaluation circuit 40 for the
touch-sensitive momentary-contact switch 10, as shown in FIG.
3.
[0033] In this case too, the basic design of the inventive
evaluation circuit 40 is a voltage divider circuit which contains a
first resistor R1 and a first transistor Q1 between which the
evaluation signal V.sub.IN is tapped off and is input at an input
IN of the microprocessor 42 for further handling and evaluation. In
addition, a series circuit containing a second transistor Q2 and a
second resistor R2 is connected in parallel with the first resistor
R1, the second resistor R2 being chosen to have a very low value
(for example a few k.OMEGA.) and the second transistor Q2 being
controlled by a changeover signal from a control output UM of the
microprocessor 42. Preferably, a third (preferably high-value)
resistor R3 is also connected in parallel with the first transistor
Q1.
[0034] The way in which this modified voltage divider circuit in
the evaluation circuit 40 works is as follows. In the normal state,
when the second transistor Q2 is not receiving a changeover signal
from the microprocessor 42 and is therefore off, the evaluation
signal V.sub.IN is set up essentially by the voltage divider made
up of R1 and Q1. In other words, the evaluation signal V.sub.IN in
this circuit state corresponds to the "normal" evaluation signal.
When the microprocessor 42 outputs the changeover signal, on the
other hand, the second transistor Q2 is turned on, so that the
voltage divider is determined essentially by the low-impedance
series circuit containing Q2 and R2 and by the first transistor Q1.
In comparison with the "normal" evaluation signal, the level of the
evaluation signal V.sub.IN is now shifted in the direction of the
supply voltage V.sub.dd, however. The third resistor R3, connected
in parallel with the first transistor Q1, ensures that the shift in
the evaluation signal level V.sub.IN can be produced by the
changeover signal even when it is dark on the momentary-contact
switch 10.
[0035] The two measures described above, i.e. a measurement signal
V.sub.E even when the momentary-contact switch 10 is not operated
and a shift in the voltage divider ratio, are utilized by the
evaluation circuit 40 in the following manner to identify a fault
in the optical sensor 14, 16.
[0036] The signal profile of an evaluation signal V.sub.IN in the
inventive momentary-contact switch 10 is first described below with
reference to FIGS. 4 and 5 for the case of an operable optical
sensor 14, 16.
[0037] As FIG. 4 shows, the momentary-contact switch 10 is
evaluated in multiplex mode in the time window t.sub.A to t.sub.B.
Within this time window t.sub.A-t.sub.B, there exist in succession
a transmission cycle t.sub.a to t.sub.b, in which the transmitter
14 emits radiation, and a changeover cycle t.sub.C to t.sub.D, in
which the microprocessor 42 outputs the changeover signal to the
second transistor Q2. Outside the time window t.sub.A-t.sub.B, the
multiplexer mode is switched to other momentary-contact switches in
the control device.
[0038] In another embodiment, by not using multiplex mode, this
circuit also allows only a single key to be used and evaluated.
[0039] FIG. 4 shows the signal profile for an evaluation signal VIN
when the momentary-contact switch 10 is not operated and when the
momentary-contact switch 10 has no flare. In response to the
radiation emitted by the transmitter 14, the receiver 16 produces a
measurement signal V.sub.E, which results in a slight lowering of
the evaluation signal level V.sub.IN (swing) during the
transmission cycle t.sub.a-t.sub.b. This lowering of the evaluation
signal V.sub.IN would be significantly more pronounced if the
momentary-contact switch were operated, as indicated by a dashed
signal profile in FIG. 4. Following this, the evaluation signal
level V.sub.IN is shifted in the direction of the supply voltage
Vdd during the changeover cycle t.sub.c-t.sub.d (step). The basic
level of the evaluation signal V.sub.IN is between 0V and Vdd
closer to Vdd in this case.
[0040] If the momentary-contact switch 10, i.e. its optical sensor,
has a high level of flare on account of the incidence of light from
an external source, so that the basic level of the evaluation
signal V.sub.IN falls to 0V, as illustrated in FIG. 5, then the
swing described above during the transmission cycle t.sub.a-t.sub.b
cannot be detected by the evaluation circuit. On the other hand,
the evaluation circuit 40 can still detect the step during the
changeover cycle t.sub.c-t.sub.d even in this case. Despite the
missing swing in the transmission cycle t.sub.a-t.sub.b, the
evaluation circuit 40 can therefore tell from the step in the
changeover cycle t.sub.c-t.sub.d that the optical sensor 14, 16 is
operable.
[0041] Just from the two signal profiles in FIG. 4 and FIG. 5, it
is therefore possible to see that the evaluation circuit 40 needs
to take the basic level of the evaluation signal V.sub.IN into
account in order to assess that the optical sensor 14, 16 is
faulty. Depending on the basic level of the evaluation signal
V.sub.IN, various indicators are crucial for assessing that there
is a fault in the optical sensor 14, 16.
[0042] FIGS. 6 to 8 are now used to describe various signal
profiles for the evaluation signal V.sub.IN in each case for a
faulty optical sensor 14, 16 and a faulty momentary-contact switch
10.
[0043] In the example in FIG. 6, the basic level of the evaluation
signal V.sub.IN is at the level of the normal evaluation signal
between 0V and Vdd. In the time window t.sub.A-t.sub.B for this
momentary-contact switch 10, however, only the step in the
changeover cycle t.sub.c-t.sub.d can be seen; there is no swing
during the transmission cycle t.sub.a-t.sub.b. The microprocessor
42 can use this evaluation signal V.sub.IN to assess that the
momentary-contact switch 10 is faulty, to be more precise that the
transmitter 14 is faulty or that a connection on the receiver 16 is
open, for example.
[0044] In FIG. 7, the basic level of the evaluation signal V.sub.IN
has been lowered to 0 V and neither the swing in the transmission
cycle t.sub.a-t.sub.b nor the step in the changeover cycle
t.sub.c-t.sub.d are present. In this case, the microprocessor 42
likewise infers that the momentary-contact switch 10 is faulty, to
be more precise that the receiver 16 is shorted, for example. This
fault could still be detected even if the momentary-contact switch
10 had a flare, since, as FIG. 5 shows, an operable
momentary-contact switch 10 would necessarily have at least the
step during the changeover cycle t.sub.c-t.sub.d.
[0045] FIG. 8 shows a further fault case for the momentary-contact
switch 10, in which the receiver 16 (or another component) is at
the level of the supply voltage Vdd. In this case, the basic level
of the evaluation signal V.sub.IN is pulled up to the supply
voltage Vdd, and there is neither a swing during the transmission
cycle t.sub.a-t.sub.b nor a step during the changeover cycle
t.sub.c-t.sub.d.
[0046] A person skilled in the art will have no difficulty in
recognizing the signal profile of the evaluation signal V.sub.IN,
which signal profile is produced for other special fault cases for
the momentary-contact switch 10 which can likewise occur, without
all possibilities needing to be discussed within this
application.
[0047] A crucial element for assessing that the momentary-contact
switch 10 is faulty is that, in addition to the presence or absence
of the swing during the transmission cycle t.sub.a-t.sub.b and of
the step during the changeover cycle t.sub.c-t.sub.d, the
respective basic level of the evaluation signal V.sub.IN is also
taken into account at the same time.
[0048] In addition, it is naturally also possible to provide a
touch-sensitive momentary-contact switch 10 which has just one
error detection measure. Although this inevitably results in that
not all possible types of faults in the momentary-contact switch 10
can be identified without any doubt, this would nevertheless
signify an improvement in the conventional momentary-contact
switches without any error detection.
[0049] If the above evaluation circuit 40 assesses that the
momentary-contact switch 10 is faulty, appropriate measures can be
taken, such as automatically switching off the appliance, in order
to increase safety.
[0050] To increase operational reliability further, it is also
advantageous if, once a fault in the momentary-contact switch 10
has been identified, it is stored in the form of an appropriate
marker, for example, so that this fault is identified at a later
time, even if it were not able to be detected on account of the
optical sensor currently having a flare, for example. When the
momentary-contact switch 10 is repaired, these markers would
naturally be able to be reset.
[0051] In principle, the circuits in FIGS. 2 and 3 can also be
produced with reversed polarity, which likewise results in reversed
polarity for the illustration in FIGS. 4 to 8.
[0052] This application claims the priority, under 35 U.S.C. .sctn.
119, of German patent application No. 10 2005 025 782.8, filed Jun.
4, 2005; the entire disclosure of the prior application is herewith
incorporated by reference.
* * * * *