Note: Descriptions are shown in the official language in which they were submitted.
CA 02002908 1999-02-12
Universal Output Circuit
The invention relates to a method for the automatic identification or
recognition of the polarity of the electrical connection of a load and the
automatic association of the corresponding current source or drain with
the load, as well as to an output circuit in the sense of an interface between
two circuits for carrying out the method. This output circuit is in
accordance with the preamble of claim 7.
Power-switching output circuits are generally designed with transistors.
In the context of the present invention, output circuits are involved which
in actual fact switch, i.e. carry a switching current. As a function of the
use of the transistors, they can be of the npn or pnp type, which have
opposite current directions, i.e. switch against a positive or a negative
potential. The circuits carrying the switching current are designed
accordingly and therefore this also applies with regards to the circuits
switched with the switching current.
In order to have greater freedom here, with the increased circuit
complexity use is made of output circuits, which can carry a switching
current against both the negative and positive potential, an example being
a push-pull circuit. Using this circuit as a basis, there are user-related
modifications with corresponding advantages and disadvantages.
Reference is made to position sensors as a typical user problem. These can
be position sensors, which operate inductively, ultrasonically, optically or
capacitively. It is clear that a multiplicity of circuits are possible, which all
have an output circuit for "switching" any user. Such position circuits
either have an output swi*hing against positive potential, or an output
switching against negative potential, with optionally the possibility for
both, it not being possible to simultaneously use the latter possibility, e.g.
a push-pull output circuit. The switching function can be such
Q 8
that through the physical sensor function the release of
the switch is brought about (normally open contact, NOC)
or withdrawn (normally closed contact, NCC). On
S connection, the user must either adopt a positive
normally open contact and therefore a negative normally
closed contact, or a negative normally open contact and
therefore a positive normally closed contact. Further
developed variants in the direction of a universal output
circuit must always be rewired, in order to obtain the
desired switching polarity.
The problem of the present invention is therefore to
provide a method for the automatic identification of the
polarity of the electrical connection of a load and the
automatic association of the corresponding current source
or conversely the corresponding drain with the load,
together with an output circuit in the sense of an
interface between two circuits for carrying out the
method and in particular an output circuit for switching
networks, which do not have these disadvantages and
instead automatically sets the desired switching polarity
without any wiring change or line interchange. In
addition, this output circuit should have a minimum
circuit complexity, so that a broad range of uses is not
hindered by constructional and economic considerations.
Various aspects of the invention are as follows:
A method for the automatic identification of the
polarity of an electrical connection of an output circuit
to a load and the automatic connection of a selected
source to the load comprising the steps of:
a) connecting an output circuit to the load so that
the load is only between a common terminal of the output
circuit and a selected one of two differently poled
terminals of the output circuit during operation times of
said output circuit, the output circuit having a two-
state storage device and two current sources one of which
L?
- 2a - ~ ~ Q ~ 9 Q ~
is properly connectable to the load by the storage
device for each of two possible polarities of the load;
b) measuring the polarity of a voltage in the output
circuit in response to current flow between the output
circuit and the load;
c) setting the state of the storage device to
correspond with the measured polarity of the voltage; and
d) selectively connecting one of the current sources
to the load in response to the set state of the storage
device.
An output circuit for supplying current to a load
having a polarity in accordance with the polarity of the
load, the output circuit having a common terminal and two
differently poled terminals for connection of the load
between the common terminal and one of the differently
poled terminals, the output circuit comprising the
combination of:
first and second current sources of opposite
polarities;
means connected to the load for sensing the polarity
of the load;
storage means having two states, said storage means
2s being connected to said sources so that only one of said
sources is operatively connected to said load in each of
the states during operation times of said output circuit;
and
means responsive to said means for sensing for
setting the storage means to one of said states in
accordance with the polarity of said load.
The invention is described in greater detail hereinafter
relative to a non-limitive embodiment and the attached
drawings, wherein show:
Fig. 1 a to c the three aforementioned variants of
circuit outputs according to the prior art, a
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- 2b -
against a positive potential, b against a negative
potential and c in the form of a push-pull circuit
against one or other potential.
Fig. 2 the basic circuit of an inventive embodiment with
current scanning
.~~
CA 02002908 1999-02-12
Fig. 3 the basic circuit of an inventive embodiment with voltage scanning.
The essential part of the inventive output circuit is a relatively
uncomplicated measurement circuit. The invention is based on the idea of
generating an indicator current in the output circuit, which flows e.g.
across a blocking element, in much the same way as through a valve,
through the external wiring, i.e. the user wiring or, in the case of reversed
polarity, due to the valve it does not flow at all. The measurement circuit
can consequently detect whether the load at the terminals (user circuit) is
switched against a negative or positive potential. In place of the sensing
of an indicator current, it is also possible to connect a balanced voltage to
the user circuit. As a function of the polarity, it draws said symmetry
towards one or other polarity and causes the circuit to carry out a counter
reaction eliminating the asymmetry again, which indicates whether the
user circuit is switched against a negative or a positive potential. Thus, in
both cases of current or voltage scanning, the output circuit connects to the
load a npn or pnp driver stage, both already being provided in the output
circuit. Thus, there is no need for polarity reversal, rewiring or the like,
which naturally helps to prevent incorrect connections during assembly.
Thus, e.g. a proximity switch with the output circuit according to the
invention has two "neutral" connections, which are connected to the user
circuit and everything else is carried out by the output circuit. The other
important effect is the greatly reduced storage capacity, it no longer being
necessary to store different output stage types (pnp or npn normally open
or closed contacts).
It is clear that the transistor outputs according to the prior art shown in
figs. la, lb and lc do not have these advantages, because they either
operate in the pnp or npn mode and in the case of the corresponding
signal at the base connect through in the only possible current direction.
In the case of the push-pull circuit shown at c the situation is the same,
because it either operates in the npn
CA 02002908 1999-02-12
or in the pnp mode, as a function of the terminals between which the load
is switched.
Figs. 2 and 3 show the completely automatic switching of the output stage
to one or other driver type.
Basic principle of the inventive output circuit:
The basic principle is that a measurement circuit in the output circuit of
the sensor measures at the user circuit applied to its terminals the voltage
polarity against which it is connected. The detection of one or other of the
two states will fix it in a storing element M and will switch the correct
driver to the output terminals. This state is maintained for as long as there
is no change to the polarity of the output terminals. However, if there is
an interchange of terminals, e.g. due to the replacement of a defective
relay and consequently there is no specification as to how the connection
is to take place, then the measurement circuit correctly resl~res the stored
state, so that the correct driver is associated with the user circuit.
Fundamentally the measurement circuit can comprise two indicators,
namely for current scanning or voltage scanning, an embodiment for each
of the two possibilities being given hereinafter.
Current scanning of output terminals (fig. 2):
A current Ic is passed from a current source I through a diode D1.
If the load is now switched against a lower potential, as is the case with
RT~ then the current k can flow through the diode. This current flow is
detected and amplified by means of a current reflector S, downstream of
which is connected a (transimpedance) amplifier A, which at its output
supplies a voltage proportional to the detected current. This voltage is
evaluated in a following circuit for allocation to one or other driver.
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However, if the load is switched against a higher potential, as is the case
at RH~ then no current can flow through the diode. This is naturally
noticed by the current reflector M and the latter indicates to the series-
connected amplifier A "no current", which is made apparent at the
amplifier output by a corresponding voltage signal.
Thus, at the output of amplifier A it is possible to read off the two states
against which potential, i.e. high or low, the attached load is connected.
These two measurement signals can now be used for the particular
switching state to be retained by a storing circuit and on the basis thereof
the appropriate driver stage is switched on.
Voltage scanning of the output terminals (fig. 3);
An identical embodiment uses a "voltage information" in place of a
"current information" and at this the voltage caused in the load by the
indicator current is scanned. The supply voltage Vcc can be
symmetrically divided and the two Vcc 1/2 can be compared with a
referellce potential. As a function of the connection of the external load
there is an asymmetry to one or other polarity, which leads to a
compensation of the circuit, e.g. the driving of one of the two transistors of
a push-pull circuit and this current (signal) can be used for setting the
storage element, e.g. a flip-flop.
Operation of a proximity sensor with the inventive output circuit:
The automatic load detection ~l~e~dbly takes place in the starting phase
during the time of the starting pulse ~u~l~ression of the proximity sensor.
Starting pulse suppression lasts 20 to 40 ms and this time is long enough
for measuring and positioning the storage element. On cancelling out the
suppression, then the interface and therefore the sensor connected thereto
has the correct polarity relative to the user circuit in the form of a load.
Thus, during starting the time interval is used up entirely at the start, so as
to be able to determine the load with the aid of the indicator current. The
CA 02002908 1999-02-12
,
result, i.e. the state, is stored in a storage circuit, e.g. a flip-flop and thecurrent direction released by the load. This is either in the direction of a
positive source through a npn driver transistor, or in the direction of a
drain through a pnp driver transistor, as a function of the flip-flop output
setting. This ensures that the two drivers are not simultaneously switched
on.
The measurement circuit in the output circuit of the sensor measures with
the user circuit applied to its terminals against which voltage polarity it is
connected. The detection of one of the two states is used for fixing said
state in a storing element and for connecting the correct driver to the
output terminals. This state is maintained for as long as there is no change
in the polarity of the output terminals. If e.g. through the replacement of a
defective relay the terminals are interchanged, then the measurement
circuit directly restores in correct manner the stored state, so that the
correct driver is always associated with the user circuit. However, if e.g.
through the replacement of a control card or system positive instead of
negative switching sensors are now required, unlike hitherto, there is no
need to replace the equipment. The equipment is instead initialized
through the inventive measure on switching in the voltage and the state
corresponding to the new circumstances is set.
