Communications: electrical – Systems – Selsyn type
Reexamination Certificate
1998-03-02
2001-04-24
Crosland, Donnie L. (Department: 2736)
Communications: electrical
Systems
Selsyn type
C340S315000, C340S635000, C340S650000, C340S643000, C307S040000, C307S030000, C361S055000, C361S088000, C361S171000
Reexamination Certificate
active
06222441
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a process for connecting at least one load to a line which is provided both for supplying operating energy and for data transmission, the data signals and operating energy being decoupled with at least one reactor. The invention further relates to a circuit for connecting at least one load to a line which is provided both for supplying operating energy and for data transmission, with at least one reactor for decoupling of data signals and operating voltage. A reactor is an electrical component with inductive operating characteristics.
2. Description of the Related Technology
A process and circuit of this type are known in conjunction with two-wire bus lines, one of these bus lines being the so-called actuator-sensor interface bus, abbreviated ASI. Connected to the ASI bus are sensors such as photoelectric barriers, proximity switches, etc., with signals or information derived therefrom relayed to a master device and from there to consumers or actuators, such as solenoid valves, electromagnetic actuators, etc., via the bus. All system components such as the master device, power source, sensor and actuator electronics are connected exclusively by the ASI bus line which can be branched in any way to the different system components. Not only data signals are transmitted between the master device and sensors or actuators go via the two wires of the bus system, but the sensors and actuators are also supplied with the necessary operating energy via these two wires.
To make the wiring as simple as possible, the cable for the ASI bus is a simple unshielded two-wire line. The data signals are modulated symmetrically onto the line. This symmetry prevents the influence of noise on the bus system due to incident radiation of outside electromagnetic fields on the cable. In addition, the line symmetry prevents emission of electromagnetic noise by the cable caused by the high frequencies of the data signals.
The sensors and actuators connected to the ASI bus system and their built-in electronics do not influence the bus system symmetry if the two bus lines are not connected, for example, to the housing, and the capacitive loading of the two wires is roughly the same.
The sensors and actuators offered by manufacturers in most cases have a two- or three-lead terminal for connection to a control unit. These “binary sensors” are neither suited nor designed for connection to the ASI bus system. However, for connection of these components to the ASI bus system so-called user modules are available which convert the bus information into binary signals and vice versa. The sensors and actuators can be connected to these user modules using conventional DC voltage technology.
One example of a circuit in this prior art user module is shown schematically in
FIG. 2
for connection of an actuator, for example an electromagnetic valve with inductive load
1
. There is one reactor
4
,
5
in each of the plus and minus bus line
2
,
3
. Reactor
4
of plus bus line
2
is at one terminal of inductive load
1
via switch
6
and reactor
5
is joined directly to the other terminal of inductive load
1
. Between the terminals of reactors
4
and
5
, facing inductive load
1
, is electrolytic capacitor
7
and on the other side of switch
6
diode
8
and Zener diode
9
are parallel to inductive load
1
, the anodes of diodes
8
,
9
being connected to one another.
Reactors
4
,
5
are used for decoupling of data signals from the operating voltage in two bus lines
2
,
3
. Electrolytic capacitor
7
prevents the bus current from having an overly high current gradient, i.e., an overly high value di/dt, when the load is connected and disconnected.
Normally the sensors represent a small ohmic or capacitive load and the user module can easily handle such a small load. The current necessary for the actuators is generally much higher than the current for the sensors. Switch
6
, conventionally a relay switch, is necessary for connecting the actuator and is located between the actuator and electrolytic capacitor, so that the bus current does not reach overly high di/dt values when the load is connected and disconnected. Since this higher current flows through reactors
4
,
5
of the user module, they must be made relatively large. Loads greater than approximately 2.5 watts cannot be supplied with electric power from the bus, but are dependent on an outside power source which must additionally be connected to the user module.
SUMMARY OF THE INVENTION
An object of the invention is to provide a much simpler and more cost-effective circuit and process for the user modules.
This object is achieved in a first embodiment by using the inductance of the load as the decoupling reactor.
Nearly all actuators have a small capacitance but a large inductance, as is the case, for example, in solenoids, electromagnetic valves, etc. Therefore the load inductance is already many times larger than that of the decoupling reactors of the conventional user modules. These decoupling reactors in the user module can therefore be eliminated with the advantage that the circuit is less expensive and losses due to decoupling reactors do not occur. A consumer with an inductive load can therefore be connected directly to the ASI bus system when this invention is used. The electrolytic capacitor can also be eliminated.
According to one advantageous embodiment of the invention, the line between the user module and actuator is a two-wire, symmetrical bus line. When the switch is conductive the actuator is directly on the bus. Only a direct current flows through the actuator due to its inductance. The bus is therefore not unduly loaded. When the switch is opened only one of the two bus lines of the ASI bus system is connected to the load, making the bus strongly asymmetrically loaded. By AC linking of the switch with a small capacitance which represents only a small resistance for the high frequency data signals, the bus line in which the open switch is located is AC-linked to the ASI bus system, so that symmetry is re-established even when the switch is not conductive.
When the inductive load is disconnected the energy stored in the coil of the consumer, for example in the magnet coil, must be reduced. Discharge via a diode or combination of diode and Zener diode connected parallel to the inductive load (compare
FIG. 2
) is not possible, since
1
) the diode capacitance would represent an undue load on the ASI bus, and
2
) due to the lack of a combination of reactors and electrolytic capacitors, when the switch is opened an unallowable di/dt value would arise because the coil current would be suddenly rerouted from the bus line to the diodes. The energy stored in the load inductance must discharge into the bus line via a diode when disconnected. According to one embodiment of the invention, instead of protective diodes parallel to the load, a Zener diode is used which is parallel to the switch. After opening the switch, the coil current flows in a slowly decreasing manner through the Zener diode, which has a breakdown voltage that should preferably be above the maximum voltage which occurs on the bus lines.
When a short circuit occurs in or behind the load, which can be a user module, the remaining bus system and especially the signal and data transmission which travel over the bus system should not be disrupted. This means that the symmetry of a two-wire bus system should not be adversely affected. Short circuit current limitation or disconnection is already conventional in ordinary user modules. According to one advantageous embodiment of the invention, therefore, both AC and DC are interrupted on the line when a short circuit occurs. The AC interruption is especially necessary when the switch is AC-linked because this prevents the data signals from being short circuited.
This object is also achieved by a circuit of the first embodiment in which, as described, the inductance of the load is provided as a reactor for decoupling. The advantages described in conjuncti
Crosland Donnie L.
Fulbright & Jaworski L.L.P.
Richard Hirschmann GmbH & Co.
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