EP1109177B1 - Method for switching a load - Google Patents

Abstract

The method involves switching a switching voltage suddenly to a first predetermined voltage corresponding to the rated load voltage, detecting the load current in a first time interval, holding the voltage constant until a switch-off time if the load current falls or remains the same during the time interval, and performing sudden or timed reduction of the switching voltage to a maximum value if the load current increases during the time interval. Independent claims are also included for the following: a circuit for implementing the method and a digital output unit for a speech programmable controller.

Description

The invention relates to a method for switching a load, to which a switching voltage can be supplied.
In addition, the invention relates to a circuit arrangement for performing the method.

A method and a device for protecting an AC circuit are known from the closest prior art DE 41 32 208 C1. Measures are provided which enable an inductive load to be switched on without the occurrence of undesirably high inrush currents.

EP 0 618 667 B1 discloses a method for controlling the alternating current in a load circuit and a device for carrying out the method. A test program determines the type of the connected load, so that controllable semiconductors can be operated in the phase control with inductive load and in the phase control with capacitive and / or ohmic load.

DE 38 17 770 A1 describes a device for the clocked activation of an electromagnetic valve. Measures are provided which enable the electromagnetic valve to operate effectively.

A drive system for a solenoid valve is known from US Pat. No. 5,938,172. The drive system can be used to generate two types of high voltages with simple means.

The present invention is therefore based on the object of specifying a method of the type mentioned which, regardless of the type of load to be switched, be it an ohmic load, a lamp load, a capacitive load, a inductive load with or without moving parts, this load can be switched. According to the invention, the object is achieved by a method according to claim 1. In addition, a circuit arrangement is to be specified in claim 4, which is suitable for performing the method.

An embodiment of the invention according to the measures specified in claim 2 causes a lower energy requirement when the inductive load is switched with movable parts and also speeds up shutdown processes. The invention can be used in particular in digital output units for programmable logic controllers.

The invention, its configurations and advantages are explained in more detail below with reference to the drawing, in which an exemplary embodiment of the invention is illustrated.

Figur 1

eine Schaltungsanordnung zum Schalten einer induktiven Last mit bewegbaren Teilen,

Figur 2

eine Darstellung von Strom- und Spannungsverläufen,

Figur 3

eine Darstellung von Schaltspannungen,

Figur 4

eine Schaltungsanordnung zum Schalten mehrerer induktiver Lasten,

Figur 5

eine Schaltungsanordnung zum Schalten einer Last und

Figur 6

eine weitere Darstellung von Strom- und Spannungsverläufen.

Show it

Figure 1

a circuit arrangement for switching an inductive load with movable parts,

Figure 2

a representation of current and voltage profiles,

Figure 3

a representation of switching voltages,

Figure 4

a circuit arrangement for switching several inductive loads,

Figure 5

a circuit arrangement for switching a load and

Figure 6

another representation of current and voltage profiles.

Essential components of the circuit arrangement according to FIG. 1 are a sensor unit 1, which is provided to detect the change in a load current 11, a controllable switch 3 in the form of a MOSFET switch and a voltage generating unit 4. A DC supply voltage 5 can be supplied to the voltage generating unit 4 , from which the voltage generation unit 4 generates 6 switching voltages depending on a control signal 6 generated by the sensor unit 1 and supplied to the voltage generation unit 4. In a practical exemplary embodiment of the invention, two switching voltages are provided, a maximum voltage of 48 VDC and a holding voltage of 16 VDC, which are generated from a supply voltage of 24 VDC.
A control signal 9 can be fed to the controllable switch 3 via a control output 7 of a programmable logic controller and via potential-isolating means 8, an activated control signal 9 closing the switch 3. This has the effect that a switching voltage 10 is supplied to the load 2 and the load current 11 through the load 2 via a ground connection M flows off. Further components of the circuit arrangement such as storage choke 12, quenching element 13 and overvoltage protection device 14 are of no importance for the invention and therefore do not need to be explained in more detail.

To illustrate the invention, reference is made to FIG. 2, in which current and voltage profiles are shown.

At a time T0, the load 2 (FIG. 1) is supplied with an abrupt maximum voltage Um, which, for. B. corresponds to twice the nominal load voltage Un. This maximum voltage Um causes a rapid increase in a load current I. During a time interval between the time T0 and a time T1, the sensor unit 1 detects a current shoulder Ss in the load current profile, which, for. B. is caused by the movement of an anchor and the flow change caused thereby. The sensor unit 1 then activates the control signal 6, as a result of which the voltage generating unit 4 at the time T1 suddenly reduces the switching voltage from the maximum voltage Um to a holding voltage Uh, which in a practical exemplary embodiment of the invention is two thirds of the nominal load voltage Un. Due to the increased switching voltage Um between times T0 and T1 and the reduced switching voltage Uh from time T1, on the one hand, the inductive load 2 is switched quickly and, on the other hand, the energy requirement during switched load 2 is reduced, with a holding current from time T2 in the steady state Ih flows through the load 2.
Instead of reducing the switching voltage after the detection of the current shoulder Ss to the holding voltage Uh, one can also proceed in the manner of reducing the switching voltage after a predefinable time interval has elapsed. The time interval is selected in accordance with the technical specifications in the data sheets of the inductive load to be switched so that it is ensured that the current shoulder Ss occurs within this predetermined time interval. In this case the circuit arrangement according to FIG. 1 is closed modify that a time interval monitoring unit is to be provided instead of the sensor unit 1. It can happen that e.g. B. an armature in a coil cannot be moved because the movement is blocked due to a disturbance. In this case there is no current shoulder and in order to prevent the maximum voltage from being constantly applied to the coil and thereby damaging the coil, it is advantageous to reduce the maximum voltage to the holding voltage after a predefinable time interval.

In the following, reference is made to FIG. 3, in which switching voltages are shown. 3a shows a switching voltage in the form of a DC voltage, the maximum voltage Um being twice the nominal load voltage Un and the holding voltage Uh being two thirds of this nominal load voltage Un. Such a DC voltage with variable amplitude is generated by the voltage generating unit 4 (FIG. 1), which varies the switching voltage as a function of the control signal 6.

FIG. 3b shows a clocked version, with the DC component of the holding voltage of two thirds of the nominal load voltage being achieved from an instant T3 by an AC voltage with a corresponding amplitude and clock rate.

Such a pulsating DC voltage with constant amplitude and variable pulse-pause ratio (duty cycle) can advantageously be used as a switching voltage in a circuit arrangement shown in FIG. 4 for switching several inductive loads with movable parts. For the sake of simplicity, the control of only one output channel is shown in FIG. The same parts in Figures 4 and 1 are provided with the same reference numerals.
A voltage generating unit 4 'connects the maximum voltage Um (FIG. 3b) to the inductive load 2 via the controllable switch 3 and a sensor unit 1'. In the event that the sensor unit 1 'detects a current shoulder and / or a predeterminable time interval has elapsed, the sensor unit 1 'connects an AND logic element 16 to a pulse-pause signal 6', as a result of which the controllable switch 3 switches the maximum voltage Um in accordance with the pulse-pause ratio (duty cycle) of this pulse-pause signal switches on or off. This switching on or off of the maximum voltage Um in accordance with the duty cycle that can be predetermined by the sensor unit generates a constant component from time T3 (FIG. 3b), which corresponds to the holding voltage Uh (FIG. 3a).

A circuit arrangement for switching a load, regardless of the type of load to be switched, be it an ohmic load, a capacitive load, an inductive load with or without movable parts, is shown in simplified form in FIG. The same parts in Figures 1 and 5 are provided with the same reference numerals. In contrast to the circuit arrangement according to FIG. 1, the circuit arrangement according to FIG. 5 has a time generator 15, which is provided for specifying evaluation time intervals. A first evaluation time interval is provided to recognize whether the load to be switched is an inductive or another load, e.g. B. is an ohmic, capacitive or lamp load. If an inductive load is detected, a second time interval is provided, in which it can be detected whether the inductive load is an inductive load with or without moving parts. The respective start and end of the time intervals are indicated by the time generator 15 of the voltage generating unit 4, which in this time intervals supplies the switching 2 with the corresponding switching voltages as a function of the control signal 6 via the switch 3, as will be shown below.

For a more detailed illustration of the function and mode of operation of the circuit arrangement shown in FIG. 5, reference is made to FIG. 6, in which current and voltage profiles are shown, with voltage and current profiles of an ohmic, a capacitive and a lamp load being shown in FIG. 6a between a switch-on point in time t1 and a switch-off point in time t4, a voltage and current curve of an inductive load without movable parts between these points in time are shown in FIG. 6b and a voltage and current curve of an inductive load with movable parts between these points in time in FIG. 6c.

It is assumed that at time t1, during the duration of a first evaluation time interval between time T1 and time T2, a first switching voltage Un, which essentially corresponds to the nominal voltage of the load 2 to be switched, is suddenly switched to the load 2 to be switched , As described, the sensor unit 1 detects the load current I and supplies the voltage generating unit 4 with a control signal 6 corresponding to this load current I. In the event that the sensor unit 1 detects a current drop or no change in the current during this first time interval (FIG. 6a), which indicates that the load 2 is an ohmic, a capacitive or a lamp load, the voltage generating unit 4 switches the Load 2 continues to the first switching voltage Un until the switch-off time t4.

In the event that the sensor unit 1 detects a current rise (FIGS. 6b, 6c), which indicates an inductive load, the voltage generating unit 4 first increases the switching voltage to a maximum switching voltage Um in a sudden or clocked manner, as a result of which the inductive load is switched quickly is effected. In order to recognize whether the inductive load is an inductive load with movable parts or an inductive load without movable parts, it is necessary that the sensor unit 1 during a predefinable second time interval following the first time interval between the time t2 and a third time t3 continues to record the load current. In the event that no load current shoulder is detected during this second time interval between the time t2 and the time t3, which is indicated indicates that the load 2 is an inductive load without moving parts (Figure 6b), due to the control signal 6 generated by the sensor unit 1, the voltage generating unit 4 from step t3 to the switch-off time t4 reduces the switching voltage to the first switching voltage in a sudden or clocked manner U.N.
In contrast, in the event that the sensor unit 1 detects a load current shoulder (FIG. 6c), which indicates an inductive load with moving parts, the voltage generating unit 4 reduces the switching voltage in a step-wise or clocked manner to a holding voltage from the third time t3 to the switch-off time t4 Uh, which is less than the nominal load voltage Un, which reduces the energy consumption.

Claims (6)

1. Method of switching a load (2) to which a switching voltage (U, Un, Um, Uh) can be fed, characterized by the following method steps:

   a) step-like application of the switching voltage to a first predeterminable voltage that is substantially equal to the rated voltage (Un) of the load (2) to be switched,

   b) determination of the load current (I) during a first predeterminable time interval between a first time instant (t1) and a second time instant (t2),

   c) keeping the first predeterminable voltage (Un) constant up to the switching-off of the switching voltage at a first switch-off time instant (t4) if the load current (I) drops in the first time interval or remains the same,

   d) step-like or clocked increase of the switching voltage to a maximum switching voltage (Um) if the load current rises in the first time interval, in which case, if a load current shoulder (Ss) is registered during a predeterminable second time interval following the first time interval between the second time instant (t2) and a third time instant (t3) the switching voltage is reduced step-like or clocked to a holding voltage (Uh) from the third time instant (t3) up to the switch-off time instant (t4) and if no load current shoulder (Ss) is registered during the second time interval, the switching voltage is reduced step-like or clocked to the first switching voltage (Un) from the third time instant (t3) up to the switch-off time instant (t4).
2. Method according to Claim 1, characterized in that the holding voltage (Uh) is less than the load rated voltage (Un).
3. Method according to Claim 1, characterized in that the switching voltage is a direct voltage having variable amplitude or a pulsating direct voltage having constant amplitude and variable mark-space ratio (duty cycle).
4. Circuit arrangement for performing the method according to any one of Claims 1 to 3, wherein

   - means (1) are provided for registering the load current shoulder (Ss) and means are provided for setting a time interval,

   - wherein said means (1) are connected in series with the load (2) and a controllable switch (3),

   characterized
   in that said means (1) are connected to voltage-generating means (4) that generate a switching voltage (Un, Um, Uh) that can be fed via the controllable switch (3) to the load (2), wherein a time generator (15) is provided that predetermines for the voltage-generating means (4) how long the respective switching voltages (Un, Um, Uh) are to be fed to the load (2).
5. Digital output unit for a memory-programmable control system with a circuit arrangement according to Claim 4, wherein a control signal (6) can be fed to the controllable switch (3) by a CPU of the memory-programmable control system.
6. Digital output unit according to Claim 5, having a plurality of output channels, wherein there can be connected to every channel

   - a load (2) via a controllable switch (3) and

   - means (1) for registering the load current shoulder (Ss)