METHOD FOR PROTECTING A NONMOBILE WORK MACHINE DRIVEN BY AN ELECTRIC MOTOR, AND NONMOBILE WORK MACHINE DRIVEN BY AN ELECTRIC MOTOR

Abstract

A method for protecting a nonmobile work machine driven by an electric motor includes determining, via a measuring unit, at least one measured value of a time-critical parameter of the work machine. The work machine is switched off when the determined measured value of the time-critical parameter is outside a predefined setpoint range. The determined measured value of the time-critical parameter is quantized in a level signal and transmitted as a first signal to an evaluation unit via an interface, and a second signal for further information concerning the work machine, to be transmitted from the measuring unit to the evaluation unit, is modulated to the first signal.

Claims

1. A method for protecting a nonmobile work machine driven by an electric motor, at least one measured value of a time-critical parameter of the work machine being determined via a measuring unit, the work machine being switched off when the determined measured value of the time-critical parameter is outside a predefined setpoint range, and the determined measured value of the time-critical parameter being quantized in a level signal (i.sub.1, i.sub.2, i.sub.3, i.sub.4) and transmitted as a first signal to an evaluation unit via an interface, characterized in that a second signal for further information concerning the work machine, to be transmitted from the measuring unit to the evaluation unit, is modulated to the first signal.

2. The method according to claim 1, characterized in that a fluid energy machine or a conveyor system or a hoist is used as the work machine.

3. The method according to claim 1, characterized in that the determined measured value of the time-critical parameter for representing different states of the work machine is quantized in at least two different levels and transmitted as the first signal.

4. The method according to claim 1, characterized in that the second signal is a digital data signal having a defined data transmission rate.

5. The method according to claim 1, characterized in that the second signal is modulated to the first signal at a predefined amplitude.

6. The method according to claim 1, characterized in that the second signal is modulated to the first signal at an amplitude that is smaller than the smallest difference between all provided levels of the first signal.

7. The method according to claim 4, characterized in that the second signal is formed from a higher signal level and a lower signal level.

8. The method according to claim 4, characterized in that the second signal is frequency-modulated and formed from two different frequencies.

9. The method according to claim 4, characterized in that the second signal is modulated by pulse width modulation, wherein the digital data signal of the second signal is made up of two different pulse widths of the positive pulse, of the negative pulse, or both.

10. The method according to claim 1, characterized in that a demodulation is provided, wherein the first signal and the second signal are evaluated separately, and thus independently of one another.

11. The method according to claim 1, characterized in that the work machine may be placed in a programming mode in which data are transmitted from the evaluation unit to the measuring unit via the interface.

12. The method according to claim 1, characterized in that a current interface, voltage interface, optical interface, or some other physical interface is used as the interface between the evaluation unit and the measuring unit.

13. A nonmobile work machine driven by an electric motor, and having a protective device that includes at least one measuring unit and one evaluation unit, which are connected to one another for transmitting information via an interface, a first signal to be transmitted from the measuring unit to the evaluation unit being designed as a level signal, and the evaluation unit being connected to a switch-off device for switching off the work machine as a function of the first signal, characterized in that a second signal to be transmitted from the measuring unit to the evaluation unit is modulated to the first signal.

14. The work machine according to claim 13, characterized in that the measuring unit has at least one first sensor for determining a time-critical parameter of the work machine.

15. The work machine according to claim 13, characterized in that the switch-off device has at least one first protective relay that assumes a deactivated or activated state as a function of the first signal in order to switch off the work machine in the event of a malfunction.

16. The work machine according to claim 13, characterized in that the evaluation unit also has at least one display unit or data interface for outputting further information that is transmitted via the second signal.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Further advantages and embodiments of the invention are explained in greater detail with reference to the following description and the drawings.

[0016] The drawings show the following:

[0017] FIG. 1: shows a block diagram of the work machine according to the invention,

[0018] FIG. 2: shows a quantized signal pattern (first signal) of the measured value of the time-critical parameter,

[0019] FIG. 3: shows a signal pattern of a digital data signal (second signal according to a first variant) at a predefined amplitude and at a defined data transmission rate (baud rate),

[0020] FIG. 4: shows a signal pattern of a digital frequency-modulated data signal (second signal according to a second variant) that is formed from two different frequencies, and

[0021] FIG. 5: shows a signal pattern of the mixed signal, the digital data signal (second signal) according to FIG. 2 being modulated to the first signal.

DETAILED DESCRIPTION

[0022] The block diagram in FIG. 1 shows a work machine 1, which in particular is a fluid energy machine (a compressor or a pump, for example) or a conveyor system or a hoist. The work machine in particular has an electric motor 2, a measuring unit 3, and an evaluation unit 4. The measuring unit 3 includes at least one sensor 5, which is a temperature sensor, for example, situated in one of the windings of the electric motor 2. The evaluation unit 4 is connected to a switch-off device 6 which includes at least one first protective relay 7 that assumes a deactivated or activated state as a function of the first signal in order to switch off the work machine 1, in particular the electric motor thereof, in the event of a malfunction. The transmission of the information between the measuring unit 3 and the evaluation unit 4 takes place via a (current) interface 8, with a current loop I for transmitting information between the measuring unit 3 and the evaluation unit 4. In addition, a line 9 to the voltage supply, and a ground line 10 are provided.

[0023] The signal transmitted between the measuring unit 3 and the evaluation unit 4 via the current loop I is a mixed signal made up of a first signal 11 and a second signal 12 (FIG. 5). In the illustrated exemplary embodiment, the first signal, which transmits the time-critical parameter determined via the sensor 5, may assume four different predefined levels i.sub.1, i.sub.2, i.sub.3, i.sub.4 (FIG. 2), each corresponding to different states of the work machine. Thus, for example, it may be specified in the evaluation unit 4 that at a level i.sub.4, the switch-off device 6 or its protective relay 7 causes the work machine 1 to switch off. The other three levels i.sub.1, i.sub.2, i.sub.3 indicate states of the work machine that are still noncritical, and depending on the level, may correspond to different temperatures of the motor winding, for example.

[0024] The second signal 12 may be a digital data signal having a predefined amplitude (FIG. 3), the digital data signal being made up of a higher (high) and a lower (low) signal level. According to FIG. 5, the second signal 12 in FIG. 3, having a predefined amplitude, is modulated to the first signal 11.

[0025] While the information content of the first signal 11 in the illustrated exemplary embodiment is only 2 bits (4 states), a significantly higher information content of typically several kB may be transmitted via the second signal.

[0026] The time-critical parameter, which is transmitted as the first signal, indicates in real time the instantaneous state of the work machine, and therefore may cause the work machine to switch off within a very short time if the time-critical parameter, which is determined by the sensor 5, should be outside a predefined setpoint range. The information of the second signal, which requires a significantly longer time for transmission, thus does not delay the transmission of the first signal. The second signal 12 is not safety-relevant, and therefore also does not result in the work machine being switched off. Consequently, there is also no real-time requirement here.

[0027] The digital data signal may be formed by other modulation methods such as period modulation, frequency modulation, or pulse width modulation (FIG. 4). Similarly, the second signal 12 according to FIG. 4 may also be modulated to the first signal 11 (FIG. 2).

[0028] In addition to the transmission of the first and second signals 11 and 12 between the measuring unit and the evaluation unit, it is also possible to transmit information from the evaluation unit 4 to the measuring unit 3 via the current loop, for example by placing the work machine 1 in a particular programming mode. This information may be, for example, a changed number of predefined signal levels for the time-critical signal 11, a new association of the levels with the temperature ranges, and/or other configuration values for the measuring unit 3. The work machine 1 may be brought into the particular programming mode, for example, by connecting a very uncommon resistance value, which is never to be expected during normal operation of the work machine 1, to the measuring unit 3 at the location of the temperature sensor 5 within the first three seconds after the supply voltage is switched on.

[0029] The evaluation unit 4 may also have least one display unit 13 or a data interface for outputting further information that is transmitted via the second signal 12.