DE3436750A1 - Method for error-free detection of an excessively low rotational speed - Google Patents

Abstract

In order to decide whether the indication of excessively low rotational speed of slow-starting machines having mechanical starting clutches is due to a fault, for example a loose contact, or a genuine excessively low rotational speed, the path of the rotational speed measuring signal is branched and the presence of the two reference signals is checked in an electronic circuit in the case of an excessively low rotational speed. If one reference signal is missing, "FAULT" is indicated.

Description

Method for error-free detection of a speed

The invention relates to a method for error-free Detection of underspeed of difficult-to-start machines with mechanical ones Centrifugal couplings.

Such a speed monitoring serves to protect the mechanical Starting couplings against overload.

Incorrect speed monitoring messages caused by encoder malfunctions, e.g. at KohlemUhlen, have repeatedly led to a shutdown, although none The speed was not reached.

The failure of a coal mill means at least a reduced power plant unit output. Under certain circumstances it can even lead to the failure of the entire block.

The object of the invention is to provide a method of the type mentioned at the beginning Kind of creating that enables a real underspeed of the mechanical drive to differentiate between brief conductor interruptions (loose contact) and encoder faults.

This is achieved according to the invention in that the eg a speed measurement signal branches and if the speed is not reached, the presence of both signals is checked will.

The invention is illustrated schematically with the aid of one in the drawings Embodiment explained in more detail.

They show: Figure 1: The devices between a proximity switch a drive shaft to be monitored and a drive, Figure 2: the circuit diagram a circuit arrangement for carrying out the method.

In Fig. 1, 19 denotes a proximity switch, as it is used for Measurement of speeds is used. It is an oscillator by itself one Coil approaching tooth on the output side of the clutch shaft attenuated briefly, resulting in an encoder measurement signal. The proximity switch 19 is via an isolating switching device 18 with a circuit arrangement 16 for fail-safe Limit value detection connected to which a speed monitor 17 is coupled. Further are terminals A, B and E on the circuit arrangement 16 for the UNDER SPEED limit value REAL "," GE-BERSTORUNG and "DRIVE ON / START OVERLAP" are provided. the clamp A for the limit value "UNDER SPEED REAL" is with the OFF switch for the motor M connected.

The circuit arrangement according to FIG. 2 is designed as follows.

A sensor measuring signal pulse is sent from the isolating switchgear 18 (FIG. 1) via terminal H by a light emitting diode D1 of a double optocoupler 13 optically via a phototransistor T1 to a terminal G in the speed monitor 17 (Figure 1) and through a light emitting diode D2 passed, which is optically coupled to a further phototransistor T2. Whose Emitter is with retriggerable monoflops 9 and 3, with a binary band filter 15 and the input of a D flip-flop 2 connected.

From a further terminal D from the speed monitor 17 (Figure 1) originates a measurement signal when the speed falls below the limit value, which is in the circuit arrangement is compared with the encoder measurement signal from the isolating switching device 18 (Figure 1).

The terminal D is connected to a first input of an AND gate 6 and via a switch-on delay 1 and via the D input of the D flip-flop with a second input of AND gate 6 connected. The binary band filter 15 is on the output side both with a third input of the AND gate 6 and with a second input another AND gate 14 connected.

The retriggerable monoflop has a first input on the output side of the AND gate 14 and a switch-on delay 4 with a fourth input of the AND gate 6 connected. The retriggerable monoflop 3 and the switch-on delay 4 together form a "binary filter".

Terminal E (drive on / start-up override) has a switch-on delay 5 both with a fifth input of the AND gate 6 and via one Further Switch-on delay 8 connected to a first input of an AND gate 10, while the retriggerable monoflop 9 on the output side to a third input of the AND gate, the output of which is connected to a negated input of AND gate 10 connected is.

A terminal F (failure of the power supply) and the output of the AND gate 10 each lead via an input to an OR gate 11, the output side is connected to an RS flip-flop 12 (encoder fault).

On the output side, the AND gate 6 leads to an RS flip-flop 7, the switches off the drive via terminal 8 in the event of a real underspeed. the RS flip-flops 12 and 7 can be reset via a switch 20 in line C. become (acknowledge).

The circuit arrangement works as follows: At a real underspeed a limit value "UNDER SPEED" is output by the speed monitor 18 via terminal D. Since the reference clock from H is available from the optocoupler 13, it will be at the B input of the D flip-flop 2 pending limit value signal to the second input of the AND gate 6 given, while at the same time it goes directly to the first input. The fifth entry of AND gate 6 is assigned to start-up bypass E and at this point in time set. The binary filter consisting of a retriggerable monoflop 3 and switch-on delay 4 switches a signal to the fourth input of AND gate 6. The binary bandpass filter If there is no damping error, 15 switches a signal to the third input of the AND gate 6.

Since now all five inputs have an H signal, the AND gate switches 6 and sets the RS flip-flop 7, which switches off the motor M (Figure 1) via terminal H.

"GEBERSTCRUNG" refers to errors that indicate a loose contact, Line break, failure of devices 17, 18 19 (Figure 1) and damping errors are to be returned.

If the contact is loose, the "UNDER SPEED" limit is set by the speed monitor 17 (Figure 1) via the switch-on delay 1 to the D input of the D flip-flop 2 switched. Since no reference signal from the optocoupler during the interruption 13 is present, the limit value cannot be switched through by the D flip-flop 2 will. The retriggerable monoflop 3 is also reset. At the fourth entrance of AND- Gate 6 behind the binary filter is an L signal at. The AND gate 6 is thus blocked.

Because of the missing reference clock, the retriggerable monoflops 3 and 9 are blocked, the AND gate 14 receives L signals at two inputs. Of the one input of the downstream AND gate 10 is negated, so that an H signal occurs. Since the start-up bypass E is set, the AND gate is at the output 10 an H signal, which via the OR gate 11, the RS flip-flop 12 GEBERSTÖRUNG actuated.

If the reference clock from the optocoupler 13 is missing due to an encoder fault, so the D flip-flop 2 is not switched through, and the two retriggerable monoflops 3 and 9 show L signals on the output side, thereby blocking AND gate 6, however, the AND gates 14 and 10 as well as the OR gate 11 and RS flip-flop 12, such as already described, switched through.

With a recurring reference cycle (encoder o.k.), terminal D the pending limit value signal from D flip-flop 2 to the second input of the AND gate 6th switched through. The AND gate 6 is still due to the missing fourth Input signal from binary filter 3, 4 blocked because the recurring reference clock the retriggerable monoflop 3 switches through directly, however, due to the switch-on delay 4 is blocked. The time t1 of the switch-on delay 4 is set so that the H signal to the fourth input of AND gate 6 only returns after the Limit value "UNDER SPEED" is no longer pending.

Encoder malfunction also includes errors that affect the damping of the proximity switch. For example, it will be one with two segment teeth damped proximity switch only damped by a segment tooth, so halved the reported speed. The speed monitor would lead to shutdown. Around To prevent this, the binary sand filter 15 is used, which consists of an exclusive OR gate with two upstream retriggerable monoflops and a downstream switch-on delay exists and only issues an L signal at the output at half the speed. When not steaming of the proximity switch by a segment tooth is activated by the speed monitor via terminal T. a limit value "UN- TERSREHZAHL ". Since the reference clock from H is present from the optocoupler 13, this is at the D input of the D flip-flop 2 pending delayed limit value signal on the second input of AND gate 6 given, while at the same time it goes directly to the first entrance. There with one Attenuation error of the output of the binary band filter 15 without delay to an L signal is set, there is a L signal at the third input of AND gate 6. So that's that AND gate blocked. At the same time, the L signal is from the output of the binary filter 15 switched to the second input of AND gate 14 and thereby triggers the message 'GENERAL FAULT ".

If the attenuation error no longer exists, the output of the binary band filter 15 is set to an H signal with a switch-on delay. The time of the switch-on delay of the "binary band filter '15 is to be set so that the H signal to the third Input of AND gate 6 only returns after the limit value "UNDER SPEED" no longer pending.

Claims (1)

Procedure for the error-free detection of an underspeed Method for the error-free detection of an underspeed of difficult-to-start machines with mechanical centrifugal clutches, characterized in that the path of a speed measurement signal branches off and if the speed falls below the The presence of both signals is checked.