KR100872909B1 - Control circuit for emergency generator and driving method thereof - Google Patents

Abstract

A control circuit for an emergency generator and a driving method thereof are provided to improve operation reliability by applying a power outage signal to a microprocessor by operating a second photo coupler even though a contact of a relay is short circuited or damaged. An alternating voltage source applies the AC voltage to the load. Both ends of a coil are electrically connected to the alternating voltage source in a relay. A first photo coupler is electrically connected to the contact point of the relay. The second photo coupler and the relay are connected in parallel with the alternating voltage source. The first photo coupler and the second photo coupler are electrically to a microprocessor. The microprocessor outputs a driving signal to a starting motor by receiving the power outage signal from one of the first and second photo couplers.

Description

Emergency generator control circuit and its driving method {Control Circuit For Emergency Generator And Driving Method Thereof}

The present invention relates to an emergency generator control circuit and a driving method thereof, and more particularly, to an emergency generator control circuit and its driving method that can improve the failure to detect a power failure due to breakage or failure of the relay contact.

In general, an electric device that requires continuous operation includes an emergency generator therein, and an emergency generator control circuit for controlling the driving of the emergency generator. The emergency generator consists of a starting motor and an engine driven by it. In the emergency generator control circuit, when a power failure occurs, the relay connected to the voltage source is short-circuited (open depending on the circuit configuration) to apply an electric signal to the MICOM. In addition, the microcomputer receives the electric signal and applies a driving signal to the starter motor, and the starter motor drives the engine to generate power to be supplied to the load.

However, when the contact point of the relay is short-circuited, the electric signal cannot be applied to the microcomputer. That is, in this case, even though no voltage is applied from the voltage source, the microcomputer does not recognize the microcomputer, and thus the microcomputer cannot drive the emergency generator. In addition, when the contact point of the relay is broken, even if the voltage source is normally driven in the microcomputer, the microcomputer determines that the power failure causes the emergency generator to continue to drive.

Therefore, even if a power failure occurs because the voltage source does not operate, the emergency generator is not driven, causing a problem that voltage is not supplied to the load. In particular, such a problem is a serious problem because the load may be directly connected to a serious problem that cannot be recovered, such as the occurrence of human injury, especially when a motor is used for an elevator or the like.

The present invention is to overcome the above-mentioned conventional problems, an object of the present invention is to provide an emergency generator control circuit and its driving method that can improve the failure to detect the power failure due to the breakage or failure of the relay contact. .

In order to achieve the above object, the emergency generator control circuit according to the present invention includes an AC voltage source for applying an AC voltage to a load, a relay electrically connected at both ends of the coil, and a first end electrically connected to one end of the contact of the relay. A photo coupler, a second photo coupler connected in parallel with the relay to the AC voltage source, and electrically connected to the first photo coupler and the second photo coupler, and outage from at least one of the first photo coupler and the second photo coupler It may include a microcomputer receiving a signal to output a drive signal to the starter motor.

Here, the contact of the relay may be a contact or b contact.

And a first resistor electrically connected to the other end of the relay and electrically connected between the first voltage source, the first voltage source, and the first photo coupler to supply a first voltage to the first photo coupler when the relay is turned on. This can be further formed.

Further, a second resistor connected in series between the first photo coupler and the microcomputer, a third resistor having one end connected to the second resistor, and a second voltage source connected to the other end of the third resistor to supply a second voltage Can be further formed.

In addition, a first capacitive element may be connected between the second resistor and the contact point of the microcomputer and the ground to apply an electrical signal to the microcomputer.

Further, a fourth resistor connected between one end of the AC voltage source and one end of the second photo coupler between the AC voltage source and the second photo coupler, and a fifth resistor connected to the other end of the AC voltage source and the other end of the second photo coupler. This may be further formed to form a loop.

Further, a sixth resistor connected in series between the second photo coupler and the microcomputer, a seventh resistor having one end connected to the sixth resistor, and a third voltage source connected to the other end of the seventh resistor to supply a third voltage. Can be further formed.

In addition, a second capacitive element may be connected between the sixth resistor and the contact point of the microcomputer and the ground to apply an electrical signal to the microcomputer.

In addition, in order to achieve the above object, a method of driving an emergency generator control circuit according to the present invention includes a first photo coupler connected to the AC voltage source through a relay and a second photo coupler connected in parallel with the relay to the AC voltage source. A signal determination step of determining whether a power failure is received from at least one selected, a start motor driving step of driving the start motor by the microcomputer, and an ACB driving of the engine connected to the start motor by driving the microcomputer by the microcomputer The method may include a start motor stop step of stopping the start motor by the microcomputer and an ACB stop step of stopping the engine by the micom stopping the ACB.

Here, a delay time determining step may be further performed between the signal determining step and the starting motor driving step to determine whether a predetermined delay time has elapsed since the microcomputer receives the power failure signal.

In addition, between the start motor driving step and the ACB stop step, the microcomputer measures the driving frequency of the starter motor to determine whether to drive or stop the starter motor, and the microcomputer drives the starter motor. A start motor stop step may be further made to stop.

The determining of the driving frequency may include determining that the microcomputer stops the starting motor when the driving frequency reaches the reference frequency by comparing the frequency of the starting motor with a reference frequency.

In addition, the frequency driving determination step may be that the reference frequency is 550rpm.

As described above, the emergency generator control circuit and the driving method thereof according to the present invention may include a first photo coupler to apply a more accurate signal to the microcomputer, and include a second photo coupler connected in parallel with the relay to contact the relay. If the second photo coupler is operated even if it is broken or shorted, the electrostatic signal can be applied to the microcomputer, thereby increasing the reliability of the operation.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily practice the present invention.

Hereinafter will be described the configuration of the emergency generator control circuit according to the present invention.

1 shows an emergency generator control circuit according to the invention.

Referring to FIG. 1, an emergency generator control circuit according to the present invention includes an AC voltage source, a relay RL connected to the AC voltage source, and a first photo coupler PC1 connected to the relay RL. And a second photo coupler PC2 connected to the AC voltage source AC in parallel with the relay RL, a microcomputer MICOM connected to the first photo coupler PC1 and a second photo coupler PC2. do. In addition, an anti-parallel diode D3 may be further connected between the AC voltage source AC source and the second photo coupler PC2.

The AC voltage source applies an AC voltage to a load (not shown) to drive the load. In addition, the AC voltage source (AC source) is connected to the MICOM (MICOM) through the emergency generator control circuit according to the present invention to apply an electrical signal. Therefore, when a power failure occurs because the AC voltage source is not driven, the microcomputer MICOM may operate to drive an emergency generator.

The relay RL is electrically connected to the AC voltage source. The relay comprises a coil and a contact. Here, both ends of the coil are electrically connected to both ends of the AC voltage source. One end of the contact is connected to the first voltage source VS1 and the other end is connected to the first resistor R1. Further, the contact may be a normally open turn-off that is open at a time when current is applied to the coil and shorted at a power failure in which the current is not applied to the coil, and vice versa May be a b contact (normally turn-on) which is shorted and opened upon power outage. Hereinafter, the case where the contact point is a contact point b will be described as an example.

When the AC voltage source AC source is normally operated, the relay RL is short-circuited by a contact. Therefore, the first voltage of the first voltage source VS1 is applied to the light emitting diode D1 constituting the first photo coupler PC1 through the first resistor R1 so that a current flows. On the contrary, in the case where the AC voltage source does not operate, that is, when a power failure occurs, the contact of the relay RL is opened to the light emitting diode D1 of the first photo coupler PC1. No current flows.

The first photo coupler PC1 is connected to the first voltage source VS1 by the relay RL to be driven. The first photo coupler PC1 includes a light emitting diode D1 and a photo transistor T1.

When the AC voltage source AC is driven in a normal state, the LED D1 is connected to the first voltage source VS1 through the relay RL to emit light. In addition, when the AC voltage source AC source does not operate, the relay RL is disconnected, so that the LED D1 does not emit light.

The photo transistor T1 is electrically insulated from the light emitting diode D1. Since the first photo coupler PC1 has a configuration in which the light emitting diode D1 and the photo transistor T1, which are components, are electrically insulated, the first photo coupler PC1 may reduce a noise signal. Therefore, the emergency generator control circuit according to the present invention may include the first photo coupler PC1 to transmit a more accurate signal to the MICOM.

In addition, the photo transistor T1 is optically matched to the light emitting diode D1 to receive the light of the light emitting diode D1. In addition, the photo transistor T1 is turned on when the light emitting diode D1 emits light. Therefore, the photo transistor T1 applies a signal of ground to the microcomputer MICOM through the second resistor R2. On the other hand, when a power failure occurs and the light emitting diode D1 does not emit light, the photo transistor T1 is turned off so that the second voltage source VS2 is connected to the second resistor R2 through the third resistor R3. Is connected to. Therefore, the second voltage of the second voltage source VS2 is supplied to the microcomputer MICOM through the first capacitive element C1.

Therefore, if the signal applied from the first photo coupler PC1 is ground, the microcomputer MICOM determines to be in a normal state, and the signal applied from the first photo coupler PC1 is connected to the second voltage source VS2. If it is the second voltage, it is determined that the power failure.

The second photo coupler PC2 is connected to the AC voltage source through a fourth resistor R4 and a fifth resistor R5. The second photo coupler PC2 is connected to the AC voltage source AC source in parallel with the relay RL to receive a voltage from the AC voltage source AC source. The second photo coupler PC2 may apply a signal to the microcomputer MICOM through a path separate from the relay RL.

The second photo coupler PC2 is connected to the AC voltage source without a separate relay. Accordingly, the second photo coupler PC2 receives an electrical signal due to the voltage of the AC voltage source AC even when the contact of the relay RL to which the first photo coupler PC1 is connected is broken or short-circuited. It may be applied to the MICOM. That is, the second photo coupler PC2 may form a path that is electrically independent of the relay RL to stably apply a signal in the event of a power failure to the microcomputer MICOM.

The second photo coupler PC2 includes a light emitting diode D2 connected to the AC voltage source and a photo transistor T2 optically matched to the light emitting diode D2. When the AC voltage source operates normally, the light emitting diodes D2 and the phototransistor T2 are turned on at the same period as the AC voltage source according to the polarity of the AC source. Repeat turn off. When the photo transistor T2 is turned on, a ground voltage is applied to the microcomputer MICOM through the sixth resistor R6. In addition, when the photo transistor T2 is turned off, the third voltage source VS3 forms an electrical path through the seventh resistor R7, the sixth resistor R6, and the second capacitor C2. The voltage of the third voltage source is transferred to the MICOM. Therefore, when the AC voltage source (AC source) is operating, a square wave having the same period as the AC voltage source is applied to the MICOM.

 In addition, when the AC voltage source AC source does not operate, the second photo transistor T2 is turned off, so the seventh resistor R7, the sixth resistor R6, and the second capacitor C2 are turned off. ), A third voltage of the third voltage source VS3 is continuously applied to the microcomputer MICOM. In this case, the third voltage source VS3 may use the second voltage source VS2 depending on the circuit configuration.

Therefore, if the signal applied from the second photo coupler PC2 is a square wave signal, the microcomputer MICOM determines that it is in a normal state, and the signal applied from the second photo coupler PC2 is the third voltage source VS3. If the DC voltage of the third voltage is maintained, it is determined that the power failure.

The antiparallel diode D3 is connected in parallel with the second photo coupler PC2. More specifically, the antiparallel diode D3 is connected in antiparallel with the light emitting diode D2 of the second photo coupler PC2. The antiparallel diode D3 protects the light emitting diode D2 from an AC voltage source. That is, when the reverse voltage is applied to the light emitting diode D2 by the AC voltage source, the antiparallel diode D3 forms a loop to allow current to flow. Accordingly, the anti-parallel diode D3 prevents the reverse voltage from being applied to the light emitting diode D2, thereby preventing the light emitting diode D2 from being damaged.

The microcomputer MICOM is electrically connected to the first photo coupler PC1 and the second photo coupler PC2. When the AC voltage source operates normally, the photodiode T1 of the first photo coupler PC1 is turned on, and a ground voltage is applied to the microcomputer MICOM. In addition, when the AC voltage source operates normally, the photodiode T2 of the second photo coupler PC2 periodically turns on and off, and the AC voltage source AC is applied to the microcomputer MICOM. A square wave having the same period as the source is applied.

On the other hand, when the AC voltage source AC source does not operate, the photodiodes T1 and T2 are turned off, and the microcomputer MICOM is formed from the second voltage source VS2 and the third voltage source VS3. A second voltage and a third voltage are applied. At this time, even when the contact of the relay RL is broken or short-circuited and thus the second voltage of the second voltage source VS2 is not applied, the second photo coupler PC2 is connected to the microcomputer MICOM. The third voltage of the third voltage source VS3 may be supplied.

The microcomputer MICOM drives a starter motor (not shown) when the continuous voltage of the second voltage source VS2 or the third voltage source VS3 is supplied. In addition, the microcomputer MICOM opens the solenoid valve and supplies fuel to an engine (not shown) connected to the starting motor to generate power. Therefore, when a power failure occurs, the microcomputer MICOM drives an emergency generator composed of a starting motor and an engine to supply the load.

As described above, the emergency generator control circuit according to the present invention may include the first photo coupler PC1 to apply a more accurate signal to the MICOM. In addition, the emergency generator control circuit according to the present invention includes a second photo coupler PC2 connected in parallel with the relay RL, so that the second photo coupler PC2 operates even if a contact of the relay RL is broken or shorted. By doing so, the electrostatic signal can be applied to the MICOM, thereby increasing the reliability.

Hereinafter will be described the operation of the emergency generator control circuit according to the present invention.

2 is a drive waveform diagram for explaining the operation of the emergency generator control circuit according to the present invention.

Referring to FIG. 2, the voltages applied to the nodes a, b, and c of the emergency generator control circuit according to the present invention, the sequence voltage S, and the driving voltage M of the starting motor are provided for each period (T1 to T6). Is shown. Hereinafter, the driving waveform of FIG. 2 will be described together with the control circuit of FIG. 1.

The T1 period shows a state in which an AC voltage source operates normally. The voltage of the AC source may be, for example, an AC voltage having a frequency of 60 Hz and an effective voltage of 220 V.

During the T1 period, the voltage of the AC voltage source is applied to the node a. Since the photo transistor T1 of the first photo coupler PC1 is turned on, the ground voltage is applied to the node b.

On the other hand, the light emitting diode D2 of the second photo coupler PC2 is repeatedly turned on and off according to the sign of the voltage applied from the AC voltage source AC source. That is, when a positive voltage is applied to the node a, the light emitting diode D2 is turned on. When a negative voltage is applied, the light emitting diode D2 is turned off. In addition, the turn-on and turn-off of the phototransistor T2 are determined according to whether the light-emitting diode D2 is turned on or off. Therefore, the ground signal is applied to the node c when the photo transistor T2 is turned on, and the second voltage of the second voltage source VS2 is applied when the photo transistor T2 is turned off. Accordingly, the voltage of the node c is represented by a square wave having a shape opposite to that of the AC source supplied to the node a.

In addition, since the microcomputer MICOM does not need to drive an emergency generator during the T1 period during which the AC voltage source AC operates normally, the microcomputer MICOM does not apply the sequence signal S and the motor driving signal M. FIG. Do not.

The T2 period illustrates a state in which the AC voltage source does not operate, that is, a state in which a power failure occurs. During period T2, no voltage is applied to node a. In addition, since the AC voltage source AC is turned off, the photo transistor T1 of the first photo coupler PC1 is turned off, and the second voltage of the second voltage source VS2 is applied to the node b. In addition, since the photo transistor T2 of the second photo coupler PC2 is turned off, the third voltage of the third voltage source VS3 is applied to the node c.

In addition, the T2 period corresponds to a delay time, and during this period, the microcomputer MICOM does not supply the sequence signal S and the start motor driving signal M. This is to ensure certainty in determining whether the microcomputer (MICOM) has a power outage by giving a margin during the T2 period.

The microcomputer MICOM applies the voltage to the starter motor M to drive the starter motor M during the T3 period. The starting motor M is driven to reach a frequency sufficient to drive the engine.

In addition, during the T3 period, the microcomputer MICOM inputs a sequence signal S to open a solenoid valve (not shown) to supply fuel to the engine. In addition, the microcomputer MICOM drives an ACB (Auto Circuit Breaker, not shown) when the rotation frequency of the starting motor M reaches a predetermined level. Here, the rotation frequency of the starting motor (M) is generally 550rpm, but is not intended to limit the content of the present invention. In addition, the ACB serves to drive the engine to operate as a generator.

The T4 period is a period in which the microcomputer MICOM stops supplying the voltage applied to the starter motor M. FIG. The starting motor M stops driving in the period T4 when a frequency sufficient to drive the engine has been reached. At this time, the frequency of the drive motor (M) is generally 550rpm or more, but the content of the present invention is not limited. In addition, of course, in the T4 period, the engine operates as a generator to transfer power to the load.

At the beginning of the T5 period, the AC generator resumes normal operation. Therefore, the AC voltage signal is displayed again at the node a connected to the AC generator during the T5 period. In addition, the node b and the node c will also receive the same voltage signal as the T1 period.

On the other hand, during the T5 period, the microcomputer MICOM maintains the sequence signal S in the T4 period. This is to confirm whether the MICOM recovers the AC voltage source by securing a delay time.

At the start of the T6 period, the microcomputer MICOM stops the application of the sequence signal S to stop the fuel supply to the engine. In addition, the ACB is stopped in the T6 period, and driving of the engine is stopped. Accordingly, the engine does not operate as a generator during the T6 period, and the AC voltage source operates as a voltage source. That is, after the T6 period, the power is normally supplied to the load by an AC voltage source.

As described above, the control circuit of the emergency generator according to the present invention may operate, and as described above, a power failure occurs in the microcomputer MICOM along the second photo coupler PC2 connected in parallel with the relay RL of the control circuit. By applying an electrical signal according to the reliability of the emergency generator operation can be improved. In addition, although not separately illustrated, when the contact point constituting the relay RL is a contact point (normally turn-on), the driving waveform appearing at the node b may appear in the opposite form to that shown in FIG. 2.

Hereinafter will be described a driving method of the emergency generator control circuit according to the present invention.

3 is a flowchart for explaining a method of driving an emergency generator control circuit according to the present invention.

Referring to FIG. 3, the driving method of the emergency generator control circuit according to the present invention includes a signal determination step S1, a delay time determination step S2, a starter motor driving step S3, an ACB driving step S4, and a driving frequency. The determination step S5, the start motor stop step S6, and the ACB stop step S7 may be included. Hereinafter, each step of FIG. 3 will be described with reference to FIGS. 1 and 2 together.

First, a signal determination step S1 is performed in which the microcomputer MICOM receives an electrical signal from the first photo coupler PC1 and the second photo coupler PC2. At this time, the microcomputer MICOM generates a power failure when the signal by the first photo coupler PC1 maintains the second voltage or the signal by the second photo coupler PC2 maintains the third voltage. After the determination, the steps are as follows.

Thereafter, a delay time determining step S2 is performed in which the microcomputer MICOM determines whether a delay time of T2 has elapsed since a power failure occurs. At this time, the MICOM proceeds to the following steps after the period of T2 elapses. Accordingly, the microcomputer MICOM may check the occurrence of the power failure through the time margin of T2.

Thereafter, the microcomputer MICOM applies a voltage to the starter motor M to drive the starter motor driving step S3. The starter motor M serves to drive the engine in an emergency such as a power failure. In addition, the microcomputer MICOM applies a sequence signal S to open the solenoid valve to supply fuel to the engine, thereby maintaining a state in which it can be driven later.

Subsequently, an ACB driving step S4 is performed in which the microcomputer MICOM drives the ACB. The ACB drives the engine to operate the engine as a generator. In general, when the driving frequency of the starter motor M reaches 550 rpm, the ACB is generally driven.

Subsequently, a driving frequency determination step S5 is performed in which the microcomputer MICOM determines the driving frequency of the starting motor M and compares it with a reference value. The microcomputer MICOM measures the driving frequency of the starting motor M to determine whether the reference value exceeds 550 rpm. In addition, when the driving frequency of the starter motor M exceeds 550 rpm, the microcomputer MICOM proceeds with the following steps.

Thereafter, a start motor stop step S6 is performed in which the microcomputer MICOM stops driving the start motor M. FIG. When the driving frequency of the starter motor M exceeds 550 rpm, the starter motor M is stopped because it is sufficient to drive the engine, after which only the engine operates as a generator.

Subsequently, when a voltage is supplied from an AC voltage source again to restore power, an ACB stop step S7 is performed in which the MICOM stops the ACB. At this time, the ACB may be stopped after the period of the T5 even after the recovery. The ACB also stops the engine from running. Therefore, the AC voltage source (AC source) instead of the engine is operated as the voltage source of the load by the ACB stop step (S7) can be driven in a normal state.

As described above, the control circuit of the emergency generator according to the present invention may be driven, and the relay RL is connected to the first photo coupler PC1 and the AC voltage source AC source connected to the AC voltage source AC by a relay. The reliability of the emergency generator operation may be improved by applying an electrical signal due to a power failure to the microcomputer MICOM along the second photo coupler PC2 connected in parallel.

1 shows an emergency generator control circuit according to the invention.

Figure 2 shows a drive timing diagram for explaining the operation of the emergency generator control circuit according to the present invention.

3 is a flowchart for explaining a method of driving an emergency generator control circuit according to the present invention.

<Explanation of symbols for the main parts of the drawings>

AC source; Alternating voltage source RL; relay

VS1; A first voltage source R1; First resistance

PC1; First photo couplers D1, D2; Light emitting diode

T1, T2; Phototransistor VS2; Second voltage source

R2; Second resistor R3; Third resistance

C1; First capacitive element R4; Fourth resistance

R5; Fifth resistor PC2; 2nd photo coupler

D3; Antiparallel diode VS3; Third voltage source

R6; Sixth resistor R7; 7th resistance

C2; Second capacitive element MICOM; Micom

Claims (13)

An AC voltage source for applying an AC voltage to the load; A relay electrically connected at both ends of the coil to the AC voltage source; A first photo coupler electrically connected to one end of the relay; A second photo coupler connected in parallel with the relay to the AC voltage source; And And a microcomputer electrically connected to the first photo coupler and the second photo coupler to receive an electrostatic signal from at least one of the first photo coupler and the second photo coupler and output a driving signal to the starter motor. Emergency generator control circuit. The method of claim 1, Emergency contact control circuit, characterized in that the contact point of the relay is a contact or b contact. The method of claim 1, A first voltage source electrically connected to the other end of the relay and supplying a first voltage to the first photo coupler when the relay is turned on; And And a first resistor electrically connected between the first voltage source and the first photo coupler. The method of claim 1, A second resistor connected in series between the first photo coupler and the microcomputer; A third resistor having one end connected to the second resistor; And And a second voltage source connected to the other end of the third resistor to supply a second voltage. The method of claim 4, wherein And a first capacitive element connected between the second resistor and the contact point of the microcomputer and the ground to apply an electrical signal to the microcomputer. The method of claim 1, Between the AC voltage source and the second photo coupler A fourth resistor connected to one end of the AC voltage source and one end of the second photo coupler; And And a fifth resistor connected to the other end of the AC voltage source and the other end of the second photo coupler to form a loop. The method of claim 1, A sixth resistor connected in series between the second photo coupler and the microcomputer; A seventh resistor having one end connected to the sixth resistor; And And a third voltage source connected to the other end of the seventh resistor to supply a third voltage. The method of claim 7, wherein And a second capacitive element connected between the sixth resistor and the contact point of the microcomputer and the ground to apply an electrical signal to the microcomputer. A signal determining step of determining whether a power failure occurs by receiving a power failure signal from at least one selected from a first photo coupler connected to an AC voltage source through a relay and a second photo coupler connected to the AC voltage source in parallel with the relay; A start motor driving step of the micom driving a start motor; An ACB driving step in which the microcomputer drives an ACB to drive an engine connected to the starting motor; A start motor stop step of stopping, by the microcomputer, the start motor; And And an ACB stop step of stopping the engine by the microcomputer stopping the ACB when the AC voltage source is restored. The method of claim 9, Between the signal determination step and the starting motor driving step of the emergency generator control circuit further comprises a delay time determination step of determining whether the predetermined delay time has passed since the microcomputer receives the power failure signal. Driving method. The method of claim 9, Between the start motor driving step and the ACB stop step A driving frequency determination step of determining, by the microcomputer, the driving frequency of the starting motor to determine whether the starting motor is driven or stopped; And And a start motor stop step of stopping the driving of the start motor by the microcomputer. The method of claim 11, In the driving frequency determination step, the microcomputer compares the frequency of the starting motor with a reference frequency, and determines to stop the starting motor when the driving frequency reaches the reference frequency. The method of claim 12, The driving method of the emergency generator, characterized in that the reference frequency is 550rpm.

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