Pump Control

Abstract

A pump control system for controlling a fluid pump powered by an AC signal. The pump control system includes a signal phase detector coupled to the fluid pump to detect the AC signal supplied to the fluid pump and to generate phase signals indicating a phase parameter of the AC signal. The pump control system also includes a micro-controller to receive the phase signals and to generate a rectified output signal based on the phase signals, and a relay to control the power supplied to the fluid pump based on the output signal of the micro-controller.

Description

RELATED APPLICATION

This application claims the benefit of U.S. Patent Application No. 60/575,136, titled “Pump Control,” filed on May 28, 2004, the entire content of which is incorporated herein by reference.

BACKGROUND

The present invention relates to a pump, and more particularly to a control system for the pump.

A submersible pump is typically activated to pump water from a well into a connected water tank such that the water pressure within the tank remains within predetermined levels. However, the submersible pump can overheat in a relatively short amount of time if water is unavailable to be pumped to the tank. Additionally, since the number of pump-on times is directly proportional to pump wear, more pump-on time will wear out the pump at a faster rate.

SUMMARY

Accordingly, there is a need for a pump control system that detects water availability. In one form, the invention provides a pump control system that includes a water pump, a pressure transducer, a current phase detector, a voltage phase detector, and a micro-controller (“MCU”). When an AC signal is supplied to the pump, the current transducer and related circuitry will sample the AC signal and send the sampled AC signal to a current phase detector whose output indicates an operating current phase of the pump. The output signal of the current phase detector is then fed into the MCU. Meanwhile, an operating voltage of the pump is fed into a voltage phase detector whose output indicates an operating voltage phase of the pump. The output signal of the voltage phase detector is similarly fed into the MCU.

The system also includes a current transformer from which the pump operating current is sampled. The extracted pump operating current is sent to an amplifier to yield a squared current signal. Similarly, the voltage signal is also fed to a second amplifier to yield a squared voltage signal. Both the squared current signal and the squared voltage signal are subsequently sent to the MCU for processing. The MCU determines an actual phase angle difference between the squared current signal and the squared voltage signal. Since the determination process is performed digitally, variations in the operating voltage signals and current signals have minimum or no effect on the process. In this way, inaccuracy and inconsistency of phase angle detection caused by inaccuracy and inconsistency of transistors and amplifiers of the circuits can be minimized or avoided. Furthermore, discretely processing the phase angle allows the system to adjust or control the phase angle settings when different pumps are used for the system.

Additionally, modified amplitudes of the current and voltage signals are filtered and fed into a comparator circuit. The comparator circuit then compares the filtered signals with some reference values. The comparator outputs are subsequently fed into the MCU. The MCU thus outputs a signal to activate a plurality of solid state relays. A display such as an LED, can also be coupled with the MCU to indicate the water pressure detected by one or more semiconductor pressure transducers.

In one construction, the invention provides a pump control system for controlling a fluid pump powered by an AC signal. The pump control system includes a signal phase detector coupled to the fluid pump to detect the AC signal supplied to the fluid pump and to generate phase signals indicating a phase parameter of the AC signal. The pump control system also includes a micro-controller to receive the phase signal and to generate a rectified output signal based on the phase signals, and a relay to control the power supplied to the fluid pump based on the output signal of the micro-controller.

In another construction, the invention provides a pump control system for controlling a fluid pump powered by an AC signal. The pump control system includes a signal phase detector to detect the AC signal supplied to the fluid pump. The AC signal typically has an AC current component and an AC voltage component. As a result, the signal phase detector then generates a phase signal indicating a phase shift between the AC current component and AC voltage component. The pump control system also includes a micro-controller to receive the phase signal and to generate a rectified square wave signal based on the phase shifts, the AC current component and AC voltage component, and a relay to disconnect and to connect the power supplied to the fluid pump based on the rectified square wave signal of the micro-controller.

Other features and advantages of the invention will become apparent to those skilled in the art upon review of the following detailed description, claims, and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a pump control and protection system incorporating the invention.

FIG. 2 is a circuit diagram of the electrical components of one construction of the pump control and protection system of FIG. 1.

FIG. 3 is a circuit diagram of one construction of a phase detector capable of being used in the pump control and protection system of FIG. 1.

FIG. 4 is a circuit diagram of one construction of a reset circuit capable of being used in the pump control and protection system of FIG. 1.

FIG. 5 is a block diagram of a three-phase pump control and protection system incorporating the invention.

DETAILED DESCRIPTION

Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless limited otherwise, the terms “connected,” “coupled,” and “mounted” and variations thereof herein are used broadly and encompass direct and indirect connections, couplings, and mountings. In addition, the terms “connected” and “coupled” and variations thereof are not restricted to physical or mechanical connections or couplings.

FIG. 1 illustrates a block diagram of a pump control system 100 incorporating the invention. The pump control system 100 is generally powered by an alternating current (“AC”) power source, and includes an amplifying module 104 that is coupled to a micro-controller 108. A pressure range selection circuit 112 is also coupled to the micro-controller 108 to select an operating range for a pump 116 and a pressure tank 120, both of which are coupled to the micro-controller 108. The pump control system 100 also includes a display unit 128 that is configured to display various system information such as water pressure in the pump 116 and other operational status. Although FIG. 1 shows only the control system 100, the pressure tank 120, and the pump 116, other pump system devices and components, such as a starting circuit, can also be connected to the system 100. Additionally, while the starting circuit may be connected to the control system 100 via electrical conductors, the water pressure tank 120 is connected to the pump 116 using a water line.

FIG. 2 shows a circuit diagram of one construction of the pump control system 100 of FIG. 1. Particularly, as shown in FIG. 2, the amplifying module 104 includes first and second subsystems having overlapping components. The first subsystem includes a zero-pressure tuning circuit 132. The zero-pressure tuning circuit 132 includes a potentiometer 136 and an operational amplifier 140 coupled to the potentiometer 136. Adjusting the potentiometer 136 will tune the amplifier gain, thereby tuning an output of the amplifying module 104. Specifically, under zero pressure condition, the potentiometer 136 can be adjusted such that the display unit 128 is set to display zero pressure. In this way, an operator of the system 100 can calibrate the display 128 to display all zeros by adjusting the zero-pressure tuning circuit 132, and in particular, by turning the potentiometer 136, when no pressure is applied to any pressure fitting of the system 100.

The second subsystem includes a pressure signal amplifying circuit 144. The pressure signal amplifying circuit 144 includes a plurality of operational amplifiers 140, 146, and 148, and potentiometers 136, 150, 152, and 154. Among the potentiometers, potentiometers 136, 150, and 152 are used to adjust or tune a zero-pressure balance of the amplifying module 104, while the other potentiometer 154 is generally used for gain adjustment. In this way, the operator of the system 100 can adjust the potentiometer 154 to calibrate the pressure reading when a reference pressure is applied to the pressure fitting. As a result, no adjustment is necessary for manufacturing or producing these parts in general. This allows the operator to use other similar pressure transducer while maintaining linearity of the pressure transducer.

The pressure range selection circuit 112 includes a hydraulic pressure adjustment circuit 156. By fine tuning the hydraulic pressure adjustment circuit 156, the pump control system 100 can regulate a maximum amount of hydraulic pressure the MCU 108 can measure. The hydraulic pressure adjustment circuit 156 includes a voltage divider circuit 160 that connects to a 2-position dipswitch 164. The voltage divider circuit 160 includes a plurality of resistors R2, R22, and R23. With the two-position dip switch 164 being set to provide four different values, the voltage divider circuit 160 can therefore generate four specific voltage output values. The voltage output of the voltage divider circuit 160 is then fed to an A/D input port PB7 168 of the MCU 108. In this way, output values of the voltage divider 160 are sampled to obtain a plurality of operating ranges of the pump 116. Furthermore, an operating hydraulic pressure range of the pump control system 100 can be pre-determined and set. In one construction, there are eight ranges. These ranges are between 20 and 40 (or 30) lb/in², between 30 and 50 (or 40) lb/in², between 40 and 60 (or 50) lb/in², and between 50 and 70 (or 60) lb/in².

A feedback differential pressure tuner 172 is also coupled to the MCU 108 and is configured to fine-tune a feedback differential pressure to a desired pressure level. Specifically, the feedback differential pressure tuner 172 includes a second voltage divider 176 arranged with a plurality of capacitors, and a second 2-position dipswitch 180. Depending on how the second 2-position dipswitch 180 is set, different levels of electrical signals are generated. As a result, the feedback differential pressure can range between 10 lb/in² and 20 lb/in². Furthermore, the feedback differential pressure tuner 172 also includes a fifth potentiometer 184 that can be adjusted to tune a maximum water pressure range to 50 lb/in² and 70 lb/in². In this way, with an increment step of X between 0 lb/in² and 19 lb/in², the pressure range is between 50+X lb/in² and 70+X lb/in².

Furthermore, the display unit 128 includes a plurality of indicators or LED's 200, a digital display 204, and a drive circuit 208. The display unit 128 uses the LED's 200 to display a plurality of operating status of the control system 100 and the pump 116. In one construction, there are six LED's in the display unit 128 to indicate a low-water status detected by the system, an overload status, a rapid-cycle status, an undervoltage status, and an overvoltage status.

The pump control system 100 also includes a reset button K1 212 and a set button K2 216 for setting or resetting the pump control system 100 under conditions such as system failure, low-water alarm, and overload alarm. During the setting or the resetting process, the LED's 200a, 200b will flash for the low water alarm and the overload conditions, while the LED 200d will indicate an alarm threshold value.

In some constructions, after pressing K1 212 and holding for a short period of time, such as 2 seconds, the system 100 will enter into a phase angle setup mode. The overload indicator light 200b flashes while the display 204 shows a factory set overload phase angle protection value. The phase angle will reduce 1 degree by pressing K2 216 once. The phase angle will reduce continuously at a 2 Hz rate by pressing and holding K2 216 until the required value is reached. Pressing K1 212 again, the low water indicator light 200a flashes while the display 204 shows the factory set low water protection value. The phase angle will increase 1 degree by pressing K2 216 once. The phase angle will increase continuously at a 2 Hz rate by pressing and holding K2 216 until the required value is reached. Pressing K1 212 again exits the setup mode.

FIG. 3 shows a phase detecting circuit 300. A current transformer 304 is connected to a current detector 308. An operational amplifier LM358(B) 312 is configured to compare an output of the amplifier module 104 and a predetermined value that is obtained by determining a ratio between the coupled resistors R52 and R53. Thereafter, the operational amplifier LM358(B) 312 sends out a square-wave signal indicating a present current phase, which will be sent to the MCU 108 through a first lead 316. Meanwhile, another operational amplifier LM358(A) 320 of a voltage phase detector 324 produces a square-wave signal by comparing a sampled voltage from the power source and predetermined voltage value. The square wave signal is then fed to the MCU 108 through a second lead 328. A phase difference between the voltage signal and the current signal is determined by the MCU 108 and is used to detect and control the pump 116.

FIG. 4 shows a power circuit 400 of the pump control system 100 according to the invention. The power circuit 400 includes a power supply circuit 404 that supplies power to the system 100, a power-on reset (“POR”) circuit 408 that is coupled to the MCU 108, a solid state relay driver 420 to drive a relay configured to connect or disconnect power from the power supply to the pump 116, a power supply voltage detecting circuit 424, a crystal oscillating circuit 428, and a voltage fluctuation detecting circuit 430, among other things.

The POR circuit 408 includes components such as dynatron 432, resistors, and capacitors. The POR circuit 408 generates reliable signals in order to ensure that the MCU 108 works normally under abnormal conditions, such as a low voltage reset. The power supply voltage detecting circuit 424 includes components such as potentiometer 436, resistors R9 440 and R6 444, and a Zener diode 448 parallel to a capacitor C3 452 and the resistor R6 444. An analog-to-digital module of the MCU 108 is also configured to convert the analog differential pressure voltage sensed by the amplifying module 104 into a digital differential pressure voltage. The MCU 108 compares the digital differential pressure voltage with a high voltage alarm threshold value and a low voltage alarm threshold value to ensure that the pump 116 operates within a pre-determined range, and to protect the pump motor from damages by overcurrent, overvoltage, or undervoltage. Therefore, adjusting or tuning the potentiometer W6 436 allows the reference threshold values of the high and low voltages to be adjusted. Furthermore, the crystal oscillating circuit 428 includes components such as a 4 MHz oscillator OSC 452 parallel to a resistor R1 454 and capacitors C1 456 and C2 458. The crystal oscillating circuit 428 provides a standard high frequency clock-pulse signal for the operation of sequential circuitry of the MCU 108.

In some constructions, adjusting potentiometer 436 slightly clockwise reduces the power supply nominal voltage that is typically set at 230 VAC. In this way, the operating voltage range can be lowered. However, to raise the operating voltage range, the potentiometer 436 is adjusted slightly counter-clockwise to increase the power supply nominal voltage. In general, adjusting the potentiometer 436 does not alter the minimum specification for pump operation, for example, about −15% to stop pump and about −10% automatic reset for the under voltage protection, about +15% to stop pump and about +10% automatic reset for over voltage protection.

In one construction, the MCU 108 is programmed to turn the solid state relay driver 420 and the LED's 200 on and off in response to different control signals. The MCU 108 also includes internal clock circuits for performing the various timing functions. Although the MCU 108 is a micro-controller in the pump control system 100, other types of devices such as a microprocessor or an application specific integrated circuit (“ASIC”) can also be used.

An analog water pressure signal from the amplifying module 104 is fed into the A/D conversion port 168 of MCU 108 through the operational amplifier circuit 144. The MCU 108 will determine the water pressure condition according to the detecting A/D value. The two-position dip switch 164, and a one position dip switch on the system 100 allows the pressure range to be preset to one of eight ranges: 20-40 pounds per squared inch (lb/in²), 30-50 lb/in², 40-60 lb/in², 50-70 lb/in², 20-30 lb/in², 30-40 lbs/in², 40-50 lb/in², and 50-60 lb/in². In addition, the adjustable potentiometer W5 can adjust the working range between 50-70 lbs/in² and 50-60 lbs/in² to (50+X)-(70+X) lbs/in² and (50+X)-(60+X) lbs/in² where X is between 0 and 19 lbs/in². The overvoltage or undervoltage circuit functions to generate overvoltage or undervoltage signals for the MCU 108, and for the overvoltage or undervoltage LEDs. Furthermore, the power supply transformer 404 functions to lower the voltage to a value more suited for the system.

FIG. 5 shows a pump protection controller 500 that connects a three-phase pump 504 to a junction box 508. The junction box 508 includes an overcurrent protection device 512, a thermal relay 516 with the three-phase protection device 512 and an AC connector controlled by a solid state relay 520. A three-phase power supply having inputs L1, L2, L3, N, PE is divided into two parts. Inputs L3, N and PE are connected with the pump protective controller system 100, and L3 is series connected with the output end of the solid state relay 520 after passing a current transducer loop L3. Inputs L3, L1, and L2 are all connected into the junction box 508, in which the AC connector loop will start and stop under the control of the solid state relay of the pump control system 100.

The operation of the pump control and protection system 100 is summarized by the following examples. For example, during normal operation of the pump 116, power from the power supply is provided to the system 100. Once the system 100 has been reset, the MCU 108 resets, and the LED 200f is off. If the MCU 108 only detects a low water pressure signal from the amplifying module 104, the relay and the LED 200f are switched on, and thus activates the pump 116. However, if the MCU 108 only detects a high water pressure signal, the relay and the LED 200f are switched off, and thus deactivates the pump 116.

For another example, when the MCU 108 detects a low water condition, such as when the pump 116 is underloaded, the relay is turned off. Once the relay has been turned off, a timer with a specific amount of time delay will be set, and the LED 200a is lit. Once the amount of time delay has elapsed, the relay is switched back on. Furthermore, if the MCU 108 detects that the water pressure is high, the relay is switched off, the LED 200a is turned off, and the system 100 returns to a normal operating condition. Otherwise, if an idle condition persists, the relay is switched off, and a timer with a delay time is set. Once the delay time has elapsed, the relay is switched on.

For another example, if the MCU 108 detects that the pump 116 has been overloaded, the LED 200b is lit, and the relay is switched off until the MCU 108 has been reset. However, if the MCU 108 detects an overvoltage or undervoltage from the pump 116, the relay is switch off, either the LED 200d or the LED 200e is lit, respectively, until the voltage phase detector detects normal level of voltage is supplied.

Additional functions of the pump control and protection system 100 is summarized by the following examples.

EXAMPLE 1

Functions of Regulating Eight Water Supply Pressure Ranges

The analog water pressure signal is loaded to the A/D converter port of the MCU 160 through a linear operational amplifier. The MCU 108 examines or determines a state of water pressure based on an A/D value, and allows the pressure range to be preset at one of the eight ranges through the 2-position dip switch 164 and 1-position dip switch of the system 100. Furthermore, adjusting potentiometer 184 adjusts a differential pressure fed to the MCU 108, thereby controlling maximum water supply pressure operating ranges at 50-70 lb/in² and 50-60 lb/in² via an internal conversion routine. With an adjustment range X between 0 and 19 lb/in², the converted operating range is therefore (50+X)-(70+X) lb/in² and (50+X)-(60+X) lb/in².

EXAMPLE 2

Function of Adjusting Feedback Differential Pressure Value of the Pump 116

The feedback differential pressure circuit 172 includes resistors R7, and R5 1, capacitor C30, and switch 180. Depending on the dipswitch position, which is either “ON” or “OFF,” a high or low logic level is generated. With these logic levels, the system 100 can choose a differential pressure between 10 lb/in² and 20 lb/in².

EXAMPLE 3

Application of Pump Motors of Different Phase Characteristics

The system 100 has an operation for regulating the phase of an electric motor, as to be applied to different phase characteristics with different load conditions. The operator presses K2 216 to set the lower limit phase angle, and presses K1 212 to regulate the alarm phase angle. The operator presses K2 216 again to set a higher limit phase angle, and presses K1 212 to regulate the alarm phase angle. The operator presses K2 216 again to confirm and save the setting values.

EXAMPLE 4

Application of Pressure Transducers of Different Output Characteristics

Adjusting the potentiometer 154 can regulate the magnified signal of pressure transducer. Adjusting the second and the third potentiometers 150, 152 can regulate the linearity of the pressure transducer signal. While the “zero” value of the pressure transducer can be regulated through adjusting the fourth potentiometer 136. Thus, the circuit can use different types of transducers.

Pressing K2 216 and K1 212 regulates the motor alarm phase threshold values, which also can be seen through the LED display 200. A data set will be stored in a FLASH ROM of the MCU 108 and will not be lost during a power outage. The over/under voltage alarm threshold value is set by way of software, and can be adjusted by the potentiometer 184.

EXAMPLE 5

Application of the Connected Junction Box 508 with Three-Phase Pump 504

The pump control system 100 may connect to a three-phase pump 504 with a junction box 508. Junction box 508 can be applied to a three-phase pump motor with different inputs, since the motor may include an overcurrent protector that can set an operating current, a thermal relay with phase-lock protection, and an AC contactor controlled by a solid state relay in the pump protector.

Various features and advantages of the invention are set forth in the following claims.

Claims

1. A pump control system for controlling a fluid pump configured to be powered by an AC signal, the pump control system comprising:

a signal phase detector coupled to the fluid pump, and configured to detect the AC signal supplied to the fluid pump, and to generate phase signals indicating a phase parameter of the AC signal;

a micro-controller coupled to the phase detector, and configured to receive the phase signal and to generate a rectified output signal based on the phase signal; and

a relay configured to control the power supplied to the fluid pump based on the rectified output signal of the micro-controller.

2. The pump control system of claim 1, further comprising an adjustable pressure range input coupled to the micro-controller, and configured to adjust a pressure range detected by the micro-controller.

3. The pump control system of claim 1, wherein the adjustable pressure range input comprises an adjustable pressure range switch.

4. The pump control system of claim 1, further comprising a calibratable gain input coupled to the micro-controller, and configured to adjust a gain for the signal phase detector.

5. The pump control system of claim 1, further comprising a waterproof seal configured to waterproof the control system.

6. The pump control system of claim 1, further comprising a plurality of adjustable inputs coupled to the micro-controller, and configured to adjust a plurality of operating ranges of the system.

7. The pump control system of claim 6, wherein the adjustable inputs comprise a power supply nominal voltage input configured to adjust a power supply voltage, and a zero-adjust input configured to calibrate a zero pressure reading when no pressure is detected.

8. The pump control system of claim 1, further comprising a phase angle adjust input coupled to the micro-controller, and configured to adjust a phase angle based on a type of the fluid pump.

9. The pump control system of claim 8, wherein the phase angle is adjusted at an increment of at least one of 1 degree, and 2 Hz.

10. The pump control system of claim 1, wherein the AC signal comprises at least one of a current signal and voltage signal, and wherein the signal phase detector comprises a current phase detector configured to detect a current phase of the current signal, and a voltage phase detector configured to detect a voltage phase of the voltage signal.

11. The pump control system of claim 1, wherein the phase signals comprise at least one of a current phase signal and a voltage phase signal.

12. The pump control system of claim 1, wherein the phase parameter comprises a phase shift between the phase signals.

13. The pump control system of claim 1, wherein the rectified output signal has a rectified frequency, and wherein the rectified output signal comprises a square wave having the rectified frequency.

14. The pump control system of claim 1, wherein the micro-controller comprises a microprocessor configured to detect the AC signal supplied to the fluid pump, and to generate phase signals indicating a phase parameter of the AC signal.

15. A pump control system for controlling a fluid pump configured to be powered by an AC signal, the pump control system comprising:

a signal phase detector coupled to the fluid pump, and configured to detect the AC signal supplied to the fluid pump, the AC signal having an AC current component and a AC voltage component, the signal phase detector also configured to generate a phase signal indicating a phase shift between the AC current component and AC voltage component;

a micro-controller coupled to the phase detector, and configured to receive the phase signal and to generate a rectified square wave signal based on the phase shifts, the AC current component and AC voltage component; and

a relay configured to disconnect and to connect the power supplied to the fluid pump based on the rectified square wave signal of the micro-controller.

16. The pump control system of claim 15, further comprising an adjustable pressure range input coupled to the micro-controller and configured to adjust a pressure range detected by the micro-controller.

17. The pump control system of claim 15, further comprising a calibratable gain input coupled to the micro-controller, and configured to adjust a gain for the signal phase detector.

18. The pump control system of claim 15, further comprising a waterproof seal configured to waterproof the control system.

19. The pump control system of claim 15, further comprising a plurality of adjustable inputs coupled to the micro-controller, and configured to adjust a plurality of operating ranges of the system.

20. The pump control system of claim 19, wherein the adjustable inputs comprise a power supply nominal voltage button configured to adjust a power supply voltage, and a zero-adjust input configured to calibrate a zero pressure reading when no pressure is detected.

21. The pump control system of claim 15, further comprising a phase angle adjust input coupled to the micro-controller, and configured to adjust a phase angle based on a type of the fluid pump.

22. The pump control system of claim 21, wherein the phase angle is adjusted at an increment of at least one of 1 degree, and 2 Hz.

23. The pump control system of claim 15, wherein the micro-controller comprises a microprocessor configured to receive the phase signal and to generate the rectified square wave signal based on the phase shifts, the AC current component and AC voltage component.

24. A method for controlling a fluid pump configured to be powered by an AC signal, the fluid pump is coupled to a micro-controller, a phase detector and a relay, the method comprising:

determining an AC current component from the AC signal at the phase detector;

determining an AC voltage component from the AC signal at the phase detector;

determining a phase shift between the AC current component and the AC voltage component at the micro-controller;

generating a control signal based on the phase shift at the micro-controller; and

disconnecting and connecting the power supplied to the fluid pump based on the control signal from the micro-controller at the relay.

25. The method of claim 24, further comprising:

adjusting an adjustable pressure range input; and

adjusting a pressure range corresponding to the adjustable pressure range input.

26. The method of claim 24, further comprising:

calibrating a calibratable gain input; and

adjusting a gain for the signal phase detector.

27. The method of claim 24, further comprising adjusting a button to reduce a power supply nominal voltage.

28. The method of claim 24, further comprising adjusting a zero-adjust input to calibrate a zero pressure reading when no pressure is detected.

29. The method of claim 24, further comprising adjusting a phase angle adjust input to adjust a phase angle based on a type of the fluid pump.

30. The method of claim 29, wherein the phase angle is adjusted at an increment of at least one of 1 degree, and 2 Hz.