METHOD FOR DETERMINING THE VOLUME FLOW OF A PUMP ARRANGEMENT AND ASSOCIATED PUMP ARRANGEMENT

Description

[0001] The invention relates to a method for determining the total volume flow of a pump arrangement comprising at least a first and a second pump unit operated in parallel, each of which is operated at a predeterminable speed.

[0002] Pump arrangements with two or more pump units operating in parallel are known, for example, as double pumps or multi-pumps, or are used between two Y-pipes. They are used where the discharge pressure of a single pump unit is insufficient or where reliability is desired. In the latter case, it may be more energy-efficient to operate two or more pumps simultaneously instead of using alternative modes.

[0003] A double pump comprises two drive units connected to a common pump housing. The pump units are thus structurally combined. The pump housing contains two spatially independent pump chambers, each of which rotates an impeller driven by one of the two drive units. A common suction channel splits in the pump housing to flow into each of the two pump chambers, and a pressure channel branches off from each of the two pump chambers, which merge into a common pressure channel in the pump housing.

[0004] An alternative arrangement of two pump units operating in parallel is achieved by using two Y-pipes. In this case, each pump unit has its own pump housing and the pump units are structurally independent.

[0005] However, they form a structural unit in the overall arrangement. The division of the suction channel and the convergence of the pressure channels are each achieved by a Y-shaped Y-pipe, which is arranged upstream and downstream of the two pump units in the direction of flow. In the case of a multi-pump system, also known as a booster system, two or more pump units operate in parallel, fed from a common pressure line with individual suction lines branching off in a T-shape, and pumping via individual pressure lines into a central pressure line, into which they discharge in a T-shape.

[0006] To control and / or regulate a pump arrangement with two or more pump units, it is often necessary to know the volume flow delivered by the arrangement. For example, reference is made to US 2018 / 129177 A1, which discloses such a system for controlling a multi-pump unit in which an alternative determination of the total volume flow is used. In some cases, knowledge of the delivered volume flow is also of interest independently of the control and / or regulation of the pump arrangement. To determine the volume flow, a sensor that measures the volume flow directly can be used. However, such a sensor is prone to errors and increases the manufacturing costs of the pump arrangement. Methods are also known for calculating the volume flow from the speed and power consumption of the pump unit. However, such methods only provide reliable values within a limited operating range of the pump unit.

[0007] European patent EP 3123033 B1 describes a method for determining the volume flow rate of a single pump unit without the use of a sensor. The method involves modulating the pump unit's speed with an excitation signal and evaluating the resulting system response. This method is applicable across virtually the entire operating range of the pump unit. The content of this patent is hereby expressly incorporated by reference.

[0008] Investigations have shown that the application of the method known from EP 3123033 B1 to a double pump is not effective. If each of the pump units executes the method from EP 3123033 B1 autonomously, mutual interference occurs due to the proximity of the pump units. The system response depends not only on the excitation signal, but also on the delivery status of the other pump unit. It can also happen that one pump unit delivers into the other pump unit.

[0009] It is therefore an object of the present invention to provide a method that enables the determination of the volume flow in a pump arrangement with two or more pump units operating in parallel without the need for a volume flow sensor. Furthermore, it is an object of the invention to provide such a pump arrangement for implementing the method. This object is achieved by a method having the features of claim 1 and by a pump arrangement having the features of claim 10. Advantageous further developments are specified in the subclaims and are explained below.

[0010] Further investigations have shown that the mutual influence of the pump units is due to the fact that the discharge head or the generated differential pressure of one pump unit is not at its maximum at the same time as the discharge head or the generated differential pressure of the other pump unit. In other words, the fluctuating discharge heads are not in phase. It was determined that this is due to the different excitation of the speed, or more precisely, to a phase difference in the excitation signals, which in turn is caused by the fact that each pump unit, or rather its pump electronics, determines its own excitation signal based on a time base provided by its own timer.

[0011] In order to avoid the above-mentioned disadvantage, the method according to the invention proposes that a control variable of the first pump unit is subjected to a first periodic excitation signal and a control variable of the second pump unit (1) is subjected to a second periodic excitation signal, so that the differential pressure of the respective pump unit is modulated, the first and second pump units each determine the value of a mechanical or electrical variable as a system response to the excitation signal and, from the determined value, determine the current value of the respective pumped volume flow using a link between the variable and the volume flow, and that the determined current values of the respective pumped volume flow are added to obtain the total volume flow, where the excitation signals are synchronized.

[0012] The synchronization ensures that the phase position of one excitation signal is adjusted to the phase position of the other excitation signal, so that both pump units are excited identically, ie modulated in phase.

[0013] A pump unit is understood below to be a structurally or functionally interacting combination of a drive unit, a centrifugal pump with pump housing, which is driven by the drive unit, and pump electronics for controlling and / or regulating the drive unit, whereby two centrifugal pumps can also have a common pump housing, as is the case with a double pump.

[0014] The formation of the excitation signal, the design of the connection and the evaluation of the system response can be carried out according to the method described in European patent EP 3123033 B1, so that reference is made to this document.

[0015] For example, in each pump unit, the product of the system response and a periodic function of the same or a multiple of the frequency of the excitation signal, or the product of the system response and the alternating component of the mechanical or electrical variable of the pump unit, can be calculated. The integral of this product can be calculated over a specified integration period, with the volume flow being determined from the value of the integral using the link. The periodic function can be a sine function, for example.

[0016] The link can be a table or at least a mathematical function that assigns an integral value to each value or to a number of flow rate values at a specific speed or multiple speeds. The relationship between the integral value and the flow rate at a specific speed can be empirically determined by the manufacturer of the pump assembly for a variety of speeds. If a specific speed is specified for the first or second pump unit during operation of the pump assembly, the flow rate can then be determined from the link using the calculated integral value.

[0017] The manipulated variable can be a target speed or a target torque of the respective pump unit. Furthermore, the mechanical variable can be the torque output by the respective pump unit or its actual speed. The electrical variable can be the electrical power or current consumed by the respective pump unit.

[0018] The excitation signal is, for example, a sine signal or a signal containing a sine function. The frequency of the excitation signal is preferably between 0.01 Hz and 100 Hz. Furthermore, the amplitude of the excitation signal can be less than 25% of the specified speed of the pump unit, in particular between 0.1% and 25% of the specified speed.

[0019] To synchronize the two excitation signals, one design variant can provide the first excitation signal to the second pump unit as an analog signal, for example, a voltage signal. This is done via a wired analog interface, in the simplest case via a two- or multi-pole terminal, which can be present on each of the pump units and are connected to each other via a cable. The pump units then receive the same excitation signal at the same time.

[0020] Since the analog signal is time-continuous, it contains the phase information of the first excitation signal. It can then be used to adjust the phase position of the second excitation signal to the phase position of the first excitation signal. For this purpose, the second excitation signal can, for example, be replaced by the analog signal or the analog signal can form the second excitation signal. In other words, the second pump unit can use the analog signal directly as its own excitation signal. The second pump unit can alternatively evaluate the phase position of the analog signal, for example by determining the time of the zero crossing of the analog signal and comparing it with the time of the zero crossing of the second excitation signal. The comparison can, for example,by forming the difference, whereby the phase of the second excitation signal is adjusted depending on the difference, so that the second excitation signal oscillates in phase with the analog signal.

[0021] As an alternative to the first excitation signal, angle information used to calculate it can be provided as an analog signal, for example, a voltage signal. In short, the angle information ωt, rather than the excitation signal itself, is transmitted to the second pump unit as an analog signal. Thus, the pump units have the same time base for calculating the respective excitation signal.

[0022] According to another embodiment, a digital interface can be provided between the pump units to provide the first excitation signal or angle information used to calculate it to the second pump unit as a digital signal. However, such an interface must enable sufficient real-time transmission speed. The transmission rate depends on the selected excitation frequency and the permissible angle error. With a permissible error of 3.6° (1 / 100 period) and an excitation frequency of, for example, 10 Hz, this results in a transmission rate of at least 1 kHz.

[0023] The digital interface can be an electrical or an optical interface.

[0024] According to a further embodiment, the pump units can communicate with each other via a communication interface, in particular in the form of a bus, for example, via a serial bus. Synchronization information of the first excitation signal is preferably transmitted to the second pump unit via the communication interface, whereupon the phase position of the second excitation signal is adjusted to the phase position of the first excitation signal.

[0025] Ideally, the bus is the communication connection that already exists between the two pump units to control the operation of the pumping arrangement. One of the pump units can act as the master, the other as the slave. For example, the first pump unit can act as the master, and the second pump unit as the slave. The transmission of only one synchronization information enables the use of a communication interface with a low transmission rate. For example, the transmission rate (the temporal resolution) can be as low as 100 ms.

[0026] Preferably, the synchronization information is or contains a time indication indicating the occurrence of a specific event in the first excitation signal. The time indication can, for example, be a timestamp that the first pump unit generates upon the occurrence of the event based on its system time supplied by a timer in its pump electronics. Ideally, the occurrence of the event triggers an interrupt so that the event can be detected outside of the normal communication cycle on the bus.

[0027] An event can be, for example, the case where the excitation signal has a positive zero crossing (crossing through zero from negative to positive values), or reaches its positive or negative maximum value, or the end of a period. The end of a period can be determined, for example, based on a falling edge in the angle information used to calculate the first excitation signal, where the angle information forms the remainder of dividing the argument ωt by 2π (360°).

[0028] Alternatively, the time specification can be a reference time from which the time of occurrence of the event can be determined. For example, the time specification can be formed from a time stamp that is generated when the event occurs and a delay time added to it, which includes, for example, the duration for signal processing on the first pump unit and / or the duration of data transmission via the communication interface to the second pump unit. This takes into account that the synchronization information is not sent instantaneously when the time stamp is generated, but that a certain time delay can occur before it is sent. It must also be taken into account that the data transmission to the second pump unit takes time. As a result, these delays lead to the synchronization information being received by the second pump unit later than the time the time stamp was generated.Since the second pump unit doesn't know how long the delay is or was, it can't correctly relate the timestamp to its own system time. This situation is avoided by considering the sum of the delays in the time specification. It should be noted, however, that the delay time can be ignored if the total delay is negligible.

[0029] An empirically determined, average constant delay from the generation of the timestamp to the receipt of the synchronization information at the second pump unit can be used as the delay time.

[0030] The second pump unit, in turn, can determine the time of occurrence of the same event in the second excitation signal, for example, by generating a timestamp. Thanks to the synchronization information, it can then determine the time difference between the events and adjust the phase position of the second excitation signal by the difference.

[0031] Although the first pump unit can communicate the occurrence of each event to the second pump unit by transmitting corresponding synchronization information, the second pump unit is not required to synchronize the second excitation signal for each event, since it can be assumed that the system times between the pump units will not have diverged, or will not have diverged too much, since the last event occurred. For this reason, it can be provided that only every nth piece of synchronization information, for example, only every tenth or twentieth, is used to align the phase position of the second excitation signal with the phase position of the first excitation signal. Thus, a correction is only performed every n cycles.

[0032] According to the invention, a pump arrangement according to claim 10, in particular a double pump unit or multi-pump unit, is also proposed, comprising at least a first pump unit and a second pump unit operated in parallel, each of which can be operated at a predeterminable speed, wherein the pump arrangement is designed to carry out the method according to the invention.

[0033] In the pump arrangement, the first pump unit can, for example, act as the master and the second pump unit as the slave.

[0034] Further features, advantages and properties of the method according to the invention and of the pump arrangement in which the method is implemented are explained below with reference to exemplary embodiments and the attached figures.

[0035] It should be noted that, in the context of this description, the terms "have," "comprise," or "include" in no way exclude the presence of other features. Furthermore, the use of the indefinite article for an object does not preclude its plural.

[0036] The reference symbols retain their meaning from one figure to the next. Identical reference symbols indicate identical or at least functionally equivalent elements. They show: Fig. 1: a schematic representation of a pump arrangement with two parallel pump units Fig. 2: a diagram showing the course of the angle information over time Fig. 3: a representation of the integrated system response multiplied by a sine function without synchronization of the pump units Fig. 4: a representation of the integrated system response multiplied by a sine function with synchronization of the pump units Fig. 5: a simplified block diagram showing communication in a pump arrangement with three pump units Fig. 6: a simplified block diagram showing two pumps, each with a controller for motor and hydraulic control.

[0037] Fig. 1 shows a schematic representation of a pump arrangement 1 of the type of a double pump with two parallel pump units 2, 3, each having a drive motor and pump electronics 6, 7 as well as a common pump housing. A central suction channel 4 splits into individual channels, each leading into a pump chamber of the pump housing, from which in turn a pressure channel branches off, which opens into a common pressure channel 9 at a connection point 9, at which a non-return valve is present. A first pump unit 2 with first pump electronics 6 delivers a first volume flow Q1 at a target speed predetermined by the latter, a second pump unit 3 with second pump electronics 7 delivers a second volume flow Q2 at a target speed predetermined by the latter, the volume flows in the pressure channel 5 adding up to a total volume flow Qtotal.The two pump electronics 6, 7 communicate with each other via a serial bus 8.

[0038] To determine this total volume flow Qges, the target speed n 0 of the first pump unit 2 is subjected to a first periodic excitation signal f A,n (t) and the target speed n 0 of the second pump unit 3 is subjected to a second periodic excitation signal f A,n (t), so that the actual speed and consequently the differential pressure of the respective pump unit 2, 3 are modulated. The excitation of the respective pump unit 2, 3 is thus achieved by modulating the stationary target speed n 0 with an excitation signal f A,n (t), so that the new target speed n soll to be set by the pump electronics 4 results from the sum of the previously specified target speed n 0 and the excitation signal f A,n (t): n soll = n 0 + f A , n t

[0039] The first and second excitation signals f A,n (t) are sinusoidal signals that are identical in amplitude and frequency. They are described, for example, by f A , n t = n 1 sin ωt with the amplitude n 1 and the frequency ω = 2 πf.The amplitude is, for example, 1% of the target speed n 0 . Although the first and second excitation signals f A,n (t) are mathematically equal, the two pump units 2, 3 are not excited identically. This is because in practice there is a phase difference between the excitation signals f A,n (t) which is due to different system times or differences in the timing of the timers (clocks) in the pump units 2, 3. This is because each pump electronics unit 6, 7 has a timer and a microcontroller (CPU) for regulating / controlling the respective pump unit 2, 3. The timer clocks the operating speed of the microcontroller, which calculates the respective excitation signal based on the clock rate specified by the timer. Firstly, the numerical calculation of the excitation signals in the first and second pump units 2, 3 does not start at exactly the same time, and secondly the timers or clocks are running.the system clock times diverge from time to time.

[0040] Figur 2 illustrates purely as an example the angle information ωt of the first and second excitation signals over time, which is used to numerically calculate the respective excitation signals. It corresponds to a sawtooth curve that runs linearly from -180° to +180°, and then, at the end of a full period, starts again at -180° with a falling edge. This curve is obtained by using the remainder of a division with remainder (modulo function) of a counting variable n 1° by 360° and shifting it by 180° for symmetry around 0°: ωt =mod ( n·1° / 360°) - 180°. In the Fig. 2 In the example shown, the angle information ωt of the first pump unit 2 globally by the time ΔT S to the angle information ωt of the second pump unit, which leads to a corresponding phase shift between the first and second excitation signals. For this reason, the method known from EP 3123033 B1 for determining the volume flow rate for a single pump unit cannot be readily applied to a pump arrangement 1 with more than one pump unit 2, 3, provided that these are located close to each other, as described in Fig. 1 This is illustrated by the two diagrams in Fig. 3 clearly.

[0041] To determine the respective volume flow, the first and second pump units 2, 3 first determine their power consumption as the system response X(t) to the respective excitation signal. Subsequently, the current value of the respective pumped volume flow Q1, Q2 is determined from this power consumption using a link between the power consumption and the volume flow. This is done in such a way that the integral I(t 0 +T) of the product of the system response X(t) and a periodic function S(t) = sin( ωt ) is calculated over a period T. The periodic function can be a sine function of the same or a multiple of the frequency (f) of the excitation signal. The link is given by a table or at least a mathematical function that assigns a value of the volume flow Q to the value of the integral I(t 0 +T) for each preset speed n 0 . This relationship has been empirically determined in advance at the factory and in Fig. 4 to recognize.

[0042] The two diagrams in Fig. 3 show values of the calculated integral I(t 0 +T) over the measured flow rate Q for different speeds at the first pump unit 2, left diagram, and at the second pump unit 3, right diagram. As can be seen from a comparison of the right diagram with the left diagram, the integral values differed extremely. Furthermore, the integral I(t 0 +T) for the second pump unit 3, right diagram, does not provide any meaningful values, whereas the values in the left diagram are meaningful up to a flow rate of 20 m 3 / h. This is due to the mutual influence of the pump units 2, 3 during modulation by the excitation signal. It should be noted that these curves in Fig.3 Although representative, they are random because they depend on the phase position. This means that a measurement at a different time would produce different curves.

[0043] To minimize this influence, the excitation signals are synchronized in the method according to the invention by adjusting the phase position of the second excitation signal to the phase position of the first excitation signal. For this purpose, the first pump unit 2 or its pump electronics 6 generates synchronization information TS,1 in the form of a time stamp or point in time, which is generated at a falling edge of the angle information ωt which is used to calculate the first excitation signal. For example, when a falling edge of the angle information ωt an interrupt is triggered. The first pump unit 2 transmits this synchronization information TS,1 with low latency to the second pump unit 3. The second pump unit 3 or its pump electronics 7 receives the synchronization information TS,1 with low latency and in turn generates a time stamp TS,2 or time when a falling edge of the angle information ωt occurs, which is used to calculate the second excitation signal. The second pump unit 3 then calculates the difference ΔT S between the time stamp TS,1 of the synchronization information and the last self-generated time stamp TS,2 and shifts the phase position of the second excitation signal by this difference in order to align its phase with the phase of the first excitation signal.

[0044] Thus, the speeds of the two pump units 2, 3 are excited synchronously, i.e. in phase. The result of this synchronous excitation is shown in the diagrams in Fig. 4 that correspond to the diagrams in Fig. 3 It can be seen that the integral values I(t 0 +T) for both pump units 2, 3 for the different speeds increase linearly over the flow rate and that there is a clear correlation between the integral value and the flow rate. The values shown in the two diagrams of Fig. 4 The values shown form the above-mentioned link for the respective pump unit 2, 3 in the form of a table or an equation, which assigns a corresponding volume flow from the calculated integral value I(t 0 +T) for a certain target speed n 0 . Thus, the diagrams in Fig. 4 the first volume flow Q1 and the second volume flow Q2. These determined current values of the respective delivered volume flow Q1, Q2 are then added to obtain the total volume flow Qtotal of pump arrangement 1.

[0045] For the synchronization of the excitation signals, it is irrelevant whether the first pump unit 2 or the second pump unit 3 forms the master in the pump arrangement 1. Thus, either the master can adapt its excitation signal to the excitation signal of the slave, or vice versa. However, if the pump arrangement comprises more than two pump units and therefore two or more slaves are present, it is advisable for reasons of control sovereignty for all slaves to adapt to the master. This illustrates Fig. 5 Using the example of a multi-pump system, in which the first pump unit 2 represents the master and the second pump unit 3 represents a first slave. The master 2 transmits the synchronization information TS,1 not only to the second pump unit 3, i.e., the first slave, but also to a third pump unit 3a, i.e., a second slave. Its pump electronics 7a then performs identical synchronization of its excitation signal to the first slave 3, 7.

[0046] Fig. 6shows an embodiment of a pump arrangement 1 with two pump units 2, 3, whose pump electronics 6, 7 each have a system controller 11, 13 and a motor controller 10, 12. While the system controller 11, 13 specifies the target speed based on a specific pump regulation or pump control, the motor controller 10, 12, which also includes a frequency converter, regulates this target speed. The modulation of the speed by the excitation signal is also carried out by the motor controller 10, 12. The activation of this modulation and evaluation of the system response, however, takes place in the respective system controller 11, 13. Both controllers 10, 11, 12, 13 have their own microcontroller and a timer to execute their respective tasks. These motor controllers 10, 12 generate the respective time stamp TS,1 , TS,2 at a falling edge of the respective excitation signal and send it to the respective system controller 11, 13.The system controller 13 of the first pump unit 2 transmits the time stamp TS,1 in the synchronization information via its communication interface 15 and the bus 8 to the second pump unit 3, which receives the synchronization information via its communication interface 14.

[0047] Due to this internal structure of the pump electronics 6, 7, a delay may occur due to the processing of the synchronization information TS,1 in the first pump unit 2. Data transmission via bus 8 may also cause a noticeable delay. This may result in the time stamp TS,1 of the synchronization information in the system controller 11 of the second pump unit 3 being incorrectly compared with a more recent time stamp TS,2. To avoid this, the potentially occurring delays during signal processing and data transmission from the system controller 13 are added to the first time stamp TS,1, and the resulting time information T' S,1 is transmitted as synchronization information to the second pump unit 2.Its system control 11 then forms the difference between this time indication T' S,1 and the time stamp TS,2 and shifts the phase position of the second excitation signal by this difference in order to match its phase to the phase of the first excitation signal.

[0048] Although the first pump unit transmits corresponding synchronization information to the second pump unit on each falling edge, the second pump unit does not need to adjust its excitation signal on a periodic basis. It is sufficient to use only every nth synchronization information piece to adjust the phase position of the second excitation signal to the phase position of the first excitation signal. For example, this only occurs every tenth or twentieth synchronization information piece.

[0049] It should be noted that the foregoing description is provided merely by way of example for the purpose of illustration and in no way limits the scope of the invention. Features of the invention stated as "may," "exemplary," "preferred," "optional," "ideal," "advantageous," "optionally," or "suitable" are to be considered purely optional and do not limit the scope of protection, which is determined exclusively by the claims. To the extent that the foregoing description recites elements, components, method steps, values, or information that have known, obvious, or foreseeable equivalents, these equivalents are encompassed by the invention as long as such embodiments actually fall within the scope of the claims.

[0050] Likewise, the invention includes any changes, variations or modifications of embodiments that involve the replacement, addition, change or omission of elements, components, method steps, values or information, as long as such embodiments actually fall within the scope of the claims, regardless of whether the change, variation or modifications result in an improvement or deterioration of an embodiment.

[0051] Although the above description of the invention mentions a multitude of physical, non-physical, or method-related features in relation to one or more specific embodiments, as long as such embodiments actually fall within the scope of the claims, these features can also be used in isolation from the specific embodiment, at least as long as they do not require the mandatory presence of further features. Conversely, these features mentioned in relation to one or more specific embodiments can be combined with each other as desired, as well as with further disclosed or undisclosed features of shown or not shown embodiments, at least as long as the features do not exclude each other or lead to technical incompatibilities and as long as such embodiments actually fall within the scope of the claims.

Claims

1. Method for determining the total volume flow (Qges) of a pump arrangement (1) comprising at least a first and a second pump unit (2, 3) operated in parallel, each of which being operated at a predeterminable speed, wherein - a manipulated variable of the first pump unit (2) is superimposed with a first periodic excitation signal and a manipulated variable of the second pump unit (3) is superimposed with a second periodic excitation signal, so that the differential pressure of the respective pump unit (2, 3) is modulated, wherein each pump unit (2, 3) determines its excitation signal itself according to its own time base that comes from its own internal clock, - the first and second pump unit (2, 3) each determine the value of an own mechanical or electrical variable as a system response to the excitation signal, and - determine the current value of the volume flow (Q1, Q2) delivered in each case from the determined value using a connection between the variable and the volume flow, and - the determined current values of the respectively conveyed volume flow (Q1, Q2) are added to obtain the total volume flow (Qges), characterised in that the excitation signals are synchronised.

2. Method according to claim 1, characterised in that the first excitation signal or an angle information used to calculate it provided to the second pump unit (2) as an analogue or digital signal, and the phase position of the second excitation signal is adjusted to the phase position of the first excitation signal on the basis of this signal.

3. Method according to claim 1, characterized in that the pump units (2, 3) communicate with one another via a communication interface (14, 15), notably a serial bus (8), and a synchronisation information element of the first excitation signal is sent to the second pump unit (2) via the communication interface (14, 15), and wherein thereupon the phase position of the second excitation signal is adjusted to the phase position of the first excitation signal.

4. Method according to claim 3, characterized in that the synchronization information element is or contains a time specification that specifies the point of time of the occurrence of a specific event in the first excitation signal.

5. Method according to claim 4, characterized in that the event is a positive zero crossing, the reaching of a maximum or minimum of the first excitation signal or a zero crossing of the angle information used to calculate the first excitation signal.

6. Method according to claim 4 or 5, characterized in that the time specification is a time stamp that is generated when the event occurs, or the time specification being a reference time from which the time at which the event occurred can be determined.

7. Method according to claim 5 or 6, characterized in that the time specification is formed by a time stamp generated when the event occurs, and a delay time added to it for signal processing on the first pump unit (2) and / or for data transmission.

8. Method according to claim 4, 5, 6 or 7, characterized in that the second pump unit (3) determines the point of time of occurrence of the same event in the second excitation signal, determines the time difference between the events, and adjusts the phase position of the second excitation signal by the difference.

9. Method according to one of the claims 3 to 8, characterized in that only every n-th synchronisation information element is used to adjust the phase position of the second excitation signal to the phase position of the first excitation signal.

10. Pump arrangement, notably a dual pump unit or multi-pump unit, comprising at least one first and one second pump unit (2, 3) operated in parallel, each of which can be operated at a predeterminable speed, wherein each pump unit (2, 3) comprises a drive unit, a centrifugal pump with pump casing driven by the drive unit, and pump electronics (6, 7) for closed loop control and / or open loop control of the drive unit, and in which each pump unit (2, 3), and its pump electronics (6, 7) respectively, determines its excitation signal itself according to its own time base that comes from its own internal clock, characterised in that the pump arrangement is configured to carry out the method according to one of the preceding claims.