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Method for diagnosing operating states of a synchronous pump, and device for carrying out said methodRelated Patent Categories: Pumps, Condition Responsive Control Of Pump Drive Motor, Responsive To Accumulation Of Pumped Liquid In ReceiverMethod for diagnosing operating states of a synchronous pump, and device for carrying out said method description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070172360, Method for diagnosing operating states of a synchronous pump, and device for carrying out said method. Brief Patent Description - Full Patent Description - Patent Application Claims
[0001] This invention relates to a method for diagnosing operating states of a synchronous pump in a liquid circuit, particularly in a dishwasher or similar. [0002] Dishwashers often make use of synchronous pumps, that is pumps driven by synchronous motors, to pump the water used for washing back from the bottom of the interior of the appliance to the spray arms, thereby creating a closed liquid circuit. This arrangement is widely used in order to save fresh water. [0003] In an ideal case, the volume of circulating water remains constant, and the synchronous pump used to circulate the water works at a constant output. Problems can occur, however, if water becomes trapped at points inside the machine from which it cannot flow away, or be pumped away, and hence is no longer available to be recycled to the spray nozzles. Such liquid reservoirs are created, in particular, by saucepans or similar containers which tip over during washing so that they finish up with their open ends facing upwards and collect the water which is directed downwards onto the items to be cleaned. Another problem is caused when water is prevented from circulating due to clogging of the filter disposed in the floor on the inside of the appliance at the inlet of the feed line of the synchronous pump. If the volume of circulating water falls below a certain minimum, the incident-free functioning of the appliance can no longer be guaranteed. Irrespective of the fact that dirty objects are not cleaned as they should be, there is a risk in this case of damage to the synchronous pump. [0004] Hence it is desirable to be able to determine the momentary operating state of the water circuit and, in particular, to ascertain that the pump is functioning correctly. Methods are known for measuring the volume of water fed into the circuit prior to the washing process. It is possible, for example, to convey the water via a wheel which will then rotate at a speed proportional to the volume of water conveyed across it. The advantage of this arrangement is that it is inexpensive, but the results are relatively inaccurate. There is no permanent monitoring of the volume of water in circulation whilst the machine is in operation. [0005] Document DE 196 30 357.5 A1 discloses a device for controlling the volume of water in a dishwasher, whereby the torque of the synchronous motor driving the pump is monitored to determine the operating state of the synchronous pump. For this purpose the power uptake of the stator winding is measured and a dosing valve for supplying the water for washing is controlled as a function thereof, thereby guaranteeing permanent monitoring of the volume of water in circulation. [0006] Document DE 24 15 171.1 A1 further discloses the measuring of the operating state of a synchronous motor by means of the phase shift between the alternating voltage applied to the motor and the alternating current. A momentary phase shift can then be assigned to a particular operating state. [0007] The prior art solution is directed towards providing a means of monitoring the operating state of synchronous machines with asynchronous start-up, and of signalling asynchronous functioning. The intention is to economise the costly and generally used method of measuring the speed of rotation, replacing it with a less expensive means of monitoring. For the particular application on which this invention is based, however, this method is only suitable to a very limited degree as not all the operating states of a dishwasher can be unambiguously identified by this prior art method. This is particularly true of the above-described problems in connection with a liquid circuit. [0008] The task of this invention is, therefore, to provide a method for diagnosing operating states of a synchronous pump of the type described above, the goal of said method being to ensure the easiest, most reliable and most cost-effective means possible of detecting and identifying a variety of operating states of the synchronous pump corresponding to malfunctions in the liquid circuit, in particular a fall in the volume of water in circulation below a minimum level and clogging of the filter. [0009] This task is solved according to the invention by means of a method according to claim 1. [0010] In the method according to the invention, an initial measurement step involves taking at least one measurement of the alternating voltage applied to, and the alternating current through, the motor. In a subsequent determination step, the extent of a phase shift occurring between the alternating voltage and the alternating current is measured. The phase shift ascertained is used in a subsequent assignment step to identify a pump's operating state. [0011] This diagnostic method is based on the knowledge that the phase shift between the voltage and the current of the synchronous pump can be used as an indicator of a pump malfunction. If, for example, a certain volume of water is withdrawn from the dishwasher water circuit, say by an upturned saucepan, there will be a change in the phase shift due to the occurrence of an air-water mix in the pump housing. Action can then be taken to correct the malfunction. The volume of water in the circuit can be topped up with fresh water, for example. It may also be possible to trigger a warning signal to alert an operator. All the steps in the method are relatively simple and inexpensive to execute, on top of which the phase shift measurement is reasonably accurate compared to conventional methods. Ongoing monitoring of the water level means that fresh water can be added exactly as required, thereby achieving a resources-saving water circuit. An additional energy-saving effect is achieved in that only the water in the circuit need be heated for the individual washing cycles. [0012] In a preferred embodiment of the method according to the invention the extent of the phase shift in the assignment step is assigned to a predetermined phase shift value range linked to a certain pump operating state. [0013] Furthermore, preferably in the determination step, the difference between the measured extent of the phase shift and a saved predetermined phase shift can be determined and in the subsequent assignment step this phase shift difference is assigned to a pump operating state. In this case, the state of the pump is identified not with reference to the measured extent of the phase shift, but to its deviation from a predetermined target value. [0014] In a preferred embodiment of the method, the determination step involves measuring the extent of the phase shift at various intervals so that the chronological progression of the phase shift can be determined from the recorded measured values. A characteristic of the chronological progression of the phase shift is ascertained for assignment to a predetermined pump operating state in the assignment step. [0015] The ascertained feature is preferably assigned to a predetermined characteristic value range linked to a pump operating state. [0016] The gradient of the slope of the chronological progression of the phase shift is preferably determined in the determination step and in the assignment step it is assigned to a predetermined slope value range linked to a pump operating state. Here, then, the gradient of the slope of the chronological progression of the phase shift is used to identify the pump operating state, e.g. a clogged filter. [0017] In a further preferred embodiment, the determination step comprises a transformation step in which the chronological progression of the phase shift is submitted to a Fourier transform and the amplitude of the Fourier transforms in a predetermined frequency range is determined. In this case, the assignment step serves to assign the previously ascertained amplitude to a predetermined amplitude value range which is in turn linked to a pump operating state. [0018] Hence in this case, the analysis is conducted in the frequency range. If, for example, the chronological progression of the phase shift exhibits high-frequency signal components this may indicate that there is an air-water mixture in the pump housing preventing the pump from operating at full capacity. [0019] The Fourier transform may preferably be a discrete Fourier transform (DFT) or the special form of the DFT, the so-called fast Fourier transform (FFT). [0020] The determination of the chronological progression of the phase shift in the determination step may preferably include a sliding averaging. [0021] The measurement step may preferably include converting the measured alternating voltage signal and the measured alternating current signal into rectangular signals. [0022] A device for carrying out the method according to the invention comprises a microcontroller with a timer comprising a voltage inlet for recording a start signal and a current inlet for recording a stop signal. These voltage and current inlets are configured to interpret the exceeding of a predetermined voltage or current level as a start or stop signal. The content of the timer is proportional to the chronological gap between the start and stop signals. The microcontroller further comprises a memory for recording the timer content. [0023] The timer of the above-mentioned microcontroller can be used to measure the extent of the phase shift. The content of the memory, which is accessed by other analytical devices, is proportional to the phase shift so that the device according to the invention offers a simple means of analysing the pump operating state. [0024] In one preferred embodiment the memory comprises a number of memory cells for saving a sequence of memory contents. Continue reading about Method for diagnosing operating states of a synchronous pump, and device for carrying out said method... Full patent description for Method for diagnosing operating states of a synchronous pump, and device for carrying out said method Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Method for diagnosing operating states of a synchronous pump, and device for carrying out said method patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. 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