Patent ID: 12247568

DETAILED DESCRIPTION

For detecting the switching times of a rotating machine, in particular of a pumping set, the inventors have identified three important characteristic features for which the recorded measured data of one or more temperature sensors can be examined.

1. A short-time drop/gradient of the temperature measured in the bearing region, or at the bearing support, which indicates that the set has been switched on.

2. A short-time rise/gradient of the temperature measured in the bearing region, or at the bearing support, which indicates that the set has been switched off.

3. Number and size of the gradients of the temperature measured in the bearing region, or at the bearing support, with respect to the ambient temperature of the machine.

In order to explain features 1 and 2, reference is made to the diagrammatic representation ofFIG.1. The diagram shows the temperature measured at the bearing support, more precisely at the surface thereof, of a centrifugal pump over time. Position A marks a short-time negative temperature peak, which shows a short-time drop in the temperature in the region of the bearing of the machine. This phenomenon occurs as a result of the fact that, when the pump drive is started up, an air-mass flow is generated, which brings with it a cooling effect on the bearing or the bearing support. This cooling effect is additionally enhanced by a fan of the electric motor of the pump drive. This ultimately leads to delayed, friction-induced heating of the bearing support.

It will be seen in the diagrammatic representation that the characteristic of this peak at position A differs significantly from the remainder of the temperature profile, in particular the gradient of the temperature profile is significantly greater than in the case of the preceding temperature fluctuations and the subsequent temperature fluctuations between position A and position B. These temperature fluctuations are caused by external influences (for example ambient temperature) and also operation-related influences such as load changes.

The gradient at position A is thus evaluated by the evaluation unit of the pump as a clear indication of a switch-on process of the pump drive.

At the marked position B, by contrast, a short-time rapid rise in the measured temperature at the bearing support is to be seen. Such behavior occurs immediately after the pump drive has been switched off, since the cooling air-mass flow decreases or stops completely as a result of the absence of rotational movement, so that the operating temperature of the bearing/pump initially leads to a short-time rapid temperature increase of the bearing support, and cooling of the bearing support, or of the machine, to ambient temperature occurs only with a certain delay. The gradient marked at position B also differs significantly from the other gradients of the usual temperature fluctuations, so that here too, the evaluation unit can definitely conclude that a switch-off process has taken place.

In the present case, the evaluation unit can distinguish the detected gradients at positions A, B from one another on the basis of the gradient sign and also on the basis of the maximum magnitude of the temperature change, that is to say the peak height, in order thus to be able to definitely allocate the gradients to a switch-on or switch-off process of the machine. Specifically, the gradient for a switch-on process at position A is initially negative, until a sign change occurs owing to the delayed temperature increase induced by bearing friction. By contrast, the gradient in the case of the switch-off process is initially positive, and the sign change then occurs with the delayed cooling of the machine as a result of the machine being stopped.

An extended solution of the invention will be explained with reference to the diagrammatic representation ofFIGS.2a,2b. InFIG.2a, the gradients of a temperature difference profile over time are plotted. Specifically, in this example the ambient temperature of the machine is detected at the same time as the bearing temperature, and a difference is formed from the two temperature values. The gradient profile shown according toFIG.2ais then determined from this profile of the temperature difference over time. By means of this measure, heating at the bearing support can be determined largely without environmental influences and evaluated.

Here too, use is made in the evaluation of the above-described phenomena that characteristic temperature gradients are present during a switch-on and switch-off process, which are detected by the evaluation unit and used as an indicator for detecting a switch-on or switch-off process. InFIG.2a, a total of five such characteristic gradients can be seen, which are distinguished by a significantly higher value of the gradient compared to gradients in the case of load- or time-induced temperature fluctuations. These gradients are marked by points a-e, wherein positions a, b, e carry a positive sign while gradients c, d are negative. In conjunction with features 1, 2 described above and with consideration of the size of the gradients a-e, it is possible to identify whether the machine has been switched on or off.

For better comparability, only the gradient magnitude is considered, that is to say a sign reversal is carried out for the negative gradients, which is shown inFIG.2b.FIG.2bnow clearly illustrates that gradients c, d are higher than gradients a, b and e. Considering the preceding explanations, according to which higher gradients are present in the case of a switch-off process, the evaluation unit can now determine that gradients c, d indicate switch-off processes while gradients a, b, e stand for switch-on processes.

For the further evaluation of the operating times of the centrifugal pump, the detected gradients a-e are then counted, in order thus to be able to determine the number of switching processes which have taken place. With knowledge of the number of switching processes of a machine, it is then possible also to determine the operating and stoppage times of the machine.

The different procedures for switching process identification on the basis ofFIG.1andFIGS.2a,2bcan of course also be combined with one another in order further to optimize the quality of the detection.

FIG.3shows, schematically, a rotating machine in the form of a centrifugal pump10. The centrifugal pump10comprises a rotating shaft14which on the one hand receives the pump impeller and on the other hand is driven by the pump drive. The shaft is rotatably mounted by means of at least one bearing, wherein the bearing is seated within the bearing support13shown. The rotation of the shaft causes bearing friction, which leads to heating of the machine10and in particular of the bearing support13. For the method according to the invention, the temperature in the region of the bearing, in particular at the surface of the bearing support, is then detected.

In principle, the temperature of the bearing support13can be measured at any desired points. Preference is given, however, to a measurement as close as possible to the bearing point, that is to say at a surface, close to the bearing, of the bearing support, in order to be able to provide precise information about the temperature development caused by bearing friction. A potential measuring point for the temperature of the bearing support is marked with reference numeral11.

Measurement of the ambient temperature should preferably be carried out at a sufficient distance from comparatively hot or cold components of the machine, but nevertheless in the immediate vicinity of the machine.FIG.3also shows a potential measuring point for the ambient temperature with reference numeral12.

The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.