Pumps – Condition responsive control of pump drive motor – Single motor control element responsive to means sensing...
Reexamination Certificate
2002-08-02
2004-07-06
Dolinar, Andrew M. (Department: 3747)
Pumps
Condition responsive control of pump drive motor
Single motor control element responsive to means sensing...
C417S020000, C417S022000, C700S282000
Reexamination Certificate
active
06758655
ABSTRACT:
The present invention relates to a process for determining a nominal value equipment curve of an installation for controlling the capacity of a pump actuated by an electric motor with speed control, by means of which pump a fluid is transported in said installation via predetermined conduits and consumers in an installation, the number and inside cross-sectional area of which are variable, in which controlling process a physical variable representative for the capacity of the pump is detected and an electrical signal proportional to this physical value is input in a controller as an actual value, the controller controlling the rotational speed of the electric motor and thus the pump capacity on the basis of the curve of nominal values of the installation.
Pumps actuated by an electric motor, in particular rotary or centrifugal pumps, are frequently used in installations wherein the pump capacity demanded by the installation changes with time. This is for instance the case with pumps in heating installations. Here, maximum capacity is only required if all consumers are connected. In practical operation, however, the consumers, for instance individual heaters, are operated at reduced level only or are completely disconnected at certain times, which may result in completely different operating conditions with different capacity requirements variable with time. However, the maximum capacity of the pump in such an installation always has to be set so that all consumers within the installation can be supplied sufficiently even if all of them are connected at maximum consumption at the same time. If the pump is operated at full capacity all the time, i.e. also at reduced capacity requirements, the capacity of the machine will—unnecessarily—be raised beyond the level required. This behavior is illustrated with reference to a rotary fluid pump in the upper part of the graph of
FIG. 1
, showing a family of characteristic curves of the rotary pump, i.e. the pumping head H as a function of the capacity Q at a certain rotational speed n. This graph only shows the characteristic curve of the pump for its rotational speed of n=50 Hz in its entirety, other characteristic curves of the pump for n=40.5 Hz, n=32.4 Hz, n=26.3 Hz, and n=23.2 Hz are only shown as curve portions.
Dimensioning of the required capacity of such a rotary pump in an installation results from setting an operation value Bmax, which is the point of intersection of a demanded maximum volume pumped Qmax (in this example 80 m
3
/h), when all consumers are fully connected, and the pumping head H required for smooth operation of the installation (in this example 13 m). The characteristic pump curve intersecting this operating point Bmax (in this example the curve for n=50 Hz) gives the maximum rotational speed of the pump necessary for maintaining the required pumping head at 100% consumption (=Qmax). But if the actual consumption within the installation decreases and the pump continues to be operated at the same rotational speed n=50 Hz, the pumping head H rises, i.e. the instantaneous point of operation rises toward the left along the characteristic pump curve. Thus it can be seen that operating an installation in this way is highly uneconomical. In addition there may be disturbing noise resulting from flow if the output is considerably higher than that actually needed in the installation.
In order to improve a pump's energy consumption and its noise level, it is known to control the pump output (=pumping head×volume pumped) of a rotary pump in such a way that a constant pumping head results at the pump outlet regardless of the respective volume pumped, which pumping head may be measured by means of a pressure sensor and fed to a controller as an actual value.
However, controlling at a constant pumping head in such a way does not take into consideration the actual conditions within the installation. In particular, it does not take into consideration the inevitable pressure drops within the circuit system and the consumers connected thereto.
In order to improve control of the pump of such an installation it is thus necessary to define a curve of nominal values for the installation, taking into consideration the installation losses as a function of the volume pumped at least to a certain extent.
The controlling behavior of such an installation with a variable curve of nominal values therefor is shown in the graph of
FIG. 1
, once as the curve of nominal values for the installation H
installation
(Q) in the graph of pumping head versus amount pumped, and again as the curve of nominal values for the installation P
installation
(Q) in the graph of power uptake versus amount pumped. Both curves of nominal values for the installation are approximately parabolic in shape, but they have different slopes.
The graph of power uptake versus amount pumped also includes the respective energy savings with a pump control employing the given characteristic curve of nominal values for the installation as compared to operation of the pump at a constant rotational speed of n=50 Hz.
In practical operation, however, there is the problem of how to obtain an appropriate characteristic curve of nominal values for the installation. It is known to establish such curves of nominal values for an installation in tabular form by means of conduction and consumer ratings, or to define loss curves as mathematical functions. Both processes are theoretical approaches with which it is not possible to take into consideration the actual conditions within the installation, for instance a reduction of the cross-section of the conduit due to clogging or calcification, leaks of the installation, eddying because of bends or pronounced turns of the conduits. Thus many pumping systems also offer an operator the possibility to manually input tables of nominal values in a controller, which values have been fixed on the basis of experience or previous measurements of the installation (see e.g. DE-OS 37 04 756). It can easily be seen, however, that in all the above processes, the conditions within the installation are not taken into consideration to a sufficient extent.
European Patent No. 0,444,269 discloses regulating the power output of a pump which is driven by a speed-regulated electric motor in a closed system comprising conduits and consumers by first, during a calibration process for some arbitrary initial state of the system, recording, at least step-wise, the electrical signal from a probe detecting the rate of fluid flow at a plurality of points using particular settings of the pumping power and the appertaining percentage rates of flow of the fluid, from the static state of the pump up to 100% power output thereof, which corresponds to a 100% rate of flow, and supplying this respective signal as measurement value to a computer which produces a characteristic curve passing through each of the test values delivered by the probe, regulation of the output of the pump by the computer initially being in correspondence with this characteristic curve as long as it is within the limits set by the calibration process, until such time as, due to changes in the system, a greater rate of flow of the fluid occurs than for a 100% power output of the pump during the calibration process, whereupon the computer defines the highest value of the rate of flow as a new test value for a 100% power output of the pump on an extension of the characteristic curve, and the computer displaces each of the percentage values of the rate of flow along the characteristic curve by an amount which corresponds proportionately to the ratio of the new highest rate of flow to the preceding one, while an adaptation of the characteristic curve is effected in a manner analogous thereto by the computer whenever a further increase in the rate of flow occurs.
The present invention provides a process for determining a curve of nominal values for an installation with which the above disadvantages of the prior art will be avoided
Dolinar Andrew M.
Merchant & Gould P.C.
Pumpenfabrik Ernst Vogel Gesellschaft m.b.H.
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