Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – With coupling means
Reexamination Certificate
1999-09-01
2004-10-05
Nguyen, Vinh P. (Department: 2829)
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
With coupling means
C324S11700H, C324S1540PB
Reexamination Certificate
active
06801031
ABSTRACT:
FIELD OF THE INVENTION
My present invention relates to a determination of the current draw of an electronically-controlled pump and to a pump provided with such a current-draw measurement.
BACKGROUND OF THE INVENTION
Pumps, especially electronically-controlled centrifugal pumps, can be driven by an electric motor having a motor control circuit and supplied with power by a conventional power line. The operation of the pump can be monitored, inter alia, by measuring the current draw of the pump as a measure of the loading of the motor and, therefore, the loading of the pump. Other operating parameters can be monitored also for this and other pump operation purposes.
If an increase of the current draw is detected, that can represent an increased loading of the pump which may signal an overload and require the pump to be shut down. The pump may have an emergency shutdown circuit which can respond to that overload or potential overload. It is also possible to use the information, i.e. the current draw, for control of the pump speed or for other purposes.
In the past it has been common to provide within the motor control circuit a resistor, usually connected between the power line and the input terminal of the motor, i.e. in the power part of the circuit, and to measure the voltage drop across this resistor as an indication of the current drawn by the power section and hence by the motor.
Such a measurement resistor has the drawback that it is an extra component which must be introduced at additional coot and must be mounted on the circuit board or the like in additional soldering steps. Since there is a continuing desire for simpler and inexpensive pumps, the provision of additional elements such as special measurement resistors and devices for tapping a voltage across such resistors, runs counter to the principle of simplification. Furthermore, special resistors as have been provided heretofore, contribute to power loss, undesirable heating of the electronic circuitry and, especially for continuously operating pumps, to significantly increase costs. The current which must be supplied is likewise increased and this can require the wiring for the pump to be more massive than is desirable.
OBJECTS OF THE INVENTION
It is, therefore, the principal object of the present invention to provide a method of determining the current draw of a pump which can provide both high accuracy and in a simple manner, measurement of the current draw while nevertheless minimizing the operating and fabricating cost of the pump.
It is another object of the invention to provide an improved pump which can be fabricated relatively inexpensively and operated inexpensively but which will nevertheless allow measurement of the current draw.
A further object of this invention is to provide a method of and an apparatus for measuring the current draw of a pump without the drawbacks of earlier systems or with mitigation of such drawbacks so that, for example, power losses are minimized.
SUMMARY OF THE INVENTION
These objects are achieved, in accordance with the invention, in a method of determining a current draw of a pump driven by an electric motor having a power line and a motor-control circuit connected to the power line, the method comprising the steps of:
(a) measuring a voltage drop across at least a portion of a conductor having a definite resistance and connecting the power line with the motor-control circuit; and
(b) calculating the current draw from the voltage drop.
The pump assembly, according to the invention, can comprise:
an electric motor having a power line connected thereto for energizing the electric motor;
a motor control circuit connected to the motor and the power line for electronically controlling the pump assembly;
a pump driven by the motor; and
means for measuring a voltage drop across at least a portion of a conductor having a definite resistance and connecting the power line with the motor control circuit and calculating the current draw from the voltage drop.
According to the invention, therefore, a segment of a conductor between the control electronics, i.e. the motor control circuit, and the power line is used as the voltage drop segment and the voltage drop is detected across this segment and the output of the detector is converted into a measurement of the current. As a consequence it is not necessary to solder a separate component such as a measuring resistor into the pump and is hence for the measurement of the current no additional fabricating costs are involved.
In small circulating pumps for heating purposes, this can amount to a saving of about 2% when, instead of the extra resistance, a segment of the connecting conductor, which is customarily provided, is used. It is, of course, self-understood that the resistance of the wire segment used for measurement should be known and hence defined. The use of the connecting conductor makes the separate incorporation of the measuring resistor superfluous and therefore simplifies fabrication as well.
The use of the connecting conductor segment has made the reliability of the measurement and thus the reliability of the pump greater since the system eliminates a separate component which can be an additional error source. The elimination of a measurement resistor, moreover, eliminates a component which can decrease the efficiency of the pump, give rise to undesired heating in the pump or in the electronic circuitry, and pose problems with respect to positioning, mounting and the like. The space required for electronic circuitry and hence the pump dimensions can be held low since the additional component is not required and that permits the pump to be used in limited environments. The invention is particularly advantageous for small pumps in circulating hot-water systems.
An especially precise current measurement is possible when a processor, especially a microprocessor or microcomputer, in incorporated in the motor control circuit and is used to detect the voltage drop over the segment of the connecting conductor. Such a microcomputer can calculate in an especially simple way the current drawn by the pump from the value of the current determined in the conductor segment. Furthermore, the microcomputer can permit factors which may influence the measurement of the current draw, such as the temperature of the conducting segment or the influence of the motor-control circuit on the current drop to be taken into consideration. The consideration of such factors is important since a relatively small current in the motor-control circuit is used to indirectly provide a measurement to the much larger current draw.
It has been found to be especially advantageous to use a segment of the connecting conductor which itself has a well-defined resistance and can be composed from so-called resistance wire, namely, a wire having a predetermined specific resistance, this resistance wire can be cut to a predetermined length and used in the pump circuitry. Such resistance wires have within a temperature range an entirely predictable relationship between current flow and voltage drop so that the temperature characteristic of the wire segment can be programmed into the microcomputer as a data set or as a correction instruction for calculating the current.
In an especially advantageous embodiment the conductor is cold-soldered or bonded between a plug contact to which the power line is connected and the printed circuit board of the motor control circuit and can have a resistance of about 1-5 m&OHgr;.
REFERENCES:
patent: 720335 (1903-02-01), Eastman
patent: 1446995 (1923-02-01), Sines
patent: 4032766 (1977-06-01), Hughes et al.
patent: 4369354 (1983-01-01), Goedecke et al.
patent: 4584525 (1986-04-01), Harnden et al.
patent: 4978909 (1990-12-01), Hendrix et al.
patent: 5049815 (1991-09-01), Kliman
patent: 5234319 (1993-08-01), Wilder
patent: 5319304 (1994-06-01), Whipple, III
patent: 5386188 (1995-01-01), Minneman et al.
patent: 5514978 (1996-05-01), Koegl et al.
patent: 5630325 (1997-05-01), Bahel et al.
patent: 5739698 (1998-04-01), Bowers et al.
patent: 5804979
Dubno Herbert
Nguyen Vinh P.
Wilo GmbH
LandOfFree
Method and apparatus for current measurement for... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for current measurement for..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for current measurement for... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3320097