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Method for estimating flow through a pump and displaying that estimate

IP.com Disclosure Number: IPCOM000032786D
Publication Date: 2004-Nov-12
Document File: 3 page(s) / 40K

Publishing Venue

The IP.com Prior Art Database

Abstract

This document describes a simple method of estimating and displaying a continuous flow readout on the display of a pump controlled by a motor controller, in particular a frequency converter. Through the use of a calibration process, where the flow through the pump is monitored over a range of operating conditions, information is gathered which is later used by the frequency converter to produce an estimate of the flow. This estimate is based on data gathered during the calibration process and on measurements directly available to the frequency converter (i.e. the frequency of operation and the power drawn). The flow estimation does not use any additional hardware (such as a flow meter) under normal operation.

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Method for estimating flow through a pump and displaying that estimate

This document describes a simple method of estimating and displaying a continuous flow readout on the display of a pump controlled by a motor controller, in particular a frequency converter.

Through the use of a calibration process, where the flow through the pump is monitored over a range of operating conditions, information is gathered which is later used by the frequency converter to produce an estimate of the flow. This estimate is based on data gathered during the calibration process and on measurements directly available to the frequency converter (i.e. the frequency of operation and the power drawn). The flow estimation does not use any additional hardware (such as a flow meter) under normal operation.

Background

The use of frequency converters for the infinitely variable speed control of three phase electric motors is common. Modern frequency converters may contain

* electronics for the control and measurement of the motor power and driving frequency,
* a display to assist in controlling and programming the unit and also for supplying relevant data to the user and
* a controller to control these functions, for example a DSP or microprocessor.

It can be an advantage to the operator of a pump to know the flow through the pump at any particular time. One method of supplying this information is to install a dedicated flow meter in series with the pump. This, however, requires additional hardware with its attendant cost. Modern frequency converter units contain sufficient processing power, and have access to sufficient data, for it to be possible to provide an estimate of the flow without additional hardware. Further, they have an in-built display on which the flow estimate may be shown continuously.

The method described here allows such an estimate to be provided. The method is characterised by two phases. The first phase consists of a calibration process during which data are gathered to enable the estimation of flow during the second phase, that of normal operation.

The two phases are described in detail below.

Calibration Process

During the calibration process the following equipment is required:

The pump unit undergoing calibration (1)

The frequency converter (2) used to control the pump unit.

A continuously adjustable valve (3)

A flow meter (4)

An appropriate computing device (for example a desktop or laptop computer, PDA, palmtop or cellular phone) with appropriate software (5).

The equipment is connected as in Figure 1.

Simple Flow Readout.doc 1/3

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Figure 1. Disposition of equipment during the calibration process.

Thus the pump (1) forms part of a closed circuit (6) in which it is connected in series with the valve (3) and the flow meter (4).

A first motor drive frequency (for example 60 Hz) is chosen. The valve (3) is opened fully, and the flow allowed to stabilise. The flow, as measured by the flow meter (4) is then recorded (for examp...