GB2144884A

GB2144884A - Fluid flow regulation

Info

Publication number: GB2144884A
Application number: GB08321702A
Authority: GB
Inventors: Nicolas Andrew Higgins; Thomas William Ottley
Original assignee: PA Consulting Services Ltd
Current assignee: PA Consulting Services Ltd
Priority date: 1983-08-11
Filing date: 1983-08-11
Publication date: 1985-03-13
Also published as: GB8321702D0

Abstract

A liquid dispensing arrangement comprises means for regulating liquid flow; a reservoir (22) for containing liquid (24) to be supplied via the regulating means; means (26,28) for measuring the weight of the reservoir and contents and for generating signals representative of the measurements; and computer control means (14) for controlling the regulating means in response to the signals from the measuring means. The principle of operation of the arrangement is that by measuring the rate of loss of weight from the reservoir of liquid, the regulating means can be controlled to maintain a steady flow rate. For ease of use, the regulating and control means are preferably provided together in a single unit, with the control means conveniently being pre-programmed. <IMAGE>

Description

SPECIFICATION Improvements in or relating to fluid flow regulation Field of invention This invention relates to fluid flow regulation and concerns a liquid dispensing arrangement and also a method of dispensing liquid.

Background to the invention There are various applications, eg in medical, chemical and biochemical fields, where it is important to be able to supply liquids in accurately controlled quantities.

Peristaltic pumps have various advantages and as a result are widely used in such fields.

However, the accurate and controlled supply of liquids by peristaltic pumps has always been limited by two major factors: 1. The squeezing action of the pump rollers on the tubing can cause a distortion of the tubing, which leads to reducing flow rates with time.

2. Any variations in supply voltage can cause the pump speed to vary.

Developments aimed at overcoming such problems have, to-date, concentrated on improving pump roller design and motor performance, resulting in expensive pumps which still fail to meet the long term accuracy requirements of many applications, such as media feed in continuous culture fermentation.

It is accordingly an object of the present invention to provide a novel arrangement and method for providing an accurately controllable flow of liquid, eg from a peristaltic pump.

The invention According to one aspect of the present invention there is provided a liquid dispensing arrangement, comprising means for regulating liquid flow; a reservoir for containing liquid to be supplied via the regulating means; means for measuring the weight of the reservoir and contents and for generating signals representative of the measurements; and computer control means for controlling the regulating means in response to the signals from the measuring means.

The principle of operation of the arrangement is that by measuring the rate of loss of weight from the reservoir of liquid, the regulating means can be controlled to maintain a steady flow rate.

The means for regulating liquid fluid flow may comprise valve means, eg a solenoid operated valve, for regulating the flow of liquid supplied. The liquid may be supplied to the valve means in any convenient manner and may for example be pumped thereto or fed thereto by a simple gravity feed.

The regulating means may alternatively comprise a pump, eg a peristaltic pump.

The reservoir conveniently stands on a weighing platform containing a load cell. Because weight differences are measured, absolute accuracy of measurement is not required of the load cell; however, the load cell should be able to measure small differences in weight with high resolution, particularly for low flow rate applications.

For ease of use, the regulating and control means are preferably provided together in a single unit, with the control means conveniently being pre-programmed. In a preferred embodiment the unit thus conveniently comprises a peristaltic pump head and motor/gear box assembly together with a microprocessor controller with associated keyboard and display for user interface.

Hence, in a preferred aspect the present invention provides a liquid dispensing arrangement comprising a reservoir for containing liquid to be supplied to means for regulating liquid flow; means for measuring the weight of the reservoir and contents and for generating signals representative of the measurements; and means for regulating liquid flow with integral preprogrammed computer control means for controlling the regulating means in response to signals from the measuring means.

In a further aspect the present invention also provides a method of dispensing liquid comprising supplying liquid from a reservoir to means for regulating the liquid flow; monitoring the weight of the reservoir and contents; and controlling the regulating means in response to the weight measurement to maintain a desired flow rate.

The invention will be further described, by way of example, with reference to the accompanying drawing in which Fig. 1 is a schematic view of one preferred arrangement in accordance with the present invention and using a peristaltic pump.

Detailed description of the drawing The illustrated arrangement includes a unit 10 comprising a peristaltic pump including a pump head 1 2 and motor/gear box assembly, the unit also comprising a microprocessor controller 1 4 with associated keyboard 1 6 and display 1 8 for user interface. Provision may also be made for interface with an external computer (not shown).

The peristaltic pump includes a pump tube 20 leading from a reservoir 22 containing liquid 24 to be pumped. The reservoir 22 stands on a weighing platform 26 containing a load cell 28 capable of measuring very small weight differences with high resolution. The load cell 28 includes means for generating signals representative of the measured weight differences and for supplying the signals via line 30 to the controller 14. The signals are fed via a high performance amplifier to a sixteen-bit A/D converter and are used as feedback control to regulate pump speed to achieve a desired pumping rate.

The arrangment has the following characteristics: Maximum weight of reservoir : 30kg Minimum measurable weight of platform : 200g Flow range : 50-SOOg/hour Accuracy : + / 5 ,ó over lhr period + / - 2% over 10her period Operating temperature range : 15-25 C Input/Output of System Keyboard entry of a) Mass flow : 50-500g/hour b) Volumetric flow . 50-500mls/hour c) Fluid density (if (b) is required) : 0.5-2.0gXml d) Pump voltage (as a % of maximum): 0-100% A three-digit, seven-segment display will show either entered, or actual parameters for any of the above.

In addition warning lights will be provided for - no reservoir (weight < 250g) - no flow (no weight change in 30 mins) - invalid data entry - increased vveight - rapid variation of flow rate - pump at maximum speed - weight > 30kg

Claims

1. A liquid dispensing arrangement. comprising means for regulating liquid flow; a reservoir for containing liquid to be supplied via the regulating means: means for measuring the weight of the reservoir and contents and for generating signals representative of the measurements; and computer control means for controlling the regulating means in response to the signals from the measuring means.

2. An arrangement according to claim 1, wherein the means for regulating liquid flow comprise valve means.

3. An arrangement according to claim 2, wherein the valve means comprise a solenoid operated valve.

4. An arrangement according to claim 2 and 3, wherein the liquid is supplied to the valve means by gravity feed.

5. An arrangement according to claim 2 or 3, wherein the Iquid is pumped to the valve means.

6. An arrangement according to claim 1, wherein the regulating means comprise a pump.

7 An arrangement according to any one of the preceding claims, wherein the reservoir stands on a weighing platform containing a load cell.

8. An arrangement according to claim 7, wherein the load cell is able to measure small differences in weight with high resolution.

9 An arrangement according to any one of the preceding claims, wherein the regulating and control means are provided together in a single unit.

10. An arrangement according to claim 9, wherein the control means are pre-programmed.

ii. A liquid dispensing arrangement comprising a reservoir for containing liquid to be supplied to means for regulating liquid flow; means for measuring the weight of the reservoir and contents and for generating signals representative of the measurements; and means for regulating liquid flow with integral pre-programmed computer control means for controlling the regulating means in response to signals from the measuring means.

1 2. A method of dispensing liquid comprising supplying liquid from a reservoir to means for regulating the liquid flow; monitoring the weight of the reservoir and contents; and controlling the regulating means in response to the weight measurement to maintain a desired flow rate.

1 3. A liquid dispensing arrangement substantially as herein described with reference to, and as shown in the accompanying drawings.

14. A method of dispensing liquid substantially as herein described with reference to the accompanying drawings.