CA1059337A - Measurement and control of fluid flow - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
An improved method and apparatus for measuring fluid flow and controlling fluid flow systems. The invention uses magnetically responsive float normally resting in contact with a stop element positioned in the flow conduit, with magnetic means positioned upstream. The requisite increase of magnetic force to pull said float element from the stop element against the direction of fluid flow is related to the flow rate, thus serving to indicate same for metering or control purposes.
Normally, the increase in current to an electromagnet required to overcome the force of fluid flow is preferred. This system can also be employed to determine fluid viscosity.

Description

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. 9 ' 10 12l 13 BACI~GROUND OF INVENTION
14 Control and measurement of ~low of fluids, both gases . . , . .~
and liquids, has presen~ed considerable problems to the prior 16 art, particularly at extremely low flow rates. Typical:ly, 17 prior art systems for use at low to modera~e flow rates e.g.
18 rates o lcm3/hr. to 1000 ft3/hr. have proven to be either 19 relatively inaccurate or fairly expensive in terms of having an accurate measuring system. Typical of known devices or 21 this purpose are orifice or capillary meters connected to 22 differential pressure txansmitters, or, for larger flow~, 23 turblne meters.
24 The presen~ invention teaches means for readily indicating 10w rates o gases or liquids with a high degree 26 of accuracy over a very wide range of flow rates by a c ~; , ~ ' , ' . , , .; ~

~V 5~ 3 37 1 relatively simple and inexpensive system. It can be automated

2 to the point of adjusting flow conditions responsive to the

3 measurement it obtains of fluid flow, and/or setting off

4 suitable warning devices or the like when flow is above or below desired levels. The present system, which may use a 6 glass or ceramic coated iron float in a quartz tube, can be 7 used in very corrosive environments and/or at high temperatures.
8 Due to its ability to inexpensively measure fluid flow at low 9 flow rate, e.g. 5 cm3/hr. to lOOO cm31hr., it offers the possibility of being used for intravenous flow control as ll described in U.S. Patent 3,605,741.

14 SUMMARY OF THE INV~NTION
In accordance wlth the present invention, a float 16 which normal~y may be in the form of a ball or the like and 17 which is responsive to magnetic orce rests against a stop l8 element positioned in the conduit or flow tube~by virtue of 19 the movement of the fluid pressing the float against the stop.
Upstream of the location of the stop element are positioned 21 one or more magnetic means~ Means are provided for controllably 22 increasing magnetic force o said magnetic means so as to 23 attract said float away from the stop element and move it 24 against the direction of fluid flow. Said means gradually increase the magnetic force continuously or stepwise until 26 such tlme as its action on the magnetically responsive float 27 overcomes the force of fluid flow and any gravitational forces.
~8 The requisite increase of magnetic force to said magnetic 29 means to overcome the force of fluid flow is determined and , ., ~ ~5~3 ~7 1 related to the flow rate ln the conduit thereby indicating 2 its value.
3 Typically, the means or increasin'g the magnetic 4 force exerted by said magnetic means may be means for gradually increasing current to an electromagnet, such as a current ramp 6 generator or staircase generator (increases current in discrete 7 s~eps). The generator builds up the magnetic force of the 8 magnetic means until the point at which the float is pullled 9 back from the stop element. This point is detected by any of a variety of detection means responsive to a change of position 11 of ~he float element.
12 In a preferred aspect of the present inven~ion, the 13 detection means can be an optical detector which send~ off 14 a beam of light passing across the tube or condult in the area lS of said stop element and float resting against it. In this ~6 embodiment, the conduit in this area would be tr~nsparent and 17 the 10at would serve to obscure the beam of light passing 18 across the transparent tube, thereby preventing its impingement 19 on a photodetector positioned on the opposite side of said tube.
WheT~ the 10at is moved away from its rest position against the 21 stop, the light beam is able to pass across the transparent 22 tube and impinge upon the photodetector which in turn actuates 23 the measurement of the-current to the magnetic means, or other 24 means for increasing the magnetic ~orce required to cause said movement of the float element.
26 Alternati~e detectors can be used. By way of ex~mple, 27 two plates of a capacitor can be positioned on either side of 28 the normal resting point of the float element, and connected to 29 an oscillator circuit. When the float element ve~ from its '~
~, , lq.~S~337 1 position between the plates it will change the capacitance 2 of the capacitor, thus changing the frequency at which the 3 osc~llator operates and causing a sensing measurement to be 4 taken of the relevant increase of magnetic f~Drce of said magnetic means to cause the float ~o move from its rest 6 position. ~lternative detection means include a strain - 7 gauge or piezoelectric sensor attached to the stop element, 8 or means for passing a current through the float by contacts 9 on the stop element, or an induction coil mounted near thle stop element, all of which would reflect movement of the float 11 away from the stop element. Means for detecting the change in -12 the inductance or magnetic flux o the magnetic means as the 13 10at moves with respect to it can also be used.
14 The float element, which preferably is the form o a ball, or right circular cylinder, generally has a cross 16 sectional area of about 50 to 95%, preferably 70 to 90%, of 17 the condult cross section in the area whi~h it rests agai~st 18 the stopping element. It can be made of various materials so 19 long as it is responsive to a magnetic ~ield for moving it from its original position against the force of fluid flow. Thus, it 21 can be a sphere of soft iron, ~ plastic or glass having a 22 magnetically responsive material incorporated therein, e.g.
23 iron or iron oxide powder, a ball of plated or unplated 2~ magnetic stainless s~eel, chrome plated sof~ iron or the like.
Floats designed to produce either laminar or 26 turbulent flow conditions over a wide range of flows are 27 also contemplated.
28 The conduit in the area containing said stop element 29 may be ~he usual conduit through which the fluid flows or ~ - 4 - -:.

1~?5~337 1 alternatively may be a special section utilized for flow 2 measurement. In the latter case, ~t can be an especially 3 tapered tube although normally a cylindrical tube is quite 4 adequate. It can be mounted in any position9 e.g. vertically9 horizontally or at an angle. In cases when using a ligh~
6 source detector at least the area surrounding said stop element 7 would be made of a transparent material, e.g. plastic, glass 8 or fused quartz9 so as to permit a light source detector to 9 operate and detect the movement of the float element from its rest position against the stopping element.
11 The stopping element can be any means or halting the 12 further flow of the magnetically responsive float without 13 substantially impeding the flow of fluids through the conduit 14 system. It can be made of plastic, glass, non-magnetic metal, wood, etc. The relative diameter of the conduit, float element, 16 and stopping element should be related so that ~he float rests 17 against the stop element in normal position without blocking -18 passage of fluid flow through the conduit. By proper design 19 o~ the stop element, the taper, if any, of the tube ln the ~rea o flow measurement, the pole pieces of the magnet and 21 the shape and weight of the 10at or ball, the latter can 2Z be caused to leave its position against the stop element 23 rapidly and cleanly with a "snap action" whe~ the critical 24 increase of magnetic ~orce, e.g. crltical current increase, is reached for overcoming the force of fluid flow. This gives 26 a meter of h~gh accuracy and sensi~ivity.
27 Normally, a pair of fixed electr~agnets positioned 28 upstream from said stop element is used together with means for 29 increasing the current to said electromagnets so ac to increase . ~ . .
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1 ~59 3 37 1 magnetic force and cause the float element to move away from 2 its rest position. Howeverg it is possible t:o alternatively 3 increase the magnetic force applied to said magnetically 4 responsive float by other means. By way of example, the relative position of the magnetic means can be changed, e.g. brought 6 closer to the stop element to thereby increase the magnetic 7 force. The position at which it serves to move the float B element away from the stop element can then be related to the 9 fluid flow rate through the conduit.
Alternatively, but less desired, one could increase 11 the number of magnetic elements brought into position until 12 such point as the requisite magnetic orce was reache~ the 13 increase in number being related to ~luid flow.
14 Of course, the resultant reading of fluid flow rate given by the aforesaid flow measuring system can be inter-16 related with a flow control system for varying fluid flow 17 responsive to the reading thus obtained, and/or alternatively 18 serve to actuate a warning system to indicate necessary changes lg to conditions.
20 ~ The flow control system of the present invention is ;;
21 useful both for measuring gases and liquids. $ome typical uses 22 for such device include the following: measurement of gas 23 supplied to pressured telephone lines or electrical cables, 24 measurement and control of gases in a~alytizal units, measurement of low flow rates of li~uids such as in intravenous 26 feeding systems~ measurement of flows to instruments such as 27 smoke or explosive gas or radiation or pollution detectors, 28 and metering of fluids ln blending of food or cosmetios 29 production. The present system is particularly advantageous .. ..

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1 in situations wherein a low cost, remote indication 2 (digital if desired), wide range, accurage flow metering 3 system, and/or possibly sterile disposable fluid contacting 4 element is required.
In another ~mbodiment of the present invention, 6 the present system can be modified to serve to measure viscosity 7 of fluids. More specifically, by shaping the magnetic float 8 element so as to maintain laminar flow through the conduit 9 (at least in the area between the magnet and the stop element) and maintaining 1uid velocity constant, the ~orce on the 10at 11 will be represented by the followlng equation:
12 Force ~ kcOnstan~ (~luid velocity) (fluid viscosity) 13 With constant fluid velocity, the force required to 14 move the float from its position against the stop element can provide a viscosity measurement, and t~e apparatus serve as a 16 linear viscosity meter. Such a linear viscosity meter is of 17 particular value in monitoring reactions, e.g., fermentation, 18 polymerization, paint formulation, food product preparation 19 such as ketchup, soup manufacture, etc., cosmetics manufacture, pharmaceutical processes, etc., wherein viscosity changes are 21 an important indication of reaction conditions, and the need 22 for changing the operating environment. Accordingly, the 23 linear viscosity meter thereby obtained can serve to actua~e 24 changes to reaction conditions to the system being monitored when defined viscosity values are reached, e.g. temperature 26 change, altering of feed reactants to system, mixing conditions, 27 etc.
28 The present invention is distinguished from other `~
29 flow control systems such as described in inventor's UcS.
Patent 3,662,598. The latter utilizes the cyclic movement - ~5~337 ` :-:

1 of a 10at between a sensor and a magnet with the cyclic 2 frequency of the float element being related to the fluid 3 flow rate. In such system the transit time of the float varies 4 with fluid velocity. In contrast, the present invention utilizes a stop element against which the float is normally 6- in s~ationary position by virtue of the fluid flow forces 7 pressing against it. The necessary increase in magnetic 8 force, e.g. current to an electromagnet, required to overcome 9 the force of fluid flow to move said float element away from its normal stationary position, is related to fluid flow and 11 utilized to measure and control same, or used to determine l2 viscosity.
13 The various aspects o the present invention will 14 be made more clearly apparent by reference to the following drawings and accompanying description.
- 16 DRAWI~S
17 Figure 1 illustrates a preferred flow control system 18 employing the present invention;
19 Figure 2 depicts a typical float element in the form of a plastic, ceramic or glass ball having an iron core;
21 Figure 3 is a logic diagram of a preerred oper~ting 22 method for flow control;
23 Figure 4 illustrates a float shaped to produce laminar 24 flow and accordingly serving as a means of determining fluid ~
25 viscosity. - -26 With reference to Figure 1 s~own herein is a 27 simplified system illustrating the present invention. Fluid 28 is ~lowing in the direction shown by the arrows through a 29 conduit. The portion of the conduit in the area of fluid flow .~

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1~59337 1 measurement is shown in the drawing as flow tube 10. In a 2 typical case this can be a length of transparent tubing~
3 e.g. transparent plastic or glass connected :in a normal 4 -conduit path. Transparent tubing is normally preferred both S to afford an opportunity to use a light source detector and/or 6 afford an opportunity to visually observe the operation of the 7 flow measurement system.
8 Positioned in flow tube 10 is stop element 12. Stop 9 element 12 can be a tubular appendage, button, screen, rod or wire, normaLly positioned in a central portion of the flow tube 11 so as to halt the normal flow o the float element 11 and 12 maintain it in the position shown as Pi. The stopping element 13 should not be of such a size as to impede the flow of fluid 14 past it and should be shaped to prevent signific~nt eddy flow -15 currents or the like which might affect the accuracy of the -16 system. In the embodiment shown, flow tube 10 is a plastic 17 conduit of 2 mm diameter, and stopping element 12 is a tubular 18 element of 0.2 mm diameter made of stainless steel. It is 19 held in position by being an integral part of the tube or f~xed to its walls. Float 11, which in this embodiment takes 21 the form of a ball, would have a diameter of about 1.8 mm.
22 It fits more or less loosely in the tube 10 and yet is held 23 back from flow by stopping element 12. In the specific `
24 embodiment illustrated, the float is a ball of magnetic stainless steel.
26 Positioned upstream of stopping element 12 are a 27 pair of magnet poles 13 and 14. Normally the m~gnets are in 28 fair~y close position both to ~he flow tube 10 as well as the ~9 resting position Pi of the float element since the magnetic _ 9 _ . . .

~5~ 3 37 -1 force ultimately will have to move float element 11 away rom 2 its rest position against the force of fluid flow to position 3 Pm. In the embodiment shown the magnets are about 5 mm ~way 4 from the top of stopping element 12, and within 0.5 mm o the outer wall of the flow tube 10.
6 In a preferred embodiment, the detector for indicating 7 the movement of the float element 11 away from its rest position 8 takes the form of a light source 15 and detector 16 which 9 operate as an optical detector system. A ligh~ beam shown by `~
the arrow emitted by source 15 is blocked by opaque stainless 11 steel ball 11 when the latter is in its rest position P~.
12 When the unit is to be used to measure fluid flow, current is 13 increased to the electromagnets 13 and 14 by current ramp 14 generator 18. The measurement cycle begins as the logic circuit 17 triggers the current ramp generator and the current 16 to the electromagnet begins to increase monotonically and 17 perhaps, but not necessarlly, linearly. The logic circuit 17 ... .
18 itself can be actuated by the operator or a timer moving a 19 button or switch to initiate the operation of the flow measuring s-ystem. As the current from generator 18 increases the magnetic 21 ~orce exerted by magnets 13 and 14 on the ball also increase.
22 The increase in magnetic force eventually overcomes the flow 23 and perhaps gravita~ional forces keeping float element 11 24 against stop 12. When this point is reached the float element leaves the stop position and moves against the fluid flow 26 towards the poles of the electromagnet to position Pm.
27 In the embodiment illustrated, at this point the 28 light beam i5 no longer blocked by float 11, and the ligh~
29 detector 16 is thereby activated~ This event in turn is 1 ~9 ~ 37 1 detected by the logic circuitry and the magnet current or 2 voltage given off by generator 18 necessary to reach this -3 point sampled. The current needed to pull float lL rom its 4 stop position is related to th~ pressure drop across the float or fluid flow rate, and serves as a measurement of the latterr 6 Typically one or more calibration curves would c~me -7 with the unit (as is typical with flow meter devices), wherein 8 the current was related to fluid flow rate for liquids within 9 a gi~en viscosity and density range; or alternatively the user -~
10 would previously have calibrated the unit himself. `-11 Logic circuit 17 is shown schematically. Typically, 12 it will be actuated by the photodetector when the baLL leaves 13 the stop element. It will cause a signal proportional to the 14 magnet current to be sent to the readout device 19 ~or indicating fluid flow.
16 The logic circuit will then normally cause the magnet 17 current to be reset to zero for a time sufficient for the float 18 to return to the stop element. The unit is then ready for 19 another measurement.
20 r Figure 2 illustrates an alternative form of float 11 21 in the form of a plastic or glass sphere 20 h~ving a magnetically 22 responsive core 21 of soft iron, metal filings or the like.
23 In another preferred embodiment, as illustrated in 24 Figure 3, the logic circuit may operate as follows to determine fluid flow rate: -26 At the beginning of a flow measurement, an oscillator 50 27 which produces a train of square waves is switched on and the 28 output is sent to a digital counter 51 and to an ~ntegrator 52.
29 ~he output of the integrator, whlch rises stepwise from zero .

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1 ln a linear fas~hion, is used to control by means of a current 2 generator 53 the current to the electromagnets 54, which 3 current also rises in a linear stepwise fashion.
4 When the magnet current has increased to such a level that the float or ball is pulled, against the ~low 6 forces, away from the stop element, the ~ight beam passes 7 through the flow tube and is detected by the photo sensor 55. -8 At this point the oscillator 50 is turned off by the logic 9 el~ment 56 and the counts accumNlated in the digital counter 51 `
are directly proportional to the magnet curren~ needed to move 11 the ball from the stop, and thus directly related to the fluid 12 flow rate. Alternatively under the control o~ logic element 56, 13 the magnet current can be displayed on the meter 61.
14 Thus a very simple, low-cost, reliable digital output is achieved, so that the meter can be easily alternatively 16 coupled to one or more of digital display 57, a digital 17 computer 58, or to a flow controller 59.
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18 When the output of the meter has been acquired by 19 the desired output devices, the integrator and thus the magnet current is reset to zero for a period long enough for the float 21 or ball to return to the stop element, and the counter 51 is 22 reset to zero (or possibly to a negative n~mber to compensate 23 for the effect of gravitational forces if the flow tube is 24 mounted vertically). The meter is then ready to make another ~ -25 measurement of fluid flow rate. ~;
26 In a modification of the above embodiment, the 27 output of the first integrator 52 is integrated again, and ~he 28 output of the second integrator 60 is used to'controL the 29 magnet ~urrent. The magnet current will then be proportlonal - 12 - ;

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-" ~6~5g337 1 to the square of the number of pulses emitted by the 2 oscillator 50. If the flow forces are proportional to the 3 square of the fluid velocity due to the presence of turbulent 4 flow, the output of the counter will vary Linearly with the flow rate, which in some applications will be most advantageous 6 to permit the direct reading of flow rate.
7 Figure 4 illustrates an alternative embodiment 8 of the present invention wherein its basic principle is 9 utilized to indicate fluid viscosity, and in particular the present element serves as a linear viscosity meter.
11 The elements of Figure 4 are labeled similarly to 12 Figure 1. Conduit or flow tube 110 contains float element 111 13 which in its normal position rests against stop element 112.
14 In the embodiment shown stop element 112 is in the o~ of a 1at grid or the Like.
16 Means not shown are provided for maintaining a 17 constant flow of fluid through conduit 110 in the direction 18 shown by the arrow. Typically, such constant fluid flow can 19 be maintained by a gear pump, piston pump (with constant velocity piston), or the like.
21 The float element lLl is especially shaped to ensure ~2 that fluid flow is laminar in the area in which the float 23 moves. Typically, this may be done by using an elongated 24 float element having multi-vanes a, b, and c, as shown in the drawing, although the invention contemplates any float 26 element shaped to provide such laminar fluid flow conditions, 27 such as a cylindrical float with a narrow clearance to the 28 walls of the conduit.

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1 The embodiment shown as a multi-vaned magnetic 2 float can be made of stainless s~eel or bQ plated iron.
3 Alternatively, a magne~ic section can be connected to a 4 non-magnetic vaned section upstream or downst:ream of the magnetic portion of the float.
6 Under conditions of laminar flow the force exerted 7 in the float will be represented by the equation: -8 Force = (constant coefficient) (fluid velocity) ~fluid Accordingly, with the fluid velocity being held 11 constantg the viscosity of the fluid will be proportional to the 12 magnetic force required to move the float element 111 from 13 stop element 112, and the resultant magnetic force can~be 14 utilized to indicate fluid viscosity.
Accordingly, in the same manner as described relative 16 to the measurement of flow rate, the magnetic force exerted -17 on the float element 111 by magnetic means 113 is increased 18 until such time as the float moves away from stop 112. This -19 in turn ~s sensed by the combination of light beam 115 and sensor 116. The requisite force is ascertained as described 21 previously relative to flow rate measurement and related to 22 fluid viscosity. The required current or other indication of ;`
23 magnetic force mNltiplied by a calibration cons~ant factor will 24 provide an indication of viscosity. The calibration factor for the system would previously have been ascer~ained by running 26 fluids of known viscosity through the system at constant flow 27 rate, and solving the foregoing equation.
28 The above system accordingly is capable of acting 29 as an inexpensive viscosity meter capable of providing prompt and accurate viscosity measurements.

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Various modifications as to elemenl:s of the present 2 in~rention will suggest themselves to those skilled in the art, 3 and are deemed ineluded by the system defined in the following 4 claims.
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Claims (24)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS;

1. Apparatus for indicating flow rates of fluids comprising a conduit, a float element having a magnetic responsive material associated therewith positioned in said conduit, a stop element positioned in said conduit which limits the motion of said float element in the downstream direction, magnetic means positioned in an upstream portion about said conduit before said stop element, means for increasing the magnetic force of said magnetic means so as to move said float element away from said stop element and against the direc-tion of fluid flow, means for detecting the movement of the float element away from the stop, and means for relating fluid flow to the degree of requisite increase of magnetic force to move said float element away from said stop element.

2. Apparatus for measuring flow rates of fluids comprising a conduit, a float element having a magnetic responsive material associated therewith positioned in said conduit, a stop element positioned in said conduit which limits the motion of said float element in the downstream direction, electro-magnetic means positioned in an upstream portion about said conduit before said stop element, means for gradually increasing the current to said elec-tromagnetic means to thus increase the magnetic force of said electromagnetic means so as to move said float element away from said stop element and against the direction of fluid flow, said means for gradually increasing current to said electromagnetic means increasing current in a gradual stepwise manner to accurately measure the magnetic force required for the float to leave the stop element, means for detecting the initial departure of the float element away from the stop, and means for relating fluid flow to the degree of current required to move said float element away from said stop element.

3. The apparatus of claim 1 wherein said magnetic means is an electro-magnet, and said means for increasing magnetic force comprises means for increasing current to said magnetic means so as to thereby increase its magnetic field intensity, the degree of current increase required to move said float element from said stop element being related to fluid flow rate.

4. The apparatus of claim 3 where said means for increasing current to said magnetic means is a current ramp or staircase generator.

5. The apparatus of claim 1 which further comprises sensor means positioned in the area of said stop element, said sensor means being actuated when said float element moves away from its position against said stop element, said sensor means thereby sampling the requisite reading of said means for increasing magnetic force which caused the movement of said float element from its rest position.

6. The apparatus of claim 2 wherein the means for detecting the departure of the float element is positioned in the area of said stop element, said sensor means being actuated when said float element moves away from its position against said stop element, said sensor means thereby sampling the requisite reading of said means for increasing magnetic force which caused the movement of said float element from its rest position.

7. The apparatus of claims 1 or 2 wherein the conduit in the area of said stop element is transparent.

8. The apparatus of claims 1 or 2 wherein the conduit in the area of said stop element is transparent and said sensor means is an optical sensor.

9. The apparatus of claims 1 or 2 wherein said float means is a sphere having sufficient magnetically responsive material therein to be responsive to magnetic force of said magnetic means.

10. The apparatus of claim 1 wherein said means for increasing magnetic force comprises means for changing the position of said magnetic means thereby changing the magnetic force applied to said float element.

11. The apparatus of claims 1 or 2 which further comprises control means actuated by said means for indicating fluid flow rate, said control means adjusting fluid flow when it varies from a predetermined level.

12. Apparatus for indicating fluid viscosity comprising:
(a) a conduit;
(b) a float element having a magnetic responsive mater-ial associated therewith positioned in said conduit, said float element being shaped to provide laminar flow of fluid between its surfaces and the interior of the conduit;
(c) a stop element positioned in said conduit which limits the motion of said float element in the downstream direc-tion;
(d) means for providing a constant rate of flow of fluid through said conduit;
(e) magnetic means positioned in an upstream area about said conduit and before said stop element;
(f) means for increasing the magnetic force of said magnetic means so as to move said float element away from said stop element and against the direction of said fluid flow;
(g) means for detecting the movement of the float ele-ment away from the stop element; and (h) means for relating fluid viscosity to the degree of requisite increase of magnetic force to move said float element away from said stop element.

13. The apparatus of claim 12 wherein said float element is an elongated multi-vaned float.

14. The apparatus of claim 12 wherein a gear pump serves to maintain constant fluid flow.

15. The apparatus of claim 12 which further comprises a system being monitored for supplying fluid to said conduit, and means for changing a variable to said system being monitored in response to the fluid viscosity measurement obtained by said apparatus.

16. Apparatus for measuring flow rates of fluids comprising a vertical conduit, a float element having a magnetic responsive material associated therewith positioned in said conduit, a stop element positioned in said conduit which limits the motion of said float element, electromagnetic means positioned above said stop element, means for gradually increasing the current to said elec-tromagnetic means to thus increase the magnetic force of said electromagnetic means so as to move said float element away from said stop element, said means for gradually increasing current to said electromagnetic means increasing current in a gradual step-wise manner to accurately measure the magnetic force required for the float to leave the stop element, means for detecting the init-ial departure of the float from the stop element, and means for relating fluid flow to the degree of current required to move said float element away from said stop element.

17. Apparatus for measuring flow rates of fluids comprising a conduit, a float element having a magnetic responsive material associated therewith positioned in said conduit, a stop element positioned in said conduit which limits the motion of said float element in the downstream direction, electromagnetic means posi-tioned in an upstream portion about said conduit before said stop element, means for gradually increasing the current to said elec-tromagnetic means to thus increase the magnetic force of said electromagnetic means so as to move said float element away from said stop element and against the direction of fluid flow, means for detecting the initial departure of the float element away from the stop, and means for relating fluid flow to the degree of requisite increase of current to cause movement of said float element away from said stop element, said means for gradually in-creasing current comprising an oscillator, and an integrator, and which apparatus further contains a digital counter, said oscilla-tor producing a wave train sent to the digital counter, said inte-grator controlling the current to the electromagnetic means pro-portional to the output of the integrator, said oscillator being turned off when said float element departs from said stop element, the accumulated counts in the digital counter being directly re-lated to fluid flow rate.

18. The apparatus of claim 17 which further comprises a second integrator, the output of the first integrator being inte-grated in said second integrator and the output of said second integrator being used to control the means for increasing current to said electromagnet, so that the current is proportional to the output of the second integrator, the output of said digital count-er thereby being capable of linear variation with fluid flow.

19. The apparatus of claim 17 wherein said means for grad-ually increasing current to said magnetic means increases in a grad-ual stepwise manner.

20. The apparatus of claim 17 wherein the means for detecting the departure of the float element is positioned in the area of said stop element, said sensor means being actuated when said float ele-ment moves away from its position against said stop element, said sensor means thereby sampling the requisite reading of said means for increasing magnetic force which caused the movement of said float element from its rest position.

21. The apparatus of claim 20 wherein the conduit in the area of said stop element is transparent.

22. The apparatus of claim 21 wherein said sensor means for detecting float departure is an optical sensor.

23. The apparatus of claim 17 wherein said float element is a sphere having sufficient magnetically responsive material therein to be responsive to magnetic force of said magnetic means.

24. The apparatus of claim 17 which further comprises control means actuated by said apparatus for indicating fluid flow rate, said control means adjusting fluid flow when it varies from a pre-determined level.