FIELD OF THE INVENTION The invention described relates to apparatus and methods for monitoring and measuring fluid flow rates in ducts and the like, where multiple measurement points are required.

BACKGROUND

In a number of industries it is required to monitor and control the operation of equipment and systems in which there are multiple flows of fluids (i.e. gases or liquids). It may for example be required to measure flow rates (either absolute or relative to some baseline value) in a number of ducts, sometimes in the presence of contaminants, and to operate alarms or implement control responses where particular results or patterns of results are found.

As a particular example, papermaking machinery installations may be provided with multiple dust removal hoods that may over time accumulate excessive amounts of dust and clog or otherwise lose performance, with unacceptable results for the product, the equipment and the operators. Monitoring of the flows in such hoods is desirable. The hoods may also have to deal with differing particulate loads in the air that flows through them and require (or be able to benefit from) adjustments of the flow rate from time to time. Monitoring systems based on large numbers of transducers and displays or recorders distributed at various measuring points can be very expensive to provide, maintain, calibrate and use effectively with limited manpower. Systems in which there are multiple transducers and where signals or readings are transmitted electrically to a central point for display can suffer from similar shortcomings.

Systems are known in which large numbers of fluid pressures are measured by successively placing them in contact with a smaller number of transducers using special scanning valves (eg as formerly made by the Scanivalve Corporation of the USA), but such valves are not suitable for most industrial applications (as opposed to some research applications). Nevertheless, it is sometimes acceptable to obtain adequate information about a system or equipment item by determining the state of flow

at a number of points without necessarily maintaining a truly continuous watch at any one of those points. This presents opportunities for providing monitoring/measuring systems that avoid at least some of the above problems. However, such systems do not appear to have been provided. In particular, dust control systems for installations such as papermaking are typically monitored by comparatively primitive means.

A significant problem in papermaking installations and other installations where flows laden with particulates are encountered is that of contamination of pressure measurement ports by the particulates, with resulting inaccurate readings. Systems that lend themselves to the provision of purging are desirable for such applications.

The present invention addresses these needs for systems where there are flows in multiple ducts, particularly where such flows are or may be contaminated with particulate and/or condensable substances and where comparatively low costs and high control/alarm capability are required. In particular, the invention is applicable to dust control installations.

SUMMARY OF THE INVENTION

The invention provides in a first aspect a flow measurement and control system comprising: a plurality of solenoid operated selecting valves each having firstly an inlet port connectable to a pressure line and secondly an outlet port; pressure transducer having a pressure transducer inlet port and adapted to provide an output signal corresponding to a pressure of a fluid communicating with the pressure transducer inlet port; a manifold by means of which the outlet ports of said valves are in fluid communication with the pressure transducer inlet port; signal conditioning means for receiving the pressure transducer output signal and displaying and/or transmitting to a remote location information derived by said signal conditioning means from the said output signal; and control means adapted to operate the said valves so as to place the outlet port of a selected one of said valves in fluid communication with said pressure transducer inlet port whiie isolating the outlet ports of other valve pairs therefrom.

The invention takes advantage of the availability of very suitable solenoid operated valves and modern electronic developments for operating them, to provide an alternative to both mechanical scanning arrangements and systems having very large numbers of transducers - one per pressure tapping or pair of pressure tappings. This leads to cost and simplicity advantages.

Preferably, said selecting valves are separate discrete valves.

The control means may be adapted to automatically place members of said plurality of selecting valves in fluid communication with the pressure transducer inlet port, one at a time, in a predetermined sequence or pattern.

Alternatively or additionally, the control means may be adapted to initiate the said sequence or pattern in response to a control signal applied to said control means.

The control means may be adapted to modify said sequence or pattern responsively to outputs read from the pressure transducer meeting a specified criterion.

It is preferred that said control means is operable under control of a stored program.

The control means may be or include at least one of a programmable logic controller (PLC), a microcontroller (MCU), and a computer.

At least a portion of the functionality of said signal conditioning means said control means is provided by the control means.

The control means may be adapted to be connected to a data network and to exchange data via said data network. (For example and without limitation, this could be of the Controller Area Network (CAN) type.)

The system preferably has a solenoid operated purge valve operable by the control means to place a purging fluid supply in fluid communication with said manifold so that by opening others of the valves on said manifold those selecting valves and pressure lines connected to their inlet ports can be purged.

The system may further comprise an isolating valve between the manifold and the pressure transducer inlet port said isolating valve being operable by the control means to isolate the pressure transducer when purging fluid is supplied to the manifold.

In a particularly preferred embodiment of the invention: the solenoid operated selecting valves connectable to pressure lines comprise pairs of solenoid operated selecting valves; the said manifold is one of first and second manifolds; one member of each said pair of selecting valves has its outlet port in communication with the first manifold and the other member of said pair of selecting valves has its outlet port in communication with the second manifold; the first and second manifolds are in fluid communication with first and second inlets of a differential pressure transducer respectively, and said control means is adapted to operate a selected one of said pairs of said solenoid operated selecting valves to place its valves in fluid communication with their respective manifolds and thereby the inlet ports of the differential pressure transducer while isolating the other said pairs from said manifolds, so that said measurement and control means is adapted to measure the differences in pressure between inlet ports of solenoid operated selecting valves of said pairs. This embodiment lends itself very well to measurement of flow rates due to the suitability of measurements of differential pressures across Venturis, orifice plates or the like for floiw rate measurements. Fluid temperature measurement means may be incorporated in the system to assist in density estimation for gaseous fluids.

Preferably, each of said first and second manifolds has a separate solenoid operated purge valve operable by the control means to place a purging fluid supply in fluid communication with that manifold so that by opening selecting valves on said manifold those selecting valves and pressure lines connected to inlet ports thereof can be purged. The system may further comprise a pair of isolating valves each between one manifold and the pressure transducer inlet port connected to that manifold said isolating valves being operable by the control means to isolate the pressure transducer when purging fluid is supplied to the manifolds.

The solenoid operating selecting valves, manifolds and pressure transducer may be enclosed in a single enclosure. This can be a very convenient arrangement particularly where the system may be used for

different applications rather than being dedicated to particular equipment installations.

In a further aspect, the invention provides a method for monitoring a set of pressure tappings in communication with flowing fluids comprising the steps of: providing a flow measurement and control means according as disclosed herein; connecting each pressure tapping of said set to an inlet port of a solenoid operated selecting valve of said flow measurement and control means; by said control means operating said selecting valves to successively place pressure tappings in fluid communication with said pressure transducer while isolating other pressure tappings from said pressure transducer.

Also, the invention in this aspect provides a method for monitoring a set of pairs of pressure tappings in communication with flowing fluids comprising the steps of: providing a flow measurement and control means as disclosed where a differential type pressure transducer is used, and paired selecting valves, connecting members of each pair of pressure tappings of said set to members of a said pair of inlet ports of solenoid operated selecting valve of said flow measurement and control means; by said control means operating said pairs of selecting valves to successively place pairs of pressure tappings in fluid communication with respective inlet ports of said pressure transducer while isolating other said pairs of pressure tappings from said pressure transducer. In this case, members of at least one pair of pressure tappings are positioned to provide a pressure difference in the presence of a fluid flow and including the step of deriving a fluid flow rate from measurement of said pressure difference. In one very suitable application, the flowing fluids may be flows of air in an air conditioning system.

In another very suitable application, the flowing fluids may be flows of air in a dust control system including at least one dust extraction hood.

Other suitable applications could be installations of spray booths, fume cupboards and the like.

In a further aspect the invention provides a method for controlling fluid flows in apparatus including the steps of: monitoring fluid flows in said apparatus with, a fluid flow measurement and control system as disclosed herein; and operating one or more controls of the apparatus in response to information derived from the flow measurement and control system. The control means may be used to provide commands for such operation of controls, or alternatively the commands may be made by other controlling means.

Additional inventive features embodiments and possible enhancements and variations of the invention are disclosed below.

In order that the invention may be better understood there will now be described, non-limitingly, a preferred embodiment as shown in the attached Figures, of which:

Figure 1 is a semi-schematic diagram of a flow measurement apparatus according to the invention;

Figure 2 is a flow diagram of a software program for use in the apparatus of Figure 1 ;

Figure 3 is a semi-schematic diagram of an alternative flow measurement apparatus according to the invention. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Figure 1 shows in semi-schematic form apparatus 1 according to the invention connected to a duct 20 in which a fluid flow occurs and is to be measured. Apparatus 1 has a bank of first solenoid-operated valves 2, independent from each other, and a bank of second solenoid-operated valves 3, independent from each other. Eleven first valves and eleven second valves are shown in banks 2 and 3 respectively, but this is by way of example. Any number of valves may be provided.

Associated with valves 2 is a manifold 4 connecting outlet ports of all of the valves 2 to an inlet port of a manually-operable valve 5 via a duct 6. Associated with valves 3 is a manifold 7 connecting outlet ports of all of the valves 3 to an inlet port of a manually-operable valve 8 via a duct 9.

Alternatively, valves 5 and 8 could be operated by the control means 10, for example in response to a manually entered command.

Very conveniently, valves 2 may be of the type sold for use in controlling pneumatic cylinders. In particular, some valves of this type can be provided with manifolds to which they can be directly mounted and that are also suitable.

Apparatus 1 further includes a signal conditioning and control means 10, a power supply 11 and a voltage regulator 12. Power supply 11 provides power to unit 10 and, via regulator 12, to a differential pressure transducer 13. Inlet ports of transducer 13 are connected to respective outlet ports of valves 5 and 8 by ducts 14 and 15.

A data link 16 allows output signals from transducer 13 to be input to unit 10. Unit 10 also has a data link 17 whereby it may send data to and/or receive data from, other equipment (not shown) as required by a particular application of apparatus 1.

Not shown for clarity, but. present in apparatus 1 are links between unit 10 and each one of solenoid-operated valves 2 and 3, whereby these are operable under the control of unit 10.

The term "semi-schematic", used above in relation to Figure 1 , means that the interconnections between the various components of apparatus 1 and between apparatus 1 and duct 20 are shown without any intended implication that the positions of the various components need to be physically related to each other in the way shown. However, a practical embodiment of apparatus 1 has been conveniently built by the present applicant with the various components described above, laid out on a baseplate 101 in substantially the way shown in Figure 1. Baseplate 101 may be installed in a suitable enclosure (not shown).

In Figure 1, a duct 18 is shown connecting the inlet port of a valve 2a being one of valves 2 to an orifice 21 in a fluid-containing duct 20. Similarly, the inlet port of a valve 3a being one of valves 3 is connected by a duct 19 to an orifice 22 in a venturi portion 23 of duct 20. Flow in duct 20 leads to a pressure difference between orifices 21 and 22, the pressure being lower at orifice 22. It is possible in known manner to estimate flow rate in duct 20 from a differential pressure measurement at a venture, orifice plate (or the like) if

the gas density is known or can be estimated. While only one pair of valves 2 and 3 is shown so connected in Figure 1 , it is to be understood that this is for illustration. In use of apparatus 1, multiple pairs of valves 2 and 3 may be used to connect to multiple pairs orifices (not shown). Signal conditioning and control means 10 includes a microprocessor

(not shown) operable under the control of a program stored in a suitable medium (not shown), and is able to do the following things:

(1) Open the pair of valves (eg 2a and 3a) associated with each particular pair of orifices in sequence, while leaving the others valve pairs closed, according to a programmed sequence; and

(2) Receive output signals from the transducer 13, for a specifed period while each pair of valves is open, apply a set of computational steps to the resulting readings and send the result in a suitable digital form to an external location via data link 17.

Persons ordinarily skilled in the art will recognize that these functions require unit 10 to include:

(a) suitable driver arrangements (eg using buffering transistors in known manner) whereby the microprocessor can provide adequate power to operate the solenoids of valves 2 and 3;

(b) analog-to-digital conversion means whereby the analog output of transducer 13 is readable by the digital microprocessor; and

(c) Perform memory access operations to a secondary data storage module to record all measurements taken by the unit for future reference and review.

Signal conditioning and control means 10 is shown with a local display 24, such as an LCD or LED digital display, that may display outputs and/or alarms (see below) instead of or additional to transmission of unit outputs along link 17. The use of a microprocessor allows great flexibility in programming. As but one simple example of a suitable program, the flow diagram of Figure 2 provides for each of a number of pairs of valves 2 and 3 to be placed in communication with one of a set of orifice pairs in turn, i.e. for pairs of orifices to be scanned in turn, following receipt of a START command. The block

"delay equalization time" in Figure 2 refers to the microprocessor waiting for a preset time delay after each change of valve pairs, in order to for the pressures in the ducts (eg 18 and 19) and manifolds 4 and 7 to settle, through flow of fluid therein. A suitable delay time would be chosen, for example through trials. At the end of the scan sequence, with all valve pairs scanned, the system would revert to a SLEEP mode until arrival of a further START command.

As one example of possible refinements or different approaches, the following can be cited. The "take and store measurement" block could correspond to taking a number of readings over a preset measurement period ^' and at a preset sampling rate, and applying an averaging computation to the resulting values. As another example, the delay period, instead of being preset, could be determined by taking readings until a suitable criterion of settling to a constant reading is satisfied. Excessively slow settling could be an indication of clogging of a duct (eg 18 or 19) manifold (4 or 7) or orifice (eg 21 or 22) and be used to cause an alarm or corrective action (see below). As still another example, continuous scanning could be carried out, rather than reverting to sleep mode. Generally, the valve pairs 2 and 3 can be scanned cyclically, on request, on a periodic basis, on a basis determined by measurements themselves, or any combination of these.

A still further possible enhancement would be applicable where apparatus 1 is applied to a particular piece of apparatus (such as a dust hood apparatus) where a particular pattern of readings among a set of orifice pairs on the equipment is associated with a particular form of fault (eg clogging with particulates in a particular way). In such a case, the microprocessor could be programmed to test for such a pattern (or a trend towards such a pattern) and provide a suitable alarm instead of (or in addition to) raw pressure data.

Valves 8 and 5 allow for isolation of transducer 13 when required, eg for calibration purposes. They may be arranged if required to allow for connection of pressure reference signals to transducer 13 by additional ducts (not shown).

Although a single differential pressure transducer is shown in Figure 1 and has been described, it is to be understood that two separate transducers (not shown) could be used to provide the same functionality instead, one

being connected to each of manifolds 4 and 7, with instead of a single link 16 two links (not shown) to unit 10 so that each transducer could be read independently of the other. This arrangement allows constant monitoring of the transducers' calibration by comparing the results from both transducers, If one transducer's output varies outside a specified range an "out-of- calibration" warning can be generated under the control of the program of unit 10. It would also be possible to provide for unit 10 to connect manifolds 4 and 7 to a backup differential pressure transducer (not shown) in the event of a failure of the main one, using suitable valve(s) and duct(s) (not shown). This could be done automatically by unit 10 or manually in response to an alarm from unit 10. One could also use if required in a particular application both a differential and an absolute pressure transducer (for example where the pressure of the fluid whose flow is to be measured is widely variable).

A further enhancement is shown in Figure 1. Signal conditioning and control means 10 may have additional connection(s) 26 to other transducers or actuators (not shown) readable or controllable by unit 10- For example, transducers other than pressure transducers could be used, such as temperature transducers or species content (eg Carbon Dioxide or Methane as contaminants in an air flow). Where flow of a a gas of variable temperature is being measured, a temperature sensor in the flow can be used to estimate the gas density density, so that the pressure difference across an orifice plate or venturi of known dimensions can provide a more accurate volumetric flow rate estimate than one based on the pressure difference alone with an assumed density value. Unit 10 (or a computational device to which it is connected by link 17) can of course be programmed to provide report generation (in any desired format) from the measurements made, when required.

Unit 10 may also be provided with functionality to control a separate and additional set of valves. For example, not shown, one pair of valves 2 and 3 could be connected to additional manifolds to which members of other banks of valves (like 2 and 3) are themselves connected one-by-one under the control of unit 10 _t thus multiplying the ability of apparatus 1 to monitor a system with more orifice pairs.

1 ]

Apparatus 1 may be provided with a further enhancement for use where clogging by particulate matter or condensing flows is a potential issue. As a particular example, dust removal hoods and dust removal installations (eg in papermaking machinery) are a possible application where dust can clog orifices and small-bore ducts such as would be used for ducts 18 and 19.

Figure 3 shows an apparatus 30 similar to apparatus 1 but provided with a purging arrangement. "Purging" as used here may mean any of the following:

(i) blowing a fluid through part of an installation that includes the system of the invention In order to correct or prevent or limit clogging of one or more flow passages or orifices by particulates or fluid-borne contaminants or condensed matter;

(ii) blowing a fluid through part of an installation' that includes the system of the invention in order to remove a fluid that it is desired not to have within that part of the installation, eg a corrosive fluid.

Apparatus 30 is the same as apparatus 1, except as follows:

(1) there are two solenoid-operated valves 40 and 41 operable under the programmed control of a control and signal conditioning unit 50 similar in other respects to unit 10 of apparatus 1 ;

(2) ducts 42 and 43 connect outlet ports of valves 41 and 40 respectively to ducts 36 and 39 respectively, ducts 36 and 39 corresponding to ducts 6 and 9 of apparatus 1;

(3) valves 50 and 51 correspond to valves 5 and 8 of apparatus 1 , except that they are solenoid-operated under the programmed control of unit 50;

(4) inlet ports of valves 40 and 41 are connected to a source (not shown) of purging fluid (eg air where the apparatus 30 is used for measuring air flows) by ducting 44. This arrangement allows prevention, correction or alleviation of dogging of any of the orifices (eg 47, 48) or ducts (eg 45, 46) to which valves 52 and 53 (corresponding to valves 2 and 3 of apparatus 1) are connected. This is done by directing purging fluid through ducts 36 and 39, manifolds 34 . and 37 (corresponding to manifolds 4 and 7 of apparatus 1), valves 52 and 53

and their respective ducts (such as ducts 45 and 46). This is achieved by closing valves 50 and 51 to isolate transducer 54 (corresponding to transducer 13 of apparatus 1), opening valves 40 and 41, and opening valves 52 and 53, so that the purging fluid passes therethrough, under control of unit 50.

Valves 52 and 53 may be opened individually in sequence, in banks (for example all of valves 52 then all of valves 53) or all together or in any other suitable way, according to the programming of unit 50. Finally to complete the purge process, valves 40 and 41 are closed, valves 50 and 51 are opened and normal operation restarted, again under the control of unit 50.

Apparatus 1 and apparatus 3 lend themselves very well to such applications as, for example, dust control installations for papermaking or paper processing installations. These typically involve several dust removal hoods from which one or more fans exhaust dust laden air. Such systems may further include cyclone-type or other dust extraction or collecting systems, and present a problem of monitoring and control of air flows, potentially dust-laden, at several points. An apparatus such as apparatus 3 may be used to provide monitoring of flow at such points, with a facility to provide alarms or in the event of fouled ducts or other flow-affecting abnormal conditions. Information from the signal conditioning means of a system according to this invention may also be used as part of a control loop for closed-loop controller of such an installation.

The invention further provides an improvement to an air conditioning installation wherein flow in at least one duct is monitored by a system according to the present invention. The system may further include means to adjust controls in the system at least partially in response to measurements of said flows. Air conditioning systems are often designed to have the ability to respond to thermostats in particular locations by adjusting the flow and/or temperature of the air directed to a particular location. However, a flow monitoring system according to the invention allows for enhanced control of air conditioning systems. For example, it is known for flows in ducts of a system to vary in an uncontrolled manner according to wind and sunlight conditions, changes of room configurations and the like. The system of the invention allows the convenient and inexpensive monitoring of flows at

multiple points in such systems, and its output information can be used to control air flows.

In the above description, systems 1 and 30 having only a single differential-type pressure transducer has been described. It may be desirable in some situations (notably those where substantial pressures are encountered, as opposed to near-atmospheric pressures of applications such as air conditioning and dust hood systems) to have an absolute pressiure measurement at one or more points in an apparatus. This can be achieved by providing a suitable additional pressure transducer suitable for such measurements, to communicate with suitable tappings via a dedicated manifold of its own (like manifolds 34 or 37 of system 30) , with selector valves (like valves 52 or 53) and its own purge valve arranged similarly to purge valve 40 or 41 and isolating valve arranged similarly to valve 50 or 51. The control means would operate all valves associated with such an extra transducer.

Although a system having a differential pressure type transducer has been described, and is preferred where the objective is to measure flow rates, in ducts or dust hoods for example, it will be recognized that where the measurement of pressure differentials is not required, the invention can be applied in systems where single-inlet pressure transducers are used.

The systems as described may often be much simpler and cheaper (suitably for industrial applications) than other multiple pressure scanning systems. Although not able to provide sampling at the high rates such competitive systems can, the rate sthey can achieve are suitable for many practical applications, including those mentioned herein.

It will be recognized that many variations may be made to the equipment as described above without exceeding the scope or spirit of the invention.

In this specification, the word "comprise" and derivatives thereof such as "comprising", "comprises", and "comprised", when applied toi a set of elements integers or steps is to be taken to indicate that the integers elements or steps are present, but not to preclude the possibility that other inteers elements or steps are also present.