CA1301483C - Portable measuring device provided with an instant gas flow rate reading - Google Patents

Abstract

ABSTRACT

A measuring device, for automatically measuring in situ and over a gas passage opening through which a gas flow passes, has a pressure difference gauge allowing the measure-ment of a pressure difference between the inside and the out-side of the funnel mouth connected to the device after the latter is placed for measuring purposes over the opening, the value of the pressure difference thereafter being transferred into an electronic signal which controls the intensity of power supply to and, also if desired its running direction, of a control fan which is located in the throat cross section of the measuring device, one and the other in such a way, that after placing the funnel mouth over the opening while operating the device for measuring the gas delivery, each measured pressure difference is reduced down to zero at a fan speed and fan running direction which corresponds to the relevant gas delivery and its relevant direction of gas flow which flow rate values become instantly readable from a reading window which is connected to the measuring device; the device is easy to handle and may be made portable.

Description

The invention relates to a funnel type measuring device. Measuring devices for measuring air flow rates are indispensable, e.g., for instantly and exactly fixing in situ at an air terminal device or an air intake device or the like, as part of an air treatment appliance, an air fan appliance, an air heating installation or such like installations, the air flow rate which is blown out or which is suctioned per unit of time. The invention has as an object to provide for a measuring device which is easy to handle, promptly operating and also portable, which fully and reliably satisfies all requirements.

According to the invention, this is obtained by a measuring device, more particularly a portable measuring device for automatically measuring in situ and over an air passage opening through which a gas flow passes, the rate of volume of such a gas flow per unit of time - hereinafter called gas flow delivery - which measuring device is provided with a pressure difference gauge allowing the measurement of a pressure difference between the inside and the outside of the funnel mouth connected to said device after the latter is placed for measuring purposes over said opening, the value of the pressure difference thereafter being transferred into an electronic signal which controls the intensity of power supply to and, also if desired, its running direction, of a control fan which is located in the throat cross section of the measuring device, one and the other in such a way, that after placing the funnel mouth over said opening while operating said device for measuring the gas delivery, each measured pressure difference is reduced down to zero at a fan .~

13~1483 speed and fan running direction which corresponds to the relevant gas delivery and its relevant direction of gas flow which flow rate values become instantly readable from a reading window which is connected to the measuring device.

The operation of the pressure difference gauge which is built in the measuring device is such like, that the fan speed is measured by an electronic speed measuring device and is transferred by calibration into a value indicating the extent of gas delivery (air flow rate) which becomes instantly readable from the said reading window.

The relationship between the fan speed and the air flow rate is fixed by calibration. By means of a revolutions counter the speed of revolutions of the fan is measured and transferred in the corresponding air flow rate, which is instantly made readable in analogous or digitals from a reading window which is provided at the measuring device. The measuring range of the measuring device can, e.g., vary from lO m3/h till 500 m3/h. This large measuring range area is obtained by using measuring areas overlapping each other, and this is effected by mounting to the underside of the measuring device a flow resistance disc. This flow resistance disc is provided by a disc having one or more holes.

Also, the temperature of the air flowing through the measuring device is measured and made readable from a reading window, which is provided to the measuring device. By means of the measuring device the most ._,. . ~ !,~
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13(1~ 33 relevant values for air flow rate through a passage opening can so exactly be measured, e.g., the air flow rate and temperature of the flowing air or gas.

The measuring device can be fitted with an adapted mounting piece for use with terminal devices and air intake passages of various dimensions. For operational purposes the measuring device is provided with a pair of handles. The most important operating means are mounted and located in such a way so that they can be easily operated when the user holds the handles. The manipulation and the simplicity of use of the measuring device, as well as the speed for measuring with the measuring device under practical circumstances, are highly furthered by providing the power supply to the fan and to the entire electronic measuring / and control system by means of a preferably rechargeable battery, all located in a portable bag and connected to the measuring device by means of a connection cable. It will be clear that where the measurement would relate to the suctioning or the blowing of gas or air respectively, the difference will become readable and visible upon the reading window.

The measuring device offers the following measuring possibilities:
1. Signals generated by the pressure difference gauge automatically select for the direction of turning and the number of revolutions of the fan in such a way, that the static pressure difference inside and outside the funnel mouth / mounting piece is reduced to zero (0). In the event of fluctuations in the air flow rate, automatic control of the number of revolutions is effected so that the 13~1~83 point of zero is again obtained and retained respectively. Air flow rates which are generated during this operation, appear on the reading window of the measuring device. An optical signal is shown when the point of zero is again reached. The measuring procedure starts by pushing a knob nearby the handle and the process is stopped by pushing that knob again;

2. Since gas flow rates passing through passage openings do often and sometimes fluctuate to a relative strong extent, the air flow rate is defined in such event by the measured average value during a certain defined period of time. The measuring device enables this by retaining the measuring procedure under 1 during a period which is long enough and then it defines an average value of all such air flow rates which are measured in the said period. The last average value is shown and retained in the reading window. This automatic procedure is finished by pushing the knob nearby the handle. By again pushing said knob, the reading window becomes empty again and a next measurement can be effected;

3. In the event that the differential width of the fluctuations is larger than the preset differential width at the measuring device, than this procedure as described under 2 will not result into a readable rate value and alternately the differential for fluctuations on the measuring device must be set at a greater value, or the procedure under 1 must be followed;

4. The procedure as described under 2 can also be finished without showing intermediate air flow rates;

13~ 33 5. The measuring device offers the possiblity to preset the direction of turning and the number of speed revolutions of the fan by hand. The measuring time is thereby shortened because proceeding this way, the fan will quickly start and reach its desired number of revolutions in the desired direction of turning;

6. The temperature of the air or gas is measured and can be read analogous or digital;

7. The measuring device offers possibilities for simplifications, such as:
7.1 Switching of the automatic pressure difference = 0 searching system, enabling to measure air flow rates totally by hand;
7.2 No measurement of temperature;
7.3 Permanent mounting of the pressure difference gauge upon the mouth of the measuring device, in which case, while using a mounting piece, the pressure difference gauge need not be mounted to the mounting piece, causing, however, a slight measuring error, which can be corrected later on and if desired, by means of a calibration graph, or automatically (e.g., by means of a microprocessor).

In the drawing a preferred embodiment of the invention will be explained hereinafter:
Fig. 1 is a perspective view of the portable measuring device;
Fig. 2 schematically shows an axial cross section through the measuring device;
Fig. 3 is a circuit diagram of the pressure difference gauge;
Fig. 4 is a circuit diagram of the measuring- and control system for the measuring device;

13~14E~3 The measuring device 1 in Figs. 1 and 2 consists of a funnel housing 2 which is composed of a cylindrical part and a reducing piece going from a round shape to a square shape. In the cylindrical part, a fan 3 is mounted in an axial direction by means of radial supporting means, as well as by a parallel flow passage director 4, and it is provided with a ring shaped lower flange 5. By means of a ring shaped folded edge 6, the reducing piece running from a round shape to a square shape, is connected and fixed to the cylindrical part. At its upper and lower side the funnel housing is provided with both holes 7 and 8 respectively. At the outside of the funnel housing are provided diametrically two handles 9 and between these handles 9 there is located a box 10 having a reading window 11, two position switches 12 ("automatic" and "continuous") and 13 ("hand operation switch"), a connection 14 for battery power supply, an indicator 15 for pressure differences ( + or 0 or - ) and a gauge 16 for the calibration of the funnel measuring device. Upon the box 10 there is an optional switch 17 for handsetting the calibration scale which corresponds to the measuring range ~including or not the use of a flow resistance disc 18) and an adapted mounting piece 19. A mounting piece 19, provided in various dimensions and shapes can be fixed upon the measuring device 1 by means of bolting to be set via holes 8 in the square flange 20 at the upper side of the funnel mouth 21 and holes 22 in the connectable square flange 23 of the mounting piece 19. For quick mounting and removal respectively of a mounting piece 19, it will be clear that use can be made of quick closing means instead of the bolting described before. Integrated in or nearby the :
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' ' handle 9 there is provided an on/off switch 24 and an operating knob 25 for hand control/presetting of the fan 3. For connection against the lower flange 5 of the measuring device 1, a flow resistance disc 18 can be provided by means of via bolt holes 17 or in a similar way.

Mounting piece 19 can be rigid or of foldable shape.
If the latter applies, the flexible wall 26 consists, e.g., of impregnated nylon or rubber cloth that is stretched by means of a number of cloth stretching means 27, each of which is located in a corner of the mounting piece. Such a stretched structure, which is per se known for other purposes, will not be further described here.

The temperature of the flowing air or gas is now measured and the measured value is readable from window 11, or from a separate window 28. The art by which temperatures of gasses are measured and are being made readable in an analogous or digital scanner, is already known from other applications and will not be further described herein. The pressure difference gauge of measuring device 1 or mounting piece 19 is further shown by reference number 29.

Fig. 3 schematically shows the principle of the measurement for the static pressure difference. In fact, it is based upon measurement of an air flow.
If the static pressure pl in space I is greater then the static pressure p2 in space II, then a gas flow is generated from 01 to 02, which touches NTC
thermistor A, however it does not touch NTC
thermistor B. This will cause electrical voltage 13~1483 differences between A and B and these indicate the magnitude and direction (pl is greater than p2) of the static pressure difference. In the event of a reversed direction of flow, where pl is smaller than p2, and if there is no flow at all, pl = p2(zero).

A recorder connector 30 provided on the measuring device makes registration of the measurement possible.

Fig. 4 shows the principle of the measuring - and control system of the measuring device. The battery in the portable bag 31 provides for the power supply to the entire system. Preferably battery 31 will be rechargable and thereto it can be coupled to a battery charger 32.

For carrying out the measurements, battery 31 is connected to the supply main 33. Supply main 33 generates from the power supply a number of different voltages which are desired in the system.
Via a central control unit 34, the system can be started by means of an on/off switch 24. By actuating this switch for the second time, the system can be stopped. In operation, after the measuring device 1, whether or not provided with a mounting piece 19, is placed over a gas passage opening, the measuring system is started up by means of switch 24. The central control unit 34 generates a. o. a signal to the power supply main 33, in order to bring other parts of the system also under voltage. Furthermore, the central control unit 34 generates a signal to the reading window 11 for showing the measured values and also, by means of *~

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a + or - sign to show the direction of turning of the fan 3. The direction of turning indicates the direction of flow of the gas through the device and thus provides for an indicator to show if the air or gas flow is blown into or suctioned from respectively the gas flow passage. The central control unit 34 activates also the calibration of the air flow rate 35. Correct calibration must be handset by means of the selecting switch 17. Each calibration position of the selecting switch 17 corresponds to two circuits, one for each direction of turning of the fan 3. The direction of turning is switched on in the control signal converter 36 and except that it is being passed on to the band width controller 37, it is also passed on to the central control unit 34 and via the latter on to the air flow calibrating means 35.

Calibration may take place by using the measuring device, with or without flow resistances 18 and also the combinations of the measuring device with the flow resistances 18 and mounting pieces 19, with an exact air flow rate measuring instrument, e.g., a measuring range with a measuring flange, measurable in both directions of turning of the fan. The air flow rate is proportional with the number of revolutions of the fan. With the aid of the potentiometer or a microprocessor (which allows a very great exactness) for each combination and direction of turning, the correct relationship between the number of revolutions of the fan and the air flow rate can be set. The manner in which the setting of the potentiometer or the microprocessor takes place is already known from other applications and it will therefore not be described here further.

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Pressure difference gauge 29 measures the static pressure difference between the pressure inside and outside the measuring device 1 or the mountiny piece 19 and also if this pressure difference is of a positive or negative value. The system itself will try to render this pressure difference as small as possible. Pressure difference gauge 29 sends the measuring signal to the pressure difference indicator/switch 38. The latter controls indicator 15, consisting of three LED's (LED = Light Emitting Diode). By means of the indicator 15 the user can check if the pressure difference is positive, zero or negative and thereby know in which operational state of control the system actually is.

Now the operation will be described whereby switch 13 is in the position "switch on". Pressure difference indicator/switch 38 emits also four switching signals. Three signals are received by the zero control means 39. All these three switch signals are related to so called signal windows, a very small window and symmetrically surrounding it a larger window. In this way, the range of signals is divided into five different areas. The outgoing signal of the pressure difference gauge 19 may be located in one of these areas. Depending on the position of the signal, there will be carried out a quick or a very slow control activity. In the event that the outgoing signal is located within the small signal window, the pressure difference indicator/switch 38 will not carry out a control activity and there will be only a memory function.
In the last event, the outgoing voltage of the zero control means 39 will remain constant; this situation corresponds to a static pressure .

13~ 3 difference of zero. The output of zero control means 39 serves as a variable setpoint for a second control loop. This signal reaches control signal converter 36. This second control loop is constituted by fan 3, counter measurement 40, control signal converter 36 and signal width control means 37. This second control loop follows the setpoint. The control loop may follow the setpoint only by changing the direction of turning and the number of revolutions of the fan 3. Corresponding to a defined setpoint, there is only one number of revolutions and corresponding direction of turning of the fan 3 and this is just the combination of number of revolutions and the direction of turning which, at the output of the measurement for the revolutions 40, will generate a voltage which is fully equal to that of the setpoint. The output at the control signal converter 36 controls band width control means 37, which in its turn controls the fan 3.

Once the setpoint has obtained a value by which the measuring system indicates a static pressure difference of zero value, then by means of the fourth switch signal, derived from the pressure difference indicator/switch 38, the zero point detector 41 is activated. Zero point detector 41 then generates a switch signal which is sent to the central control unit 34 via switch 12. In the position "automatic" of switch 12, a certain period of time will lapse after the zero point detector 41 has issued a switch signal to the central control unit 34, whereafter the measurement is automatically stopped. During this time, there is carried out an averaging of the measured values which have been 130~3 offered during this period. It is this average value which, after the average time has gone by, is shown on the reading window 11. By retaining this average value, it can be read also after the measurement has been finished. In the event that switch 12 is in the position "continuous", the switch signal, derived from the zero point detector 41, is blocked and then the user himself must finish the measurement by pushing in the on/off switch 24.
The positon "continuous" of switch 12 is necessary, in the event that the air flow rate demonstrates such large fluctuations, that the setpoint will never be stable enough to arrive to automatic switching off.

If switch 13 is set in the position of "hand operation", then switch 12 is also set in its position "continuous". In this position of "hand operation" of switch 13, the automatic control of the fan to a value, in which the pressure difference inside and outside the measuring device/the mounting piece is zero, is blocked and by means of a potentiometer 25 any given setpoint and so any given number of revolutions of the fan and its direction of turning can be chosen. Potentiometer 25 is hand operated. In the position "hand operation" of switch 13, it will thus be possible to carry out a measurement entirely by hand, based upon the signals which appear upon the indicator 15. A much more important application, however, is the following: by hand the direction of turning and the number of revolutions of the fan is selected, lying closely to the expected air flow rate to be measured (presetting). If, thereafter, measurement is made in which the switch 13 is in its operating position 13~ 83 "switch on", then fan 3 is given a number of revolutions for starting up, which is equal to the presetting, so that the fan very quickly reaches nearly the desired number of revolutions.
Thereafter, the automatic control system comes into operation again. The time for measurement is thereby very much shortened, because the fan is reaching its number of revolutions very fast.

The value of the measurement, which is shown on the reading window 11 corresponds to the calibration of air flow rates 35. Indicator 42 shows the warning "low batt" upon the reading window 12, when the voltage of the battery will arrive under a predefined value.

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Claims (12)

1. Measuring device, more particularly a portable measuring device for automatically measuring in situ and over a gas passage opening through which a gas flow passes, the value of the volume of such a gas flow per unit of time - hereinafter called gas flow rate or delivery - which measuring device is provided with a pressure difference gauge allowing the measurement of a pressure difference between the inside and the outside of a funnel mouth connected to said device after the latter is placed for measuring purposes over said opening, the value of the pressure difference thereafter being transferred into an electronic signal which controls the intensity of power supply to a control fan which is located in a throat cross section of the measuring device, in such a way that after placing the funnel mouth over said opening while operating said device for measuring said gas delivery, each measured pressure difference is reduced down to zero at a fan speed and fan running direction which correspondss to the relevant gas delivery and its relevant direction of gas flow which flow rate values become instantly readable from a reading window which is connected to the measuring device.

2. Measuring device according to claim 1, characterized, in that the fan speed is measured by an electronic speed measuring device and is trans-ferred by calibration into a value indicating the extent of gas delivery, which becomes instantly readable from the said reading window.

3. Measuring device according to claim 1 or 2, characterized, in that an electronic circuit is provided, maintaining so the fan speed, in the state of equilibrium, in which the pressure difference has a of zero value, so by means of said electronic circuit.

4. Measuring device according to claim 3, characterized in that in the occurrence of a fluctu-ating gas delivery, the equilibrium at a pressure difference of zero value is once again maintained whereupon the fluctuating fan speeds are averaged during a controllable period of time whereafter this mean value is maintained upon the reading window.

5. Measuring device according to claim 1, 2 or 4, characterized in that said funnel mouth is pro-vided with a mounting piece, said mounting piece being provided with a pressure gauge having an individual connection.

6. Measuring device according to claim 5, wherein said mounting piece has a flexible airtight sealing edge for fixing it over the said opening in order to adapt it to at least one of the size and the shape respectively thereof.

7. Measuring device according to claim 1, 2, 4 or 6, characterized in that carrying handle means are provided and that nearby a carrying handle there is provided a control switch for operating the device.

8. Measuring device according to claim 1, 2, 4 or 6, characterized in that the power supply to the control fan is provided by means of battery means housed in a portable bag in which also a connection cable to the measuring device is included.

9. Measuring device according to claim 1, 2, 4 or 6, characterized in that in the event of a pres-sure difference being measured at the funnel mouth, indicating means are provided making automatically readable if the gas flow rate measurements results from fan suctioning or fan blowing gas respectively through said opening.

10. Measuring device according to claim 1, 2, 4 or 6, characterized in that temperature indicating means are provided for measuring the temperature of the gas flow and indicating it respectively in a reading window.

11. Measuring device according to claim 1, 2, 4 or 6, characterized in that connection means are provided for connecting the device to a recording apparatus for recording the measured values of the gas flow rate through said opening.

12. Measuring device according to claim 1, 2, 4 or 6, characterized in that said electronic signal controls the running direction of the control fan.

#21 11/22/1990 16