CONTAINER CONTENTS MEASURING APPARATUS

Abstract: A measuring apparatus comprises a load member (2) that can be stressed by positioning a part of a container on the load member and measuring the stress produced on the load member as the container is subject to a predetermined tilt. Offset facilities to enable automatic deduction of the stress produced by an empty container are provided.

Description: CONTAINER CONTENTS MEASURING APPARATUS This invention relates to measuring apparatus and in particular though not exclusively to apparatus for measurinq the content of vessels such as beer kegs, oil drums and the like. There are many commodities which are sold in or used from containers, the containers holding either a variable quantity of the commodity at the time of the transaction or the commodity being used in such a way that from time to time it is necessary to ascertain the amount that remains. Notable examples are oil in drums, beer in kegs and gas cylinders; althouqh solid materials, especially powders or pellets, may also be stored in a similar manner. In order to ascertain the quantity of commodity in or remaining in the container it is often impractical, or impossible, to empty the commodity out for measuring purposes and the commodity may be impaired, escape or be hazardous if this is done. Thus at the present it is common for the container to be weighed and the weight, in relation to the weight of the container when full, to * be converted to the appropriate measure of the remaining commodity: frequently this will be a fluid measure such as litres. The disadvantage of this method is that a computation is required and also the containers have to be lifted for the weighing process. In view of these difficulties it is not uncommon for the container to be merely tilted and the contents estimated by a combination of guesswork and experience. Needless to say this latter technique is inaccurate and not admissible as a method of measurement at a sales point. OMPI N tø*/ATl The present invention is directed towards alleviatino the above mentioned disadvantaqes and to providing an apparatus for measurinq the contents of a container without the necessity for liftinq and in such a way that a direct reading of the amount of commodity may be obtained. Accordingly the invention provides a measurinq aooaratus comprisinq a load member that can be positioned adjacent a part of a container and stressed by applying a predetermined tilt to the container, the extent of the stress beino indicative of the quantity of content of the container. The invention is now described by way of example with reference to the accompanyinq drawings in which: Figure 1 is a circuit diagram for an apparatus accordinq to the invention: Fiqure 2 illustrates a control panel of an apparatus accordinα to the invention viewed from above: Figures 3 and 4 are side views of an apparatus accordinq to the invention; Fioures 5 and 6 are, respectively, rear and front views of an apparatus accordinq to the invention; Figure 7 shows the strain qauge bar and * connections in an embodiment of the invention; Fiqure 8 illustrates the method of measurinq with an apparatus accordinq to the invention; Figure 9 is a circuit diagram of another embodiment of the invention. Referring now to Figures 2 to 6, the external features of an apparatus for measurinq the contents of a container are shown. Viewed from above, as in Figure 2, it may be seen that the apparatus comprises a housing 1 for electronic components, a load bar assembly comprisinq a load bar 2, container support bar 3 and load bar cover 4. The housing and load bar assembly are mounted to a base plate 5, the load bar being attached to the base plate by a spacer bar 6 (see Fiqure 6) which is located at the opposite end of the load bar to the container support bar 3. On top of the housinq 1, there a a selector knob 7, an on/off switch 8, a meter 9 and a meter illumination switch 10. As the apparatus may be used in locations in which connection to an electricity supply is not possible, it is desiqned to be battery operated (although the possibility of mains operation is not excluded), the battery being housed in a drawer tyoe compartment 11 that is accessible from one side of the housinσ (see Figure 3). To the rear of the housing 1, that is on the opposite side to the load bar, a series of access pqrts 12, 13, 14 to the electronic controls are provided. In operation a container is placed on the load bar in the manner illustrated in Figure 8: the container is not lifted, but tilted so that one part of the bottom of the container adjacent its perimeter rests on the support bar 3. As shown in Fiqure 6, the support bar is of part circular cross section. A bumper 15 is provided to protect the housing durinq location of the container. The load bar 2 is essentially cantilevered at the end where it is attached to the base olate via the spacer bar, and thus loadinq the bar at the end opposite to this causes the bar to be strained. This strain is measured by strain gauqes located on the load bar and the measured strain is converted by the electronic components into a measure of the contents of the container. In another embodiment the load bar may be supported at both ends and the load point of the container positioned centrally with respect to the load bar supports. OMPI Figure 7 illustrates the connection of the strain gauqe on both the tensioned and compressed sides of the load bar, i.e. both on the upper and lower surface. Referring now to Fiqure 1, a circuit for providing an output measure from the strain gauge input is illustrated. The input from the strain gauge appears across terminals A, 8, C, and the selector switch is connected to swla and swlb, the six marked positions for the selector switch connecting in pairs of the potentiometers psl to psl2, psl and ps7 beinq connected in position 1, ps2 and ps8 in position 2 etc. The-ports marked 1 to 6 are the adjustment ports 13, 14 which are accessible from the rear of the housinq and via these the settings of the potentiometers psl to 12 may be varied. Potentiometer psl3 may be adjusted via port 12 and compensates for drift. Sw2 is the on/off switch and sw3 is the meter illumination switch. In choosing components for the circuit it is important to minimise temperature dependence. Suitable components for the exemplary circuit of Fiqure 1 are as follows: Resistors: Rl and R4 = 180K ohms R2 and R5 = 120K ohms R6 = 1M ohms R7 = 56K ohms R3. and R8 = 500R ohms By eliminating Rl and R4 and by charging the value of R3 and R8 to 5K ohms precision wire wound resistors it is possible to sliqhtly reduce temperature drift further. Rl, R2, R4, R5, R6 and R7 are all i watt 1% metal film resistors. R3 and R8 are precision wire wound, tolerance 0.1?-. power tarino 0.33 watts at 85°C. (These are used for their ultra hiqh stability for temperature control). Capacitors: Cl, C2, C3 are 0.1 μF Suppression class 'X- metallised polyester O film with temperature ranqe: -55°C to + 100°C C3 ± inn α F at 16 volts workinq (standard). Miniature Pre-set Potentiometers: Ps 1 to 13 are 10 ohms miniature horizontal mounting cermet presets with carbon brush wipers, linear track rating 0.75 watt at 40°C (0.5 watt at 70°C) operating temperature ranqe - 40°C to +125°C. Tolerance 20?ή. Ps 13 can be a panel mounted potentiometer of conductive plastic of 10 K ohms value, as this is the drift control. Miniature 25 Turn Trimmer: VR1 this is a 25 turn cermet trimmer, value 22 K ohms and has a slipping clutch at both ends. Temperature ranoe - 50°C to + 125°C. Mechanical tolerance 25 turns ±5 turns. Electrical tolerance 10?ό. Voltaqe Regulator: Voltage Regulator: this is a fixed 100 mA regulator with internal over-load, thermal and short circuit protection, total dissipation 600 m watts at ambient temperature of 25°C with a positive output voltaqe of 5 volts. Tolerance ±5?ό. Switches: SWl is a standard two pole six way wafer type switch (this ranqe can be increased if required, alono with gain and tare pre-set potentiometers). SW2 is a single pole single throw switch such as a rocker type rated at 28 volts DC at 4 amps, contact resistance 5 M ohms. S 3 is a sub-miniature push button momentary action type switch rating 100 m amps at 30 volts DC (max.) Inteqrated Circuit: I.C.I is an ultra low off-set voltage operational amplifier (eight pin device). This particular device provides excellent low noise, high accuracy amplification of very low level signals. (A P.M.I. [Bourns] type O.P. - 07 - E.P.) '-ζ KE OMPI • ^ WIPO - - Strain Gauqes: SGI - 2 are strain qauqes these are precision strain gauqes which give continuous static measurements over a temperature range of - 75°C to + 175°C ( - 195 α C to + 205_°C for short term exposure). It has self temperature compensation matched to the load bar characteristics. Also, they are 350 R ohms 0.15K giving extremely low current drain (a PP39 volt battery is used to power the exemplary unit. ) Meter: This is a liquid crystal display 3 digit meter with a built-in back light inccrporating a dual - slope - integrating analogue - to - digital converter. It has a precision voltage reference. It also features a battery voltage monitor which causes low battery warning [BAT.] to be shown when battery voltaqe drops to 7.25 volts. It has an operating temperature range of 0°C to + 50°C. The meter also uses a 9 volt 35 A 1000 hour life bulb for illumination of the scale. Before use the apparatus must be calibrated, and it is so designed that the user may calibrate for their own particular requirements. For calibration purposes an empty container and one full container are required. First the selector switch is put in the position for which calibration is to be carried out, say in position 1, the apparatus is switched on and the empty container is tilted and the bottom rim or edge is placed on the container support bar. Attention must be paid to ensure that the part of the container on the support bar is diametrically opposite the part in contact with the floor, and that the container is properly bearing down on the load bar: this latter condition may be ensured by.pressinq down on the container and then releasing it. A screwdriver, or other tuning tool, is then inserted into the port 13 corresponding to the selector position number (1 in this instance) and adjustment made until the meter reads zero. The container is then removed, replaced by a full container and the procedure repeated only this time adjustment is made via the porthole 14 correspondinq to selector settinq 1 until the meter reads an amount correspondinq to the known quantity in the full container, that is for example until the meter reads 40 litres for a 40 litre cask or drum. It is preferable to then replace the empty container and re-check the zero for any drift. Once this is done, with the selector switch in position 1 partly full similar 40 litre containers can be positioned on the the apparatus in the same way as described above and the meter will display the content of the container directly in litres. A similar calibration may be carried out for other containers of different types with the selector switch in the other positions. The drawinqs illustrate a six position selector switch, but greater or fewer selector positions may be provided by modification of the circuit. It will be noticed that the geometry of the apparatus and the position of buffer 15 is such that it may aid in ensuring that the containers registering in the same location on the suDport bar. The method of converting the strain gauge measurement to a display is now described in more detail with refernce to Fiqure 9. The circuit of Fiqure 9 includes an offset circuit which is adjustable for different sizes of container and also an automatic drift compensating circuit. Two strain gauges 101 and 102, arranged as previously described, are connected at their opposite ends to terminals 103 and 104, the junction of the strain gauges being connected to terminal 105. Terminal 103 is connected to an accurate reference voltage provided by any suitable form of regulator (not shown), and terminal 104 is earthed. The voltage representing the effective weight of the container appears at terminal 105. Typically a full scale signal will be of the order of 4mV, giving (for fluid measure) a signal of the order of 8uV per half litre. The container weight (as experienced by the load bar) provides, via the strain gauges, a weight signal that is input to an amplifier OMPI 1PO 106, which is preferably a type 7650 precision instrumentation amplifier, giving a full scale output of about 2 volts. The other input of amplifier 106 is the output of a comparator amplifier 107 of which one input is a reference voltage of a terminal 108 and the other input is taken from the slider of a potentiometer 109 connected in series with resistors 110 and 111 between the reference voltage terminal 103 and the earthed terminal 105. Potentiometer 109 and amplifier 107 provide an adjustable reference voltage for the amplifier 106 so that the output of amplifier 106, which determines the final display, can be properly zeroed. The output of the amplifier 106 is smoothed by a capacitor 112 and sealed by a voltage divider 113, of which the output terminal 113a is connected to the signal input of a unit 114. Unit 114 is a combined voltmeter and display driver circuit (type No.7126 marie by ICL ) which drives a compatible liquid crystal display 115 (such as a standard 3 digi Sharp LCD>« Uni 114 and display 115 are driven by transistor 115a connected in known manner. The final display, which is determined by the output of amplifier 106 offset by a selectable siqnal representiπq the tare weight of the container, is adjustable to display the content (in litres or other measure) of the container within a ranqe selectable by means of a switch 116 couplinq pin 36 of unit 114 to any potentiometer in a set 117. A further net of potentiometers 118 is enerqised from the reference voltage terminal 103, these potentiometers beiπq set in accordance with the tare weight of various containers (as previously described) and the respective voltages that they provide are selectable by the multiposition switch 119. An automatic tare circuit 120 comprises a comparator amplifier 121, of which the non-inverting input terminal is coupled to-the output terminal of amplifier 106 and of which the invertinq input terminal is connected to the common terminal of switch 119 so as to receive the selected tare voltage. The circuit 120 includes a further comparator amplifier 122 of which the nαn-iπvertinq input terminal is connected to the output terminal of amplifier 121 by way of a series switch 123, input resistor 124 and a pair of oppositely poled diodes 125 in parallel. The inverting terminal of the amplifier 122 is connected directly to the output terminal of the amplifier and is connected to input resistor 124 by way of resistor 126. A feedback loop is completed by a switch 127 and series resistor 128, which couple the output terminal of the amplifier 122 back to the first input of amplifier 106. The purpose of this arrangement is to cause the output of amplifier 106 to be compared, when the loop is closed, with the selected tare voltaqe so as to zero the offset of the voltage output of amplifier 106 in accordance with the selected tare voltage. One advantage of the arrangement described is that any drift in the strain gauges and the input amplifier is automatically compensated. The offset voltage is held by a capacitor 129 connected between the input terminal of amplifier 122 and earth. If desired, power for the arrangement can be derived from a delay circuit, including a battery source, which on actuation provides power to the measuring and display circuits for only a limited period, such as three minutes, before the delay circuit automatically times out and interrupts the supply of power from the battery.

Claims: CLAIMS : 1. A measurinq apparatus comprisinq a load member that can be positioned adjacent a part of a container and stressed by applying a pre-determined tilt to the container, the extent of the stress being indicative of the quantity of content of the container. 2. A measurinq apparatus accordinq to claim 1 in which the load member is positioned beneath the container at the edπe thereof, and the container is tilted about a point opposite to the point of contact of the container with the load member. 3. A measuring apparatus according to claim 1-or claim 2 in which the load member is a cantilever. 4. A measuring apparatus according to claim 1 or claim 2 in which the load member is a beam supported at both ends. 5. A measuring apparatus according to any preceding claim in which at least one strain gauge is attached to the load member, the strain gauge giving a signal indicative of the force experienced by the- load member. 6. A measurinq apparatus according to claim 5 including means for providing an offset signal correspondinq to the stress produced by an empty container. 7. A measuring apparatus according to claim 6 in which the offset signal is variable. 8. A measuring apparatus accordinq to any precedinq claim including means for automatically compensating for drift in zero readings. 9. A measuring apparatus accordinq to any precedinq claim including a stop for abutting a further part of the container to assist in correctly locating the container on the load member. 10. A measuring apparatus according to any preceding claim including a display for indicating the quantity of content of the container. - < gUREA OMPI \ φ? ATl

Inventors: CAIRNES WILLIAM, CAIRNES, WILLIAM
Applicants: CAIRNES WILLIAM, CAIRNES, WILLIAM
Application year: 1983
Main classification: G01F23
IPC codes: G01F17, G01F23, G01G3