The invention concerns a detection system for the registration of an amount of fluid, comprising a meter housing in which scanning units are disposed and a unit which can be rotated in relation to the meter housing.

In connection with the measuring of fluid amounts, it is known to use a mechanical arrangement whereby a spindle io maHo - rs rnta p hv mpanc; o-F tho naopaπo rs-F -t-Vio fln-f 1

The rotation of the spindle is detected by means of an infra-red light, and via a conversion said rotation will indicate the amount of fluid which has passed. The system can not be placed in the fluid flow itself, which is naturally to be preferred, in that it is the fluid flow which is required to be measured/determined. Moreover, the system is made up of many mechanical, moving parts, which in itself gives rise to a certain degree of un¬ reliability. Furthermore, the moving parts become worn with time, which again gives rise to inaccuracies.

It is the object of the invention to provide a detection system which does not have the disadvantages of the known systems, and whereby it is possible to place the system directly in the fluid flow and thus minimize the risk of inaccuracies. Moreover, the number of moving parts of this system will also be minimized, which in itself will increase the reliability of the system. With the in¬ vention, there is hereby achieved a detection system which is able to measure an amount of fluid with ex¬ ceptionally great precision.

This object is achieved with a detection system of the kind disclosed in the preamble, and where in addition the meter housing comprises a through-going passage through which the fluid can flow, and where the rotatable unit is provided with a number of metallic elements, said unit

during rotation passing the scanning units for the activation of said units.

The detection system is thus placed in relation to the fluid in such a manner that the fluid is able to pass directly through the through-going passage. During this passage of the fluid, the rotatable unit is made to rotate, which in turn will result in the scanning units in the meter housing itself being activated. There hereby arises a measure for the amount of passing fluid. The system is thus more simple to position and has no limitations in relation to the fluid which is to pass through it. Consequently, the system can be used both in connection with petrol pumps as well as for the measure- ment of quite ordinary fluids, which is also the case where it can be desirable to measure the passage of gas¬ ses.

By configuring the detection system according to the in- vention as disclosed in claim 2, an expedient form of rotatable unit is achieved, and which is usable for as¬ sembly and also ensures an optimum interaction between the rotatable unit and the scanning units.

By configuring the detection system according to the in¬ vention as disclosed in claims 3 and 4, an optimum con¬ figuration of the system is achieved, in that the Hall elements will provide a very clear signal, whereby the risk of incorrect information is minimized. Moreover, by using at least three Hall elements, the possibility is achieved with the third element of registering possible errors and taking appropriate action with regard to such errors.

By configuring the detection system according to the in¬ vention as disclosed in claim 5, it is achieved that the scanning elements are protected against direct physical

contact .

By configuring the detection system according to the in¬ vention as disclosed in claim 6, it is achieved that an effective shield is formed which obstructs false signals from externally-arising electrical fields, and which also serves as a magnetic shield.

By configuring the detection system according to the in- vention as disclosed in claim 7, it is achieved that the mutual positioning between the Hall elements and the rotatable unit is easier to optimize and effect, in that the output/signal itself is dependent upon the inter¬ action between these units.

The invention will now be described in more detail with reference to the drawing, where

fig. 1 shows a section through the meter housing,

fig. 2 shows the meter housing seen from the end with the steel plate mounted,

fig. 3 shows the assembled detection system with meter housing and rotatable unit,

fig. 4 shows a section through the rotatable unit,

fig. 5 shows the rotatable unit seen from the bottom, from the side and from above,

fig. 6 shows the output for electrical pulses.

Figure 1 shows a section through a meter housing 2, said meter housing being made of a non-magnetic material where a typical choice can be moulded aluminium. In design, the meter housing 2 is box-shaped and has a through-going

passage 3 formed as a circular or an oval channel, the end part 3' of which is flat. The meter housing can, how¬ ever, also be horseshoe-shaped, the essential point being that the meter housing 2 has a channel through which the fluid has free passage.

At the one end, the meter housing 2 comprises a recess 4 in which various electrical components are mounted. In this recess there is placed a PBA unit (Print Board As- sembly) which supports at least three Hall sensors 5, a microprocessor and various auxiliary components. The third Hall sensor is used to generate an internal signal which is used by the microprocessor for the measurement of incorrect pulses and illegal bit patterns. The PBA is connected to a cable 9 by means of a connection element 22 which leaves the meter housing 2 via a rubber grommet 19. The positioning of the Hall elements 5 in the meter housing 2 depends upon the positioning of the rotatable unit itself, which will be discussed below. The meter housing 2 also has an earth connection 12, and on the one surface is seen a cover for the recess 4, said recess preferably being filled out with an epoxy material, which is of significance in dangerous environments, after which there is mounted a plate 8 of magnetizable material, typically steel. This is then covered with a self- adhesive tape 10. The object of the steel plate is to form a shield against external electrical fields.

The meter housing 2 is typically configured with outer cavities 17, partly to reduce material weight and partly to facilitate the moulding. Moreover, the meter housing 2 is also provided with four assembly elements 18. For extra protection, the meter housing 2 is connected to earth via a connection element, for example an earth terminal.

Figure 2 shows the meter housing 2 seen from the end.

where the extent of the steel plate 8 can be seen, and which preferably covers up to 95% of the end surface. This is secured to the rest of the construction by means of rivets 20.

The interaction between the meter housing 2 and the rotatable unit 13 appears from figure 3, where it will be noted that the rotatable unit's metallic elements in the form of magnets 14 are disposed in such a manner that this is made to rotate by the fluid through the passage 3, and at the same time that this rotation will extend past the scanning elements in the form of Hall elements 5. These Hall elements 5 are shown mounted in a position which is different from that shown in figure 1. The physical positioning of the scanning elements 5 is thus a function of the position of the rotatable unit itself.

Figure 4 shows the rotatable unit 13 with metallic elements 14 embedded. The rotatable unit is made of a non-magnetic material, typically plastic, and here comprises four magnets which are assembled in an alternating north-south sequence. The disk-shaped unit is secured to a spindle 15 and rotates when a liquid or a gas is pumped through the fluid passage 3. The magnets 14 are thus positioned at a predefined distance in relation to the Hall sensors, and the north-south ends of the mag¬ nets activate the Hall sensors. This results in a clear and well-defined alternating on-off sequence which gives rise to a wave-form and cycle.

Figure 5 shows the rotatable unit 13 seen from the bot¬ tom, from the side and from above, and how the metallic elements in the form of magnets are disposed. These are positioned on the disk-shaped unit displaced at 90 degrees in relation to one another on a circle, the centre of this circle being coincident with the centre of the disk-shaped unit.

At the moment that the disk-shaped unit rotates and a north pole passes a Hall element, this element is activated and a pulse is obtained. These are shown in figure 6, where the three Hall elements produce a pulse A, B and C. The time is given along the X-axis and the voltage along the Y-axis. There must be at least three Hall elements in order to provide a signal. Each given signal is phase displaced, so that the phase displacement from the first Hall element A to the second B in the drawing is 90 degrees, and the phase displacement from the first to the third Hall element, A and C in the drawing, is 135 degrees. However, these phase displace¬ ments may well assume other magnitudes. The object of having the third Hall element is that this detects pos¬ sible errors, which will be registered by the micro¬ processor. In the event of the microprocessor registering an error, either as a result of incoming external pulses in the form of magnetic fields or an attempt being made to turn the disk the opposite way, this will be registered and the power supply will be cut off. The power consumption will thus be registered as zero by the user. In this way, possible errors are detected.

The meter housing 2 is preferably made of aluminium, the reason being that this is both cheap and non-magnetic, and at the same time also an explosion-safe material, in that the detection arrangement is typically used in ex¬ plosive fluids such as in petrol pumps and the like. The unit can tolerate temperature variations from minus 50 to plus 70 degrees Celsius, and resist pressures up to 13 Bar, whereas a typical working pressure will lie around 2 Bar.

The object of filling the recess with epoxy is to exclude air pockets, which is necessary whenever the unit is mounted in an explosive environment, for example in a

flow of petrol.

The electrical fields from the magnets, which are very strong and which are produced by the disk-shaped unit, help to safeguard against illegal magnetic influence from external sources, because they will continue to activate the Hall sensors, also with the presence of an illegal influence, and thus result in an irregular bit pattern and a subsequent alarm status.