DOSING AND WEIGHING DEVICE AND METHOD FOR DETERMINING THE WEIGHT OF A PRODUCT IN A DOSING AND WEIGHING DEVICE

Abstract

A dosing and weighing device (1) comprising a housing (2) having an inlet opening (3) and an outlet opening (4), and a weighing surface (5), which is operatively connected to at least one weight sensor (7), a mechanism (9) for detecting a pressure difference between a pressure in the housing upstream and a pressure in the housing downstream of the weighing surface (5). Via a control unit (8), the detected pressure difference is used to correct the weight detected by the weight sensor (7).

Claims

1-8. (canceled)

9. A dosing and weighing device for bulk materials comprising: a housing with an inlet opening and an outlet opening for a product to be weighed and dosed; a weighing surface which is movable between a weighing position and a dosing position by an operating device and is operatively connected to at least one weight sensor, wherein in the weighing position a product flow between said inlet opening and said outlet opening is prevented and thus a weight of the product loaded on the weighing surface can be determined by the at least one weight sensor, and in the dosing position, the product flow between said inlet opening and said outlet opening is at least partially enabled, and a control unit which is designed at least for controlling the operating device and is connected to the at least one weight sensor, wherein means for determining a gas pressure difference between a pressure in the housing upstream, in a product flow direction, and a pressure in the housing downstream, in the product flow direction, of the weighing surface are provided, and that by the control unit the determined pressure difference is used to correct the weight determined by the weight sensor.

10. The dosing and weighing device according to claim 9, wherein said weighing surface is pivotable between the weighing position and the dosing position.

11. The dosing and weighing device according to claim 9, wherein the means for determining the gas pressure difference is designed as a pressure difference sensor.

12. The dosing and weighing device according to claim 9, wherein the means for determining the gas pressure difference comprise a pressure sensor arranged upstream of the weighing surface and a pressure sensor arranged downstream of the weighing surface.

13. The dosing and weighing device according to claim 9, wherein the gas pressure difference is an air pressure difference.

14. The dosing and weighing device according to claim 9, wherein the housing is airtight towards the outside.

15. The dosing and weighing device according claim 9, wherein the inlet opening and the outlet opening have equally large cross-sectional areas.

16. A method for determining the weight of a bulk product, in a device according to claim 9, the method comprising: a housing with an inlet opening and an outlet opening for a product to be weighed and dosed and a dosing and weighing unit with a weighing surface which is operatively connected to at least one weight sensor, wherein in a product flow direction between said inlet opening and said outlet opening: means are provided for determining a gas pressure difference between a pressure in the housing up-stream of the dosing and weighing unit and a pressure in the housing downstream of the dosing and weighing unit, comprising the steps: determining the weight of the product loaded on the weighing surface by the at least one weight sensor, and using a determined gas pressure difference to correct the weight determined by the weight sensor.

17. The method according to claim 16, wherein an air pressure difference is determined by the means for determining a gas pressure difference.

Description

[0021] The invention is better described below using a preferred embodiment in conjunction with the drawing. Therein it is shown:

[0022] FIG. 1 a schematic representation of a device according to present invention, and

[0023] FIG. 2 a graphic representation of the measurement error without differential pressure compensation.

[0024] FIG. 1 schematically shows a dosing and weighing device 1. It comprises a housing 2 through which a product flows. Arrows 3 and 4 respectively indicate an inlet opening and an outlet opening for the product. A weighing surface 5 in the form of a pivotable flap is arranged in the housing. The weighing surface 5 can be reversibly pivoted from a weighing position into a dosing position by means of an operating unit 6.

[0025] In the weighing position, product flow between inlet opening 3 and outlet opening 4 is prevented. The product coming from the inlet opening accumulates on the weighing surface 5. The weighing surface is connected to a weight sensor 7 so that a weight of the product loaded on the weighing surface 5 can be determined.

[0026] In the dosing position, on the other hand, the product flow between inlet opening 3 and outlet opening 4 is enabled.

[0027] There are no ventilation openings or the like in the housing 2.

[0028] A differential pressure sensor 9 is provided to compensate for pressure fluctuations in the housing which can influence the weight determination. Via lines 10 and 11, a pressure difference between a pressure in the housing downstream (line 10) and upstream (line 11) of the weighing surface 5 can be determined.

[0029] A control unit 8 is connected to the operating unit 6, the weight sensor 7 and the differential pressure sensor 9 via a connecting cable 12, which can be wired or wireless.

[0030] When weighing the product, pressure differences occurring in housing 2, which could have an influence on the weight determination by means of weight sensor 7, can thus be detected and used by the control unit 8 to correct the weight determined by the weight sensor 7.

[0031] If the pressure downstream of the weighing surface 5 is higher than the pressure upstream of the weighing surface 5, the weight sensor 7 will detect less weight than there actually is on the weighing surface 5. On the other hand, at a higher pressure upstream of the weighing surface 5, the weight sensor 7 will determine more weight than there actually is on the weighing surface 5.

[0032] By using the pressure difference, the weight determined by the weight sensor 7 can be corrected, and only then the operating unit 6 for dosing will be triggered.

[0033] FIG. 2 shows the weight curves G1 and G2 of the weight determined by a weight sensor 7 in a device without differential pressure compensation.

[0034] The left ordinate axis shows a pressure difference P in Pa measured in the housing 2, and the abscissa axis shows a dimensionless variation in time t.

[0035] In the weight measurement G2, the pressure upstream of the weighing surface 5 was reduced compared to the pressure downstream of the weighing surface 5 by suction of air.

[0036] As can be seen from the weight curve G2, the weight determined by the weight sensor 7 is lower than the weight curve G1, so that at the end of the measurement there is a deviation, which however is only to be attributed to the suction of air.

[0037] Furthermore, it can be seen from the curves P1 and P2 (each assigned to the weight curves G1 and G2) that during the operation pressure differences occur in the housing 2, which result in the two weight curves drifting apart (cf. e.g. between points t2 and t3).

[0038] With a device or method in accordance with the present invention, such a deviation is essentially avoided, since the differential pressure is always used to correct the weight determined by the weight sensor 7.