DE20115010U1 - Device for measuring the throughput of a mass flow - Google Patents

Description

Patent attorneys

Dip!:-Math. Siegfried Knefel

Dipl.-Phys. Cordula Knefel

Wertherstrasse 16, 35578 Wetzlar

PO Box 1924, 35529 Wetzlar

Telephone 06441/46330 - Fax 06441/48256

F G 1060

Claus-Friedrich

Wood mill
35457 Lollar

Device for measuring the flow rate of a mass flow

Description

The invention relates to a device for measuring the throughput of a mass flow according to the Coriolis measuring principle.

According to the state of the art (DE 33 46 145 A1, EP 0 146 902 A2), the measuring element is formed by an impeller that is driven at a constant speed. This impeller is axially acted upon by a bulk material flow. The bulk material is fed radially to the guide vanes via a guide device and accelerated by them to a constant peripheral speed of approximately 10 m/s (meters per second). The torque required for this is exactly proportional to the weight throughput.

• · · ♦

The measured value to be evaluated in this weighing system is the exact torque measurement.

However, the following problems arise here. Measuring the power on the motor is too imprecise, and measuring the torque directly on the drive shaft of the impeller is very complex, so the motor has previously been mounted in a pendulum-like manner and the reaction torque recorded using a load cell. This torque measurement is very precise, but it is somewhat problematic to record very low torques at low throughputs due to the relatively high weight of the motor.

The technical problem underlying the invention is to provide a device with which a throughput measurement of a mass flow can be carried out using simple technical means while at the same time maintaining a high level of accuracy.

This technical problem is solved by a device having the features of claim 1.

The problem is solved by the fact that the impeller is mounted axially rotatably on the drive shaft and is driven by a spring element.

The impeller is driven by the drive shaft through a driver, which is designed as a spring element and is firmly connected to the drive shaft. The impeller is mounted so that it can rotate relative to the drive shaft using a corresponding bearing. The impeller experiences a changed torque due to the impact of the bulk material. This results in an angular offset from the drive shaft to the impeller depending on the

required torque and thus the throughput. This angular offset is recorded in time by two proximity switches for each revolution. The time interval between the rigid drive shaft and the impeller driven by a spring corresponds to the required torque and thus the mass throughput.

In the evaluation electronics belonging to the measuring system, the respective mass throughput in kg/h (kilograms per hour) is calculated from the pulse interval times.

As already mentioned, the impeller is mounted so that it can rotate on the drive shaft. The maximum angular offset between the impeller and the drive shaft is advantageously limited by an overload stop.

The impeller, which is mounted axially on the drive shaft, is mounted in a smooth-running bearing, in particular a ball bearing. However, it is also possible to mount the impeller in other types of rolling or plain bearings.

It is also possible to mount the impeller without bearings directly in two or more leaf springs, which then advantageously serve directly as a drive and measuring element.

A particular advantage of the measuring device according to the invention is that the constant vibrations of the impeller during the product passage largely compensate for measurement errors that could be caused by bearing friction. A further advantage over measuring devices with load cells is that vibrations at the installation location of the measuring device do not cause errors.

·

• *

Further details of the invention can be found in the subclaims.

The drawing shows an embodiment of the invention, in which:

Fig. 1 shows a device according to the invention in cross section;

Fig. 2 shows a modified suspension of the impeller in plan view.

According to Fig. 1, an impeller (2) with guide vanes (3) is arranged vertically in a round housing (1). This impeller is driven by an electric motor (4) via a belt drive (5), via the drive shaft (6) and via a spring rod (9) at a constant speed. The impeller (2) is mounted on the drive shaft (6) by means of a ball bearing (7) so that it can rotate axially relative to the drive shaft (6).

A driving pin (8) is rigidly connected to the drive shaft (6). This driving pin (8) drives the axially rotatable impeller (2) via the spring rod (9) and a driving pin (10) rigidly connected to the impeller.

The mass flow (11) of the bulk material (not shown) is fed to the impeller (2) via a guide device (12) and accelerated radially by the guide vanes (3).

•4 »»♦* »·■ „·*, *

Depending on the mass throughput and the stiffness of the spring (9), the axially rotatable impeller (2) is displaced by a defined angle relative to the drive shaft (6). This angular displacement is recorded contactlessly by two proximity switches (14, 15) with each revolution. The first proximity switch (14) is located on the drive wheel (13), the second proximity switch (15) is arranged on the impeller (2). These two proximity switches (14, 15) are set so that with each revolution the first proximity switch (14) first delivers a pulse edge and shortly afterwards the second proximity switch (15) delivers another pulse edge. These pulse edges are recorded and evaluated using precise time measurement.

According to Fig. 2, the impeller (2), which is mounted axially rotatably on the drive shaft (6), has a bearingless suspension of the impeller with four leaf springs (17), which serve directly as a drive and measuring element.

_t '· · S . ..” ♦♦ JJ

Reference symbols

1 housing

2 Impeller

3 guide vanes

4 Electric motor

5 Belt drive

6 Drive shaft

7 ball bearings

8 driving pins

9 Spring bar

Driving pin Mass flow guide device Drive wheel Proximity switch Proximity switch Leaf springs

Claims (5)

1. Device for measuring the throughput of a mass flow, which contains an impeller driven at a constant speed, to which the material flow is fed, the mass flow being accelerated by the impeller, and the torque being measured, characterized in that the impeller ( 2 ) is mounted on the drive shaft ( 6 ) so as to be axially rotatable relative to the drive shaft ( 6 ) and is designed as an impeller ( 9 ) driven via a spring element ( 9 ), and that two proximity switches ( 14 , 15 ) are provided for measuring the angular offset between the drive shaft ( 6 ) and the impeller ( 2 ). 2. Device according to claim 1, characterized in that the angle through which the impeller ( 2 ) can be rotated relative to the drive shaft ( 6 ) is limited by an overload stop. 3. Device according to claim 1, characterized in that the impeller ( 2 ) is mounted in a rolling or sliding bearing ( 7 ) on the drive shaft ( 6 ) so as to be axially rotatable. 4. Device according to claim 1, characterized in that the impeller ( 2 ) is suspended without bearings in at least two leaf springs ( 17 ) and is designed as an impeller ( 2 ) driven via these leaf springs ( 17 ). 5. Device according to claim 1, characterized in that at least one guide device ( 12 ) is provided in the device for deflecting the material flow.