Method and measuring instrument for measurement of the casting level in a mould

Abstract

A method for measurement of the casting level in a mould incudes the steps of: a) impressing a temporal current profile into a transmitting coil that is arranged at the mould, during a measuring time interval; b) measuring a temporal signal profile resulting in a receiving coil during the measuring time interval, wherein the receiving coil is coupled inductively to the transmitting coil; c) selecting a time window within the measuring time interval, and d) evaluating the measured temporal signal profile within the selected time window to determine the casting level.

Claims

1. A method for measuring a casting level in a mould, the method comprising the steps of: a) impressing a temporal current profile (i(t)) into a transmitting coil that is arranged at the mould, during a measuring time interval (MZI); b) measuring a temporal signal profile (Ue(t)) resulting in a receiving coil during the measuring time interval (MZI), wherein the receiving coil is coupled inductively to the transmitting coil; c) selecting a time window (ZF) within the measuring time interval; and d) evaluating the measured temporal signal profile (Ue(t)) within the selected time window (ZF) to determine the casting level (L); wherein the temporal current profile (i(t)) is a non-sinusoidal temporal current profile.

2. The method according to claim 1, wherein the temporal signal profile (Ue(t)) resulting in the receiving coil is a temporal voltage profile (Ue(t)) that is induced in the receiving coil as a result of the temporal current profile (i(t)) impressed into the transmitting coil.

3. The method according to claim 1, wherein the temporal current profile (i(t)) is a ramp-shaped current profile.

4. The method according to claim 3, wherein the ramp-shaped current profile is a linear ramp-shaped current profile.

5. The method according to claim 1, further comprising: ascertaining a gradient (m1, m2) of the measured temporal signal profile (Ue(t)) within the selected time window; and evaluating the ascertained gradient (m1, m2) to ascertain the casting level (L).

6. The method according to claim 1, wherein the impressing of the temporal current profile (i(t)) into the transmitting coil during the measuring time interval comprises the steps of: specifying a temporal current-setpoint profile; and regulating a current (i(t)) flowing through the transmitting coil to track the temporal current-setpoint profile.

7. The method according to claim 1, wherein the steps a), c) and d) are repeated continuously.

8. The method according to claim 1, wherein the steps a), c) and d) are repeated periodically.

9. The method according to claim 1, further comprising the steps of: e) measuring a further temporal signal profile arising during the measuring time interval (MZI) in at least one further receiving coil that is coupled inductively to the transmitting coil; and f) evaluating the measured further temporal signal profile within the selected time window (ZF) to determine the casting level (L).

10. The method according to claim 1, wherein the time window (ZF) within the measuring time interval (MZI) is selected depending on a geometry of the mould.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a highly schematic block diagram of a measuring instrument according to an embodiment of the invention;

(2) FIG. 2 shows properties of a voltage profile induced in a receiving coil depending on different casting levels;

(3) FIG. 3 shows an embodiment of the measuring instrument according to the invention with multiple receiving coils; and

(4) FIG. 4 shows a filling level calibration curve with two reference points that are determined by a differential reading of two receiving coils each.

DETAILED DESCRIPTION OF THE DRAWINGS

(5) FIG. 1 is a highly schematic block diagram of a measuring instrument 100 for measurement of the casting level of liquid metal or casting metal 9 in a mould 1.

(6) The measuring instrument 100 comprises a transmitting coil 2 that is arranged at/on the mould 1.

(7) The measuring instrument 100 further comprises a receiving coil 3 that is also arranged at/on the mould 1 and which is coupled inductively to the transmitting coil 2 via the mould 1 and the liquid metal 9 which may be located in the mould 1.

(8) The measuring instrument 100 further comprises a regulated current source 6 that is designed to effectuate a temporally linear ramp-shaped current profile i(t) in the transmitting coil 2 during a measuring time interval MZI

(9) The measuring instrument 100 further comprises a measuring apparatus 7 that is designed to measure a temporal voltage profile Ue(t) that is induced in the receiving coil 3 as a result of the current profile i(t).

(10) The measuring instrument 100 further comprises an evaluation apparatus 8 that is designed to evaluate the measured temporal voltage profile Ue(t) to ascertain the casting level L.

(11) A time window ZF is selected within the measuring time interval MZI to measure the casting level, and the temporal voltage profile Ue(t) resulting or induced in the receiving coil 3 during the time window ZF is evaluated. The time window ZF within the measuring time interval MZI is selected depending on a geometry of the mould 1.

(12) FIG. 2 shows properties, in the form of a gradient, m1 or m2, of the voltage profile Ue(t) induced in the receiving coil 3 depending on different casting levels L1 or L2—see also FIG. 4. To measure the casting level L, the evaluation unit 8 ascertains the resulting gradient m1 or m2 during the time window ZF, and then ascertains the casting level L depending on the gradient m1 or m2.

(13) The steps described above are repeated continuously for continuous measurement of the casting level L.

(14) FIG. 3 shows an embodiment of the invention in which the measuring instrument 100 comprises three receiving coils 3, 4 and 5. In this embodiment, all of the temporal voltage profiles induced in the receiving coils 3, 4 and 5 during the time window ZF are measured and evaluated.

(15) The precise form of the temporal voltage profile Ue(t) in a respective receiving coil 3, 4 and 5 depends, inter alia, on the form of the transmitting coil 2 and of the receiving coils 3, 4 and 5, the position of the coils 2 to 5 in the casting mould, the mould itself and, to a certain extent, also on the composition of the liquid metal 9 that is to be measured, and must be learned once in each case.

(16) The position and shape of a filling level calibration curve can be subsequently adjusted through the addition of the differentially read receiving coils 4 and 5. It has namely been found that a differential evaluation signal AS1 or AS2, based on receiving coil pairs 3/4 and 4/5, see FIG. 4, reaches a maximum when the filling level L is located precisely between the two differentially read receiving coils of the receiving coil pair 3/4 or 4/5. Since this position is precisely mechanically determined by the known position of the receiving coils 3, 4 and 5, the filling level calibration curve can thus be subsequently adjusted with sufficient accuracy, in particular when sprue casting.

(17) FIG. 4 shows such a filling level calibration curve, in which the filling level L is plotted against the gradient m of the voltage profile Ue(t). The differential signal AS1 between the voltage profiles of the receiving coils 3 and 4 has its maximum at reference point R1, so that at the reference point R1 the gradient m1 can be assigned to a known filling level L1. The differential signal AS2 between the voltage profiles of the receiving coils 4 and 5 has its maximum at reference point R2, so that at the reference point R2 the gradient m2 can be assigned to a known filling level L2.

(18) The invention provides an inductive measuring principle not based on eddy currents for the contactless measurement of filling levels of conductive materials, in particular of liquid metals, in casting moulds with locally selective resolution, and highly independent of temperature.

(19) The invention enables a reliable measurement of the casting level independently of disturbing conductive materials in the vicinity of the coil system, which can, furthermore, be calibrated easily. The invention is also applicable to small casting mould formats, since the sensitive region can easily be specified through the selection of the time window ZF.

(20) The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.