METHOD FOR OPERATING A NUCLEAR MAGNETIC FLOWMETER AND NUCLEAR MAGNETIC FLOWMETER

Abstract

A method for operating a nuclear magnetic flowmeter in which the necessary time for determining a longitudinal relaxation time constant of the medium is reduced in comparison to the prior art by at least one nuclear-magnetic measuring process being carried out on a magnetized medium in the measuring tube. The at least one nuclear-magnetic measuring process includes an inversion pulse and acquisition sequences, each acquisition sequence beginning at a starting point in time in respect to the at least one nuclear-magnetic measuring process and has an activating pulse, a first waiting interval, a first refocusing pulse, an echo interval with a duration, a second refocusing pulse, a second waiting interval and a deactivating pulse. An echo signal is measured in the echo interval, and a longitudinal relaxation time constant of the medium is determined using the echo signals.

Claims

1. Method for operating a nuclear magnetic flowmeter, wherein the nuclear-magnetic flowmeter has a measuring tube, a medium in the measuring tube, the method comprising: carrying out at least one nuclear-magnetic measuring process on the medium in the measuring tube during which the medium is magnetized, performing at least one nuclear-magnetic measuring process that includes an inversion pulse and N ={2, 3, 4, . . . } acquisition sequences, beginning each of the N acquisition sequences at a starting point in time t.sub.s,n in which n={1, . . . , N}, each of the acquisition sequences comprising an activating pulse, a first waiting interval with a duration Δt.sub.d, a first refocusing pulse, an echo interval with a duration Δt.sub.e, a second refocusing pulse, a second waiting interval with the duration Δt.sub.d and a deactivating pulse, measuring an echo signal s.sub.e,n during each echo interval, and determining a longitudinal relaxation time constant T.sub.1 of the magnetized medium using the echo signal of each the N acquisition sequences.

2. Method according to claim 1, further comprising determining the duration Δt.sub.d is determined according to the relationship $\Delta .Math..Math.t_d=t_{\mathrm{ref}}-\frac{2.Math.\Delta .Math..Math.t_{90}}{\pi }$ and/or the duration Δt.sub.e is determined according to the relationship
Δt.sub.e=2t.sub.ref wherein Δt.sub.ref is a reference duration and Δt.sub.90 is a duration of the activating pulse.

3. Method according to claim 2, wherein the reference duration Δt.sub.ref is determined using a duration of decaying of interferences, wherein the interferences are caused by at least one of the activating pulse and the refocusing pulse.

4. Method according to claim 1, wherein a time span between each of two successive starting points in time t.sub.s,n and t.sub.s,n+1 is determined such that the time span increases.

5. Method according to claim 1, wherein after the N acquisition steps, a repeat interval with a duration Δt.sub.w is waited for and wherein the duration Δt.sub.w is at least as long as a largest span between two successive starting points in time t.sub.s,n and t.sub.s,n+1 or at least as long as the span from the first starting point in time t.sub.s,1 in respect to an end of the inversion pulse.

6. Method according to claim 1, wherein at least two nuclear-magnetic measuring processes are carried out such that, in each case, two chronologically successive echo signals s.sub.e,n and s.sub.e,n+1 in the echo intervals are measured in different nuclear-magnetic measuring processes.

7. Method according to claim 1, wherein a +180°.sub.x-pulse is used as the inversion pulse, a +90°.sub.x-pulse is used as the activating pulse, a −90°.sub.x-pulse is used as the deactivating pulse and a +180°.sub.y-pulse is used for both the first refocusing pulse the second refocusing pulse.

8. Method according to claim 1, wherein phase differences between the inversion pulse, the activating pulse, the first refocusing pulse, the second refocusing pulse, the deactivating pulse and the echo signal s.sub.e,n are cycled.

9. Method according to claim 8, further comprising: carrying out a first nuclear-magnetic measuring process and a second nuclear-magnetic measuring process in respect to a phase of the inversion pulse and of the activating pulse in the first nuclear-magnetic measuring process such that, in the first nuclear-magnetic measuring process, a phase difference of each of the first refocusing pulse and of the second refocusing pulse is 90°, a phase difference of the deactivating pulse is 180° and a phase difference of the echo signal s.sub.e,1 is 0° and in the second nuclear-magnetic measuring step, a phase difference of each of the inversion pulse and of the activating pulse is 180°, a phase difference of each of the first refocusing pulse and of the second refocusing pulse is 90°, and a phase difference of the deactivating pulse is 0° and a phase difference of the echo signal s.sub.e,2 is 180°.

10. Method according to claim 8, further comprising: carrying a first nuclear-magnetic measuring process, a second nuclear-magnetic measuring process, a third nuclear-magnetic measuring process and a fourth nuclear-magnetic measuring process in respect to a phase of the inversion pulse and of the activating pulse in the first nuclear-magnetic measuring process, such that, in the first nuclear-magnetic measuring process, a phase difference of each of the first refocusing pulse and of the second refocusing pulse is 90° and measuring a phase difference of the deactivating pulse is 180° and a positive real part of the echo signal s.sub.e,1 with a first channel and a positive imaginary part of the echo signal s.sub.e,1 with a second channel, in the second nuclear-magnetic measuring process, a phase difference of each of the inversion pulse and of the activating pulse is 180°, a phase difference each of the first refocusing pulse and of the second refocusing pulse is 90° and a phase difference of the deactivating pulse is 0° and that a negative real part of the echo signal s.sub.e,2 is measured with the first channel and a negative imaginary part of the echo signal s.sub.e,2 is measured with the second channel, in the third nuclear-magnetic measuring process, a phase difference of each of the inversion pulse and of the activating pulse is 90°, a phase difference of each of the first refocusing pulse and of the second refocusing pulse is 180° and a phase difference of the deactivating pulse is 270° and a negative real part of the echo signal s.sub.e,3 is measured with the second channel and a positive imaginary part of the echo signal s.sub.e,3 is measured with the first channel, and in the fourth nuclear-magnetic measuring process, a phase difference of each of the inversion pulse and of the activating pulse is 270°, a phase difference of each of the first refocusing pulse and of the second refocusing pulse is 180° and a phase difference of the deactivating pulse is 90° and a positive real part of the echo signal s.sub.e,4 is measured with the second channel and a negative imaginary part of the echo signal s.sub.e,4 is measured with the first channel.

11. Nuclear-magnetic flowmeter, comprising: a measuring tube, a magnetization means, a measuring unit, and a magnetized medium in the measuring tube during operation, wherein the measuring unit has means for: carrying out at least one nuclear-magnetic measuring process on the magnetized medium in the measuring tube that includes an inversion pulse and N={2, 3, 4, . . . } acquisition sequences, each of the N acquisition sequences beginning at a starting point in time t.sub.s,n with n={1, . . . , N} in respect to the at least one nuclear-magnetic measuring process and having an activating pulse, a first waiting interval with a duration Δt.sub.d, a first refocusing pulse, an echo interval with a duration Δt.sub.e, a second refocusing pulse, a second waiting interval with the duration Δt.sub.d and a deactivating pulse, measuring an echo signal s.sub.e,n in each echo interval, and determining a longitudinal relaxation time constant T.sub.1 of the medium using the echo signal s.sub.e,1, . . . , s.sub.e,N.

Description

BRIEF DESCRIPTION OF THE DRAIWNGS

[0040] FIG. 1 shows an embodiment of a nuclear magnetic flowmeter and

[0041] FIG. 2 is a schematic diagram over time, not shown to scale, of a method for operating the nuclear magnetic flowmeter.

DETAILED DESCRIPTION OF THE INVENTION

[0042] FIG. 1 shows the nuclear magnetic flowmeter 1 in an abstract, perspective view. The nuclear magnetic flowmeter 1 has the measuring tube 2, the magnetization unit 3 and the measuring unit 4. Since the nuclear magnetic flowmeter 1 is in operation, the medium 5 is present in the measuring tube 2 and the magnetization unit 3 magnetizes the medium 5 present in the measuring tube 2.

[0043] The measuring unit 4 carries out the following method for operating the nuclear magnetic flowmeter 1. The method runs continuously during operation, which is why successive nuclear magnetic measuring processes are carried out continuously in terms of time on the medium 5 present in the measuring tube 2. After termination of the method, the measuring unit 4, for example, carries out a method for flow measurement of the medium 5 through the measuring tube 2.

[0044] In FIG. 2, the first measuring process 6 and a part of the second measuring process 7 are shown schematically and not to scale. Each of the measuring processes 6, 7 has the inversion pulse 8 and N=2 acquisition sequences, i.e., the first acquisition sequence 9 and the second acquisition sequence 10. Normally, the number of acquisition sequences is significantly larger. However, in order to explain the method, it is not necessary to use a large number of acquisition sequences. The first acquisition sequence 9 begins at the starting point in time t.sub.s,1 (n=1) and the second acquisition sequence 10 at starting point in time t.sub.s,2 (n=N=2). The starting points in time t.sub.s,1 and t.sub.s,2 are thereby each related to the beginning of the first measuring process 6. The beginning of measuring process 6 coincides in time with the beginning of the inversion pulse 8. Each of the acquisition sequences 9, 10 respectively has the activating pulse 11 with the duration Δt.sub.90, the first waiting interval 12 with the duration Δt.sub.d, the first refocusing pulse 13, the echo interval 14 with the duration Δt.sub.e, the second refocusing pulse 15, the second waiting interval 16 with the duration Δt.sub.d and the deactivating pulse 17.

[0045] The echo signal s.sub.e,1 is measured in the echo interval 14 of the first acquisition sequence 9 and the second echo signal s.sub.e,2 is measured in the echo interval 14 of the second acquisition sequence 10. A longitudinal relaxation time constant T.sub.1 of the medium 5 is determined using the echo signals s.sub.e,1 and s.sub.e,2.

[0046] After the N=2 acquisition sequences, the repeat interval 18 with the duration Δt.sub.w is waited for before the second measuring process 7 begins with the inversion pulse 8.