Method for determining fill level on the basis of travel time of a high-frequency measuring signal

• US 7,412,337 B2
• Filed: 10/13/2006
• Issued: 08/12/2008
• Est. Priority Date: 10/13/2005
• Status: Active Grant

• Current Assignee: Endress + Hauser GmbH + Company KG (Endress+Hauser AG)
• Original Assignee: Endress + Hauser GmbH + Company KG (Endress+Hauser AG)
• Inventors: Michalski, Bernhard, Buser, Dominik, Scherr, Stefan
• Primary Examiner(s): Bui; Bryan
• Application Number:
  US11/580,109
• Publication Number:
  US 20070103333A1
• Time in Patent Office: 669 Days
• Field of Search: 702/55, 702/69, 702/74, 702/75, 702/79, 732/90.V, 73/17.3
• US Class Current: 702/55
• CPC Class Codes: G01F 23/284 Electromagnetic waves
• CPC Class Codes: G01S 13/10 using transmission of interrupted, pulse modulated waves determination of distance by phase measurement G01S13/32
• CPC Class Codes: G01S 13/88 Radar or analogous systems specially adapted for specific applications electromagnetic prospecting or detecting of objects, e.g. near-field detection, G01V3/00
• CPC Class Codes: G01S 7/285 Receivers

Abstract

A method for determining the fill level (l) on the basis of the travel time (t) of a high-frequency measuring signal (S_HF), which is transformed into a lower frequency, intermediate-frequency measuring signal (S_ZF), wherein the transformation factor (K_T) is obtained from a difference frequency (f_Sweep) between a pulse repetition frequency (f_PRF) and a sampling frequency (f_sample) The pulse repetition frequency (f_PRF) or the sampling frequency (f_sample) is altered on the basis of a control with a control variable (c_var) through an appropriate control algorithm, such that a desired value (f_{Sweep—setpoint}) of the difference frequency is controlled to; wherein a gradient (grad) of at least two values is determined, and on the basis of the gradient (grad) and the difference frequency (f_Sweep), or difference time (t_Sweep), in the case of a set control variable (c_var), an operating point (OP) of the control is determined, and the control algorithm is adjusted accordingly thereto.

Claims

1. A method for determining the fill level (l) in a container on the basis of the travel time (t) of a high frequency measuring signal (S_HF), which, by means of a transformation method with a certain transformation factor (K_T), is transformed into a lower frequency, intermediate-frequency signal (S_ZF), comprising the steps of:

producing the transformation factor (K_T) and obtained from a difference frequency (f_Sweep), or a difference time (t_Sweep), of a difference signal (S_Sweep) between a pulse repetition signal (S_PRF) having a pulse repetition frequency (f_PRF), and a sampling signal (S_Sample) having a sampling frequency (f_Sample);

altering the pulse repetition frequency (f_PRF), and/or the sampling frequency (f_Sample), on the basis of a control with control variable (c_var), through a corresponding control algorithm, such that the difference frequency (f_Sweep) is controlled to a desired value (f<sub>Sweep—

setpoint</sub>) of the difference frequency, or the difference time (t_Sweep) is controlled to a desired value (t<sub>Sweep—

setpoint</sub>) of the difference time;

determining a gradient (grad) between at least two values of the difference frequency (f_Sweep), or between at least two values of the difference time (t_Sweep), as a function of the control variable (c_var); and

determining, on the basis of the gradient (grad) and the difference frequency (f_Sweep), or difference time (t_Sweep), at a set control variable (c_var), an operating point (OP) of the control, and the control algorithm is adjusted accordingly thereto.

2. The method as claimed in claim 1, wherein:

the polarization, or sign, of the difference frequency (f_Sweep), or difference time (t_Sweep), of the difference signal (S_Sweep) is obtained by means of the gradient (grad).

3. The method as claimed in claim 1, further comprising the step of:

recording a control characteristic curve (con_char) of the difference signal (S_Sweep) by determining and storing the difference frequency (f_Sweep), or the difference time (t_Sweep), as a function of the changing control variable.

4. The method as claimed in claim 1, further comprising the step of:

restoring the operating point (OP) by the control algorithm to a defined, safe control region (E) by setting the control variable (c_var) back to a minimum value when the operating point (OP) is determined to be in a critical control region (A, B, C, F) of the control.

5. The method as claimed in claim 3, further comprising the step of:

regulating by the control algorithm the operating point (OP) to the desired value (OP_setpoint) of the operating point by steadily changing the control variable (c_var) when the operating point (OP) is determined to be in a defined safe region (E) of the control.

6. The method as claimed in claim 3, further comprising the step of:

recognizing with the control algorithm a disturbance, when the operating point (OP) is determined to be permanently in the disturbance region (D) above a maximum limit value of the difference frequency (f_Sweep), or below a minimum limit value of the difference time (t_Sweep).

7. The method as claimed in claim 1, further comprising the step of:

incrementing an error counter in the control algorithm in the case of a defined limit value of the control deviation of the difference frequency (f_Sweep) from the desired value (f<sub>Sweep—

setpoint</sub>) of the difference frequency, or of the difference time (t_Sweep) from the desired value (t<sub>Sweep—

setpoint</sub>) of the difference time, when this limit value is exceeded, or is decremented when this limit value is complied with.

8. The method as claimed in claim 7, further comprising the step of:

setting a maximum count value of the error counter, at which the error counter is cleared, the control algorithm is interrupted, and the operating point (OP) is transferred into the defined, safer control region (E) of the control characteristic curve, by setting the control variable (c_var) back to a minimum value.

9. The method as claimed in claim 1, further comprising the step of:

effecting a pulse width-modulated control signal (R_pwm) by the control algorithm, to a first tolerance value of a large control deviation of the difference frequency (f_Sweep) from the desired value (f<sub>Sweep—

setpoint</sub>) of the difference frequency, or of the difference time (t_Sweep) from the desired value (t<sub>Sweep—

setpoint</sub>) of the difference time.

10. The method as claimed in claim 1, further comprising the step of:

effecting a pulse sequence-modulated control signal (R_toggle) by the control algorithm, to a second tolerance value of a medium control deviation of the difference frequency (f_Sweep) from the desired value (f<sub>Sweep—

setpoint</sub>) of the difference frequency, or of the difference time (t_Sweep) from the desired value (t<sub>Sweep—

setpoint</sub>) of the difference time.

11. The method as claimed in claim 1, wherein:

to a third tolerance value of a tendential control deviation of the difference frequency (f_Sweep) from the desired value (f<sub>Sweep—

setpoint</sub>) of the difference frequency, or of the difference time (t_Sweep) from the desired value (t<sub>Sweep—

setpoint</sub>) of the difference time, there is no immediate counter-control with the corresponding control variable (c_var);

rather, a tendency of the control deviation is determined, and a tendential control signal (S_Drift) is produced, which is joined to the pulse sequence-modulated control signal (R_Toggle), or to the pulse width-modulated control signal (R_PWM).