Method for Operating a Flowmeter and Flowmeter

Abstract

A method for operating a flowmeter is disclosed. The flowmeter has a sensor for capturing a measured variable indicating the flow, and for converting the measured variable into a signal. The flowmeter also has a control and evaluation unit that determines a flow measurement value for the flow from the signal and outputs an output value representing the flow measurement value. The method includes: determining flow measurement values; forming smoothed flow measurement values over a plurality of flow measurement values, respectively; and activating a low flow cut-off. When the low flow cut-off is activated, the output value is set to zero if: the current smoothed flow measurement value is below a first predetermined limit value; and a predetermined number of flow measurement values has been determined with deactivated low flow cut-off or a predetermined number of smoothed flow measurement values has been formed with deactivated low flow cut-off.

Claims

1. A method for operating a flowmeter, wherein the flowmeter has a sensor for capturing a measured variable indicating the flow, wherein the sensor converts the measured variable into a sensor signal and wherein the flowmeter has a control and evaluation unit, wherein the control and evaluation unit determines a flow measurement value for the flow from the sensor signal and outputs an output value representing the flow measurement value, the method comprising: determining flow measurement values; forming smoothed flow measurement values over a plurality of flow measurement values, respectively; activating a low flow cut-off, wherein when the low flow cut-off is activated, the output value is set to zero if both of the following conditions are met: the current smoothed flow measurement value is below a first predetermined limit value; and a predetermined number of flow measurement values has been determined with deactivated low flow cut-off or a predetermined number of smoothed flow measurement values has been formed with deactivated low flow cut-off.

2. The method according to claim 1, wherein the smoothed flow measurement value is formed by forming a mean value; and wherein the mean value is a simple moving average, an exponential moving average, a weighted moving average, an arithmetic mean value, or a harmonic mean value.

3. The method according to claim 2, wherein the predetermined number of smoothed flow measurement values corresponds at least to the plurality of flow measurement values over which smoothing is performed per smoothed flow measurement value.

4. The method according to claim 1, wherein the first predetermined limit value is formed by a low flow limit value minus a first tolerance value.

5. A method for operating a flowmeter, wherein the flowmeter has a sensor for capturing a measured variable indicating the flow, wherein the sensor converts the measured variable into a sensor signal, and wherein the flowmeter has a control and evaluation unit, wherein the control and evaluation unit determines a flow measurement value for the flow from the sensor signal and outputs an output value representing the flow measurement value, wherein a low flow cut-off is activated, wherein the output value is set to zero when the low flow cut-off is activated the method comprising: determining flow measurement values; forming smoothed flow measurement values over a plurality of flow measurement values in each case; deactivating the low flow cut-off, wherein when the low flow cut-off is deactivated, an output value corresponding to the current flow measurement value is output when either of the following two conditions is satisfied: the smoothed flow measurement value is above a second predetermined limit value; or a current determined flow measurement value is above a third predetermined limit value.

6. The method according to claim 5, wherein the second predetermined limit value is formed from the low flow limit value plus the first tolerance value.

7. The method according to claim 5, wherein the third predetermined limit value is formed from the low flow limit value plus a second tolerance value.

8. The method according to claim 1, wherein, in a correction step, a zero point correction of the flowmeter is carried out when the low flow cut-off is activated.

9. The method according to claim 1, wherein the following additional method steps are carried out: determining or retrieving the reaction time of the low flow cut-off; determining the flow rate after deactivation of the low flow cut-off over the period of the reaction time of the low flow cut-off; and adding the flow rate determined over the period of the reaction time to the initial value.

10. The method according to claim 9, wherein the flow rate determined over the period of the reaction time is divided into a plurality of flow rate subsets and added up divided to a plurality of output values.

11. A flowmeter for determining a flow rate of a medium, comprising: a sensor for detecting a measured variable indicating the flow rate, wherein the sensor converts the measured variable into a sensor signal; and a control and evaluation unit, wherein the control and evaluation unit determines a flow measurement value for the flow rate from the sensor signal and outputs an output value representing the flow measurement value; wherein the control and evaluation unit is designed to carry out the following method steps in the operating state of the flowmeter: determining flow measurement values; forming smoothed flow measurement values over a plurality of flow measurement values in each case; activating a low flow cut-off, wherein when the low flow cut-off is activated, the output value is set to zero if both of the following conditions are met: the current smoothed flow measurement value is below a first predetermined limit value; and a predetermined number of flow measurement values has been determined with deactivated low flow cut-off or a predetermined number of smoothed flow measurement values has been formed with deactivated low flow cut-off.

12. A flowmeter for determining a flow rate of a medium, comprising: a sensor for capturing a measured variable indicating the flow, wherein the sensor converts the measured variable into a sensor signal; and a control and evaluation unit, wherein the control and evaluation unit determines a flow measurement value for the flow from the sensor signal and outputs an output value representing the flow measurement value; wherein the control and evaluation unit is designed in such a way that, in the operating state of the flowmeter, the control and evaluation unit carries out the following method steps when a low flow cut-off is activated, wherein the output value is set to zero when the low flow cut-off is activated: determining of flow measurement values; forming smoothed flow measurement values over a plurality of flow measurement values in each case; deactivating the low flow cut-off, wherein when the low flow cut-off is deactivated, an output value corresponding to the current flow measurement value is output when one of the following two conditions is met: the smoothed flow measurement value is above a second predetermined limit value; or a currently determined flow measurement value is above a third predetermined limit value.

13. The flowmeter according to claim 11, wherein the control and evaluation unit is further designed to carry out at least one of the following method steps in the operating state of the flowmeter: forming the smoothed flow measurement value by forming a simple moving average, an exponential moving average, a weighted moving average, an arithmetic mean value, or a harmonic mean value; forming the first predetermined limit value by a low flow limit value minus a first tolerance value; a correction step, in which a zero point correction of the flowmeter is carried out when the low flow cut-off is activated; determining or retrieving the reaction time of the low flow cut-off; determining the flow rate after deactivation of the low flow cut-off over the period of the reaction time of the low flow cut-off; and adding the flow rate determined over the period of the reaction time to the initial value.

14. The flowmeter according to claim 12, wherein the control and evaluation unit is further designed to carry out at least one of the following method steps in the operating state of the flowmeter: forming the smoothed flow measurement value by forming a simple moving average, an exponential moving average, a weighted moving average, an arithmetic mean value, or a harmonic mean value; forming the first predetermined limit value by a low flow limit value minus a first tolerance value; a correction step, in which a zero point correction of the flowmeter is carried out when the low flow cut-off is activated; determining or retrieving the reaction time of the low flow cut-off; determining the flow rate after deactivation of the low flow cut-off over the period of the reaction time of the low flow cut-off; and adding the flow rate determined over the period of the reaction time to the initial value.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0057] In detail, there is now a plurality of possibilities for designing and further developing the method according to the invention for operating a flowmeter and the flowmeter according to the invention. For this, reference is made to the description of preferred embodiments in conjunction with the drawings.

[0058] FIG. 1 illustrates a block diagram of a first design of a method for operating a flowmeter.

[0059] FIG. 2 illustrates a block diagram of a second design of a method for operating a flowmeter.

[0060] FIG. 3 illustrates a flow chart of a method for operating a flowmeter.

[0061] FIG. 4 illustrates a block diagram of a third design of a method for operating a flowmeter.

[0062] FIG. 5 illustrates a flow chart of a second method for operating a flowmeter.

[0063] FIG. 6 illustrates an exemplary graphical representation of the time course of individual values.

[0064] FIG. 7 illustrates a schematic representation of a flowmeter with a control and evaluation unit that can carry out the variations of the method shown above.

[0065] FIG. 8 illustrates a block diagram of a third design of a method for operating a flowmeter.

DETAILED DESCRIPTION

[0066] FIG. 1 shows a block diagram of a method 100 for operating a flowmeter 1. The flowmeter 1 is shown in FIG. 7 and has a sensor 2 which captures a measured variable p and converts the measured variable p into a sensor signal s. The sensor signal s is transmitted to a control and evaluation unit 3, wherein the control and evaluation unit 3 determines a flow measurement value d for the flow rate of the medium from the sensor signal s. In addition, the control and evaluation unit then outputs an output value a representing the flow measurement value d. The control and evaluation unit 3 of the flowmeter 1 shown is further designed such that, in the operating state of the flowmeter 1, it can carry out the further variations of the method 100.

[0067] In the variation of the method 100 shown in FIG. 1, flow measurement values d are determined in a step 101. In the example shown, the flow measurement values are determined continuously in time, wherein the time between two flow measurement values is constant here. In a further step 102, smoothed flow measurement values d.sub.g are formed over a plurality m of flow measurement values d in each case. In the present case, the smoothed flow measurement value d.sub.g is formed by forming a simple moving average. In a further method step 103, a low flow cut-off LFC is activated if the current smoothed flow measurement value d.sub.g,akt is below a first predetermined limit value g.sub.1 and a predetermined number n of flow measurement values d have been determined with deactivated low flow cut-off LFC. In the illustrated embodiment, the number n of flow measurement values d that have been determined with deactivated low flow cut-off LFC corresponds numerically to the plurality m of flow measurement values d over which the smoothed flow measurement value d.sub.g has been formed. In the embodiment, the first limit value g.sub.1 results from a low flow limit value g.sub.n minus a first tolerance value t.sub.1. When the low flow cut-off LFC is activated, flow measurement values d are still determined, but the output value a is set to zero. In a further step 104, the low flow cut-off LFC is deactivated if the current smoothed flow measurement value d.sub.g,akt is above a second predetermined limit value g.sub.2, or if the current flow measurement value d.sub.akt is above a third predetermined limit value g.sub.3. In the embodiment, the second limit value g.sub.2 results from the low flow limit value g.sub.n plus the first tolerance value t.sub.1. The third limit value g.sub.3, on the other hand, results, in the embodiment, from the low flow limit value g.sub.n plus a second tolerance value t.sub.2. The second tolerance value t.sub.2 is larger than the first tolerance value t.sub.1, so that the third limit value g.sub.3 is larger than the second limit value g.sub.2. Here we are talking about the absolute values of the limit values or tolerance values. The magnitude of the corresponding values depends on the direction of the flow of the medium.

[0068] FIG. 2 shows a block diagram of another embodiment of the method 100. The method shown in FIG. 2 differs from the method shown in FIG. 1 in that the low flow cut-off LFC is activated in a step 103′ when both the current smoothed flow measurement value d.sub.g,akt is below a first predetermined limit value g.sub.1 and a predetermined number k of smoothed flow measurement values d.sub.g have been determined with deactivated low flow cut-off LFC.

[0069] FIG. 3 shows a flow chart of a method 100 for operating a flowmeter 1. A current flow measurement value d.sub.akt is determined. Then, a smoothed flow measurement value d.sub.g is formed, wherein the smoothed flow measurement value d.sub.g is formed over the last m flow measurement values d. If the smoothed flow measurement value d.sub.g is below a first limit value g.sub.1 and, in addition, the number k of smoothed flow measurement values d.sub.g formed with deactivated low flow cut-off is greater than or equal to the number m of flow measurement values d over which the sliding flow measurement value d.sub.g is formed, then the low flow cut-off LFC is activated. If the two conditions are not met, there is a possibility that the low flow cut-off LFC is already activated. A check is now made to see if the current determined flow measurement value d.sub.akt is above a third limit value g.sub.3. If this is the case, the low flow cut-off LFC is deactivated. If this is not the case, it is further checked whether the current smoothed flow measurement value d.sub.g,akt is above a second limit value g.sub.2. If this is the case, the low flow cut-off LFC is deactivated. Furthermore, it is then checked whether the low flow cut-off LFC is activated. If this is the case, the current output value a.sub.akt is set to zero. If the low flow cut-off LFC is not activated, then a current output value a.sub.akt is output, which represents the current flow measurement value d.sub.akt. In addition, the number of smoothed flow measurement values d.sub.g formed is set from k to k+1 and a new current flow measurement value d.sub.akt is subsequently determined. The steps repeat with the new current flow measurement value.

[0070] FIG. 4 shows a block diagram of another method for operating a flowmeter. In the method shown in FIG. 4, the first three method steps 101, 102 and 103 are carried out as explained with respect to FIG. 2. When the low flow cut-off LFC is activated, a zero point correction of the flowmeter is carried out in a correction step 108. This further increases the measurement accuracy. In a further method step 105, the reaction time of the low flow cut-off LFC is determined or retrieved from the evaluation unit of the flowmeter. In this method step, the low flow cut-off is still activated. After deactivation of the low flow cut-off LFC—method step 104—the flow rate d.sub.t is determined over the period of the reaction time—method step 105. Due to the inertia of the deactivation of the low flow cut-off LFC, this flow rate d.sub.t is not output as output value a, since it is still set to zero; the current flow measurement value d.sub.akt is not output as current output value a.sub.akt until after the end of the reaction time. As soon as the current flow measurement value d.sub.akt is output as the current output value a.sub.akt, the flow d.sub.t is added to the current output value a.sub.akt in a further method step 107. In the illustrated design of the method, the flow rate d.sub.t is divided into a plurality t of flow rate subsets Δd. These flow rate subsets Δd are added to the next t output values a. One flow rate subset Δd is added up for each output value a. In the method shown, the flow rate d.sub.t is divided into flow rate subsets Δd of equal size. This method compensates for a loss of flow due to the inertia of the low-flow cut-off LFC, so that the overall measurement accuracy of the flow measurement is increased.

[0071] FIG. 5 shows a flow chart of a method with flow loss compensation. The method shown in FIG. 5 differs from the method shown in FIG. 3 accordingly by flow loss compensation. The flow loss is due to the reaction time of the low flow cut-off LFC when the low flow cut-off LFC is deactivated. In order to compensate for the flow loss, to compensate for the flow d.sub.t “lost” in the reaction time of the deactivation of the low flow cut-off LFC, the flow d.sub.t is determined in t partial steps, wherein the respective current flow measurement values a.sub.akt are added up over t measurements for this purpose. In the embodiment shown, t=m, so the number of flow measurement values a.sub.akt added up to determine the flow d.sub.t corresponds to the plurality m of the flow measurement values over which smoothing is carried out to determine the smoothed flow measurement value d.sub.g. The flow rate d.sub.t is divided into t flow rate subsets Δd. When the low flow cut-off LFC is deactivated, a flow portion Δd is added to the current output value a.sub.akt. This is carried out t times, with each addition reducing the value t by one (t=t−1), until t≤1. As soon as t≤1, no further flow portions Δd are added to the current output value.

[0072] FIG. 6 shows an example of a graphic representation of the time course of the individual values, namely the flow measurement value d, the output value a and the smoothed flow measurement value d.sub.g. Here, the flow rate in millimeters per second (mm/s) is plotted over time in seconds (s). The flow measurement value d is represented by the circular symbols, the output value a is represented by the square symbols, and the smoothed flow measurement value d.sub.g is represented by the star-shaped symbols. In the present case, the smoothed flow measurement value d.sub.g has been formed by taking the simple moving average, where d has been smoothed over four flow measurement values.

[0073] The low flow limit value g.sub.n is +/−5 mm/s. The first tolerance value t.sub.1 is 1 mm/s, so that the first limit value g.sub.1 is +/−4 mm/s and the second limit value g.sub.2 is +/−6 mm/s. The second tolerance value t.sub.2 is 15 mm/s, so that the third limit value g.sub.3 is +/−20 mm/s.

[0074] In the first four seconds shown, the respective current smoothed flow measurement values d.sub.g are above the first limit value g.sub.1. Accordingly, the respective current output value a corresponds to the respective current flow measurement value d. At time t=5 s, the current smoothed flow measurement value d.sub.g falls to a value below the first limit value g.sub.1. Moreover, the number k of smoothed flow measurement values d.sub.g formed with deactivated low flow cut-off LFC is k=9, which is greater than the plurality m=4 of flow measurement values d over which the smoothed flow measurement value d.sub.g is formed. Accordingly, the low flow cut-off LFC is activated and the output value a is set to zero. As can be seen from the graphic representation, the output value is set to zero between t=5 s and t=21 s, since, during that time, the smoothed flow measurement value d.sub.g remains at a value below the first limit g.sub.1. At t=22 s, the current flow measurement value d increases to a value above the third limit g.sub.3, so that one of the conditions for deactivation of the low flow cut-off LFC is fulfilled. For deactivation, it is only necessary that one of the two possible conditions is fulfilled, so that low flow cut-off LFC is deactivated. The output value a then corresponds again to the flow measurement value d. At time t=23 s, the smoothed flow measurement value d.sub.g is below the first limit value g.sub.1, so that one of the conditions for activating the low flow cut-off LFC is fulfilled. However, only one smoothed flow measurement value d.sub.g with deactivated low flow cut-off LFC has been formed, namely at t=22 s, because until t=21 s the low flow cut-off LFC was still activated, so that the second necessary condition for activating the low flow cut-off LFC is not fulfilled. The low flow cut-off LFC is thus not activated, and the output value a corresponds to the flow measurement value d. Only at a time t=28 s are both necessary conditions for activating the low flow cut-off LFC fulfilled, so that it is activated and the output value a is set to zero. At t=32 s, the smoothed flow measurement value d.sub.g increases to a value above the second limit g.sub.2. As a result, one of the conditions for deactivating the low flow cut-off LFC is met and the low flow cut-off LFC is deactivated. At t=37 s, the smoothed flow measurement value d.sub.g drops again to a value below the first limit value g.sub.1. In addition, more than four smoothed flow measurement values d.sub.g have been formed with deactivated low flow cut-off LFC, thus k>m and the low flow cut-off LFC is activated again and the output value is set to zero. At t=39 s, the current flow measurement value d increases (in magnitude) to a value above the third limit g.sub.3, so that the low flow cut-off LFC is deactivated again here.

[0075] FIG. 8 shows a block diagram of a method for operating a flowmeter. The method is carried out when the low flow cut-off LFC is activated and relates to the deactivation of the low flow cut-off LFC. In a method step, flow measurement values d are determined. In a further step 102, smoothed flow measurement values d.sub.g are determined over a respective plurality m of flow measurement values d. In a step 104′, the low flow cut-off LFC is deactivated if the smoothed flow measurement value d.sub.g is above a second predetermined limit value g.sub.2, or if a current determined flow measurement value d.sub.akt is above a third predetermined limit value g.sub.3. When low flow cut-off LFC is deactivated, an output value a corresponding to the actual flow measurement value d is output.