DE102011010170A1 - Non-interacting method for switching flows of liquid, for use in calibrating volumetric flow meter, involves decreasing flow of liquid through valves, so that liquid from supply line partially flows into derivative - Google Patents

Abstract

The method involves causing flow of liquid through supply line (14) with supply flow rate (Q0) which is the sum of flow rates (Q1,Q2) corresponding to valves (16,18). Flow of liquid through valves is decreased, so that liquid from supply line partially flows into derivative (52), and liquid pressure or supply flow rate in upstream of valves is in predetermined pressure or predetermined flow range. Independent claims are included for the following: (1) flow switching device; and (2) calibration apparatus for calibrating volumetric flow meter.

Description

The invention relates to a method for non-reactive switching of liquid streams. According to a second aspect, the invention relates to a flow-through switching device for effect-free switching of liquid streams.

For calibrating flowmeters, it is advantageous to keep the fluid pressure in the flow meter to be calibrated as constant as possible in order to minimize measurement errors. The pressure should remain constant even if the flow resistance in a discharge downstream changes behind the flow meter. Thus, it may happen that a reference standard (volume measuring device or balance) is arranged downstream of the measuring instrument to be calibrated, which is filled with liquid that has passed through the flow meter. If the reference standard is filled, it is switched to a branch line, which usually has a different flow resistance. This can result in pressure differences that are undesirable.

The invention has for its object to switch a liquid flow between two lines, without resulting in a significant pressure fluctuation in the supply line.

The invention solves the problem by a method for low-return switching of liquid streams, comprising the steps of (a) effecting a liquid flow through a supply line with an overflow, then with a first flow through a first valve or with a second flow through at least one second (B) reducing the flow through the first fitting until no more liquid flows through the first fitting; and (c) simultaneously controlling the flow rate of the first fitting and the first derivative second flow through the at least second fitting, so that the liquid flow from the supply line at least partially flows into a second discharge and a liquid pressure and / or the flow to upstream of the first fitting and the at least one second fitting a predetermined desired liquid pressure and / or a predetermined target to-flow ss correspond.

According to a second aspect, the invention solves the problem by a flow switching device for the low-return switching of liquid flows, with (i) a feed line, (ii) a first fitting, which can be supplied with liquid from the feed line and which comprises a first actuating device, by means of the first flow through the first fitting is adjustable, (iii) a second fitting which can be supplied from the supply line with the liquid and which comprises a second actuation device by means of which a second flow through the second fitting can be set, wherein the first fitting and the second fitting are arranged so that all liquid flows from the supply line either through the first valve or through the second valve, (iv) a sensor for measuring a fluid pressure and / or an in-flow in the supply line and (v) a control device with the sensor, the first actuator and the second B and is adapted to automatically perform a method comprising the steps of actuating the first actuator so that the first flow decreases until no liquid flows through the first valve, and controlled actuation of the second actuator, so that the sensor measured fluid pressure and / or to-flow in the supply line has a preset value. The default value can also be a constant value.

An advantage of the invention is that the fluid pressure and / or the flow rate through the supply line remains constant or remain. This makes it possible to arrange a flow meter in the supply line and to calibrate it at a constant pressure, even if the flow resistance in the flow path through the first valve differs from the determination resistance in the flow path through the second valve. This achieves the highest measuring accuracies and the smallest possible measurement uncertainties.

It is also advantageous that the flow switching device is suitable for liquids of different viscosities, which applies to known devices.

In the context of the present description, a low-feedback switching means, in particular, that the excess flow through the supply line and / or the fluid pressure in the supply line when switching from the first fitting to the second fitting by at most 1 percent, in particular by at most 0, 5 percent changes. In particular, the fluid pressure is determined by a sliding means over, for example, one second.

In particular, the method is suitable for feedback-free switching, if it is understood that the to-flow rate and / or the liquid pressure in the supply line fluctuate by one per thousand when switching.

The feature that the liquid flow flows through the first fitting or through the second fitting is understood in particular to mean that it is possible, but not necessary, for the liquid stream to flow completely through either the first fitting or the second fitting. As a rule, at the beginning of the process, the liquid flow flows completely through either the first fitting or completely through the second fitting. Most often, at the end of the process, the liquid flow also flows either through the second armature or the first armature.

Under the feature that the liquid flow flows through at least one second armature, is understood in particular that it is quite possible that a third armature, a fourth armature or other fittings are present. Particularly relevant, however, is the case in which only two fittings are present, since then it is a real switch.

By the feature that the first fitting and the second fitting are arranged so that all liquid flows from the supply line either through the first fitting or through the second fitting, it is understood that the sum of the first flow through the first fitting and the first fitting second flow through the second fitting is constant. This sum corresponds to the flow through a possibly available to be calibrated flowmeter.

Preferably, the reduction of the flow through the first valve takes place in that an actuating device of the first valve is in particular electrically controlled so that it closes the valve successively. The second flow rate is preferably regulated by activating a second actuating device of the second valve, this actuating device having, for example, a closing element which can be designed as a plug, and the flow rate being dependent on the position of the closing element. In terms of control technology, the fluid pressure and / or the inflow are the control variables. The manipulated variable is, for example, a position of the closing element of the second fitting.

According to a preferred embodiment, prior to decreasing the flow through the first fitting, the liquid pressure and / or the overflow through the supply line upstream of the first fitting and the at least one second fitting is measured and the measured liquid pressure is set as the desired liquid pressure and / or the measured inflow is set as the set inflow. This ensures that when switching the fluid flow from the first valve to the second valve, the pressure conditions in the supply line and thus in any existing existing in the supply line to be calibrated flow meter always remain constant.

The method is preferably a calibration method for a flowmeter to be calibrated, in which a flowmeter to be calibrated is arranged in the supply line. It is favorable if the first fitting and the second fitting are arranged downstream of a branching point and the flowmeter to be calibrated is arranged on the flow side in front of the branching point. In this case, it is favorable if downstream of the first fitting or the second fitting a reference standard is arranged, by means of which the flow rate can be determined. It may be, for example, a measuring cylinder, a balance.

In order to achieve a particularly small fluctuation of the flow or of the pressure, it is provided according to a preferred embodiment that the regulation of the second flow through the at least one second armature is such that initially a desired value for a second flow through the second Valve determining manipulated variable is determined from a stored control characteristic, the manipulated variable is set in the second valve and then the manipulated variable is adjusted based on the fluid pressure and / or the to-flow. The actuating characteristic is, in particular, an image that correlates the manipulated variable with the resulting flow.

It is advantageous if the step of extending the flow through the first fitting comprises the step of presetting a closing position of a closing element of the fitting in a time-dependent manner. In other words, the first valve is driven so that there is a predetermined course for the closed position of the closing element. For example, the closure element is a chick, in which case the closed position may be described by the angle the chick has relative to the housing. The closing element can in principle have any shape. For example, the closing element can also be designed as a slide, wherein the closed position is then indicated by the path which the slide has traveled from its open position.

The invention is based on the recognition that it is not necessary to switch the liquid flow from the first fitting to the second fitting with the least possible switching time, when the transition from the first fitting to the second fitting takes place in a known manner. Due to the time-dependent predefinition of the closed position, it is known at any time which flow or what proportion of the throughflow flows through the first valve.

It is possible that the time-dependent predetermining the closed position of the closing element a Time-dependent predetermining a flow and / or a pressure downstream of the first valve and / or in the flow direction before the valve comprises or is. Thus, it is possible that a closed position, for example in degrees, is specified, wherein it is expected that this closed position corresponds to a certain first flow. The first flow is measured directly or based on the pressure and the closed position is adjusted based on this pressure. In other words, reducing the flow through the first fitting may include the step of timing the flow through the first fitting, which may include predetermining the closed position of the closure member.

It is then known at any time, which flow flows through the first fitting, which leads to a particularly high accuracy when the method is used to calibrate a flow meter.

According to a preferred embodiment, when the first valve is closed, a closed position of the second valve is controlled so that a flow resistance of the second derivative corresponds to a predetermined desired flow resistance. In other words, it is not necessary that when the first armature is closed, the second armature is fully open. Rather, it is possible that the second valve is only partially open, this opening position is regulated by the pressure that should prevail in the supply line.

A flow-rate switching device according to the invention preferably has a digital memory in which an actuating characteristic is stored, which codes the flow as a function of at least one manipulated variable of a closing element for at least one of the valves. Alternatively or additionally, it is possible that an actuating characteristic is stored in the digital memory, which assigns a second control variable of a first closing element of the first valve a second control variable of a second control element of the second valve, wherein the first control variable and the second control variable are each selected in that a total flow resistance downstream of the supply line remains constant. If a flow meter is arranged in the feed line, this means that the flow resistance downstream of the flow meter to be calibrated is constant, independently of the flow rates through the first valve and the second valve.

It is advantageous if the first fitting and the at least one second fitting are arranged downstream of a branching point and the sensor is located in front of the branching point.

According to the invention, a calibration device for calibrating a flowmeter, which comprises a flow-through switching device according to the invention and a flowmeter to be calibrated in the supply line, is also provided.

It is expedient for the calibration device to have a reference standard arranged downstream of the first fitting or the second fitting, so that the flowmeter to be calibrated can be calibrated by passing the liquid stream into or through the reference standard.

It is always spoken in the description of liquids and liquid streams. At any point in the description, however, could always "fluid" instead of "liquid" or "gas" instead of "liquid" are. This also applies to compound words with the component "liquid".

In the following the invention will be explained in more detail with reference to the attached drawings. It shows

1 a calibration device according to the invention which comprises a flow-through switching device according to the invention for carrying out a method according to the invention,

2 a circuit diagram of a flow-switching device according to the invention for carrying out a method according to the invention and

3 a supplemented by regulatory information schematic representation of the 2 ,

1 shows a calibration device according to the invention 10 with a switching device according to the invention 12 that includes the components surrounded by a dashed-dotted line. The flow switching device 12 has a supply line 14 which is a first fitting 16 and a second fitting 18 having.

The first fitting 16 has a first actuator 20 , in the present case in the form of an electric motor, by means of a first closing element 22 can be actuated so that a flow Q ₁ through the first valve 16 can be set. The second fitting 18 has a second actuator 24 also in the form of an electric motor, by means of a second closing element 26 can be actuated so that a second flow Q ₂ through the second valve 18 can be set.

The first actuator 20 and the second actuator 24 are with a control device 28 connected the faucets 16 . 18 so can control that the position of the closing elements 22 . 26 changed.

The supply line 14 branches into a branching point 30 in a first line 32 leading to the first fitting 16 leads, and a second line 34 leading to the second fitting 18 leads. An inflow Q ₀ thus always corresponds to the sum of the first flow Q ₁ and the second flow Q ₂ . By means of a sensor 36 is the to-flow Q ₀ and / or a fluid pressure p ₀ in the supply line 14 measurable. The sensor 36 is with the control device 28 connected, for example by means of an electric cable.

Outflow side behind the first fitting 16 is a first derivative 38 arranged, becoming a reference standard 40 leads, which is realized in the present case by a measuring cylinder. From the reference standard 40 can the liquid 42 through a drain valve 44 in a storage container 46 be drained. From the storage container 46 can the liquid 42 by means of a pump 48 to a flowmeter to be calibrated 50 (meter under test, MUT) to be pumped in the supply line 14 is arranged.

Outflow side behind the second valve 18 is a second derivative 52 arranged in the storage tank 46 empties. The entire liquid 42 passing through the flowmeter 50 flows, so can by means of the flow-switching device 12 either in the reference standard 40 or in the second derivative 52 and thus in the reservoir 46 be redirected.

The control device 28 is arranged to respond to a corresponding start signal, for example from a handset or a computer, towards the first actuator 20 controls so that the first flow Q _{1 is} reduced. At the same time, the controller automatically controls the second actuator 24 so on, that of the sensor 36 measured liquid pressure p and / or to-flow Q ₀ in the supply line 14 a preset target pressure p _Soll or a preset target flow Q _Soll has. This ensures that the fluid pressure p ₅₀ , the flow meter 50 always remains constant, even if from the first fitting 16 on the second fitting 18 is switched. Under constant is understood here that a temporal deviation, for example, within 1 second, below 10 ^-2 .

1 shows that the pressure differences, which are equivalent to flow resistances, with respect to the first derivative 38 and the second derivative 52 differ. Thus, a hydrostatic back pressure Δp _{measuring cylinder} = p · g · Δh, which is usually much greater than the dynamic pressure drop across the second derivative 52 Δp _Bypass = p / 2 · (V / A) ² · ζ _Bypass , where ζ _{Bypss is} the flow _resistance of the second derivative 52 is. This makes it clear that when switching from the first valve to the second valve basically with a change in the fluid pressure p ₅₀ on the flowmeter 50 would be expected. The inventive design of the flow switching device 12 prevents this, however.

In the present case would be when switching from the first fitting 16 on the second fitting 18 the second fitting 18 not fully open, leaving the second fitting 18 always a pressure drop occurs, which is always so great that the difference to the pressure drop in the first derivative by the rules on the target pressure p _target or the target flow Q _Soll 38 is compensated.

2 shows a circuit diagram of the flow switching device 12 , Marked is a control characteristic 54 the first fitting 16 , which plots the resulting flow Q ₁ against a first manipulated variable S1. In the present case, the first manipulated variable S1 is a rotational angle φ ₁ , around which the first closing element 22 is turned. A second control characteristic 56 applies the resulting second flow Q ₂ against a second manipulated variable S2, in this case against the angle φ ₂ , below which the second closing element 26 is oriented. The two control characteristics 54 . 56 represent the respective, individual actuating properties of the control valves and can in a digital memory of the control device 28 be filed.

A method according to the invention is carried out in that first a liquid flow with the flow Q ₀ through the supply line 14 Initially, for example, only by the first fitting 16 runs. It is subsequently a control signal, for example via a control line 58 , Sent, which changes in predetermined periods of time, the first manipulated variable S1. This results in a time course Q ₁ (t) of the flow Q ₁ of the time t, with an optional sensor 60 , which may be a flow or pressure sensor, for example, is detected. Preferably, the first fitting 16 so controlled that the first flow Q ₁ (t) decreases linearly with the time t.

By means of the sensor 36 is the constant flow to Q ₀ in the supply line 14 captured and the second fitting 18 controlled so that the corresponding size remains constant. This can for example be done by first a target value Q _{2, the target} for the flow through the second valve 18 determining manipulated variable S2 from a stored actuating characteristic 62 is determined.

For example, a digitally stored table is read out or interpolated. This table is determined, for example, in preliminary tests for a large number of manipulated variables and flow rates, if appropriate for a plurality of pressures, temperatures and various liquids. The target value Q _{2, Soll} thus obtained is then sent to the second valve 18 sent, so that the second manipulated variable S2, in the present case, the second angle φ ₂ , sets. Should the second manipulated variable S2 calculated in this way not have exactly met the value that is necessary for the flow Q and / or the pressure p at the sensor 36 keep constant, then the remaining difference by the control device 28 corrected. If the first flow Q ₁ decreases linearly with time t, the second flow Q ₂ thereby increases linearly with time t.

3 shows a more detailed view of the diagram according to 2 , in which additionally dashed switching lines for a binary signal are shown. So runs over a binary control line 64 a signal from a limit switch 66 that encodes whether the closing element of the first fitting 16 has already moved due to the control. Should this not be the case, for example, because the closing element is stuck due to frictional forces, so will the second fitting 18 transmitted second manipulated variable S2 not changed. Via a second limit switch 68 can also be determined whether the closing element of the second valve is at the stop or stuck. The flow switching device according to 3 is also set up so that the manipulated variables S1, S2 are changed only when a start signal to the control device 28 has been sent.

LIST OF REFERENCE NUMBERS

10

calibration

12

Flow switching

14

supply

16

first fitting

18

second fitting

20

first actuating device

22

first closing element

24

second actuator

26

second closing element

28

control device

30

branching point

32

first line

34

second line

36

sensor

38

first derivative

40

reference standard

42

liquid

44

drain valve

46

reservoir

50

Flowmeter

52

second derivative

54

Deputy characteristics

56

Deputy characteristics

58

control line

60

sensor

62

Deputy characteristics

64

Binary control line

66

Limit switches

68

Limit switches

Q

flow

Q ₁

first flow (through first fitting)

Q ₂

second flow

Q ₀

To Flow

p

fluid pressure

p _target

Target fluid pressure

Q _target

Target flow

S1

first manipulated variable

S2

second manipulated variable

Claims (10)

Method for the low-backflow switching of liquid streams, comprising the steps of: (a) effecting a liquid flow - through a supply line ( 14 ) with an overflow (Q ₀ ), - then with a first flow (Q ₁ ) through a first valve ( 16 ) or with a second flow (Q ₂ ) through at least one second valve ( 18 ) and then into a first derivative ( 38 ), Wherein the on-flow (Q ₀ ) corresponds to a sum of the first flow (Q ₁ ) and the second flow (Q ₂ ), (b) reducing the flow through the first valve ( 16 ) until no liquid ( 42 ) more through the first fitting ( 16 ), and (c) simultaneously controlling the second flow (Q ₂ ) through the at least one second armature ( 18 ), so that (i) the liquid flow from the supply line ( 14 ) at least partially into a second derivative ( 52 ) and (ii) a liquid pressure (p) and / or the overflow (Q ₀ ) upstream of the first valve ( 16 ) and the at least one second fitting ( 18 ) correspond to a predetermined desired liquid pressure (p _setpoint ) and / or a predetermined set flow rate (Q _setpoint ). Method according to claim 1, characterized by the step: (i) before step (b) measuring a fluid pressure (p) and / or the inflow (Q ₀ ) through the supply line ( 14 ) upstream of the first valve ( 16 ) and the at least one second fitting ( 18 ) and (ii) setting the measured liquid pressure (p) as the desired liquid pressure (p _setpoint ) and / or setting the overflow (Q ₀ ) as the set inflow flow (Q _{0, setpoint} ). Method according to one of the preceding claims, characterized in that in the Supply line ( 14 ) a flow meter to be calibrated ( 50 ) is arranged. Method according to one of the preceding claims, characterized in that the regulation of the second flow (Q ₂ ) by the at least one second fitting ( 18 ) is carried out so that (i) initially a desired value (Q _{2, Soll} ) for a second flow (Q ₂ ) through the second valve ( 18 ) determining manipulated variable (S1, S2) from a stored actuating characteristic ( 62 ), (ii) the manipulated variable (S2) in the second fitting ( 18 ) and (iii) the manipulated variable (S2) is adjusted based on the fluid pressure (p) and / or the inflow (Q ₀ ). Method according to one of the preceding claims, characterized in that the reduction of the flow (Q) through the first fitting ( 16 ) the step time-dependent predefinition of a closed position of a closing element ( 24 . 26 ) of the fitting. Method according to one of the preceding claims, characterized in that the reduction of the first flow (Q ₁ ) by the first fitting ( 16 ) until there is no liquid left through the first fitting ( 16 ), is performed so that the first flow (Q ₁ ) changes at least in sections linearly with time (t). Flow switching device for low-backflow switching of liquid flows, with (i) a supply line ( 14 ), (ii) one of the supply line ( 14 ) with liquid ( 42 ) arranged to be arranged first fitting ( 16 ), which is a first actuator ( 20 ) by means of which a first flow (Q ₁ ) through the first fitting ( 16 ), (iii) one of the supply line ( 14 ) with liquid ( 42 ) arranged second armature ( 18 ), which is a second actuator ( 24 ) by means of which a second flow (Q ₂ ) through the second valve ( 18 ), the first fitting ( 16 ) and the second fitting ( 18 ) are arranged so that all liquid ( 42 ) either through the first fitting ( 16 ) or through the second fitting ( 18 ), (iv) a sensor ( 36 ) for measuring a fluid pressure (p) and / or an in-flow (Q ₀ ) in the supply line ( 14 ) and (v) a control device ( 28 ) connected to the sensor ( 36 ), the first actuator ( 20 ) and the second actuator ( 24 ) and is arranged to automatically carry out a method comprising the steps of: - actuating the first actuating device ( 20 ), so that the first flow (Q ₁ ) decreases until no liquid ( 42 ) more through the first fitting ( 16 ), and - controlled actuation of the second actuator ( 24 ), so that the sensor ( 36 ) measured liquid pressure (p) and / or to flow (Q ₀ ) in the supply line ( 14 ) has a preset, in particular a constant, value. Flow-switching device according to claim 7, characterized by a digital memory in which a control characteristic ( 54 . 56 ) stored for at least one fitting ( 16 . 18 ) encodes the flow rate (Q) as a function of at least one manipulated variable (S1, S2). Flow switching device according to one of claims 7 to 8, characterized in that the first valve ( 16 ) and the at least one second fitting ( 18 ) downstream of a branching point ( 30 ) are arranged and the sensor ( 36 ) in front of the branching point ( 30 ) is located. Calibration device for calibrating a flowmeter, characterized by a flow-through switching device according to one of claims 7 to 9, wherein in the supply line ( 14 ) is arranged to be calibrated flow meter.

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