DE102016112196B4 - Flow-generating device and method for calibrating a DUT - Google Patents

Abstract

Flow-generating device for generating a predetermined flow of a fluid (23) with (a) a manifold (12) and (b) a first pump (14.1), the - a first cylinder (16.1), - a first piston (18.1), the running in the first cylinder (16.1), - a first drive (20.1), by means of which the first piston (18.1) is movable relative to the first cylinder (16.1), and - a first position determining device (22.1) for determining a first position of the first piston (18.1) relative to the first cylinder (16.1) and - connected to the manifold (12) for discharging fluid (23) into the manifold (12), and (c) a second pump (14.2), the - a second Cylinder (16.2), - a second piston (18.2) running in the second cylinder (16.2), - a second drive (20.2) by means of which the second piston (18.2) is movable relative to the second cylinder (16.2), and a second position determining device (22.2) for determining it has the second position of the second piston (18.2) relative to the second cylinder (16.2) and is connected to the manifold (12) for discharging fluid (23) into the manifold (12), characterized by (d) a controller (30 ), which is set up to automatically control the drives (20.1, 20.2), so that the pumps (14.1, 14.2) together deliver a predetermined volume flow of fluid (23) into the collecting line (12) and (e) a relative measurement uncertainty of the flow rate Generating device of at most 10-3.

Description

The invention relates to a flow-generating device for generating a predetermined flow of a fluid with (a) a manifold and (b) a first pump having a first cylinder, a first piston running in the first cylinder, a first drive, by means of which first piston is movable relative to the first cylinder, and has a first position determining device for determining the first current position of the first piston relative to the first cylinder and which is connected to the manifold for discharging fluid into the manifold, and (c) a second pump a second cylinder, a second piston running in the second cylinder, a second drive, by means of which the second piston is movable relative to the second cylinder, and a second position determining device for determining the second current position of the second piston relative to the second cylinder and having the manifold for discharging fluid into the collection line is connected. According to a second aspect, the invention relates to a method for calibrating a test object.

Such flow-generating devices are used, for example, for the recirculated calibration of flow meters. A recirculated calibration is understood to mean that the corresponding measurement result in a chain of calibrations is attributed to the definition of an SI unit. It is desirable that the flow-generating device generates the flow with the highest possible measurement accuracy and the smallest possible measurement uncertainty.

Known flow-generating devices have the disadvantage that a continuous delivery of the fluid is not possible, since the length of the piston movement of the piston in the cylinder is limited.

Flow-generating devices are also known which have continuously conveying pumps, for example variable-speed centrifugal pumps. A disadvantage of such systems is that the flow rate can only be changed quickly in an unsatisfactory manner. In addition, the pressure and flow in these systems depend on each other.

Harvard Apparatus's "Pump 33 Dual Syringe Pump" (Harvard Apparatus: Precision Syringe & Peristaltic Pumps, 2004, http://www.harvardapparatus.com/media/harvard/pdf/PP118%20pumps.pdf, accessed on 04/04/2017 ) is a syringe pump with two syringes, which are controlled independently of each other via a stepper motor. The measurement uncertainty of the syringe pump is given as 0.35%. The pump has a unique movable limit switch mechanism that is used to reverse the direction or stop the pump. The flow can be changed quickly and unsatisfactorily even with this controlled pump.

The 975 pump from the same manufacturer has a synchronous motor that uses a gearbox to move the plunger of the syringe and that has little flutter. The measurement uncertainty in dispensing a fluid flow in such a pump is influenced inter alia by the transmission error.

The invention has for its object to improve flow-generating devices.

The invention solves the problem by a flow-generating device according to the preamble of the main claim and with (d) a control adapted to automatically control the drives so that the pumps collectively deliver a given volume flow of fluid into the manifold and (e) one relative measurement uncertainty of at most 10 ^-3 .

According to a second aspect, the invention achieves the object by a method for generating a predetermined flow of a fluid with a relative measurement uncertainty of at most 10 ^-3 , in particular at most 5 × 10 ^-4 , in which a flow-generating device according to the invention is used. The invention also solves the problem by a method for calibrating a test specimen comprising the steps of: (a) arranging a specimen in the manifold of a flow-generating device according to the invention, (b) generating a predetermined flow of a fluid, in particular a liquid, through the manifold, (c) detecting a measuring flow through the sample and detecting a deviation between the flow and the measuring flow.

An advantage of the invention is that a theoretically infinitely long fluid flow can be generated. It is possible to operate the two pistons intermittently and oscillatingly and to recirculate the fluid. It is possible to determine this flow recirculated. For this purpose, first the piston area and / or the cylinder cross-sectional area must be determined by a recirculated measurement. moreover For example, the position-determining device is preferably designed to carry out a recirculated measurement, that is to say that it is itself recirculated in a recirculated manner.

It is another advantage that the flow rate is highly constant over time. Thus, the drives are preferably independent of each other, that is, the first piston can be moved without the second piston has to be moved. The controller is designed such that it adjusts the speed of movement of the pistons so that the pumps jointly deliver the predetermined volume flow into the manifold.

It is a further advantage that the system can be constructed without a control valve. A control valve is understood to mean a valve which is designed and arranged such that the flow through the manifold and / or the pressure in the manifold can be changed by actuation. Such a control valve adversely affects the best achievable measurement uncertainty.

In the context of the present description, the manifold means a conduit into which the two pumps, in particular all pumps, feed the fluid. The manifold is the conduit in which the flow should be known with high accuracy. If the flow-generating device is used as a calibration device, which is a preferred embodiment of the present invention, then the test object is in the manifold, that is, the test sample is subjected to the flow of fluid in the manifold.

It is possible and preferred, but not necessary, for the flow-generating device to have exactly two pumps, namely the first pump and the second pump. Rather, it is also possible that the flow-generating device has three, four or more pumps. As a rule, it is advantageous if the number of pumps is as low as possible.

It is advantageous if the cylinder inner surfaces and / or the piston surfaces are the same size in the technical sense. This means that it is possible and usually inevitable that the two inner cylinder surfaces are mathematically unequal. It is favorable, however, if a relative deviation between a first cylinder inner surface of the first cylinder and a second cylinder inner surface of the second cylinder is at most 10 ^-4 .

According to a preferred embodiment, the control is set up for automatically (i) regulating a first speed v _{1 of} the first piston to a first time-dependent setpoint speed, the first time-dependent setpoint speed corresponding to a continuous function v ₁ (t), and (ii ) Controlling a second speed v _{2 of} the second piston to a second setpoint speed, wherein the second setpoint speed corresponds to a continuous function v ₂ (t). The speeds of the pistons can be measured, for example, inductively.

Preferably, the control is arranged to automatically control the first position of the first piston to a first time-dependent desired position, wherein the first time-dependent desired position corresponds to a first function whose second derivative is continuous with time. Preferably, the controller is also configured to control the second position of the second piston to a second desired position, wherein the second desired position corresponds to a second function whose second derivative is continuous with time. This has the advantage that the flow in the manifold is highly constant in time.

The feature that the first time-dependent desired position corresponds to a first function is understood in particular to mean that the function is stored in the control, for example in a digital memory. Preferably, the first function has a third derivative. It is favorable if the maximum acceleration of the first piston and / or of the second piston is less than 0.1 m / s ² , in particular 0.03 m / s ² .

Under the feature that the pumps together deliver a predetermined volume flow of fluid into the manifold, is understood in particular that a size is predetermined, which corresponds to a volume flow. So it is also possible that a mass flow is given, which results from the density of the fluid and the volume flow.

Preferably, the control is arranged to automatically control the first position and the second position so that an actual flow rate through the manifold from a desired flow rate, on the basis of which the control regulates the positions, deviates by at most 10 ^-4 .

It is favorable if the regulation is set up for the oscillating movement of the pistons, so that the pumps operate continuously and a continuous flow through the manifold results.

Preferably, the flow-generating device comprises a timing device, with the aid of which the speed of the pistons relative to the respective cylinders is calculated from the respective positions.

It is advantageous if the control is designed to automatically set a transient flow through the manifold. This means that a non-constant function is stored in the control, which describes the flow as a function of time. Due to the construction, the flow-generating device is capable of setting the given transient flow rate with a very high measurement accuracy and a very low measurement uncertainty.

By the feature that the control is designed to automatically set a transient flow, it is understood, in particular, that the flow corresponds to a predetermined flow function, which depends on the time, wherein the flow function is not constant. The argument of this flow function is the time and the functional value of the set flow through the manifold.

The first drive is preferably a linear drive, for example a linear direct drive. In addition, the second drive is preferably a linear drive, for example a linear direct drive. The first and / or the second drive may alternatively comprise a cam, a camshaft or a spindle drive. Alternatively, the drives may be pneumatic or hydraulic drives.

The flow-generating device preferably has a fluid reservoir which is connected to at least a first inlet opening of the first pump and to at least one second inlet opening of the second pump. The manifold opens into the fluid reservoir, so that a continuous operation is possible.

It is advantageous if the first pump and / or the second pump are designed to be double-acting. In other words, the fluid is conveyed into the manifold no matter in which direction the first piston moves relative to the first cylinder and regardless of which direction the second piston moves relative to the second cylinder. Such a flow-generating device usually comes with lower accelerations or can be built smaller with the same predetermined target flow.

Preferably, the control is arranged to control the drives, so that a constant flow in the manifold results. Such a constant flow is particularly suitable for calibrating flow meters.

Preferably, the flow-generating device comprises a sample that is arranged in the manifold. In addition, it is favorable if the flow-generating device has a connection device for connecting a test object to the manifold so that the flow through the manifold completely flows through the test object.

In order to achieve a particularly high measuring accuracy, the first position-determining device and / or the second position-determining device preferably has an interferometer.

In order to further increase the measurement accuracy, it is advantageous if the flow-generating device has a temperature constant holding device for keeping constant a temperature of the fluid and / or the components of the flow-generating device.

In the fluid flow direction between the first pump and the manifold, a two-way backflow preventer is preferably arranged. It is possible, but not necessary, for the two-way backflow valve to be passive, in this case, for example, a check valve. It is also possible that the two-way backflow valve is actively activated. In this case, it is preferably designed to close, and only if the flow through the two-way backflow preventer is zero. For example, the two-way backflow valve is connected to the controller, which closes the two-way backflow valve when the associated drive does not deliver fluid into the manifold.

Preferably, the flow-generating device has a pressure regulating device by means of which the fluid pressure in the collecting line can be adjusted independently of the flow through the collecting line.

According to the invention, there is also a flow production standard, which has a flow-generating device according to the invention and an associated calibration certificate. The calibration certificate indicates the re-measured relevant dimensions of the flow-generating device, for example the piston surfaces of the pistons.

According to the invention, a method for generating a predetermined flow of a fluid, in particular a liquid, by a manifold, with a relative uncertainty of at most 10 ^-3 , in particular 5 · 10 ^-4 , in which a flow-generating device according to the invention is used.

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

1 a flow-generating device according to the invention according to a first embodiment,

2 a second flow-generating device according to the invention with three pumps,

3 a flow-generating device according to the invention, in which the pumps have double-acting piston, and

4 a flow-generating device according to the invention with a pressure-regulating device and in which the pumps have two pistons per cylinder.

durch eine Sammelleitung 12, die eine erste Pumpe 14.1 und eine zweite Pumpe 14.2 aufweist. 1 shows a flow-generating device according to the invention 10 for generating a predetermined flow

through a manifold 12 that is a first pump 14.1 and a second pump 14.2 having.

The first pump 14.1 owns a first cylinder 16.1 in which a first piston 18.1 running. A first drive 20.1 , in the present case a linear direct drive, is with the first piston 18.1 connected so that this in the cylinder 16.1 can be moved in and out. The position of the piston 18.1 relative to the cylinder 16.1 is by means of a first position determining device 22.1 determinable. In the present case, the position determining device 22 formed by an interferometer.

The position determination device 22 is configured to determine a first position x _{1 of} the first piston 18.1 relative to the first cylinder 16.1 , The position is determined to an arbitrary predefinable basic position. The position determination device 22 could therefore also be referred to as a position change determining device that measures a change of the first position.

Will be the first piston 18.1 moved so that the coordinate x _{1 is} larger, so the piston moves 18.1 in the cylinder 16.1 one and one fluid 23 For example, a liquid, preferably water, is passed through a first two-way backflow valve 24.1 in the manifold 12 issued. This creates a fluid flow V. ₁ , Will the piston 18.1 out of the cylinder 16.1 moved out, so fluid flows 23 by an inflow-side two-way backflow valve 26.1 and a first inlet opening 28.1 in the cylinder 16.1 ,

The first pump 14.1 is with a scheme 30 connected to the movement of the piston 18.1 regulates and at the same time the measurement results obtained by the position-determining device 22.1 recorded. The second pump 14.2 is identical to the first pump 14.1 and also with the scheme 30 connected.

The regulation 30 regulates the first position x ₁ (t) of the piston 18.1 relative to the first cylinder 16.1 in a preferred embodiment according to the function

This results in the time-dependent velocity v ₁ (t) and the acceleration a _{1 of} the piston 18.1 a ₁ (t) currently t as indicated below. The following function is an example of pump switching 14.1 on pump 14.2 according to 1 for the achievement of a constant volume flow, in particular also during the switching process. The beginning of the switching is at t ₁ , the end at t ₂ . In this case, the time t _{2 must} not after the time of reaching the bottom dead center of the pump 14.1 lie. Below is pump 14.1 refilled before pumping 14.2 reached the bottom dead center. The switching of pump 14.2 on pump 14.1 takes place in analogy, before pump 14.2 reached the bottom dead center.

This applies to

bezeichnet den Durchfluss durch die Sammelleitung 12. It can be seen that the function v ₁ (t) is continuous and even continuously differentiable in the present case, which represents a preferred embodiment. The function a ₁ (t) is continuous. Of the

refers to the flow through the manifold 12 ,

eine nicht konstante Funktion der Zeit t sein kann. Diese Funktion ist in einem digitalen Speicher 32 der Regelung 30 abgelegt. Die Regelung 30 erfasst die jeweilige Position x₁ und x₂ der beiden Pumpen 14.1, 14.2 und steuert die jeweiligen Antriebe 20.1, 20.2 so an, dass die Position x₁, x₂ einer Soll-Position entsprechen. Daraus ergibt sich der Soll-Durch fluss

It can be seen that the flow

a non-constant function of time t. This feature is in a digital memory 32 the regulation 30 stored. The regulation 30 detects the respective position x ₁ and x _{2 of} the two pumps 14.1 . 14.2 and controls the respective drives 20.1 . 20.2 such that the position x ₁ , x ₂ correspond to a desired position. This results in the desired flow

1 schematically shows that a test object 34 , which could also be referred to as MUT (meter under test), in the manifold 12 is arranged. Optionally, the flow-generating device 10 a control valve 36 by means of which a pressure p ₁₂ in the manifold 12 can be adjusted. In an optionally available fluid reservoir 38 for the fluid 23 On the other hand, an ambient pressure can prevail.

The flow-generating device 10 can a serving 40 have their interior by means of a temperature constant holding device 42 is kept at a predetermined temperature T.

2 shows a further flow-generating device according to the invention 10 instead of the fluid reservoir 38 a third pump 14.3 having. The regulation 30 is not shown for clarity. The pump 14.3 is controlled so that they are the two pumps 14.1 . 14.2 through the manifold 12 through which it contributes to the volume flow itself.

3 shows a flow-generating device according to the invention 10 in which the pistons 18.1 . 18.2 double acting in the respective cylinder 16.1 respectively. 16.2 are arranged. A third two-way backflow valve 44.1 is through the piston 18.1 from the first two-way backflow stop 24.1 disconnects and opens when the two way backflow stop 26.1 opens. So if the piston 18.1 moves, fluid flows 23 either through the first two-way backflow stop 24.1 or through the third two-way backflow stop 44.1 , In addition, either always opens the two-way backflow valve 26.1 or a second two-way backflow valve 46.1 ,

The flow-generating device 10 also has a pressure control 47 on that with the manifold 12 is in fluid communication and a piston 48 own, which runs in a cylinder and of a pressure regulating drive 50 is movable so that the pressure p ₁₂ in the manifold 12 is adjustable.

4 shows a further embodiment of a flow-generating device according to the invention 10 in which every pump 14.1 . 14.2 a respective drive 20.1 . 20.2 having in the form of a rotary drive. The pump 14.1 also has a first piston 18.1a and a second piston 18.1b both via a gearbox 52.1 from a piston rod 54.1 can be moved by the piston rod 54.1 is turned. The position determination device 22.1 determines in this case a rotational position of the piston rod 54.1 , Will the piston rod 54.1 For example, rotated clockwise, the pistons move 18.1a . 18.1b apart and fluid 23 passes through appropriate two-way backflow valves 56.1a and 56.1b in the manifold 12 , At the same time, fluid flows through the two-way non-return valve 58.1c in the area between the two pistons 18.1a . 18.1b ,

Will the piston rod 54.1 Turned in the opposite direction, the fluid flows through the two-way backflow preventer 56.1c out and through the two-way backflow valves 58.1a . 58.1b in the cylinder 16.1 one.

LIST OF REFERENCE NUMBERS

• 10 Flow generating device
• 12 manifold
• 14 pump
• 16 cylinder
• 18 piston
• 20 drive
• 22 Positioning device
• 23 fluid
• 24 Two-way return valve
• 26 Two-way return valve
• 28 inlet port
• 30 regulation
• 32 digital memory
• 34 examinee
• 36 control valve
• 38 fluid reservoir
• 40 wrapping
• 42 Temperature-constant fixture
• 44 Two-way return valve
• 46 Two-way return valve
• 47 pressure control
• 48 piston
• 50 Pressure control drive
• 52 transmission
• 54 piston rod
• 56 Two-way return valve
• 58 Two-way return valve
• V. flow
• 
  Flow through manifold
• x position
• v speed
• a acceleration
• t time
• p pressure
• T temperature

k device constant

Claims (11)

Flow-generating device for generating a predetermined flow

a fluid ( 23 ) with (a) a collecting line ( 12 ) and (b) a first pump ( 14.1 ) - a first cylinder ( 16.1 ), - a first piston ( 18.1 ), in the first cylinder ( 16.1 ), - a first drive ( 20.1 ), by means of which the first piston ( 18.1 ) relative to the first cylinder ( 16.1 ), and - a first position determining device ( 22.1 ) for determining a first position of the first piston ( 18.1 ) relative to the first cylinder ( 16.1 ) and - with the collecting line ( 12 ) for dispensing fluid ( 23 ) to the collecting 12 ), and (c) a second pump ( 14.2 ) - a second cylinder ( 16.2 ), - a second piston ( 18.2 ), in the second cylinder ( 16.2 ), - a second drive ( 20.2 ), by means of which the second piston ( 18.2 ) relative to the second cylinder ( 16.2 ) is movable, and - a second position determining device ( 22.2 ) for determining a second position of the second piston ( 18.2 ) relative to the second cylinder ( 16.2 ) and - with the collecting line ( 12 ) for dispensing fluid ( 23 ) to the collecting 12 ), characterized by (d) a regulation ( 30 ), which is set up for automatically controlling the drives ( 20.1 . 20.2 ), so that the pumps ( 14.1 . 14.2 ) together a predetermined volume flow of fluid ( 23 ) to the collecting 12 ) and (e) a relative measurement uncertainty of the flow-generating device of at most 10 ^-3 . Flow-generating device according to claim 1, characterized in that the control ( 30 ) is arranged for automatically (i) regulating the first position (x ₁ ) of the first piston ( 18.1 ) to a first time-dependent setpoint position, the first time-dependent setpoint position corresponding to a first function (x ₁ (t)) whose second derivative (a ₁ (t)) is continuous after time (t), and (ii) regulating the second position (x ₂ ) of the second piston ( 18.2 ) to a second desired position, the second desired position corresponding to a second function (x ₂ (t)) whose second derivative (a ₂ (t)) is continuous after time (t). Flow-generating device according to claim 2, characterized in that - the third derivative of the first function after the time (t) is continuous and / or - the third derivative of the second function after the time (t) is continuous. Flow-generating device according to one of the preceding claims, characterized in that the control ( 30 ) a digital memory ( 32 ) in which the first function (x ₁ (t)) and the second function (x ₂ (t)) are stored. Flow-generating device according to one of the preceding claims, characterized in that - the first drive ( 20.1 ) is a linear drive, in particular a linear direct drive, and / or - the second drive ( 20.2 ) is a linear drive, in particular a linear direct drive, is. Flow-generating device according to one of the preceding claims, characterized in that the first pump ( 14.1 ) and / or the second pump ( 14.2 ) are double-acting. Flow-generating device according to one of the preceding claims, characterized by at least one test specimen ( 34 ) in the collecting pipeline ( 12 ) is arranged. Flow-generating device according to one of the preceding claims, characterized in that - in the fluid flow direction between the first pump ( 14.1 ) and the collecting line ( 12 ) a two way backflow valve ( 24.1 ) and / or - in the fluid flow direction between the second pump ( 14.2 ) and the collecting line ( 12 ) a two way backflow valve ( 24.2 ) is arranged. Flow production standard with a flow-generating device according to any one of the preceding claims and an associated calibration certificate. Method for generating a predetermined flow

a fluid ( 23 ) with a relative measurement uncertainty of at most 10 ^-3 , in which a flow-generating device ( 10 ) according to one of claims 1 to 8 is used. Method for calibrating a test object ( 34 ), comprising the steps of: (a) arranging a test object ( 34 ) in the collecting line ( 12 ) a flow-generating device ( 10 ) according to one of claims 1 to 8, (b) generating a predetermined flow (V.) a fluid ( 23 ), in particular a liquid, through the collecting line ( 12 ), (c) detecting a measuring flow (V.) by means of the test object ( 34 ) and (d) detecting a deviation between the flow and the measuring flow.

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