DE102013021888A1 - Measuring device for measuring a position of a medium along a path - Google Patents

Abstract

A measuring device (100) for measuring a position of a medium (36) along a path (6), in particular for measuring a level height, with a plurality of measuring electrodes (34) should be precise, wear-free and flexible in the length adjustment without very high technical complexity. This is achieved in that each measuring electrode (34) is connected to a sensor circuit comprising a control input (S4a-S4n) and an output (A4a-A4n), wherein the individual sensor circuits each form a sensor (4-4n) and spatially distributed data carrier chain are interconnected.

Description

The present invention relates to a measuring device for measuring a position of a medium along a path, in particular for measuring a level height, with a plurality of measuring electrodes.

State of the art

For level measurement, the so-called Transsonartechnik is known. It is provided that an electromechanical pulse is fed into a metal rod. The pulse is reflected at the position of a magnet displaceable on the rod and the distance to the magnet is evaluated over the pulse duration.

Another possibility for level measurement is provided by potentiometric systems. The distance is measured by connecting a float with a grinder on a long resistance track. The path is converted to a proportional resistance value or voltage value.

A level measurement is also optically possible. A transit time measurement and / or triangulation is used to evaluate a light beam reflected by the object.

Other methods use a long coil, e.g. B. in print on a long circuit board. By a displaceable metallic object, the quality and inductance are influenced and for this purpose closed on a route.

Another known method is based on a pressure measurement. A pressure sensor on the tank bottom determines the filling level.

Also known are conductive methods in which two electrodes dive into a conductive medium. With increasing filling level or rising coverage, the electrical resistance between the electrodes decreases, as a result of which a fill level can be measured.

Other methods use ultrasound or microwaves. The measurement of the distance to an object is achieved over the life of a transmitted and reflected wave. A filling level is measured over a distance of a wave transmitter arranged above the liquid level to the liquid level.

Furthermore, a submersible probe is known in which all individual capacitive measuring electrodes are arranged in segments along the filling level measuring section. These immersion probes work independently of the media properties and are adjustment-free, but they have the disadvantage that an individual line of each measuring electrode is routed to the evaluation unit. In addition to the increased technical complexity of the required shielded cable routing the maximum feasible length of the measuring section is limited due to the limited number of einbringbarer cables and increasing parasitic disturbances.

Disclosure of the invention

The invention has for its object to provide a measuring device of the type mentioned, which is precise without very high technical complexity and also meets certain hygiene requirements. The measuring device should also not be susceptible to interference, wear-free and flexible in the length adjustment.

This object is achieved by a measuring device with the features of claim 1.

A further object of the invention is to provide a method which makes it possible to measure the positions of a medium along a path in a technically simple manner. This object is solved by the features of claim 7.

By means of the invention, a measuring device or a method has been created by means of which, with little effort, any desired distribution (punctiform or extended) and the intensity of a physical measured variable along a measuring path can be measured electronically. The measured variable can be the expansion of solid objects or fill levels of liquid media or bulk material. Regardless of the type of measured variable, no adjustment by the user must be performed. The length of the measuring section is flexibly adjustable.

By the invention, an electrical displacement or position measurement of objects and levels of media in containers and tanks is possible.

The inventive method is extremely precise, but technically not very expensive. It is not susceptible to interference even with vibrations and impacts.

The method works without a float and without other mechanically moving parts, which is very hygienic and avoids, for example, jamming problems of a moving part or a float.

The measuring device according to the invention requires no complex, sometimes mechanical structures such. B. swimmers or the like. Therefore, the measuring device according to the invention is neither expensive nor susceptible to wear.

The inventive method is not susceptible to interference in comparison to optical methods in extraneous light sources. The color, texture of the object surface does not matter. An adjustment is not required in contrast to other known optical methods.

Also, compared to methods with inductive displacement measurements, the inventive method is not limited to small distances of z. B. 1 cm limited. Any level, even over one meter, can be detected.

Very advantageous is the flexibility achieved in the length adjustment, with virtually no limitation of a maximum possible length.

A measuring probe can be installed practically everywhere. An adjustment is not required. A measurement is also possible regardless of the surface condition of the liquid, the air pressure and the temperature.

With probes of the device according to the invention, the measuring electrodes do not directly touch the liquid to be detected, which is very hygienic. Also, a measurement is possible regardless of the conductivity of the medium.

The invention also avoids that in each case an individual line is required for each sensor element to an evaluation unit.

In a preferred embodiment of the device according to the invention it is provided that each sensor is designed as a capacitive measuring probe. As a result, the measuring method is adjustment-free and relatively insensitive to interference. The capacitive measuring electrodes can be easily integrated in a submersible probe.

Each sensor preferably comprises a capacitive measuring electrode which is connected to the base of a transistor, wherein the emitter or the collector of the transistor is connected to the control input of the sensor and wherein between the output of the sensor and the transistor, a decoupling diode is interposed.

It is particularly advantageous if all outputs of all sensors are connected in parallel to a common measuring line. As a result, few lines are required and it is a pulse train possible, which is easy to evaluate

According to a further advantageous embodiment of the invention a plurality of segmentally arranged individual circuits or segments are present, each individual circuit consists of a combination of a sensor circuit and associated with this circuit delay element, wherein the individual individual circuits are carried out spatially sequentially cascadable. By cascading any length of a submersible probe with little circuit complexity is possible.

Each delay element preferably consists of an RC element and a trigger circuit, in particular a Schmitt trigger circuit. As a result, only a few and inexpensive components are needed.

A further advantageous development of the measuring device according to the invention is distinguished by an embodiment in the form of a rod-shaped immersion probe, wherein the immersion probe comprises a plastic tube in which the individual measuring transducer circuits are arranged with associated measuring electrodes. This solution avoids direct contact of the electrodes with the medium to be measured.

Advantageously, a method for measuring a position of a medium along a path, in particular for measuring a level height, with the measuring device according to the invention, wherein the transducers are activated sequentially by a square wave generator and a chain of time delay elements, wherein the chain of time delay elements parallel to the sensor chain of Sensor is in communication. This approach allows a simple evaluation and measurement of a filling level, especially when a pulse train of the transducer chain is evaluated by a transition between different high pulses is defined as a measurement result.

Alternatively, it is also possible that two transitions are evaluated, so that instead of a level measurement, a position detection of individual objects is possible. A pulse train begins z. B. with small pulses, then follow high pulses and then follow again small impulses. The object is in the range of high impulses.

Brief description of the drawings

Embodiments of the invention are illustrated in the drawings and explained in more detail in the following description.

Show it:

1 a representation of a block diagram of a measuring device according to the invention,

2 a representation of a pulse delay circuit,

3 a circuit diagram with transistor circuits for capacitive sensors,

4 a pulse train at an output of the sensor circuit and an envelope,

5 an arrangement of the measuring device with a dip tube, and

5a -B embodiments of the dip tube.

Embodiments of the invention

1 shows a preferred embodiment of a measuring device according to the invention 100 ,

The measuring device 100 Used to measure a position of a medium 5 ( 1 ) or 36 ( 3 ) along a route 6 For example, to measure a level height with multiple measuring electrodes 34 , Each measuring electrode 34 is connected to a control sensor circuit comprising a control input S4a-S4n and an output A4a-A4n. The individual sensor circuits each form a sensor 4 - 4n and are connected to a spatially distributed Meßwertraufnehmerkette interconnected.

The measuring device 100 includes several sensors 4 . 4a . 4b to 4n representing a spatial arrangement or a chain along the defined route 6 form. The mode of action of each sensor 4 - 4b can in principle be based on different physical principles (capacitive, inductive, optical ...). Preferably, each sensor is 4 - 4n designed as a capacitive transducer. Every sensor 4 . 4a . 4b to 4n So has a control input S4, S4a, S4b to S4n and an output A4, A4a, 4b to A4n, as is in 1 is illustrated.

Every sensor 4 . 4a . 4b to 4n a quasi-delayed pulse is switched on. This is a pulse generator 1 with several chain-like subsequent time delay elements 2 . 2a 3a to 2n intended. The output of the pulse generator is connected to the input of the first sensor. The output of the time delay element 2 is with the input of the sensor 4a etc. connected.

Every sensor 4 . 4a . 4b to 4n is designed so that when a signal change from low to high a short pulse can be generated at its output, which corresponds to a time-limited measurement. The level and / or the pulse duration of the corresponding sensor is dependent on a measured variable 5 that z. B. is a level. All outputs A4, A4a are on a common line 7 on, giving a measuring pulse train 8th is applied to a collection output SL, as in 1 shown. The outputs A4, A4a to A4n of all sensors 4 . 4a . 4b to 4n are on the single or common measuring line 7 connected in parallel.

The chain of time delay elements 1 . 2 . 2a to 2n not only circuit-wise, but also locally parallel to the chain of sensors 4 . 4a . 4b ,

Each output of each time delay element 1 . 2 . 2a to 2n is connected to the input of the subsequent delay stage and the control input S4, S4a, S4b to S4d of the associated sensor 4 . 4a to 4n connected. The structure of all sensors 4 . 4a to 4n and time delays 1 . 2 . 2a to 2n is equal.

This is how the transducers deliver 4 and 4a at full coverage with the measurand 5 a high and wide impulse. At the sensor 4b is a slightly smaller pulse or a narrower pulse with a lower amplitude, as in 1 shown. The sensor 4b is only partially with the measurand 5 covered. A very short and small pulse is present at the outputs A4c to A4n, since the measured variable 5 the sensors 4c to 4n not reached.

The sensors 4 . 4a . 4b to 4n are thus in a chronological order according to the local order along the route 6 via their control inputs S4, S4a, S4b, to S4n consecutively activated.

The activation of the control input S4 of the first sensor 4 is done by the square edge of the control generator 1 , wherein the activation of the control inputs S4a, S4b, to S4n by the downstream chain of the time delay elements 2 . 2a . 2 B , to 2n he follows. The time delay elements 2 . 2a . 2 B , to 2n delay the square edge from the generator 1 Step by step for a constant amount of time, eg. B. each 3 μs per stage.

Thus, the first sensor generates 4 in the chain at its output A4 a first pulse, the second sensor 4a after expiry of the delay time 3a or after 3 μs at its output A4a a second pulse, the third sensor 4b after a further 3 μs, a third pulse, etc. Like the upper diagram in 1 shows deliver the time delay elements 2 . 2a . 2 B to 2n no flanks from high to low. These flanks arise only in the sensors 4 . 4a . 4b to 4n , The individual delay times are in 1 With 3a to 3d characterized.

Every impulse of the episode 8th is clearly a sensor 4 . 4a . 4b to 4n and be Measurement result assigned. The overall distribution of the measured variable 5 along the way 6 with sensors 4 to 4n can thus be at the height and width of the pulses of the episode 8th be read. Furthermore, there is only one parallel running common supply line for the power supply of all components 10 and a common ground line 11 ,

Each of the sensors 4 - 4n is designed such that it is activated by a signal change at its control input S4-S4n short to a measurement and outputs at its output A4-A4n a pulse whose time width and amplitude continuously with an influence of the measured variable 5 or a degree of coverage of a medium 36 increases.

The arrangement according to the invention is segmented along the measuring path or comprises segments 49 , Every segment 49 preferably consists of a combination of a sensor and its associated delay element z. B. 2 + 4 ; 2a + 4a ; 2 B + 4b ; etc. Thus, individual members or segments 49 ( 5 ) of the chain can be spatially cascaded in succession without additional lines having to be laid.

The measuring device 100 So includes several segments arranged like individual circuits or segments 49 , Each single circuit or segment 49 consists of a combination of the sensor circuit and a delay element associated with this circuit 2 - 2n , The individual single circuits or segments 49 are executed spatially sequentially cascadable. An output of a delay element 2 - 2n is connected to an input of a subsequent delay element and a control input S4a-S4n an associated sensor circuit with measuring electrode 34 connected.

Every segment 49 in the chain is clearly an impulse in the episode 8th assigned. The number of segments 49 and thus length of the measuring section 6 is therefore automatically available at any time via the number of pulses as information. The length of the chain or measuring section is highly flexible due to these properties selectable.

2 shows a preferred embodiment of the delay chain for the control signals of the sensor. The delay chain includes the time delay elements 2 . 2a . 2 B to 2n , Each time delay element 2 . 2a . 2 B to 2n includes an RC element with a resistor 21 and a capacitor 22 according to a low-pass filter circuit. The time delay is determined by the charging time of the capacitors 22 in conjunction with a trigger threshold of a Schmitt trigger 20 reached.

3 shows a circuit arrangement of the sensor 4 . 4a . 4b to 4n , These are as capacitive sensor elements, each with the or a single measuring electrode 34 executed. The corresponding measuring electrode 34 is with the base of a transistor 30 connected with resistors 31 . 32 and a blocking diode 33 connected is. The control input S, z. B. S4, is above the resistance 32 with the emitter of the transistor 30 connected.

A fast signal change from low to high at the control input S increases the measuring capacitance between the ground electrode 34 and a medium 36 charged suddenly. The pulse-shaped charging current is in the transistor 30 strengthened and tapped in the collector circle. The diodes 33 provide additional decoupling of the currently inactive sensor elements. The amplified pulse currents of the collector circuits of the transistors 30 be at a common resistance 37 in the voltage pulse train 8th transformed. Due to the low capacitive load many sensor elements on the line 7 be connected in parallel. Instead of PNP transistors, it is also possible to use NPN transistors with a signal change from high to low at the control input. The polarity of the diodes 33 and the impulses of the episode 8th is then swapped accordingly. The resistance 37 would then be between the line 7 and the + supply.

The sensor elements according to 3 can be paired easily with the time delays according to 2 to cascadable segments 49 be combined with little circuit complexity.

4 shows an evaluation of a pulse train to the desired level measurement with an in 5 shown immersion probe leads.

When immersing in a medium 36 are depending on the depth or level 46 all segments below the level line of the medium 36 ( 5 ) covered. All other segments 49 above a level line are uncovered. This is reflected in the pulse train 8th contrary. The covered segments 49 provide high and wide pulses and the uncovered segments provide low and narrow pulses. Important is a transition point 44 on the time axis between high and low pulses. There is the fill level line. Every segment 49 has a known length of z. B. 3 cm. The result of the filling level 46 obtained by the number of pulses to the transition point 44 multiplied by the segment length or by a simple time measurement from a start time 45 to the transition point 44 , Sampling with a sample-and-hold stage becomes an envelope 47 the pulse train 8th generated. The envelope 47 provides minima 41 and maxima 40 the episode 8th as well evaluable sizes available. It will be a threshold voltage 43 as the mean between maxima 40 and minima 41 generated. At the time stamp or transition point 44 at which the envelope 47 the threshold 43 falls below, is the level line. The time from the starting point 45 up to a trigger point 44b corresponds to the filling level or a cover height of a pipe 52 ( 5 ) of the probe.

The measurement according to the invention is independent of the dielectric constant of the medium. Only the relative change ie the transition point from maxima to minima or vice versa is considered. The absolute value of the maxima and minima is secondary here. Therefore, influences such as a temperature drift and media properties play only a minor role. Likewise, the length of the measuring section does not matter, as it exceeds the number of pulses of the sequence 8th the evaluation is always known and can be calculated automatically. As a result, the method is free of adjustment and teach-in processes for the user.

The accuracy of the measurement depends on the number of segments per measuring section. Since there are also transitional regions within a segment in which the output pulse assumes intermediate values in the range between minima and maxima depending on the degree of coverage, an analogous or stepless measurement with virtually any desired resolution is achieved in this way.

5 shows an advantageous embodiment of the arrangement according to the invention in a round ( 5a ) or rectangular ( 5b ) Plastic pipe 52 , The individual segments 49 consisting of one sensor each 4 to 4n and a time delay element 2 to 2n according to 2 and 3 , The sections can with separation points, z. B. by webs on a long, narrow, the plastic tube 52 be accommodated by pulling through the circuit board. In the case of the round design, each segment is provided with a cylindrical measuring electrode 34 ( 5a ), which adhere to the inner wall of the plastic pipe 52 snugly. In this design, the large electrode area achieves maximum signal yield even with very small measuring capacities.

In the rectangular version according to 5b can the electrode 34 be designed as a one-sided copper surface on each PCB segment. In this solution, the mechanical complexity is lower than in the solution according to 5a , Due to the separation points or webs on the long narrow circuit board, the length of the measuring section can be configured by breaking off or separating segments as desired in a production. The pipe 52 is closed at least at one, the medium-facing end and seals the electronics to the medium 36 from. The pulse series in the form of the sequence 8th shows the distribution and intensity of the measured variable at any time 5 along the measuring route 6 at.

The invention is not limited to the examples shown. Another, not shown, embodiment is designed as a distance measurement. The measuring device can with the same arrangement as immersion probe according to 5 be executed. On the tube is then z. B. a sliding metal ring which is mechanically connected to the object of the distance measurement. The position of the metal ring on the pipe 52 is known at any time, because the segment covered by it delivers in the sequence 8th a distinctive impulse with a definite maximum.

In addition to the pure position determination of an object or even several objects on the measuring section 6 With the method according to the invention, in addition, a statement about the extent, in extreme cases even about the nature of these objects possible. If an object covers several segments through its surface, this is in the pulse sequence 8th recognizable and it is an at least one-dimensional statement of the segments facing the surface possible.

An evaluation of the pulse train 8th can be done by a fast microprocessor. If the pulse train is read in by a fast AD converter, a variety of signal evaluation options are the result 8th to disposal. But the pulses can also by analog conditioning, z. B. amplitude-dependent pulse extension can be processed for slow microcontroller.

Claims (11)

Measuring device ( 100 ) for measuring a position of a medium ( 5 or 36 ) along a route ( 6 ), in particular for measuring a level height, with a plurality of measuring electrodes ( 34 ), characterized in that each measuring electrode ( 34 ) is connected to a measuring sensor circuit comprising a control input (S4a-S4n) and an output (A4a-A4n), the individual sensor circuits each having a sensor ( 4 - 4n ) and are connected to a spatially distributed Meßwertraufnehmerkette together. Measuring device according to claim 1, characterized in that each sensor ( 4 - 4n ) is designed as a capacitive probe. Measuring device according to claim 1 or 2, characterized in that the outputs of all sensors ( 4 - 4n ) on a common measuring line ( 7 ) are connected in parallel. Measuring device according to one of the preceding claims, characterized by a plurality of segmented individual circuits or segments ( 49 ), each individual circuit or segment ( 49 ) from a combination of the sensor circuit and a time delay element ( 2 - 2n ), the individual individual circuits or segments ( 49 ) are executed cascading in succession, wherein an output of a delay element with an input of a subsequent delay element and a control input (S4a-S4n) of an associated sensor circuit with measuring electrode ( 34 ) connected is. Measuring device according to claim 4, characterized in that each delay element ( 2 - 2n ) from an RC element ( 20 . 21 ) and a trigger circuit ( 20 ), consists. Measuring device according to one of the preceding claims, characterized by a design as a rod-shaped immersion probe, wherein the immersion probe is a plastic tube ( 52 ), in which the individual sensor circuits are arranged with associated measuring electrodes. Measuring device according to one of the preceding claims, characterized in that each of the sensors ( 4 - 4n ) is designed such that it is activated by a signal change at its control input (S4-S4n) to a measurement and at its output (A4-A4n) emits a pulse whose time width and amplitude continuously with an influence of the measured variable ( 5 ) or a degree of coverage of a medium ( 36 ) increases. Method for measuring a position of a medium ( 5 ) or ( 36 ) along a route ( 6 ), in particular for measuring a fill level ( 46 ), with a measuring device according to one of the preceding claims, characterized in that the sensors are sequentially timed by a rectangular generator and a chain of time delay elements ( 2a -N), the chain of time delay elements ( 2a -N) parallel to the transducer chain of the sensors ( 4a -N). Method according to Claim 8, one of the preceding claims, characterized in that a pulse sequence ( 8th ) of the transducer chain is evaluated by at least one transition between different high pulses is defined as a measurement result. A method according to claim 8 or 9 claims, characterized in that a pulse sampling takes place at an output of the transducer chain by a sample-and-hold stage. Method according to one of claims 8 to 10, characterized in that a pulse evaluation of a present at an output of the Meßwertaufnehmerkette pulse sequence ( 8th ) is done by a microprocessor.

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