DE102019201322A1 - Analog-digital mixed operation for one sensor input - Google Patents

Abstract

The invention relates to a method for communicating an analog sensor (Sa) with a control unit (10), which is set up to continue to communicate with at least one digital sensor (S1, S2, SN). The process has the following steps:
- Connecting the analog sensor (Sa) through which a first current (I1) flows to the control device (10);
- Connecting a predefined number (N) of digital sensors (S1, S2, SN), through which a second current (I2) flows, to the control unit (10), so that the control unit (10) has a total current (Isum), which consists of the first current (I1) and the second current (I2) delivers;
- Determining the second current (I2), which flows through the predefined number (N) of digital sensors (S1, S2, SN), by means of the control device (10);
- Determining the first current (I1) flowing through the analog sensor (Sa) by subtracting the second current (I2) from the total current (Isum).

Description

Field of the Invention

The invention relates to a method for communication of an analog sensor with a control device. The invention further relates to a control device, a program element and a computer-readable medium.

background

Various types of measuring devices and / or sensors are used for level measurement or for level determination, for example impedance limit switches, vibration level switches, pressure sensors, level measurement devices with a high-frequency front end, ultrasonic front end or laser front end.

Summary of the invention

It is an object of the invention to provide an alternative operation of control devices.

This object is achieved by the subject matter of the independent claims. Further developments of the invention result from the subclaims and the following description.

• - Anschließen eines analogen Sensors, durch den ein erster Strom fließt, an das Steuergerät.

Für die Kommunikation eines analogen Sensors kann ein Protokoll und ein Steuergerät verwendet werden, das den Anschluss von digitalen und analogen Sensoren unterstützt. Es kann sich dabei auch um ein anderes standardisiertes und/oder proprietäres Protokoll handeln. Ein Beispiel ist das sog. HART-Protokoll (HART: Highway Addressable Remote Transducer). Dabei kann durch digitale Sensoren, solange diese an dem Steuergerät angeschlossen sind, unabhängig von dem Signalwert des Sensors ein ähnlicher Strom fließen. Durch den analogen Sensor kann während des Betriebs, abhängig von dem Signalwert, ein jeweils unterschiedlicher Strom fließen. Der Strom durch den analogen Sensor wird als erster Strom bezeichnet.

• - Anschließen einer vordefinierten Anzahl von digitalen Sensoren, durch die insgesamt ein zweiter Strom fließt, an das Steuergerät, so dass das Steuergerät einen Summenstrom, welcher aus dem ersten Strom und dem zweiten Strom besteht, liefert. Die vordefinierte Anzahl von digitalen Sensoren kann vor, nach oder gleichzeitig mit dem analogen Sensor angeschlossen werden. Die vordefinierte Anzahl von digitalen Sensoren kann sich während des Betriebs des Steuergeräts ändern. Die vordefinierte Anzahl von digitalen Sensoren kann Null sein.
• - Bestimmen des zweiten Stroms, der durch die vordefinierte Anzahl von digitalen Sensoren fließt, mittels des Steuergeräts. Die digitalen und die analogen Sensoren werden dazu parallel an einem Sensoreingang des Steuergeräts angeschlossen, und es wird für den Sensoreingang bestimmt und/oder parametriert, wie viele digital arbeitende Sensoren angeschlossen sind und welche Grundlast am dem Sensoreingang damit verbunden ist. Das Bestimmen des zweiten Stroms kann ein „Einstellen“ des zweiten Stroms umfassen. Wenn beispielsweise die vordefinierte Anzahl N von digitalen Sensoren einem Servicepersonal bekannt ist, dann kann diese Anzahl dem Steuergerät - z.B. über eine geeignete Schnittstelle - mitgeteilt werden, beispielsweise durch Einschreiben der Anzahl in ein vordefiniertes Register. Das Bestimmen des zweiten Stroms kann, alternativ oder zusätzlich, einen Messvorgang umfassen. Beispielsweise kann über einen vordefinierten Messzeitraum der zweite Strom durch die vordefinierte Anzahl von digitalen Sensoren gemessen werden, z.B. durch Subtraktion eines Ruhestroms durch den analogen Sensor während des Messzeitraums. Das Bestimmen des zweiten Stroms kann, alternativ oder zusätzlich, die Verwendung eines digitalen Protokolls umfassen. Beispielsweise kann in einer Initialisierungssequenz des digitalen Protokolls die Anzahl der angeschlossenen digitalen Sensoren bestimmt und daraus der Stromverbrauch der digitalen Sensoren berechnet und/oder abgeschätzt werden.
• - Bestimmen des ersten Stroms der durch den analogen Sensor fließt, auf Basis des zweiten Stroms und des Summenstroms, beispielsweise durch Subtraktion des zweiten Stroms von dem Summenstrom, gemäß einer Formel $$\text{I1}=\text{Isum}-\text{I}2$$
  
  mit: I1: Strom durch den analogen Sensor; I2: Strom durch alle angeschlossenen digitalen Sensoren, I2 = N · I2i (I2i: Stromverbrauch eines einzelnen digitalen Sensors); Isum: Summenstrom. Der Summenstrom ist der Strom, der an dem Sensoreingang des Steuergeräts gemessen werden kann. Die Subtraktion kann abhängig von der gewählten Methode des Bestimmens des zweiten Stroms sein. Wenn z.B. die vordefinierte Anzahl bekannt ist - beispielsweise mittels Parametrierung oder auf Basis eines digitalen Protokolls -, dann kann daraus der zweite Strom berechnet und von dem Summenstrom subtrahiert werden. Wenn z.B. der zweite Strom bekannt ist und/oder gemessen wurde, dann kann dieser zweite Strom von dem Summenstrom subtrahiert werden. Es kann vor oder während der Auswertung der Werte des analogen Sensors noch eine zusätzliche Korrektur erforderlich sein, z.B. die Addition des Ruhestroms, welcher in dem vordefinierten Messzeitraum durch den analogen Sensor fließt.

A first aspect relates to a method for communicating an analog sensor with a control device, which is set up to continue to communicate with at least one digital sensor. The process has the following steps:

• - Connection of an analog sensor through which a first current flows to the control unit.

A protocol and a control unit that supports the connection of digital and analog sensors can be used for the communication of an analog sensor. It can also be another standardized and / or proprietary protocol. One example is the so-called HART protocol (HART: Highway Addressable Remote Transducer). As long as they are connected to the control unit, a similar current can flow through digital sensors regardless of the signal value of the sensor. Depending on the signal value, a different current can flow through the analog sensor during operation. The current through the analog sensor is called the first current.

• - Connecting a predefined number of digital sensors, through which a total of a second current flows, to the control device, so that the control device delivers a total current, which consists of the first current and the second current. The predefined number of digital sensors can be connected before, after or simultaneously with the analog sensor. The predefined number of digital sensors can change during operation of the control unit. The predefined number of digital sensors can be zero.
• - Determining the second current, which flows through the predefined number of digital sensors, by means of the control device. For this purpose, the digital and the analog sensors are connected in parallel to a sensor input of the control unit, and for the sensor input it is determined and / or parameterized how many digitally working sensors are connected and what basic load is connected to the sensor input. Determining the second stream may include “setting” the second stream. If, for example, the predefined number N of digital sensors is known to service personnel, this number can be communicated to the control unit, for example via a suitable interface, for example by writing the number into a predefined register. As an alternative or in addition, the determination of the second current can comprise a measuring process. For example, the second current through the predefined number of digital sensors can be measured over a predefined measurement period, for example by subtracting a quiescent current through the analog sensor during the measurement period. Determining the second stream may alternatively or additionally include using a digital protocol. For example, the number of connected digital sensors can be determined in an initialization sequence of the digital protocol and the current consumption of the digital sensors can be calculated and / or estimated therefrom.
• - Determining the first current flowing through the analog sensor based on the second current and the total current, for example by subtracting the second current from the total current, according to a formula $$\text{I1}=\text{Isum}-\text{I.}\mathrm{2nd}$$
  
  with: I1: current through the analog sensor; I2: current through all connected digital sensors, I2 = N · I2i (I2i: current consumption of a single digital sensor); Isum: total current. The total current is the current that can be measured at the sensor input of the control unit. The subtraction can depend on the chosen method of determining the second stream. If, for example, the predefined number is known - for example by means of parameterization or based on a digital one Protocol - then the second current can be calculated from this and subtracted from the total current. If, for example, the second stream is known and / or has been measured, then this second stream can be subtracted from the total stream. An additional correction may be necessary before or during the evaluation of the values of the analog sensor, for example the addition of the quiescent current which flows through the analog sensor in the predefined measurement period.

With this method, it is therefore advantageously possible to connect a further, analog working sensor to the sensor input of the control unit in addition to the digitally working sensors. This can increase the flexibility and the range of use of the control unit at comparatively low costs. This is particularly advantageous because at least some analog sensors are less expensive than corresponding digital sensors.

In one embodiment, each of the digital sensors has substantially the same, substantially constant, power consumption. So if e.g. the predefined number of digital sensors is known to the service personnel, whose power consumption is approximately the same and constant and the other currents at the sensor input are negligible, then the product of the number of digital sensors and the power consumption of a single digital sensor is subtracted from the total current subtracted. The predefined number of digital sensors can e.g. be communicated via an interface set up for this purpose.

In one embodiment, the first current is between 4 mA and 20 mA. Some protocols encode e.g. a measured "zero" with 4 mA and a measured "one" with 20 mA; some protocols use inverse coding. One of these protocols can be the so-called HART protocol.

mit: N: ganzzahlige Anzahl der digitalen Sensoren; Isum: Summenstrom; I1r: Ruhestrom des analogen Sensors; I2i: Stromverbrauch eines einzelnen digitalen Sensors.In one embodiment, the second current is estimated by the control device by means of an estimate of the number of digital sensors. This can be done by subtracting the quiescent current of the analog sensor and (rounded) division by the power consumption of a single digital sensor: $$\text{N}\approx \left(\text{Isum}-\text{I1r}\right)/\text{I.}\mathrm{2nd}\text{i}$$

with: N: integer number of digital sensors; Isum: total current; I1r: quiescent current of the analog sensor; I2i: power consumption of a single digital sensor.

In one embodiment, the analog sensor can be disconnected from the control unit during the measurement of the total current. Its quiescent current I1r = 0 and the number of connected digital sensors is obtained by dividing the total current by the current consumption of a single digital sensor.

In one embodiment, each of the digital sensors notifies the control unit when it is connected to or removed from the control unit, so that the control unit knows the number of digital sensors connected to it at all times. This can e.g. by the fact that when the control device and / or the protocol or bus is started up, an initialization sequence of the digital protocol is run through and the number of connected digital sensors is thus determined. From this, the power consumption of the digital sensors can be calculated and / or estimated. If the protocol and / or the interface supports life insertion, then the connection and / or removal of the digital sensors can also be carried out while the control device is operating.

In one embodiment, the control device supports the HART protocol (Highway Addressable Remote Transducer). The method mentioned can thus advantageously be used with a widespread standard protocol.

Another aspect relates to a control device which has an interface which is set up to connect an analog sensor and a predefined number of digital sensors. The control unit is set up to carry out a method as described above and / or below.

Another aspect relates to a program element which, when executed on a processor of a measuring device, instructs the measuring device to carry out the method described above and / or below.

Another aspect relates to a computer-readable medium on which said program element is stored.

Another aspect relates to the use of a control device as described above and / or below for connecting a sensor and / or measuring device for level measurement or for level determination, an impedance limit switch, a vibration limit switch, a pressure sensor, a measuring device with a high-frequency front, ultrasonic front or laser front, and / or a radiometric measuring device.

For further clarification, the invention is described on the basis of embodiments shown in the figures. These embodiments are only to be understood as an example, but not as a limitation.

Figure list

• 1 eine schematische Skizze eines Steuergeräts gemäß einer Ausführungsform;
• 2 ein Verfahren gemäß einer Ausführungsform.

It shows:

• 1 a schematic sketch of a control device according to an embodiment;
• 2nd a method according to an embodiment.

Detailed description of embodiments

1 shows a schematic sketch of a measuring arrangement 20 according to one embodiment. The measurement arrangement 20 has a control unit 10th on, at the input, via a resistor R, an analog sensor Sat and a number N of digital sensors S1 , S2 , ... to SN . In the exemplary embodiment shown, N = 3. Through the analog sensor Sat a first stream flows I1 . Through each of the individual digital sensors S1 , S2 , ... SN a current flows I2i , so in the example I21 , I22 , ... I2N . The currents of the digital sensors add up to a second current I2 . If other currents, such as a leakage current, are negligible, then a total current results Isum to: $$\text{Isum}=\text{I1}+\text{I2}$$

The total current Isum can be measured, for example, by means of the resistor R, which can act as a shunt. The second stream I2 can if the number N and the current I2i are known to be determined to: $$\text{I2}=\text{N}\cdot \text{I2i}$$

If the quiescent current I1r of the analog sensor Sat is known and is kept essentially unchanged over a predefined measurement period, according to Eq. 2 the second stream I2 be determined. If I2 is known, then the measured values of the analog sensor Sat during productive measurements - e.g. during normal operation of the control unit 10th - be evaluated.

2nd shows a flow chart 50 a method according to an embodiment for communication of an analog sensor Sat with a control unit 10th (please refer 1 ). Here is the control unit 10th set up next to the analog sensor Sat with at least one digital sensor S2 to communicate. For this, in one step 51 , the analog sensor Sat to the control unit 10th connected. It flows through the analog sensor Sat a first stream I1 . In one step 52 becomes a predefined number N of digital sensors S1 , S2 , ... SN to the control unit 10th connected. The predefined number N is an integer number and can be 0, 1, 2, .... Through the digital sensors S1 , S2 , .. SN a second stream flows overall I2 . The control unit thus delivers 10th a sum stream Isum which from the first stream I1 and the second stream I2 consists. In one step 53 becomes the second stream I2 certainly. Determining the second stream I2 happens by means of the control unit 10th . Determining the second stream I2 , which is determined by the predefined number N of digital sensors S1 , S2 , SN flows, can be done, for example, by programming a register or by a measurement sequence, for example using the quiescent current I1r of the analog sensor Sat . In one step 54 becomes the first stream I1 determined by the analog sensor Sat flows. This is done by subtracting the second stream I2 from the total current Isum .

In addition, it should be pointed out that “comprehensive” and “having” do not exclude other elements or steps, and the indefinite articles “a” or “an” do not exclude a large number. Furthermore, it should be pointed out that features or steps that have been described with reference to one of the above exemplary embodiments can also be used in combination with other features or steps of other exemplary embodiments described above. Reference signs in the claims are not to be regarded as restrictions.

Reference list

10th

Control unit

20

Measuring arrangement

50

flow chart

51-54

step

I1

first stream

I1r

Quiescent current

I2

second stream

I21, I22, I2N, I2i

Single stream

Isum

Total current of the digital sensors

S1, S2,

SN digital sensors

Sat

analog sensor

Claims (9)

Method for communicating an analog sensor (Sa) with a control device (10), which is set up to continue to communicate with at least one digital sensor (S1, S2, SN), with the steps: connecting the analog sensor (Sa) through which a first current (I1) flows to the control unit (10); - Connecting a predefined number (N) of digital sensors (S1, S2, SN), through which a second current (I2) flows, to the control unit (10), so that the control unit (10) has a total current (Isum), which consists of the first current (I1) and the second current (I2) delivers; - Determining the second current (I2), which flows through the predefined number (N) of digital sensors (S1, S2, SN), by means of the control device (10); - Determining the first current (I1) flowing through the analog sensor (Sa) based on the second current (I2) and the total current (Isum). Procedure according to Claim 1 , wherein each of the digital sensors (S1, S2, SN) has essentially the same, essentially constant, power consumption. Procedure according to Claim 1 or 2nd , the first current (I1) being between 4 mA and 20 mA. Procedure according to Claim 2 or 3rd The second current (I2) is estimated by the control device (10) by means of an estimate of the number (N) of the digital sensors (S1, S2, SN). Method according to one of the preceding claims, wherein each of the digital sensors (S1, S2, SN) notifies the control device (10) when it is connected to the control device (10) or removed again, so that the control device (10) at any time knows the number (N) of digital sensors (S1, S2, SN) connected to it. Method according to one of the preceding claims, wherein the control device (10) supports the protocol Highway Addressable Remote Transducer, HART. Control unit (10), comprising: an interface set up for connecting an analog sensor (Sa) and a predefined number (N) of digital sensors (S1, S2, SN), wherein the control device (10) is set up to carry out a method according to one of the preceding claims. Program element, which, if it is on a control unit (10) Claim 7 is executed, the control device (10) instructs a method according to one of the Claims 1 to 6 perform. Computer-readable medium on which a program element Claim 8 is saved.

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