DE102022126661A1 - Device for monitoring a load - Google Patents

Abstract

A device (100) for monitoring a load (102) of an analog output (114) is described. The device (100) comprises a signal converter (110) which has an input (112) and an analog output (114). The signal converter (110) can output an output signal at the analog output (114) depending on an input signal present at the input (112), wherein the output signal is a current or a voltage. A control unit (120) of the device (100) can detect the voltage in addition to the current as an output signal or the current at the analog output (114) in addition to the voltage as an output signal and determine the load (102) from the output signal in combination with the detected current or the detected voltage, and output an indication (104; 106) on the basis of the determined load (102).

Description

The invention relates to a device for monitoring a load, in particular at an analog output.

Traditionally, a user is provided with a data sheet specification of the permissible load on the analog output in order to correctly select or adjust the output load connected to the analog output of the connected downstream circuit. This is of particular importance for industrial signal converters with an analog output for a voltage signal, i.e. a voltage output in the range 0...10 V, for example, or a current signal, i.e. a current output in the range 0...20 mA, for example, because failure to comply with the data sheet specification may result in measurement errors, faulty control or a complete failure of the output signals, depending on the application.

For example, a voltage output can generally be operated from 10 kΩ and a current output up to 500 Ω or 700 Ω. The respective limit of the load results from the internal structure of the signal converter. In order to be able to drive a load of 10 kΩ with a voltage output at full output of 10 V, the output must be able to drive a current of 1 mA. A current output, which has its maximum value of 20 mA, must be able to build up a voltage of 10 V with a load of 500 Ω.

If these values are not adhered to, incorrect measured values and non-linearities will occur in the upper area of the characteristic curve for the relationship between the input signal and the output signal of the signal converter. The fact that a measured value or the associated output signal is incorrect due to a load connected during installation of a system is usually only noticed when the system is put into operation. Even if the connected load changes in an inadmissible way due to aging or a defect in the system, this cannot be detected preventively when the system is in operation.

The invention is therefore based on the object of specifying a technology for determining and/or monitoring a load connected to an analog output. Alternatively or additionally, the object is to achieve monitoring of the connected load with as little additional effort as possible.

The problem is or the problems are solved with the features of the main claim. Useful embodiments and advantageous further developments of the invention are specified in the dependent claims.

Embodiments of the invention are described below with partial reference to the figures.

According to one aspect of the device, a device for monitoring a load of at least one analog output is provided. The device comprises a signal converter having at least one input and at least one analog output. The signal converter is designed to output an output signal at the analog output depending on an input signal present at the input. The output signal is (for example either) a current or a voltage. The device further comprises a control unit which is designed to detect the voltage at the analog output in addition to the current as an output signal or the current at the analog output in addition to the voltage as an output signal. Furthermore, the control unit is designed to determine the load from the output signal in combination with the detected current or the detected voltage, and to output an indication based on the determined load.

By combining the control unit's knowledge of the output signal (for example as a target value) with the detection (for example measurement) of the current or voltage as the actual value complementary to the output signal for determining (for example calculation) the load, embodiments enable the monitoring of the load connected to the analog output by means of the indication. Preferably, the detection of the actual value complementary to the output signal is sufficient to determine the load with the existing knowledge of the output signal and the computing capacity of the control, so that embodiments of the device achieve the monitoring of the load with as little additional effort as possible.

The signal converter can be a measuring transducer, for example according to the standard DIN1319 In particular, the signal converter can be a measuring transducer (for example a current transformer or a voltage transformer), a measuring amplifier (for example an isolation amplifier), or a measuring converter (for example with a digital input and at least one analog output).

The load can be a resistance connected to the analog output (for example a total resistance of connecting cables and circuit connected to the analog output) or correspond to such a resistance. Furthermore, the load can optionally only include an effective component of the connected resistance and/or no apparent resistance.

The control unit can comprise a microcontroller, for example for determining (in particular calculating) the burden and/or for outputting the indication. Since the computational effort for determining the burden essentially comprises a division, embodiments of the device can achieve the monitoring of the burden without increasing the performance of the microcontroller.

The control unit can be a control unit. For example, the control unit can act as a control unit and regulate the output signal (for example, measure it and correct it in response to a deviation from a target value).

The specific burden can also be called connected burden.

The control unit (e.g. according to the device aspect) can detect the current or voltage at the analog output in an analog domain and/or as a measured value. The current detected at the analog output or the voltage detected at the analog output can be measured in the analog domain and/or detected as an actual value. An existing analog input of the control unit can advantageously be used for this purpose.

Alternatively or additionally, the output signal can be available to the control unit in a digital domain and/or as a target value. The output signal can be recorded or provided in a digital domain and/or as a target value of the signal converter (e.g. as a control variable of the control unit or as a reference variable of the output signal as a controlled variable of the control unit).

This means that a measuring unit for the analog signal can be omitted and/or the load can be determined in the digital domain (for example by calculating a division of voltage and current). Advantageously, the output signal can be available without using an analog-digital converter (technical term: "analog to digital converter" or ADC) of the control unit to determine the load. In a first example, the output signal can be provided to the control unit independently of the analog output or (in the signal processing direction) before the analog output (for example transmitted by the signal converter). In a second example, the control unit can be designed to determine the target value of the output signal based on the input signal.

The control unit (e.g. according to the device aspect) can further output a limit value of the burden. Alternatively or additionally, the output indication can depend on a comparison of the limit value of the burden with the specific burden. Alternatively or additionally, the output indication can output a residual value of the burden, for example a difference between the limit value of the burden and the specific burden. The residual value of the burden can also be referred to as a reserve of the burden. Embodiments can thereby reduce the frequency of the output of the indication or only indicate the burden in relevant situations.

The burden limit may be an upper limit (i.e., a peak or maximum) when current is the output signal. The alert may be issued when the specified burden exceeds an upper burden threshold. The upper burden threshold may be 75% to 90% of the upper burden limit.

Alternatively or additionally, the limit of the burden, when the output signal is voltage, may be a lower limit (i.e., minimum value or minimum). The indication may be issued when the specific burden falls below a lower burden threshold. The lower burden threshold may be 110% to 125% of the lower limit of the burden.

The limit value or both limit values or one or both burden threshold values may be stored in a memory (for example in a volatile memory or a read-only memory) of the control unit. For example (preferably in a signal converter switchable between current and voltage as the output signal) both the upper limit and the lower limit may be stored.

The signal converter (e.g. according to the device aspect) can output the current as an output signal at the analog output, and the control unit can output the indication when the specific burden is greater than an upper limit of the burden. Alternatively or additionally, the upper limit of the burden can correspond to a maximum value of the voltage (e.g. the largest voltage that the signal converter can build up) in order to drive or output a maximum value of the current as an output signal (e.g. an upper limit of a current interval of the output signal). As a result, embodiments of the device can output the targeted indication of the burden at this analog output or one of the analog outputs and/or point out a precise fault location in a long or complex chain of control signals.

The indication can be issued before the signal converter enters a non-linear region (for example with regard to the output signal as a function of the input signal). For example, the indication can be issued if the voltage for driving the current as an output signal is less than the maximum value of the voltage. For example, the indication can be issued if the voltage for reaching the current as an output signal is less than the maximum value of the voltage and/or greater than a voltage threshold. Embodiments of the device can thus indicate a faulty wiring of the analog output (for example a broken cable or a loose terminal) before a faulty output signal is issued or before damage to the system controlled by the output signal occurs. The voltage threshold can be 75% to 90% of the maximum value of the voltage.

The signal converter (e.g. according to the device aspect) can output the voltage as an output signal at the analog output, and the control unit can output the indication when the determined burden is less than a lower limit of the burden. Alternatively or additionally, the lower limit of the burden can correspond to a maximum value of the current (e.g. the largest current that the signal converter can drive) in order to build up or output a maximum value of the voltage as an output signal (e.g. an upper limit of a voltage interval of the output signal).

The indication can be issued before the signal converter enters a non-linear region (for example with regard to the output signal as a function of the input signal). For example, the indication can be issued if the current to reach the voltage as an output signal is less than the maximum value of the current and/or greater than a current threshold. Embodiments of the device can thus indicate a faulty state of the analog output (for example a short circuit or moisture) before a faulty output signal is issued or before damage to the system controlled by the output signal occurs. The current threshold can be 75% to 90% of the maximum value of the current.

The device (e.g. according to the device aspect) can further comprise a switch for disconnecting the connected load from the analog output. The control unit can further be designed to actuate (e.g. control) the switch for disconnection if the specific load violates the limit value of the load, for example falls below the lower limit or exceeds the upper limit. Embodiments of the device can thereby avoid (e.g. thermal) damage to the signal converter and/or the downstream circuit and/or a fire hazard due to a defective electrical connection at the analog output.

The switch (e.g. according to the device aspect) can comprise at least one field-effect transistor and/or an electromechanical relay. Alternatively or additionally, the switch can be arranged electrically between the analog output of the signal converter and a terminal for connecting the load. For example, the switch can be designed to optionally electrically connect and electrically disconnect the at least one pole of the analog output of the signal converter and a terminal assigned to the respective pole. The field-effect transistor can enable rapid disconnection in order to avoid thermal damage to the smallest masses in electronic components. The electromechanical relay can ensure galvanic isolation, for example if an overvoltage in the circuit connected downstream of the analog output is the cause of the impermissible load.

The device (eg according to the device aspect) can further comprise a memory for storing the determined burden. Alternatively or additionally, the control unit can further be designed to determine the burden at different times (eg in a time series) and/or for different output signals, and optionally to store the time series and/or a (weighted and/or temporally moving) mean or median of the determined burdens in the memory. Embodiments of the device can distinguish between gradual aging and a defect that has occurred suddenly by reading the memory during troubleshooting.

The control unit (e.g. according to the device aspect) can be designed to output the indication or a further indication if the determined burden deviates from the stored burden and/or changes over time (e.g. changes in the time series). Embodiments can thus apply a relative and/or self-adaptive criterion for monitoring the burden (e.g. for outputting the indication) and/or enable (e.g. long-term) monitoring of the burden, for example without predetermination or without input or without adjustment of the (upper and/or lower) burden threshold value of the burden (exceeding or falling below which triggers the output of the indication).

The control unit (e.g. according to the device aspect) may be configured to output the indication or a further indication of a short circuit or moisture at the analog output if the determined burden is less than a predetermined minimum value (e.g. the lower burden threshold) and/or is less than the stored burden (e.g. by at least 10% or 25%) and/or decreases in the time series (e.g. by at least 50% in a predetermined time, e.g. one second).

Alternatively or additionally, the control unit (e.g. according to the device aspect) can be designed to output the indication or a further indication of a cable break or a loose electrical connection (e.g. a faulty terminal point) at the analog output if the determined burden is greater than a predetermined maximum value (e.g. the upper burden threshold value) and/or is greater than the stored burden (e.g. by at least 10% or 25%) and/or increases in the time series (e.g. by at least 50% in a predetermined time, e.g. one second) or alternates (e.g. periodically and/or between two different burden values).

The device (e.g. according to the device aspect) may further comprise a user interface for outputting the determined burden, the limit or limits (e.g. the upper limit and/or the lower limit), the indication, the further indication and/or the residual value of the burden.

The user interface for outputting the information can output the information locally or via a network interface. For local output, the user interface can comprise a signal lamp (for example an LED), an acoustic signal generator (for example a loudspeaker) and/or a graphic display (for example for text-based output of the information). Alternatively or additionally, the network interface can comprise a wired network connection (for example Ethernet) or a wireless network connection. The wireless network connection (for example for a radio network) can be designed in accordance with the IEEE 802.11 (Wi-Fi) standard or a radio access technology of the “Third Generation Partnership Project” (3GPP), for example in accordance with “Long Term Evolution” (LTE) or the fourth mobile communications generation (4G) or in accordance with “New Radio” (NR) or the fifth mobile communications generation (5G).

Alternatively or additionally, the control unit may comprise a web server. The user interface may comprise a web-based management system.

The control unit (e.g. according to the device aspect) may be further configured to output the determined burden and/or an allowable interval for the burden, optionally by means of a graphical display and/or a web server of the device. The allowable interval may comprise the lower limit of the burden and/or the upper limit of the burden. The determined burden and/or the residual value of the determined burden may be displayed in the interval.

For additional detection of the current or voltage (ie complementary to the output signal), the control unit can include an analog input that is electrically connected to a measuring point of the signal converter. rically conductively connected. Alternatively, a digital input of the control unit can be coupled to the measuring point via an analog-digital converter (DAC) of the control unit or the signal converter.

The signal converter (e.g. according to the device aspect) can have a selection signal input. The signal converter can be designed to output either the current or the voltage as the output signal at the analog output depending on a selection signal present at the selection signal input (e.g. detected). In other words, the signal converter can be controllable (e.g. switchable) according to the selection signal, so that the analog output of the signal converter is either a voltage output or a current output.

The selection signal can be output to the selection signal input of the control unit (for example a digital output of the control unit). The selection signal can be output to the selection signal input of the control unit (for example a digital output of the control unit). The control unit can thus be designed to use the measurement voltage detected at the measuring point as either the current or the voltage at the analog output to determine the burden, complementary to the output signal (according to the selection signal).

The control unit can be designed to detect, at the same measuring point, depending on the selection signal, either the voltage as an output signal in addition to the current or the current as an output signal in addition to the voltage.

The invention is explained in more detail below with reference to the accompanying drawings using preferred embodiments which can optionally be combined with one another.

• 1 ein schematisches Blockdiagramm einer Vorrichtung zur Überwachung einer Bürde mindestens eines Analogausgangs gemäß einem ersten Ausführungsbeispiel;
• 2 ein schematisches Schaltbild eines Signalgenerators gemäß einem zweiten Ausführungsbeispiel, der in jedem Ausführungsbeispiel der Vorrichtung zur Überwachung einer Bürde einsetzbar ist;
• 3 ein schematisches Blockdiagramm der Vorrichtung zur Überwachung einer Bürde gemäß einem dritten Ausführungsbeispiel mit Eingangs- und Ausgangsanschlüsse, die in jedem Ausführungsbeispiel der Vorrichtung zur Überwachung einer Bürde einsetzbar sind;
• 4 schematisch eine Anzeige zur Ausgabe der bestimmten Bürde und einer Reserve gemäß einem vierten Ausführungsbeispiel, die in jedem Ausführungsbeispiel der Vorrichtung zur Überwachung einer Bürde einsetzbar ist für ein Stromsignal; und
• 5 schematisch eine Anzeige zur Ausgabe der bestimmten Bürde und einer Reserve gemäß einem fünften Ausführungsbeispiel, die in jedem Ausführungsbeispiel der Vorrichtung zur Überwachung einer Bürde einsetzbar ist für ein Spannungssignal.

Show it:

• 1 a schematic block diagram of a device for monitoring a load of at least one analog output according to a first embodiment;
• 2 a schematic circuit diagram of a signal generator according to a second embodiment, which can be used in any embodiment of the device for monitoring a burden;
• 3 a schematic block diagram of the device for monitoring a burden according to a third embodiment with input and output terminals that can be used in any embodiment of the device for monitoring a burden;
• 4 schematically shows a display for outputting the determined burden and a reserve according to a fourth embodiment, which can be used in any embodiment of the device for monitoring a burden for a current signal; and
• 5 schematically shows a display for outputting the determined burden and a reserve according to a fifth embodiment, which can be used in any embodiment of the device for monitoring a burden for a voltage signal.

1 shows a schematic block diagram of a device for monitoring a load of at least one analog output. The device is generally designated by reference numeral 100. The device 100 comprises a signal converter 110 which has at least one input 112. The input 112 can detect (for example receive) input signals from an input device 116.

The input devices 116 can be sensors or isolation transformers. Examples of the sensors 116 are voltage sensors for monitoring the function of a power supply and current sensors for monitoring the load of a consumer (for example an actuator). The input signal can be an analog signal or a digital signal.

The signal converter 110 can comprise the at least one analog output 114 or can be electrically connected to the at least one analog output 114 on the output side. The signal converter 110 can output an output signal at the analog output 114 depending on an input signal present at the input 112.

For example, the signal converter 110 can comprise an analog-to-digital converter 206 (also: analog-to-digital converter or in technical terms: “analog to digital convertor” or ADC), which converts the input signal for further processing in a digital domain by a processing unit 208 of the signal converter 110. The signal converter 110 can further comprise a digital-to-analog converter (in technical terms: “digital to Analog Convertor" or DAC) 202, which generates a control signal 201 for controlling a signal generator 200. The signal generator 200 generates the output signal for the analog output 114.

The output signal can be a current signal or a voltage signal. Each analog output 114 outputs the respective output signal to an output device 118. Examples of the output devices 118, which are also referred to as subsequent circuits, are actuators, isolation transformers, impedance adjustments and controllers or their inputs. A typical example of a controller is a programmable logic controller (PLC). The load is a property of the output device 118 electrically connected to the respective output 114 of the device 100 and/or the wiring between the output 114 and the output device 118.

While in 1 the operation of the analog output 114 as a voltage output is shown, the same or corresponding features of the device 100 can be provided for the (e.g. switchable) operation of the analog output as a current output 114.

The signal converter 110 can also be communicatively connected to a control unit 120. For example, the control unit 120 detects the target value of the output signal (here: the voltage U _target ). Alternatively or additionally, the control unit 120 specifies the target value of the output signal. For example, the control unit transmits the control signal corresponding to the output signal to the DAC 202 of the signal converter 110 or to the signal generator 200.

The control unit 120 detects the voltage (for example in a switchable state for the current signal) at the analog output 114 in addition to the current as an output signal or the current (for example in a switchable state for the voltage signal) in addition to the voltage as an output signal.

As a result, the control unit 120 calculates the burden from the output signal in combination with the measured current (I _mess , e.g. as in 1 shown) or the measured voltage (U _mess ).

The control unit 120 may further include or be in communication with a user interface 140 (e.g., a display) such that the control unit 120 may output an indication via the user interface 140 based on the determined burden. The user interface 140 may include, for example, a graphical user interface (e.g., a display) or a web interface to display the determined burden 102 and/or the indication 104, 106 (e.g., a message) to a user.

The user interface 140 may further receive an instruction from the user indicating whether current or voltage should be selected as the output signal. Alternatively or additionally, the control unit 120 may switch between current and voltage as the output signal.

The signal converter 110 can comprise a signal generator 200, which optionally generates the voltage U or the current I as an output signal. The signal converter 110 comprises a selection signal input for a selection signal that specifies whether the control signal 201 is interpreted as a specification for the voltage U and the current I and is output at the analog output 114.

The limit value of the load R, for example the upper limit R _max of the load for a current output or the lower limit R _min of the load for a voltage output, can be determined by design for the device 100 or in the manufacture of the device 100. During operation and/or for the operation of the device 100, a corresponding limit value of the control signal 201 or the output signal can be derived from the limit value of the load. Alternatively or additionally, the limit value for the measured current can be derived directly from the voltage as a target value or output signal.

2 shows a schematic circuit diagram of a signal generator 200 that can be switched between a current signal and a voltage signal, according to a second embodiment. The signal generator 200 can be used in any embodiment of the device 100.

In order for the voltage to be the output signal at the analog output 114, the selection transistors 155 are switched to conduction (ie closed) in accordance with the selection signal at the selection signal input 154. As a result, the lower pole 114-2 of the analog output 114 is electrically connected to ground. The voltage at the pole 114-1 of the analog output 114 is the output signal and is fed via the feedback 156 to the second input of the operational amplifier is controlled according to the control signal present at the first input 201 of the operational amplifier.

In order for the current to be the output signal at the analog output 114, the selection transistors 155 are switched to blocking (i.e. open) in accordance with the selection signal at the selection signal input 154. The current flowing between the poles 114-1 and 114-2 of the current output 114 leads to a proportional voltage drop with respect to ground at the measuring resistors 152 (and thus at the lower pole 114-2 of the analog output 114), which as feedback 158 to the second input of the operational amplifier regulates the current as an output signal in accordance with the control signal 201 present at the first input 201 of the operational amplifier.

The control unit 120 (for example a microcontroller as part of the control unit 120) uses the selection signal to determine whether either a current signal or a voltage signal is output as an output signal at the analog output 114. For example, with a selection signal of 0 V at the selection signal input 154, the output signal is a current signal (because the bipolar NPN transistor pulls the common gate voltage of the two selection transistors 155 as self-blocking field effect transistors to ground and thus blocks them). With a positive selection signal (for example of 5 V) at the selection signal input 154, the output signal is a voltage signal because the selection transistors are switched to conduct.

The second embodiment of the device 100 for monitoring a load can 2 schematically shown signal generator 200. The signal generator 200 can receive a control voltage 201 (for example a PWM command) from the DAC 202 of the device 100 at the first (positive) input of the operational amplifier.

The signal generator 200 includes measuring resistors 152 for measuring the current as an output signal, i.e. for measuring the current at the analog output 114 in its function as a current output. For example, a measuring resistor of 50 ohms can result in a voltage drop of 1 V at a current of 20 mA.

In one embodiment, the control unit 120 uses the selection signal to select the analog output 114 as the current output, i.e. the current I _desired as the output signal. The current I _desired is specified (i.e. guided and regulated) by the control voltage at the input 201. To calculate the load 102, it is necessary to measure the voltage U _measured at the analog output 114 at a measuring point 160 of the signal generator 200. For this purpose, the measuring point 160 can be connected to an analog input of the control unit 120. Alternatively, the control unit 120 or the signal converter 110 (for example the signal generator 200) can include an additional analog-digital converter (ADC) 204, which is connected on the input side to the measuring point 160 and on the output side to a digital input of the control unit 120. The ADC 204 converts the voltage U _mess of the analog output 114 into a digital value and transmits it to the control unit 120 (e.g. a microcontroller).

In each embodiment, the output signal may correspond to the (for example pulse width modulated, PWM) control signal 201 as a specification. Alternatively or additionally, the current that flows internally for feedback to the operational amplifier may be known to the control unit 120 and calculated out by it.

In a variant of each embodiment of the device 100, the analog output 114 is a current output, for example with the value range (or interval) of 0...20 mA. For example, the control unit 120 controls the analog output 110 to output a current with the maximum value of the interval (e.g. 20 mA) to determine the burden.

Table I below shows an example of the output signal as a current signal (for example of 20 mA), the voltage measured at measuring point 160 and the burden calculated based on Ohm's law.

A circuit-related offset of the burden is, for example, 50 to 60 Ω. The internal resistance of 50 to 60 Ω (for example, a large part of 50 Ω of the internal resistance of 60 Ω) is dropped across the measuring resistor 152 to determine the current as an output signal. The circuit-related offset of the device 100 can be measured by test experiments or calculated directly or by simulation software (e.g. LT-Spice).

The control unit 120 can determine the burden from the current I as output signal, the measured voltage U at the analog output 114 and, if applicable, the offset, for example according to the relationship: $$R=\raisebox{1ex}{$U$}\!\left/ \!\raisebox{-1ex}{$I$}\right.-60\Omega$$

Here, U is the voltage at the measuring point 160, I is the current signal according to the control signal 201 (e.g. PWM signal) as specification 201 which is to be output as output signal.

The value of 60 Ω given in formula F1 is an example of the circuit-related offset. Table I I _OUT (controlled by PWM) U _OUT (measuring point) Burden (calculated) Condition 20.00mA 1.2V 0Ω OK 20.00mA 1.4V 10Ω OK 20.00mA 3.2V 100Ω OK 20.00mA 5.2V 200Ω OK 20.00mA 7.2V 300Ω OK 20.00mA 9.2V 400Ω OK 20.00mA 11.2V 500Ω OK 20.00mA 11.8V 530Ω OK 20.00mA 11.9V 535Ω OK 20.00mA 12.0V 540Ω OK 20.00mA 12.2V 550Ω OK 20.00mA 12.4V 560Ω OK 20.00mA 12.6V 570Ω Burden in the border area 19.99mA 12.8V 580Ω Burden in the border area 19.70mA 12.8V 590Ω Burden too great 19.40mA 12.8V 600Ω Burden too great

The relationship according to formula F1 only applies up to a limiting voltage (i.e. the maximum value of the voltage) of 12.8 V at the measuring point 160. From then on, a valid output of the current signal (e.g. for a measurement or control) is no longer possible and the control unit 120 issues the information (e.g. an alarm message) via the user interface 140 (e.g. a web-based management, WBM).

The device 100 (or the analog output 114 as a function of the input 112) can operate linearly up to a voltage of 12.6 V at the analog output 114. This results in a maximum load of 570 Ω. From the upper limit of 570 Ω, the device 100 behaves non-linearly for the maximum value of the current signal (for example, for 20 mA) and outputs incorrect measured values or control currents from this limit. Since the current is specified as an output signal (i.e. as a target value) or is regulated by means of the signal generator (for example, by means of the operational amplifier as a controller), the load connected to the outside of the device 100 (i.e. the load), as already mentioned above, is calculated from the voltage U at the measuring point 160. The maximum value of the load (i.e. the upper limit of the load) can be determined in production. The upper limit can possibly be derived directly from the voltage U.

Table II shows another example of the calculated burden based on Ohm's law, the measured voltage at the first measuring point 160 and the output signal as current (here: 10 mA). The device 100 can operate linearly up to 12.9 V. This results in an upper limit of the burden of 1230 Ω. From the limit of 1230 Ω for the 10 mA current, the device behaves non-linearly and gives incorrect measured values or too low current signals. Table II I _OUT (controlled by PWM) U _OUT (measuring point 1) Burden (calculated) was standing 10.00mA 0.6V 0Ω OK 10.00mA 0.7V 10Ω OK 10.00mA 1.8V 120Ω OK 10.00mA 2.6V 200Ω OK 10.00mA 3.6V 300Ω OK 10.00mA 4.6V 400Ω OK 10.00mA 9.6V 900Ω OK 10.00mA 10.6V 1000Ω OK 10.00mA 11.6V 1100Ω OK 10.00mA 12.6V 1200Ω In the border area 10.00mA 12.9V 1230Ω In the border area 9.96mA 13.1V 1250Ω Burden too great 9.82mA 13.1V 1269Ω Burden too great 9.60mA 13.1V 1300Ω Burden too great 8.90mA 13.1V 1409Ω Burden too great

In addition to calculating the burden, the device 100 (e.g., the control unit 120) may display the determined value of the burden or a residual value (also: reserve) of the burden to the user in the user interface 140, e.g., in web-based management (WBM), and/or compare or offset it with the upper limit of the device 100.

For example, after switching on the device 100, the externally connected load is determined as described above (preferably by outputting the maximum value of the current as an output signal in the interval) and stored in a memory for further use (e.g. during operation of the device 100) until the next calculation.

• - Die Steuereinheit 120 gibt das Wahlsignal für ein Stromsignal aus, beispielsweise in Reaktion auf eine Eingabe eines Benutzers.
• - Der Analogausgang 114 ist ein Stromausgang und (beispielsweise über das Steuersignal 201 als PWM-Stufe) so eingestellt, dass 20 mA fließen sollten.
• - Die Steuereinheit 120 ermittelt einen internen Spannungsabfall (z. B. durch Simulationssoftware oder Auslesen aus einem Speicher).
• - Die hierfür an den Klemmen 114-1 und 114-2 des Analogausgangs 114 notwendige Spannung ist 9,2 V. Dieser Wert kann sich Zusammensetzen aus 8 V und einem internen Spannungsabfall von 1,2 V (der beispielsweise in einer Gleichung herausgerechnet wird).
• - Die bestimmte (beispielsweise berechnete) Bürde ist somit R = U/I = (9,2 V - 1,2V) / 20 mA, also R = 400 Ω.
• - Die Steuereinheit 120 stellt fest, dass die bestimmte Bürde im mit OK markierten Bereich der Tabelle I ist.
• - Die Steuereinheit 120 gibt einen Hinweis an der Benutzerschnittstelle 140 aus, dass die bestimmte Bürde zulässig (d. h. in Ordnung oder OK) ist.

Example 1: The control unit 120 can perform at least one of the following steps.

• - The control unit 120 outputs the selection signal for a power signal, for example in response to a user input.
• - The analog output 114 is a current output and is set (for example via the control signal 201 as a PWM stage) so that 20 mA should flow.
• - The control unit 120 determines an internal voltage drop (e.g. by simulation software or reading from a memory).
• - The voltage required for this at terminals 114-1 and 114-2 of the analog output 114 is 9.2 V. This value can be made up of 8 V and an internal voltage drop of 1.2 V (which is calculated out in an equation, for example).
• - The determined (e.g. calculated) burden is therefore R = U/I = (9.2 V - 1.2V) / 20 mA, i.e. R = 400 Ω.
• - The control unit 120 determines that the determined load is in the range marked OK in Table I.
• - The control unit 120 issues an indication on the user interface 140 that the determined load is permissible (ie, OK).

• - Die Steuereinheit 120 gibt das Wahlsignal für ein Stromsignal aus, beispielsweise in Reaktion auf eine Eingabe eines Benutzers.
• - Der Analogausgang 114 ist als Stromausgang so eingestellt, dass 20 mA fließen sollten.
• - Die Steuereinheit 120 ermittelt einen internen Spannungsabfall (z.B. durch Simulationssoftware oder Auslesen aus einem Speicher).
• - Die hierfür an den Klemmen notwendige Spannung ist 12,6 V, zusammengesetzt aus 11,4 V und dem internen Spannungsabfall von 1,2 V. Letzteres kann in der Gleichung F1 herausgerechnet werden.
• - Die bestimmte (beispielsweise berechnete) Bürde ist somit R = U/I = (12,6 V - 1,2 V) / 20 mA, also R = 570 Ω.
• - Die Steuereinheit 120 stellt fest, dass die bestimmte Bürde im Grenzbereich gemäß Tabelle I ist.
• - Die Steuereinheit 120 gibt an die Benutzerschnittstelle 140 den Hinweis aus, dass die bestimmte Bürde im Grenzbereich ist.

Example 2: The control unit 120 can perform at least one of the following steps.

• - The control unit 120 outputs the selection signal for a power signal, for example in response to a user input.
• - The analog output 114 is set as a current output so that 20 mA should flow.
• - The control unit 120 determines an internal voltage drop (e.g. by simulation software or reading from a memory).
• - The voltage required for this at the terminals is 12.6 V, composed of 11.4 V and the internal voltage drop of 1.2 V. The latter can be calculated in equation F1.
• - The determined (e.g. calculated) burden is therefore R = U/I = (12.6 V - 1.2 V) / 20 mA, i.e. R = 570 Ω.
• - The control unit 120 determines that the determined burden is within the limit range according to Table I.
• - The control unit 120 outputs to the user interface 140 the indication that the determined load is in the limit range.

• - Der Analogausgang als Stromausgang ist so eingestellt, dass 20,0 mA fließen sollten (tatsächlich fließen nur 19,7 mA).
• - Die an den Klemmen notwendige Spannung ist 11,6 V + interner Spannungsabfall von 1,2 V (wird in der Gleichung herausgerechnet) = 12,8 V.
• - Die berechnete Bürde ist somit R = U/I = (12,8 V - 1,2 V) / 19,7 mA, also R = 588 Ω > Obergrenze der Bürde.
• - Die Bürde ist zu groß (beispielsweise im nichtlinearen Bereich) gemäß Tabelle I.
• - Die Steuereinheit 120 sendet einen Hinweis, dass die bestimmte Bürde zu groß oder unzulässig ist an die Benutzerschnittstelle 140.

Example 3:

• - The analog output as a current output is set so that 20.0 mA should flow (actually only 19.7 mA flows).
• - The voltage required at the terminals is 11.6 V + internal voltage drop of 1.2 V (subtracted from the equation) = 12.8 V.
• - The calculated burden is therefore R = U/I = (12.8 V - 1.2 V) / 19.7 mA, i.e. R = 588 Ω > upper limit of the burden.
• - The load is too large (for example in the non-linear region) according to Table I.
• - The control unit 120 sends an indication that the determined load is too large or inadmissible to the user interface 140.

In this case, the device 100 can apply up to 12.8 V to the terminals 114-1 and 114-2 to drive the current of 20 mA. It should be noted that this is already the impermissible range of the device 100 (and should be avoided at all costs, for example). The device 100 should issue a message from a voltage of 12.6 V to signal that the load is impermissibly high. The device can display this to the user on the user interface 140 (for example via the WBM), optionally together with a calculated remaining load (residual value or reserve), which would also be possible (i.e. connectable).

In the above example case, the limit would already have been reached.

Preferably, the user interface 140 (e.g., the WBM) also provides an acknowledgement that or whether the device 100 is within its intended operating range.

If the user has connected a load that is too large (for I-Out, i.e. current signal as output signal) or too small (for U-Out, i.e. voltage signal as output signal), the user now receives a corresponding message via user interface 140, e.g. by a fault LED lighting up or as an alarm message of a faulty load (for example in the WBM).

Traditionally, a faulty load may not be detected by the user until very late. This is because in the lower range of the analog output (for example with small currents) it may not be noticed that the load is causing a measurement error or the error only occurs at larger output values.

• - Analogausgang ist als Stromausgang so eingestellt, dass 10 mA fließen sollten.
• - Die hierfür an den Klemmen 114-1 und 114-2 notwendige Spannung ist 9,6 V.
• - Die berechnete Bürde ist dann R = U/I = 8V / 10 mA, also R = 800 Ω.

Example 4:

• - Analog output is set as a current output so that 10 mA should flow.
• - The voltage required for this at terminals 114-1 and 114-2 is 9.6 V.
• - The calculated burden is then R = U/I = 8V / 10 mA, i.e. R = 800 Ω.

According to Tables I and II, the device 100 can still apply 11.5 V to the terminals to drive the 20 mA current. This gives a maximum load of 575 Ω for a maximum current of 20 mA. The device will now operate linearly up to 14.375 mA and will produce false readings or low current signals above this current limit.

In another embodiment, which can be combined with other embodiments, the control unit 120 selects the analog output as a voltage output using the selection signal. The current flowing through the analog connection 114 is measured via the voltage drop across the measuring resistor 150 at the measuring point 160 before the connection 114-1. The same measuring point is used for this. As with I-Out (i.e. the aforementioned configuration as a current output), the measured voltage also goes into a voltage limit, i.e. a maximum value of voltage that the signal generator 200 can build up. In this case, too, the connected load can be determined, provided the voltage limit has not yet been reached.

In other words, to calculate the burden, a current will be measured by measuring the voltage drop across a measuring resistor 150 (e.g. 10 Ω) as a measurement value complementary to the voltage as the output signal. The measured voltage also goes into a limit that the circuit of the device 100 can provide. The circuit-related offset of the device 100 can be measured by test experiments or calculated directly or by simulation software (e.g. LT-Spice) and/or stored in the control unit 120.

After powering up the device 100, the externally connected burden is determined as described above and stored in a memory for further use (e.g., in operation of the device 100) until the next calculation, e.g., for a different output device 118 or a change in the selected signal.

Preferably, the determined burden is displayed to the user in the user interface 140 and compared or offset against the (e.g. stored) upper limit of the burden.

Table III shows, as an example, the calculated burden based on Ohm's law, the measured voltage drop across the measuring resistor 150 at the measuring point 160 and the output signal as a voltage signal (here, for example, a target value of 10 V). Due to the known value of the measuring resistor 150 and the known value of the internal resistance (for example, 10 Ω + 1.2 Ω), the control unit can calculate the current at the analog output 114 based on the measured voltage drop. The control unit 120 can determine the burden based on the calculated current and the output voltage. Table III U _{Terminal OUT+} (Terminal OUT+) U _Source (measuring point) Burden (calculated) was standing 9.99 10.004V 10000Ω OK 10.00 10.016V 8000Ω OK 10.00 10.020V 6000Ω OK 10.00 10.028V 4000Ω OK 10.00 10.053V 2000Ω OK 10.00 10.097V 1000Ω OK 10.00 10,201V 500Ω OK 10.00 10.223V 450Ω OK 10.00 10.251V 400Ω OK 10.00 10.286V 350Ω OK 10.00 10,291V 340Ω OK 9.71 10.001V 330Ω Burden too low 9.42 9.711V 320Ω Burden too low 8.84 9.128V 300Ω Burden too low 7.39 7.670V 250Ω Burden too low

In a variant of each embodiment, the burden monitoring device 100 may also calculate the possible remaining burden (i.e., the residual value) each time the burden is determined (e.g., calculated) and output (e.g., display) it via the user interface 140. The device 100 may further calculate the burden overshoot and output (e.g., display) it to the user via the user interface 140.

If the user has connected a load that is too small in the case of U-Out (i.e. a configuration of the analog output as a voltage output), the control unit 120 issues a corresponding indication via the user interface 140, e.g. by lighting up a fault LED or as an alarm message of a faulty load (for example in the WBM).

Embodiments of the device 100 offer the user the advantage that the connected output load is measured when required or necessary. This can be used to detect not only incorrectly connected output loads, but also a line defect or cable break.

3 shows a block diagram illustrating the input and output connections of the device 100 according to a third embodiment. The third embodiment may include some or all of the features of the aforementioned embodiments or the 1 or 2 The device 100 may include one or more of the inputs 112, each of which is connected or connectable to one or more input devices 116. The embodiment of the device 100 may include at least one of the 3 shown inputs 112. Alternatively or additionally, the device 100 can be connected or connectable to one or more output devices 118 via the at least one analog output 114. The embodiment of the device 100 can 3 shown analog output 114 multiple times.

A digital-to-analog converter (DAC) 202 generates a control voltage 201 (for example by means of pulse width modulation, PWM) for a signal generator 200, which generates the output signal for the analog output 114. The signal generator 200 can be implemented according to the second embodiment or the 2 be trained.

The control unit 120 can, for example, as in 3 shown schematically, sends a selection signal to the signal generator 200 indicating which analog output signal is generated and/or which measurement variable complementary to the output signal is measured.

4 shows schematically the output of the load 102 calculated from the known current signal (as the output signal) and the measured voltage (as the measurement quantity complementary to the output signal). In the case of a cable short circuit, the load is zero or almost zero. In the case of an interruption of the cable connection, the load is infinite or very large.

In this example, the burden 102 is determined based on the current signal and the voltage measured at the first measuring point 160. The measured burden 102 is smaller than the upper limit 104 of the burden, i.e. the maximum permissible burden R _max , for the device 100. The device 100 thus operates in the linear range. Therefore, there is a residual value 106 (also: reserve) of the burden 102 by which the burden 102 could increase and the device 100 can continue to operate in the linear range. In this example, this means that the device 100 can operate linearly with higher voltage for a defined current signal.

5 shows schematically the burden 102 calculated from the known voltage signal (as output signal) and the measured current (as the measurement quantity complementary to the output signal). In the case of a cable short circuit, the burden 102 is minimal or zero, and in the case of a cable connection failure, the burden 102 is very high or infinite.

In this example, the burden 102 is determined based on the voltage signal and the current measured (for example by means of the measuring resistors 150) at the measuring point 160. The measured burden is greater than the lower limit 104 of the burden 102 (ie the minimum permissible burden R _min ) for the device 100. Thus, the device 100 operates in the linear range. Therefore, there is a so-called residual value 106 (also: reserve) of the burden 102 by which the burden 102 could decrease and the device 100 can continue to operate in the linear range. In this example, this means that the device 100 can operate linearly with higher current for a defined voltage signal.

Embodiments of the invention offer the user the advantage that the connection load 102 at the output is measured when required or necessary. Alternatively or additionally, not only can an impermissibly connected output load 102 be detected, but also a line defect, a cable break, a loose terminal (for example due to vibrations) or contact corrosion can be determined based on temporal changes in the load and/or threshold values for the load and/or output with the note.

In each embodiment, the output indication can indicate a value (e.g. amount) of the specific burden 102 (i.e. the current output-side burden) or a remaining amount 106 (e.g. a distance in ohms) until a limit value 104 of the output-side burden is reached. Alternatively or additionally, the output indication can indicate that the output signal is incorrect. For example, the output indication can indicate that a value measured by means of the signal converter 110 is incorrect (e.g. because the measured value is not correctly represented by the output signal) and/or a relationship between the input signal and the output signal does not correspond to a characteristic curve of the signal converter 110 (e.g. at a specific point on the characteristic curve of the signal converter 110 or at the current point on the characteristic curve of the signal converter). For example, the output indication can indicate a non-linearity between the input signal and the output signal.

• - eine fehlerhafte Verdrahtung am Analogausgang 114;
• - einen zu geringen Leitungsquerschnitt am Analogausgang 114;
• - eine fehlerhafte (beispielsweise nicht korrekt angezogene) Klemmstelle 114-1 oder 114-2 am Analogausgang 114;
• - eine Nutzung eines falschen Eingangs oder eines falschen Eingangstyps einer am Analogausgang 114 angeschlossenen speicherprogrammierbaren Steuerung (SPS) oder anderen nachfolgenden Schaltung;
• - eine falsche Konfiguration eines Eingangs 112 einer am Analogausgang 114 angeschlossenen SPS oder anderen nachfolgenden Schaltung;
• - Verbindungsstellen am Analogausgang 114, die über die Zeit fehlerhaft geworden sind, beispielsweise durch Korrosion, insbesondere Oxidation; und
• - einen Leitungsbruch am Analogausgang 114, insbesondere durch Vibration oder Bewegung.

Alternatively or additionally, the notice issued may indicate at least one of the following errors or causes:

• - faulty wiring at analog output 114;
• - too small a cable cross-section at the analog output 114;
• - a faulty (e.g. not correctly tightened) terminal point 114-1 or 114-2 on the analog output 114;
• - use of an incorrect input or an incorrect input type of a programmable logic controller (PLC) or other downstream circuit connected to the analog output 114;
• - an incorrect configuration of an input 112 of a PLC or other downstream circuit connected to the analog output 114;
• - Connection points on the analog output 114 that have become faulty over time, for example due to corrosion, in particular oxidation; and
• - a line break at the analog output 114, particularly due to vibration or movement.

In existing signal converters, the current or voltage that the signal converter attempts to output is, at best, available as an internal setpoint. Even if this is known to the user, it is not easy to calculate and predict the allowable range of the burden 102 for a circuit to be connected to the analog output 114 of the signal converter.

Embodiments of the device 100 are therefore designed to determine and monitor the burden 102 connected to the analog output 114.

Although the invention has been described with reference to exemplary embodiments, it will be apparent to those skilled in the art that various changes may be made and equivalents may be substituted. Furthermore, many modifications may be made to adapt a particular situation or circuit to the teachings of the invention. Accordingly, the invention is not limited to the disclosed embodiments, but includes all embodiments falling within the scope of the appended claims.

List of reference symbols

100

Device for monitoring a load

102

burden

104

Reference to the limit of the burden, for example upper limit and/or lower limit 104

106

Reference to residual value (also: reserve) of the burden

110

Device signal converter

112

Input of the device or signal converter, for example analog input or digital input

114

Analog output of the device

116

Input device, e.g. sensor

118

Output device, e.g. actuator or PLC

120

Control unit of the device, e.g. microcontroller

140

User interface, e.g. display

150

Measuring resistor for current at voltage output

152

Measuring resistors for current at current output

154

Dial signal input

155

Select transistors

156

Feedback to regulate the voltage as output signal

158

Feedback to control the current as an output signal

160

Measuring point

200

Signal generator

201

Control signal, e.g. control voltage, for signal generator

202

Digital-to-analog converter of the device

204

Additional analog-digital converter, for example in signal converter or control unit

206

Analog-digital converter of the device

208

Signal processing of the device

QUOTES INCLUDED IN THE DESCRIPTION

This list of documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions.

Cited non-patent literature

• DIN1319 [0010]

Claims (15)

Device (100) for monitoring a load (102) of at least one analog output (114), comprising: a signal converter (110) having at least one input (112) and at least one analog output (114), wherein the signal converter (110) is designed to output an output signal at the analog output (114) depending on an input signal present at the input (112), wherein the output signal is a current or a voltage; and a control unit (120) which is designed to detect the voltage in addition to the current as an output signal or the current at the analog output (114) in addition to the voltage as an output signal, to determine the load (102) from the output signal in combination with the detected current or the detected voltage, and to output an indication (104; 106) based on the determined load (102). Device (100) according to Claim 1 , wherein the control unit (120) detects the current or the voltage at the analog output in an analog domain and/or as a measured value, and/or wherein the control unit (120) has the output signal in a digital domain and/or as a target value. Device (100) according to Claim 1 or 2 , wherein the control unit (120) further outputs a limit value (104) of the burden (102) and/or wherein the output indication (104; 106) depends on a comparison of the limit value of the burden (102) with the determined burden (102) and/or wherein the output indication (104; 106) indicates a residual value (106) of the burden (102) as the difference between the limit value (104) of the burden (102) and the determined burden (102). Device (100) according to one of the Claims 1 until 3 , wherein the signal converter (110) outputs the current as an output signal at the analog output (114), and the control unit (120) outputs the indication (104; 106) if the determined burden (102) is greater than an upper limit of the burden (102) and/or greater than an upper burden threshold, optionally wherein the upper limit of the burden (102) corresponds to a maximum value of the voltage to drive a maximum value of the current as an output signal, and/or wherein the upper burden threshold is 75% to 90% of the upper limit of the burden (102). Device (100) according to one of the Claims 1 until 4 , wherein the signal converter (110) outputs the voltage as an output signal at the analog output (114), and the control unit (120) outputs the indication (104; 106) if the determined burden (102) is less than a lower limit of the burden (102) and/or less than a lower burden threshold value, optionally wherein the lower limit of the burden (102) corresponds to a maximum value of the current in order to achieve a maximum value of the voltage as an output signal, and/or wherein the lower burden threshold value is 110% to 125% of the lower limit of the burden (102). Device (100) according to one of the Claims 3 until 5 , wherein the device (100) further comprises a switch for disconnecting the connected burden (102) from the analog output, wherein the control unit (120) is further configured to actuate the switch for disconnection when the determined burden (102) violates the limit value (104), in particular the lower limit or the upper limit, of the burden (102). Device (100) according to one of the Claims 1 until 6 , wherein the device (100) further comprises a memory for storing the determined burden (102), and/or wherein the control unit (120) is further configured to determine the burden (102) at different times and/or at different output signals, and optionally to store an average value of the determined burdens in the memory. Device (100) according to Claim 7 , wherein the control unit (120) is further configured to output the indication (104; 106) when the determined burden (102) deviates from the stored burden (102). Device (100) according to one of the Claims 1 until 8th , wherein the control unit (120) is further configured to output an indication (104; 106) of a short circuit or moisture at the analog output (114) if the determined burden (102) is less than a predetermined minimum value and/or less than the stored burden (102). Device (100) according to one of the Claims 1 until 9 , wherein the control unit (120) is further designed to provide an indication (104; 106) of a cable break or faulty terminal point at the analog output output (114) when the determined load (102) is greater than a predetermined maximum value and/or greater than the stored load (102). Device (100) according to one of the Claims 1 until 10 , wherein the device (100) further comprises a user interface for outputting the determined burden (102), the indication (104; 106) and/or the residual value (106) of the burden (102). Device (100) according to one of the Claims 1 until 11 , wherein the control unit (114) is further configured to output the determined burden (102) and/or an allowable interval for the burden (102), optionally by means of a graphical display (140) and/or a web server of the device (100). Device (100) according to one of the Claims 1 until 12 , wherein the control unit (120) detects the current or the voltage at the analog output at a measuring point (160) of the signal converter (110), optionally wherein the control unit (120) comprises an analog input which is electrically connected to the measuring point (160), or wherein the control unit (120) comprises a digital input which is electrically connected to the measuring point (160) via an analog-digital converter. Device (100) according to one of the Claims 1 until 13 , wherein the signal converter (110) has a selection signal input (154) and is designed to output either the current or the voltage as the output signal at the analog output (114) depending on a selection signal applied to the selection signal input (154). Device (100) according to the Claims 13 and 14 , wherein the control unit (120) is designed to detect at the same measuring point (160) depending on the selection signal either the voltage in addition to the current as an output signal or the current in addition to the voltage as an output signal.

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