Monitoring device and method for monitoring a line section using a monitoring device

Abstract

A monitoring device is provided that includes a first line section with a first connection point and a second connection point spaced apart from the first connection point in the direction of the line, and with a control unit and with a first current sensing unit, having a current source. A first switch is inserted into the first connecting line and connects the first current source to the first connection point or disconnects it therefrom. In a first state the first switch is closed and the first current is impressed on the first line section and a first voltage determined by the amplitude of the actual current, and in a second state the first switch is open and a second voltage is determined, and the control unit is configured to ascertain the amplitude of the first actual current from the two voltages.

What is claimed is: 
     
         1 . A monitoring device comprising:
 a first line section with a first connection point and a second connection point spaced apart from the first connection point in a direction of the line;   a control unit;   a first current sensing unit comprising:
 a first current source connectable to the first connection point via a first connecting line and connectable to the second connection point via a second connecting line, the first current source being configured to output a first current; 
 a first switch having a control input, the first switch being inserted into the second connecting line and being configured to connect or disconnect the first current source to the second connection point; and 
 a first differential amplifier having a first input, a second input, and an output, the first input being connectable to the first connection point via a third connecting line, the second input being connectable to the second connection point by a fourth connecting line; 
   wherein the control unit is inserted between the output of the first differential amplifier and the control input of the first switch,   wherein an actual current is passed through the first line section,   wherein, in a first state, the first switch is closed and the first current is impressed on the first line section in addition to the first actual current and a first voltage determined by the amplitude of the actual current and the amplitude of the first current is present between the first input and second input of the first differential amplifier,   wherein, in a second state, the first switch is open and a second voltage determined exclusively by the actual current is present between the first input and second input of the first differential amplifier, and   wherein the control unit is configured to ascertain the amplitude of the actual current from the first and second voltage.   
     
     
         2 . The monitoring device according to  claim 1 , wherein the first current is a direct current or an alternating current. 
     
     
         3 . The monitoring device according to  claim 1 , wherein the first current source has a control input connectable to the control unit. 
     
     
         4 . The monitoring device according to  claim 1 , wherein the first current sensing unit includes an ADC (analog to digital converter), and wherein the ADC is connectable between the output of the first differential amplifier and the control unit. 
     
     
         5 . The monitoring device according to  claim 1 , wherein the first current source is connectable to the first line section via a first bridge switch, a second bridge switch, a third bridge switch, and a fourth bridge switch in the form of an H-bridge circuit. 
     
     
         6 . The monitoring device according to  claim 1 , wherein the first differential amplifier is connectable to the first line section via an H-bridge circuit. 
     
     
         7 . The monitoring device according to  claim 4 , wherein a first circuit arrangement includes a first differential amplifier and a first analog-to-digital converter connected to the first line section via an H-bridge circuit. 
     
     
         8 . The monitoring device according to  claim 1 , further comprising a second line section having a second current sensing unit and a second differential amplifier, wherein a second current is provided to the second line section. 
     
     
         9 . The monitoring device according to  claim 8 , wherein the second line section is directly adjacent to the first line section. 
     
     
         10 . The monitoring device according to  claim 8 , wherein the control unit has a third differential amplifier, wherein a first input of the third differential amplifier is connectable to the output of the first differential amplifier and a second input of the third differential amplifier is connectable to the output of the second differential amplifier, and wherein a first differential amplifier, a second differential amplifier, and a third differential amplifier form a multi-stage amplifier unit. 
     
     
         11 . The monitoring device according to  claim 8 , wherein the first current and the second current are essentially opposite and equal in amplitude. 
     
     
         12 . The monitoring device according to  claim 1 , wherein the control unit is configured to ascertain the amplitude of the actual current via a value of the voltage in the first state and via a value of the voltage in the second state and via the amplitude of the first current. 
     
     
         13 . The monitoring device according to  claim 1 , wherein the control unit is configured to ascertain the amplitude of the actual current without calculation or knowledge of the resistance of the first line section. 
     
     
         14 . A method for monitoring a first line section using a monitoring device, the method comprising:
 providing the first line section with a first connection point and a second connection point spaced apart from the first connection point in a direction of the line;   providing a control unit; and   providing a first current sensing unit, the first current sensing unit comprising: a first current source connectable via a first connecting line to the first connection point and connectable via a second connecting line to the second connection point, the first current source being configured to output a first current; a first switch having a control input, the first switch being configured to be inserted into the first connecting line and being configured to connect or disconnect the first current source to the first connection point; a first differential amplifier with a first input, a second input, and an output, the first input being connectable to the first connection point via a third connecting line and the second input being connectable to the second connection point by a fourth connecting line;   inserting the control unit between an output of a first differential amplifier and a control input of the switch;   passing an actual current through the first line section;   closing, in a first state, the first switch such that the first current is impressed on the first line section in addition to the actual current and a first voltage determined by the amplitude of the actual current and the amplitude of the first current is present between the first input and second input of the first differential amplifier;   opening, in a second state, the first switch such that a second voltage determined exclusively by the first actual current is present between the first input and second input of the first differential amplifier; and   ascertaining an amplitude of the first actual current from the first and second voltage via the control unit.   
     
     
         15 . The method according to  claim 14 , wherein an alternating current is fed into the first line section via the control unit, and wherein the amplitude of the actual current is ascertained via a lock-in principle. 
     
     
         16 . The method according to  claim 14 , wherein the amplitude of the actual current is ascertained by the control unit via a value of the voltage in the first state and via a value of the voltage in the second state and the amplitude of the first current. 
     
     
         17 . The monitoring device according to  claim 1 , wherein the monitoring device is configured to monitoring phase currents of a generator or an electric motor. 
     
     
         18 . The monitoring device according to  claim 1 , wherein the monitoring device is configured to ascertain a state of charge of a battery or for monitoring a current amplitude in a positive branch between the battery and a load, or for monitoring the magnitude of the current in a positive branch between the battery within the on-board power network of an automobile and a load. 
     
     
         19 . The monitoring device according to  claim 1 , wherein the monitoring device is configured to monitor a current in ground leads in a motor vehicle. 
     
     
         20 . The monitoring device according to  claim 1 , wherein the monitoring device is configured for in-situ calibration of unknown current amplitudes in a line section, and wherein a variation of the current amplitudes in the line section spans at least a factor of ten.