Electronic measuring device for detecting a process variable, in particular a radar or ultrasonic filling level measuring device, and a method for operating a measuring device of this type

Abstract

The invention relates to a method and an electronic measuring device for detecting a process variable connectable to a two-wire line ( 101 ) for providing the supply energy and for digital communication with a process control, and a method for operating such a measuring device. An inventive measuring device comprises a sensor means ( 114, 115, 123, 124; 314, 315, 323, 324 ) for measuring the process variable, a controlling device ( 117; 317 ) for controlling components of the measuring device, a voltage measuring device ( 116; 316 ) for measuring the supply voltage applied through the two-wire line ( 101 ), and a current control unit ( 122; 322 ) by means of which the current for supplying the measuring devices can be modified in a temporally appropriate manner as a function of the supply voltage measured by the voltage measuring device ( 9; 316 ).

1 . An electronic measuring device for detecting a process variable connectable to a two-wire line for providing the supply energy and for digital communication with a process control, and for this purpose in particular, comprising a two-wire terminal, and including a sensor means for measuring the process variable, a controlling device for controlling components of the sensor means, a voltage measuring device for measuring the supply voltage applied through the two-wire line, and a current control unit by means of which the current for supplying the measuring device can be appropriately set as a function of the supply voltage measured by the voltage measuring device.  
     
     
         2 . The electronic measuring device of  claim 1 , 
 wherein a device for determining the instantaneous power loss is present, and the controlling device connected with said device and the current control unit predetermining a variable desired value for the current control unit as a function of the determined power loss.    
     
     
         3 . The electronic measuring device of  claim 1 , 
 wherein a pre-given maximum value for the input current may be given to the current control unit.    
     
     
         4 . The electronic measuring device of  claim 2 , 
 wherein the device for determining an instantaneous power loss is connected with a capacitor so as to measure the temporal development of the voltage at the capacitor and thereby the power loss.    
     
     
         5 . The electronic measuring device of  claim 2 , 
 wherein the device for determining the instantaneous power loss includes a micro-controller, an A/D converter connected with said micro-controller, and a capacitor connected upstream of an ultrasonic transmitter for storing energy for the sensor means.    
     
     
         6 . The electronic measuring device of  claim 1 , 
 wherein a device is present by means of which the frequency of occurrence of sensor excitements can be determined without performing a measurement.    
     
     
         7 . The electronic measuring device of  claim 1 , 
 wherein a current limiting means is present connected with the current control unit.    
     
     
         8 . The electronic measuring device of  claim 1 , 
 wherein a power loss due to a power demand excess is dissipated by a controlled output of a pulse by the sensor means without entailing a measurement.    
     
     
         9 . The electronic measuring device of  claim 1 , 
 wherein a power loss due to a power demand excess is transformed into heat.    
     
     
         10 . The electronic measuring device of  claim 1 , 
 wherein a power loss due to a power demand excess is determined through a current sensing resistor within the current control unit.    
     
     
         11 . An electronic measuring device for detecting a process variable connectable to a two-wire line for providing the supply energy and for digital communication with a process control, and for this purpose in particular, comprising a two-wire terminal, and including a sensor means for measuring the process variable, a controlling device for controlling components of the sensor means, and a current control unit by means of which the current drawn by the measuring device through the two-wire line can be appropriately set as a function of the current drawn by the sensor means.  
     
     
         12 . The electronic measuring device of  claim 11 , 
 wherein the current control unit includes two controls, one keeping the total current constant, and one providing for the fact that a little current is flowing through a shunt arm at all times.    
     
     
         13 . The electronic measuring device of  claim 11 , 
 wherein a device for determining an instantaneous power loss is present, and the controlling device connected with said device and the current control unit predetermining a variable desired value for the current control unit as a function of the determined power loss.    
     
     
         14 . The electronic measuring device of  claim 13 , 
 wherein the device for determining an instantaneous power loss is connected with a capacitor so as to measure the temporal development of the voltage at the capacitor and thereby the power loss.    
     
     
         15 . The electronic measuring device of  claim 13 , 
 wherein the device for determining an instantaneous power loss includes a micro-controller, an A/D converter connected with said micro-controller, and a capacitor connected upstream of an ultrasonic transmitter for storing energy for the sensor means.    
     
     
         16 . The electronic measuring device of  claim 11 , 
 wherein a device is present by means of which the frequency of occurrence of sensor excitements can be determined without performing a measurement.    
     
     
         17 . The electronic measuring device of  claim 11 , 
 wherein a current limiting means is present connected with the current control unit.    
     
     
         18 . The electronic measuring device of  claim 11 , 
 wherein a power loss due to a power demand excess is dissipated by a controlled output of a pulse by the sensor means without entailing a measurement.    
     
     
         19 . The electronic measuring device of  claim 1 , 
 wherein a power loss due to a power demand excess is transformed into heat.    
     
     
         20 . The electronic measuring device of  claim 11 , 
 wherein a power loss due to a power demand excess is determined through a current sensing resistor within the current control unit.    
     
     
         21 . A method for operating an electronic measuring device for detecting a process variable connectable to a two-wire line for providing the supply energy and for digital communication with a process control, wherein the supply voltage applied through the two-wire line is measured in the measuring device, and the current for supplying the measuring device is modified in a temporally appropriate manner as a function of the supply voltage measure by the voltage measuring device.  
     
     
         22 . The method of  claim 21 , 
 wherein the voltage drop is measured at a resistor for determining an instantaneous power loss.    
     
     
         23 . The method of  claim 21 , 
 wherein the power loss instantaneously generated in the measuring device is determined for determining an appropriate power input.    
     
     
         24 . The method of  claim 21 , 
 wherein said method is realized in a measuring device including a sensor means, in which the distance from the filling product surface of a filling product present in a receptacle is determined by means of ultrasonic pulses.    
     
     
         25 . The method of  claim 21 , 
 wherein said method is realized in a measuring device including a sensor means, in which the distance from the filling product surface of a filling product present in a receptacle is determined by means of radar pulses.    
     
     
         26 . A method for operating an electronic measuring device for detecting a process variable connectable to a two-wire line for providing the supply energy and for digital communication with a process control, wherein the total current drawn through the two-wire line by the measuring device is adapted by a current control unit to a sensor current drawn by a sensor means.  
     
     
         27 . The method of  claim 26 , 
 wherein a loss current in a shunt arm is kept at a minimum.    
     
     
         28 . The method of  claim 26 , 
 wherein the power loss instantaneously generated in the measuring device is determined for determining an appropriate power input.    
     
     
         29 . The method of  claim 28 , 
 wherein the temporal development of the voltage at a capacitor connected upstream of the sensor means for measuring the process variable is measured for determining the instantaneous power loss.    
     
     
         30 . The method of  claim 28 , 
 wherein the frequency of occurrence of sensor excitements is determined without performing a measurement.    
     
     
         31 . The method of  claim 26 , 
 wherein said method is realized in a measuring device including a sensor means, in which the distance from a filling product surface of a filling product present in a receptacle is measured by means of ultrasonic pulses.    
     
     
         32 . The method of  claim 26 , 
 wherein said method is realized in a measuring device including a sensor means, in which the distance from a filling product surface of a filling product present in a receptacle is measured by means of radar pulses.