Abstract:
A current measuring element comprising a current carrying conductor having the shape of a flat rail in an insulating housing and a hall sensor which is arranged in the proximity of said conductor. The current carrying conductor is bent to form a unshaped conductor loop in the area of the hall sensor and the hall sensor is situated on a board which is arranged in the unshaped conductor loop. The board containing the hall sensor is placed upon a main board on which the signal from the hall sensor is processed. An insulating cover provided for the housing is arranged between the housing containing the current carrying conductor and the main board. The cover comprises an insulating compartment which extends inside the conductor loop and receives the board containing the hall sensor.

Description:
TECHNICAL FIELD 
     The invention relates to a current measuring device having a current carrying conductor in an insulating housing and a Hall sensor arranged in the vicinity of the conductor. Such a current measuring device is described in EP 0 538 658 A1, for example. 
     BACKGROUND OF THE INVENTION 
     Hall sensors can be used to measure the current flowing in a conductor without making contact, as is known. To concentrate the magnetic field of the current, which is responsible for the Hall effect, and to exclude interfering influences, it is general practice to use ferromagnetic elements having a clearance which contains the Hall sensor. 
     In the current measuring device which is described in the aforementioned document EP 0 538 658 and can be used in power switches and motor protective circuit breakers, the current flows through a coil which is split into two halves and whose common coil former is provided with a pocket for holding the integrated Hall circuit. 
     DE-A-34 28 392 discloses a similar current measuring device in which a current carrying conductor in the form of a coil or a bent rail surrounds a Hall sensor and is itself surrounded by a ferromagnetic core to concentrate the magnetic field. 
     Such embodiments of the current measuring device with coils and ferromagnetic cores and the like have the disadvantage that the coils and cores make the structure very large and heavy. 
     DE-A-195 49 181 discloses a current measuring device in which a Hall sensor is inserted between the limbs of a U-shaped conductor loop, without a ferromagnetic core being connected in between. This measuring device has no shield, however, and is therefore relatively inaccurate and is not suitable for measuring heavy currents, at least. 
     SUMMARY OF THE INVENTION 
     The invention is based on the object of refining the current measuring device such that it is of simple design, is small and lightweight and can thus be used universally. 
     The invention achieves this object with the features specified in patent claim  1 . Advantageous refinements of the current measuring device according to the invention are specified in the subclaims. 
     Dispensing with a coil and a ferromagnetic core or another ferromagnetic element not only simplifies the design of the current measuring device, but also means that significantly less heat is produced during operation on account of the fact that transfer losses no longer occur. This is of considerable importance particularly for use in switchboxes. 
     The two current paths, carrying flow in opposite directions parallel to one another, in the U-shaped conductor loop comprising flat busbars cause the magnetic field, and hence the signal from the Hall sensor, to be virtually doubled. 
     The current measuring device according to the invention for measuring current without making contact is so small that it can easily be incorporated in measuring boxes and switching devices. The current measuring device according to the invention already integrates the electronics for amplifying and evaluating the measured signal, a temperature compensation means and possibly a control logic unit and a digital display. 
     The fully closed, insulating cover between the housing with the current carrying conductor and the circuit board with the Hall sensors and the evaluation electronics ensures complete DC isolation of the high-voltage region from the electronic components. 
     The optionally provided metallic shield around the U-shaped conductor loop reduces the influence of interfering magnetic fields on the Hall sensor. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention&#39;s current measuring device with a Hall sensor is explained in more detail below by way of example with the aid of the drawing, in which: 
     FIG. 1 shows the structure of the current measuring device, 
     FIG. 2 shows the circuit board with the Hall sensor in detail, and 
     FIG. 3 shows a block circuit diagram for signal processing in the current measuring device. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 1 shows the structure of the current measuring device in an exploded view. The current measuring device comprises an insulating housing  10  for one or more current carrying conductors  12  in the form of flat rails of the type conventional in power engineering. The housing  10  shown in FIG. 1 comprises three conductors  12  running in parallel for the three-phase supply of current to a load, e.g. a motor. 
     The current measuring device shown is provided for use in the low-voltage/heavy-current field with current levels of up to approximately 150 A. The lowest current level which the measuring device is designed to record is between 0.1 and 1 A. 
     At the input and at the output of the housing  10 , the conductors  12  are provided with connection elements (not shown) so that each of the conductors  12  can be connected into the corresponding power supply line. The insulating covering, on the input side and the output side, for the conductors  12  and the connection elements is likewise not shown. 
     In the housing  10 , each of the flat, rail-like conductors  12  is bent in a U shape so that a conductor loop  14  which is open at the top is produced. The U-shaped conductor loop  14  extends downward out of the plane of the flat conductor  12 , that is to say it is not situated in the plane of the flat conductor  12 , but rather runs perpendicular to it. If the width of the current conductor rail  12  is 12 mm, the conductor loop  14  has, by way of example, a depth of approximately 15 mm and an internal spacing between the limbs of the U of approximately 5 to 8 mm. 
     Each of the U-shaped conductor loops  14  can be surrounded on the outside, that is to say in the region of the housing  10  below the conductor  12  and the conductor loop  14 , by a metallic shield (not shown) which reduces or eliminates the influence of interfering external magnetic fields on current measurement. The shield is preferably made of soft iron (Mu metal); however, for particular applications, a quite ordinary iron sheet can suffice to achieve the desired shielding effect. 
     A cover  20  made of insulating material is mounted on top of the housing  10 . The cover  20  seals off the housing  10  with the current carrying conductors  12  so that they are protected from accidental contact. 
     The cover  20  is provided with pockets  22 , which are likewise made of insulating material, in the region of the conductor loops  14 . The pockets  22  project downward from the cover  20  and are each situated within the conductor loops  14  when the cover  20  is mounted. The pockets  22  are open at the top at the level of the main plane of the cover  20 , but are closed on all sides at the bottom in the region of the conductor loop  14 . The width of each pocket  22  corresponds fairly accurately to the limb spacing of the conductor loop  14 , so that the outer sides of the pocket  22  are at only a short distance from the lateral limbs of the conductor loop  14 , or else even bear against the latter. The depth of the pockets  22  is less than the depth of the conductor loop  14 . The length of the pockets  22  (in the direction of the width of the conductor rail  12 ) can be greater, the same as or less than the width of the conductor rails  12 . 
     Above the cover  20 , there is a main circuit board  30 . The main circuit board  30  rests removably on the cover  20  with a small spacing. 
     Perpendicular to the main plane of the main circuit board  30 , small circuit boards  40  are mounted on the main circuit board  30  and are arranged such that they extend into the pockets  22  of the cover  20  when the main circuit board  30  is mounted on the cover  20 . 
     Hall sensors  42  are mounted on the small circuit boards  40 . As FIG. 2 shows, the Hall sensors  42  are fitted in indentations  43  approximately in the center of the bottom, free side or edge of the small circuit boards  40  such that the Hall sensors  42  are located centrally in the pockets  22  of the cover  20  and approximately centrally in the current loops  14  when the circuit board  30 , the cover  20  and the housing  10  are assembled. In this arrangement, the Hall sensors  42  are arranged such that the magnetic field of the current loop  14  permeates the Hall element in the Hall sensors  42  perpendicularly. The main plane of the Hall sensor  42  thus runs perpendicular to the main plane of the small circuit board  40 . The indentation  43 , matching the Hall sensor  42  exactly, in the bottom of the circuit board  40  simplifies correct placement of the Hall sensor  42  and ensures that the Hall sensor  42  maintains its position. 
     In the immediate vicinity of the Hall sensor  42 , the circuit board  40  is provided with a temperature sensor  44 , for example an NTC temperature sensor. In addition, an amplifier  46  which amplifies the signal from the Hall sensor  42  is located on the circuit board  40 . The amplified signals from the Hall sensor  42  and the signals from the temperature sensor  44  are passed to the main circuit board  30  via conductor tracks  48 . 
     The signals from the Hall sensors  42  and the signals from the temperature sensors  44  are processed further on the main circuit board  30 . To this end, the necessary electrical and electronic components are arranged on the main circuit board  30 , for example integrated circuits  32 , resistors, diodes, relays etc. (only some of which are shown in FIG.  1 ). The main circuit board  30  preferably includes a microprocessor. 
     The signal from the temperature sensor  44  is used to provide temperature compensation for the signal from the Hall sensor  42 . Since the temperature sensor  44  is situated in the immediate vicinity of the Hall sensor  42 , its temperature is recorded very accurately. The temperature-corrected signal from the Hall sensor  42  can be used to determine the current flowing in the conductor  12  accurately. 
     Above the main circuit board  30  with the small circuit boards  40  there is a covering  50 . The front (the outer side) of the covering  50  has an LCD display  52 , buttons  54  for entering commands, variables etc. and connectors  56  for external connections. The covering  50  is electrically connected to the main circuit board  30  via internal connectors  34  on the main circuit board and/or via cables. 
     The buttons  54  can be used to set the microprocessor on the main circuit board  30  to particular modes of operation using menu control. Thus, for example, the LCD display can alternately show the currents in the individual phase lines, the (total) power supplied and other variables, such as nominal and actual values. By specifying nominal values for current and time, the current measuring device can also be used as a protective circuit breaker, with turn-off commands and the like being picked up via the external connectors  56 . The main circuit board  30  can also contain relays and control terminals which condition and pass on the switching signals. 
     FIG. 3 shows a block circuit diagram for the electronic components of the current measuring device. The schematic illustration in FIG. 3 summarizes the processing of the signals from the Hall sensors  42  and the temperature sensors  44 , of the input signals from the buttons  54  and the connector  56  and of the output signals to the LCD display  52 , the connector  56  etc. Signal processing is carried out not only on the main circuit board  30 , but also, in part, on the small circuit boards  40  with the Hall sensors  42  and, if applicable, other components, not arranged on the main circuit board  30 , for example in the LCD display block  52  on the covering  50 . 
     As FIG. 3 shows, the current signals from the Hall sensors  42  and the temperature sensor(s)  44  are amplified in amplifiers  61  and are passed to an A/D converter  62 . From the A/D converter  62 , the signals go on to a microprocessor  63 . The input signals for the microprocessor  63  also include the “keyboard” signals supplied via a keyboard buffer  64 . These “keyboard” signals are the control and monitoring signals which are input externally using the buttons  54  and/or the connector  56 , define in which mode the microprocessor  63  is intended to operate and which can be used, within the individual modes, to stipulate, by way of example, nominal values for the current, limit values and the like. 
     The programs which the microprocessor  63  uses to operate in the individual operating modes are stored either in the microprocessor  63  itself or in separate read only memories (not shown). 
     A power supply  65  supplies the electronic components with the necessary power. 
     The input signals are processed in the microprocessor  63  on the basis of the respective mode of operation and on the basis of the respective stipulations. Depending on the result of the processing and on the mode of operation, the microprocessor  63  then outputs control signals for the LCD display  52  to an LCD display controller  66 , switching signals to a relay drive unit  67  and/or data of any type to an interface  68  for passing on the data externally on a data bus, for example. 
     By way of example, if the current measuring device is in a motor protective mode, the relay drive unit  67  can be used for directly switching relays (not shown) which interrupt the power supply to the motor under particular conditions (for example a high current over an excessively long time). In addition, or as an alternative, an alarm can be triggered, the excessively high current or the turning-off of a central control location can be reported, and other such aspects.