Abstract:
A system and method for determining the magnetic sensitivity of a Hall-effect switch through the use of a variable powered DC electromagnet having a permanent magnet attached to it. In use the electromagnet is placed in contact with a Hall-effect switch component and the DC voltage varied until a detector determines the Hall-effect switch has been triggered. The electromagnet is then moved to be in contact with a probe connected to a Gauss meter to determine the magnetic sensitivity of the Hall-effect switch.

Description:
BACKGROUND 
     Hall-effect switches may be used in a device to determine when power should be shut down to the device when the Hall-effect switch is close to a magnet. Many manufacturers provided Hall-effect switches. For the purpose of quality control in manufacturing a device utilizing a Hall-effect switch there is a need to test the sensitivity and accuracy of the switch to the strength of a specific magnetic field. The embodiments of the invention as disclosed herein address this need. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments are illustrated by way of example and without limitation in the figures of the accompanying drawings, in which like reference numerals indicate corresponding, analogous or similar elements, and in which: 
         FIG. 1  is a plan view of an embodiment of a system for testing a Hall-effect switch; 
         FIG. 2  is a schematic diagram of a magnetic sensitivity detector; 
         FIG. 3  is a plan view of an electromagnet connected to a Gauss meter; and 
         FIG. 4  is a flowchart of the process for testing the magnetic sensitivity of a Hall-effect switch. 
     
    
    
     DETAILED DESCRIPTION 
     In testing Hall-effect switches a magnetic field is applied to the switch and the magnetic field is changed until the state of the output of the switch moves from “high” to “low”. To provide a strong electromagnetic field requires a large amount of Direct Current (DC) which is taxing on many power supplies. To resolve this problem, an electromagnet connected to an adjustable power supply is provided with a permanent magnet to test the switch. This results in significantly less DC required from the power supply. By varying the DC from the power supply, it is now possible to apply “fine tuning” on the strength of the magnetic field. 
     Referring now to  FIG. 1  a plan view of an embodiment of a system for testing a Hall-effect switch is shown generally as  10 . System  10  illustrates two components; an electromagnetic coil component  12  and a Hall-effect switch component  14 . Component  12  comprises a core  16 , typically a ferromagnetic material, but any magnetic conductive material may be used. Core  16  is wrapped in a continuous series of wire coils  18 . As one skilled in the art can appreciate electromagnets can be constructed in numerous sizes with varying materials. The magnetic field inside an electromagnet is defined as:
 
 B=μNI/L  
 
where:
     B is the magnetic flux density (magnetic induction) in the core  16 , measured in Telsas where one Telsa equals 10,000 Gauss;   μ (Mu) is the permeability of core  16 , measured in Henries per meter;   N is the number of turns of wire around the core  16 ;   I is the current in amperes; and   L is the length of the electromagnet.   

     An embodiment utilized by the inventor had the following characteristics. The core  16  was a Murata FSRC280060RX000T. The number of turns of wire was on the order of 400 and the diameter of the wire was approximately 0.2 mm. The length of the electromagnet  12  was about 25 mm. 
     Electromagnet  12  receives power to coils  18  via adjustable DC power supply  20 . The power supply  20  utilized by the inventor had a range of 0 to 30 volts. Resistor  22  serves as a current limiter. In the embodiment utilized by the inventor the resistor was 470 Ohm/1 Watt. Attached to the top of electromagnet  12  is a permanent magnet  24 . 
     In one embodiment, the permanent magnet utilized was a N45 sintered NdFeB (neodymium) magnet manufactured by the Hua Zing Manufacturing Company. This magnet has a residual induction of 13.7K to 11.3K Gauss. 
     At the base of the electromagnet  12  are non-magnetic stops  26   a  and  26   b . Stops  26   a  and  26   b  aid the user in aligning the electromagnet  12  with Hall-effect switch  30 . 
     Hall-effect switch component  14  comprises a Hall-effect switch  30 , a DC power source  32  and a detector  40 . Hall-effect switch  30  is interchangeable within Hall-effect switch component  14  so that different switches may be tested. Switch  30  may, for example, be soldered to switch component  14 . In another example, switch  30  may be placed in a receptacle matching the dimension of switch  30 . When switch  30  is in contact with electromagnet  12  the magnetic sensitivity of switch  30  may be tested. Switch  30  is powered by a DC power supply  32  via Vcc  34  and GND  36 . In addition DC power supply  32  is connected to detector  40  through Vcc  34  and GND  36 . DC power supply  32  may comprise a battery or other DC power source. 
     Once in contact with electromagnet  12 , switch  30  through the use of output line  38  provides output on magnetic sensitivity to detector  40 . Detector  40  provides visual or audio confirmation to the user when the state of switch  30  changes. 
     Referring now to  FIG. 2  a schematic diagram of a magnetic sensitivity detector is shown.  FIG. 2  illustrates in further detail detector  40  of  FIG. 1 . Detector  40  receives power from DC Power  32  and is connected to ground  36  and Vcc  34  of power supply  32 . Detector  40  is further connected to Hall-effect switch  30  via output  38 . When the output of Hall-effect switch  30  changes to a state of “low”, MOSFET  50  activates indicator  52  to advise the user. Indicator  52  may take the form of an LED or a sound chime IC. Resistor  54  serves to limit current through indicator  52 . 
     Referring now to  FIG. 3  a plan view of an electromagnet connected to a Gauss meter is shown. Electromagnet  12  and its associated components are identical to those of  FIG. 1 . In use, once detector  40  has indicated to the user that switch  30  has been triggered, i.e. its output has changed to low, the user moves the electromagnet  12  to magnetic sensitivity verifier probe  70 . Magnetic sensitivity verifier probe  70  may utilize a Gauss meter  72  such as the model 410 provided by Lakeshore Cryotronics Inc. Gauss meter  72  provides a reading on the magnetic sensitivity of electromagnet  12   
     Referring now to  FIG. 4  a flowchart of the process for testing the strength of the magnetic field for a Hall-effect switch is shown. To aid the reader in following the steps we refer to the components of  FIGS. 1 and 3 . Beginning at step  80  electromagnet  12  is connected to adjustable DC power supply  20 . At step  82 , a Hall-effect switch  30  is placed in Hall-effect switch component  14 . This may be done by various means, including soldering or by placing the switch in a receptacle designed for the switch. Further at step  82 , a DC power supply  32 , which may comprise a battery is connected to switch  30  and detector  40  of Hall-effect switch component  14 . At step  84  electromagnet  12  is connected to Hall-effect switch component  14 . At step  86  power supply  20  is adjusted until detector  40  is triggered. At step  88  electromagnet  12 , while still connected to power supply  20  is moved to contact magnetic sensitivity verifier probe  70 . Finally at step  90  the magnetic sensitivity as indicated by gauss meter  72  is recorded. 
     Although one example of the use of an embodiment of the present invention is for testing Hall-effect switches, use of an electromagnet with a permanent magnet as disclosed may be utilized in other fields when determining magnetic sensitivity for a specific amount of magnetic field strength is required. 
     Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims.