APPARATUS AND METHOD TO DETECT EXTERNAL MAGNETIC INTERFERENCE
IN SPEED SENSOR
FIELD OF INVENTION
The present invention relates to the field of motion sensor systems and related methods for measuring vehicle's speed and distance travelled. More particularly, the present invention relates to motion sensor which is capable of detecting the external magnetic interference.
BACKGROUND ART
The motion sensor is intended to be installed in vehicles, more particularly in road transport vehicles. Its purpose is to provide a vehicle unit (VU) with secured motion data representative of vehicle's speed and distance travelled. The vehicle unit (VU) is located in the driver's area of the vehicle. The vehicle unit (VU) stores information relating to system faults, attempts to tamper with the system, over-speeding, calibration details and records data access details.
The motion sensor, which may be a non contact sensor and it, may be located in the vehicle's gear box or in any other part of the vehicle. In its operational mode, the motion sensor is connected only to a vehicle unit (VU), i.e they are encoded as a pair. The signals from the motion sensor are encrypted and any attempt to interfere with them is recorded in the vehicle unit.
In the present version of motion sensor unit, the drawback is that it fails to detect the presence of external magnetic interference. Often it is noticed that drivers of the vehicles position strong permanent magnet on the motion sensor unit intentionally to create external magnetic interference which lead to the communication error and false information to the vehicle unit.
In certain cases the vehicle drivers deliberately position strong magnets in the vicinity of the

sensors to prevent the effective sensing of the sensors there by preventing the sensor from sending the detail to the engine unit. Sometimes, the drivers of the vehicle indulge in such activities, to escape from the government authorities from the non compliance of the regulations such as the same driver should not drive the vehicle continuously beyond certain number of stipulated hours.
Therefore there exist needs to provide an improved motion sensor capable of detecting external magnetic interferences.
OBJECTS OF INVENTION
Accordingly it is the main object of the present invention to provide apparatus and method to detect external magnetic interference in speed sensor.
It is another object of the present invention to provide an apparatus t capable of sensing and recording information on a vehicle unit (VU), reporting a suspicious operation with external magnetic interferences in speed sensor.
It is another object of the present invention to provide a motion sensor unit with external magnetic interference detection and reporting mechanism for measuring vehicle's speed and distance travelled.
The apparatus to detect external magnetic interference in speed sensor comprising of: Housing; O-Ring; One or more Hall integrated circuit (IC);

Printed circuit board (PCB) assembly;
Holder;
Magnet;
Adaptor; and
Cup
It is another object of the present invention, wherein the PCB assembly is provided with one of the Hall IC (secondary Hall IC) and a micro processer based signal processor for detecting external magnetic interference and transmitting such information to the vehicle unit.
It is another object of the present invention, wherein the secondary Hall IC detects the presence of external magnetic interferences and transmits information to the vehicle unit.
It is another object of the present invention, wherein the adaptor is disposed to accommodate the magnet, the primary Hall IC, the holder and the PCB assembly.
According to another object of the present invention, wherein the housing is detachably fitted to the adaptor with the 'O' ring disposed in between the housing and the adaptor for effective sealing of the parts of the motion sensor unit from dust and other impurities.
According to the another object of the present invention, wherein when the presence of magnetic interference is detected in the rear side of the motion sensor by the secondary Hall IC the motion sensor runs normally and transmits information to the vehicle unit (VU), indicating the presence of the external magnetic interferences.

According to another object of the present invention, wherein when there is no magnetic interference in the rear side of the motion sensor, the motion sensor runs normally and transmits the required information to the vehicle unit (VU).
It is another object of the present invention, wherein the implementation of the hall sensor (secondary Hall IC) in the rear side of the motion sensor for detecting any attempt of suspicious operations on the motion sensor is simple and effective.
SUMMARY OF INVENTION
Thus according to the basic aspect of the present invention there is provided an apparatus to detect external magnetic interference in speed sensor comprising:
an adaptor;
a magnet;
a holder;
a PCB assembly; and
a housing,
wherein the adapter is disposed to house the magnet, the holder and the PCB
assembly,
wherein the PCB assembly comprises of a printed circuit board, one or more Hall
integrated circuit (IC), and a signal processor,
wherein the PCB comprises one or more stepped portions of pre determined width
and length,
wherein the Hall IC is positioned adjacent to face of the first stepped portion of the
PCB defining a pre determined distance,

wherein the Hall IC and the signal processor are positioned on the third stepped
portion of the PCB and interfaced with the PCB circuit for detecting external
magnetic interference,
wherein the housing is provided with one or more terminals for interfacing with
vehicle unit and is detachably mounted at one end of the adapter, and
wherein a cup is disposed for closing other end of the adapter which is located at the
Hall IC end.
It is another aspect of the present invention, wherein the adapter is cylindrical in shape and comprises of one or more cylindrical portions of pre determined inner diameter, outer diameter and length.
It is another aspect of the present invention, wherein the magnet is cylindrical in shape and is having a pre determined inside diameter, outside diameter and length.
It is another aspect of the present invention, wherein the magnet is retained in position by the first stepped portion of the PCB and the first cylindrical portion of the adapter.
It is another aspect of the present invention, wherein the Hall IC is soldered to the PCB such that on assembly, the magnet encloses the Hall IC.
It is another aspect of the present invention, wherein, the holder comprises of a cylindrical passage opening to house the magnet and a step portion disposed to support the PCB assembly.
It is another aspect of the present invention, wherein the housing is having a cylindrical inside

portion with two key like openings for locating and holding the PCB assembly.
It is another aspect of the present invention, where in cylindrical outside portion of the housing is provided with an annular groove to accommodate a 'O' ring.
A further aspect of the present invention is directed to provide a method to detect external magnetic interference in speed sensor comprising the steps of:
sending an erratic signal to a vehicle unit by a Hall IC;
sending a special signal to a micro processer based signal processor by a Hall IC;
processing of the signal by the signal processor and providing a special signal to the
vehicle unit; and
recording time and duration of such disturbance by the vehicle unit using the special
signal.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 of the drawing schematically illustrates the exploded view of the apparatus to detect external magnetic interference in speed sensor according to the present invention. Figure 2 of the drawing schematically illustrates the adapter according to the present invention. Figure 3 of the drawing schematically illustrates the holder according to the present invention. Figure 4 of the drawing schematically illustrates the PCB according to the present invention. Figure 5 of the drawing schematically illustrates the housing mounted with the 'O' ring according to the present invention.
DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE
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ACCOMPANYING FIGURES
The apparatus to detect external magnetic interference in speed sensor is usually fitted in the gear box unit of the engine. Referring to Figure 1 of the drawings, the apparatus to detect external magnetic interference in speed sensor according to the invention comprises an adapter (1) which is disposed to house a magnet(2), a holder (3), a PCB assembly (4) having a first Hall IC (6), a second Hall IC(7) and a micro processer based signal processor (8). The housing (9) is disposed to cover the cylindrical passage opening of one end of the adapter (1) and a cup (10) is disposed to cover the cylindrical passage opening of other end of the adapter (1). The other end of the adapter (1) which is located at the first Hall IC (6) end is effectively closed by the cup (10) by any of the known methods, such as chalking.
Referring to Figures 1, 2 and 3, the adapter (1) is cylindrical in shape and comprises of one or more cylindrical portions of pre determined inner and outer diameter and length. The first cylindrical portion (la) is having an inner diameter to accommodate the outside diameter of the magnet (2), the second cylindrical portion (lb) is having an inner diameter to accommodate the outside diameter of the holder (3) and the third cylindrical portion (lc) is having an inner diameter to accommodate the PCB assembly (4). The third cylindrical portion (lc) of the adapter (1) is further provided with hexagonal portion (Id) to facilitate applying the required torque for mounting/demounting the sensor from the gear box of the engine. The adapter (1) is made of non magnetic material for example stainless steel, brass.
In one of the embodiments the second cylindrical portion (lb) of the adapter (1) is threaded to facilitate fixing of the sensor in the required location.

Referring to Figures 1, 2, 3 and 4, the printed circuit board assembly - PCB assembly (4) comprises a printed circuit board -PCB (5) having one or more stepped portions of pre determined width and length. The width and length dimensions of the first stepped portion (5a) is selected such that the magnet (2) can be mounted and retained in the required axial orientation with respect to the other stepped portions of the PCB (5). The width and length dimension of the second stepped portion (5b) is selected such that the PCB assembly (4) can be held by the step portion (3a) of the holder (3). The width dimension of the third stepped portion (5c) is selected such that the PCB assembly (4) is accommodated inside the third cylindrical portion (lc) of the adapter (1). The width and length dimensions of the fourth stepped portion (5d) is selected such that on assembly of the magnet (2), the holder (3), the PCB assembly (4) and the housing (9) in the adapter (1), the PCB assembly (4) is retained in the pre determined location and orientation.
The irst Hall IC (6) is positioned adjacent to the face of the first stepped portion (5a) at a pre determined distance and soldered to the PCB (5) such that on assembly, the magnet (2) encloses the first Hall IC (6). The first Hall IC (6) is disposed to provide information such as the speed of the vehicle, the distance travelled, the time duration between switching on and off of the engine etc as known in the art.
The second Hall IC (7) is positioned on the PCB (5) at the third stepped portion (5c) and interfaced with the PCB circuit. The micro processer based signal processor (8) is interfaced with the PCB circuit. The second Hall IC (7) and the signal processor (8) are disposed to provide a special signal to the vehicle control unit when ever the signal generated by the first Hall IC (6) is erratic/no signal is generated due to magnetic interference experienced by the first Hall IC (6).

The magnet (2) is cylindrical in shape and is having a pre determined inside diameter, out side diameter and length. As described in the early part of the description, the magnet (2) is retained in position by the first stepped portion (5a) of the PCB (5) and the first cylindrical portion (la) of the adapter (1).
The holder (3) comprises a cylindrical passage opening (3b) of pre determined dimensions to house the magnet (2) with pre determined radial clearance. The holder (3) is having a step portion (3a) which is disposed to support the PCB assembly (4) by the second stepped portion (5b) of the PCB (5). The holder (3) is made of non metallic material for example plastic material, preferably nylon.
Referring to Figures 1 and 5, the housing (9) with one or more terminals (9b) for interfacing with the vehicle unit is provided for closing one end of the adapter (1) and is detachably mounted on the adapter (1). The housing (9) is made of plastic material, preferably nylon. The housing (9) is having a cylindrical inside portion with at least two key like openings (9a) for locating and holding the PCB assembly (4) by the fourth stepped portion (5d ) of the PCB (5). The terminals (9b) are disposed for interfacing of the apparatus to detect external magnetic interference in speed sensor with the engine unit and the other end of the terminals are soldered with the PCB (5). The cylindrical outside portion of the housing (9) is provided with an annular groove (9c) to accommodate a 'O' ring (11) disposed to provide effective sealing of the parts housed within the adapter (1) there by the entry of micro dust and any other fluids that present in vicinity of the engine is eliminated.
During normal working, the first Hall IC (6) sends signal to the vehicle unit for measuring and

recording the parameters such as vehicle's speed and distance travelled. Whenever the working of the sensor is intentionally disturbed by keeping strong magnet near the sensor, the sensor according to the present invention perform the following functions:
sending an erratic signal to the vehicle unit by the first Hall IC (6);
sending a special signal to the micro processer based signal processor (8) by the second
Hall sensor (7);
processing of the signal by the signal processor (8) and providing a special signal to the
vehicle unit; and
recording time and duration of such disturbance by the vehicle unit using the special
signal.

WE CLAIM:
1. An apparatus to detect external magnetic interference in speed sensor comprising: an adaptor (1); a magnet (2); a holder (3);
a PCB assembly (4); and a housing (9),
wherein the adapter (1) is disposed to house the magnet (2), the holder (3), and the PCB assembly (4),
wherein the PCB assembly (4) comprises of a printed circuit board (5), one or more Hall integrated circuit (IC) (6, 7), and a signal processor (8),
wherein the PCB (5) comprises one or more stepped portions (5a, 5b, 5c and 5d) of pre determined width and length,
wherein the Hall IC (6) is positioned adjacent to face of the first stepped portion (5a) ofthePCB(5) defining a pre determined distance,
wherein the Hall IC (7) and the signal processor (8) are positioned on the third stepped portion (5c) of the PCB (5) and interfaced with the PCB circuit for detecting external magnetic interference,
wherein the housing (9) is provided with one or more terminals (9b) for interfacing with vehicle unit and is detachably mounted at one end of the adapter (1), and wherein a cup (10) is disposed for closing other end of the adapter (1) which is located at the Hall IC (6) end.

2. The apparatus as claimed in claiml, wherein the adapter (1) is cylindrical in shape and comprises of one or more cylindrical portions (la, lb, lc and Id) of pre determined inner diameter, outer diameter and length.
3. The apparatus as claimed in claiml, wherein the magnet (2) is cylindrical in shape and is having a pre determined inside diameter, outside diameter and length.
4. The apparatus as claimed in claim 3, wherein the magnet (2) is retained in position by the first stepped portion (5a) of the PCB (5) and the first cylindrical portion (la) of the adapter (1).
5. The apparatus as claimed in claiml, wherein the Hall IC (6) is soldered to the PCB (5) such that on assembly, the magnet (2) encloses the Hall IC (6).
6. The apparatus as claimed in claiml, wherein, the holder (3) comprises of a cylindrical passage opening (3b) to house the magnet (2) and a step portion (3a) disposed to support the PCB assembly (4).
7. The apparatus as claimed in claiml, wherein the housing (9) is having a cylindrical inside portion with two key like openings (9a) for locating and holding the PCB assembly (4).
8. The apparatus as claimed in claim7, wherein cylindrical outside portion of the housing (9) is provided with an annular groove (9c) to accommodate a 'O' ring (11).

9. A method to detect external magnetic interference in speed sensor comprising the steps of:
sending an erratic signal to a vehicle unit by a Hall IC (6);
sending a special signal to a micro processer based signal processor (8) by a Hall
IC(7);
processing of the signal by the signal processor (8) and providing a special signal
to the vehicle unit; and
recording time and duration of such disturbance by the vehicle unit using the
special signal.