Apparatus for detecting ferromagnetic objects at a protected doorway assembly

Abstract

An apparatus for protecting an entrance to a protected area comprises a magnetic sensor to measure an ambient magnetic field or gradient within a first zone of sensitivity at a non-magnetic sensor means adapted to detect the presence of objects within a primary detection zone, a signal processing circuit arranged in communication with the magnetic sensor apparatus and non-magnetic sensor apparatus, and a warning device operable by an output signal from the signal processing circuit, the warning device adapted to provide an alarm. The signal processing circuit identifies temporal variations due to the movement of a ferromagnetic object within the ambient magnetic field and correlates them with instances in which the non-magnetic sensor means detects the presence of an object in its detection zone, and causes the alarm to operate in the event that the correlation is indicative of the presence of a ferromagnetic object in the primary detection zone. It also determines the direction from which an object is approaching the using signals from the non-magnetic sensor means and modifies the operation of the warning device dependent on the direction.

1 - 30 . (canceled) 
     
     
         31 . A method of protecting a doorway of a room, such as an MRI room, comprising the steps of:
 (a) measuring an ambient magnetic field or its gradient using passive primary sensing means comprising at least a magnetic sensor, and producing a corresponding measurement signal;   (b) detecting the movement of objects in the vicinity of the primary sensor means using a first non-magnetic sensing means adapted to detect the presence of objects within a respective zone in the vicinity of the primary sensor apparatus,   (c) identifying temporal variations in the measurement signal produced by the magnetic sensor means due to the movement of a ferromagnetic object within the ambient magnetic field within a localised volume of space defined by a zone of sensitivity of the magnetic sensor,   (d) assessing the identified temporal variations in the measurement signal in conjunction with movement of objects detected by the non-magnetic sensor means to determine a correlation there-between, and   (e) in the occurrence of such a correlation with both the magnetic and non-magnetic sensing means identifying the simultaneous presence of an object in their respective zones providing an indication of the presence of a ferromagnetic object,   (f) detecting the movement of objects in the vicinity of the magnetic sensor means using a second non-magnetic sensing means adapted to detect the presence of objects within a respective zone in the vicinity of the magnetic sensor apparatus which is located so that an object may enter the zone prior to entering the detection zone of the first non-magnetic sensing means, and   (g) suppressing the alarm signal for a period of time following the detection of an object in the detection zone of the second sensing means prior to entering the detection zone of the first non-magnetic sensing means.   
     
     
         32 . A method of protecting a doorway of a room, such as an MRI room, comprising the steps of:
 (a) measuring an ambient magnetic field or its gradient using passive primary sensing means comprising at least a first magnetic sensor, and producing a corresponding measurement signal;   (b) detecting the movement of objects in the vicinity of the primary sensor means using second, non-magnetic sensor means, the second sensor means comprising at least one sensor adapted to detect the presence of objects within a respective zone in the vicinity of the primary sensor apparatus,   (c) identifying temporal variations in the measurement signal produced by the first sensor means due to the movement of a ferromagnetic object within the ambient magnetic field within a localised volume of space defined by a zone of sensitivity of the magnetic sensor,   (d) assessing the identified temporal variations in the measurement signal in conjunction with movement of objects detected by the second, non-magnetic, sensor means to determine a correlation there-between, and   (e) in the occurrence of such a correlation and with both the secondary sensors identifying the simultaneous presence of an object in their respective zones providing an indication of the presence of a ferromagnetic object,   wherein the step of providing the indication of the presence of a ferromagnetic object comprises the step of producing within the vicinity of the primary sensor means at least one of an audible and a visible alarm,   (f) detecting the movement of objects in the vicinity of the primary sensor means using a third, non-magnetic sensor means, the third sensor means comprising at least one sensor adapted to detect movement of the door of the doorway; and   (g) modifying the alarm in the event that the door is moving.   
     
     
         33 . A method of protecting a doorway of a room, such as an MRI room, comprising the steps of:
 (a) measuring an ambient magnetic field or its gradient using passive primary sensing means comprising at least a first magnetic sensor, and producing a corresponding measurement signal;   (b) storing in a memory historical temporal variations in the measurement signal due to movement of a ferromagnetic object within the ambient field,   (c) detecting the movement of objects in the vicinity of the primary sensor means using second, non-magnetic sensor means, the second sensor means comprising at least one sensor adapted to detect the presence of objects within a respective zone in the vicinity of the primary sensor apparatus,   (d) identifying temporal variations in the measurement signal produced by the first sensor means due to the movement of a ferromagnetic object within the ambient magnetic field within a localised volume of space defined by a zone of sensitivity of the magnetic sensor,   (e) assessing the identified temporal variations in the measurement signal in conjunction with movement of objects detected by the second, non-magnetic, sensor means to determine a correlation there-between, and   (f) in the occurrence of such a correlation and with both the secondary sensors identifying the simultaneous presence of an object in their respective zones providing an indication of the presence of a ferromagnetic object,   wherein the step of providing the indication of the presence of a ferromagnetic object comprises the step of producing within the vicinity of the primary sensor means at least one of an audible and a visible alarm,   (g) detecting the movement of objects in the vicinity of the primary sensor means using a third, non-magnetic sensor means, the third sensor means comprising at least one sensor adapted to detect movement of the door of the doorway;   (h) in the event that the door is moving correlating the stored historical temporal variations in the measurement signal prior to the door moving with incidences in which the non-magnetic sensor apparatus detects the presence of an object in its detection zone, and   (i) modifying the alarm in the event that the door is moving by raising an alarm in the event that the correlation, albeit separated in time, is indicative of the presence of a magnetic object in the vicinity of the magnetic sensor or suppressing the alarm if the correlation, albeit separated in time, does not indicate the presence of a magnetic object in the vicinity of the magnetic sensor.