A transformer probe for sensing movement of a body of magnetic material comprising: a magnetically energisable pole piece; a sensing circuit comprising an electrical circuit having a first portion which is inductively coupled to the pole piece, the arrangement being such that movement of a body of magnetic material relative to the pole piece induces a current in the sensing circuit, and a second portion, remote from the pole piece, which forms first and second transformer primary coils (14, 16); a first output circuit comprising a first transformer secondary coil, inductively coupled to the first primary coil via a first transformer core, and terminated by a first load resistance, and means for measuring an output signal from the secondary coil, wherein the first primary coil and first secondary coil form a first transformer such that a current in the first primary coil induces a voltage across the first secondary coil; a second output circuit comprising a second transformer secondary coil, inductively coupled to the second primary coil via a second transformer core and terminated by a second load resistance and means for measuring an output signal from the second secondary coil, wherein the second primary coil and second secondary coil form a second transformer such that a current in the second primary coil induces a voltage across the second secondary coil; and an inductive coupling, or resistive electrical component (30, 31) connected across each primary coil, having an impedance within the sensing circuit such that a change from a normal circuit condition to an open circuit condition within the first or second output circuit does not significantly affect the voltage across the first and second primary coils. a magnetically energisable pole piece; a sensing circuit comprising an electrical circuit having a first portion which is inductively coupled to the pole piece, the arrangement being such that movement of a body of magnetic material relative to the pole piece induces a current in the sensing circuit, and a second portion, remote from the pole piece, which forms first and second transformer primary coils (14, 16); a first output circuit comprising a first transformer secondary coil, inductively coupled to the first primary coil via a first transformer core, and terminated by a first load resistance, and means for measuring an output signal from the secondary coil, wherein the first primary coil and first secondary coil form a first transformer such that a current in the first primary coil induces a voltage across the first secondary coil; a second output circuit comprising a second transformer secondary coil, inductively coupled to the second primary coil via a second transformer core and terminated by a second load resistance and means for measuring an output signal from the second secondary coil, wherein the second primary coil and second secondary coil form a second transformer such that a current in the second primary coil induces a voltage across the second secondary coil; and an inductive coupling, or resistive electrical component (30, 31) connected across each primary coil, having an impedance within the sensing circuit such that a change from a normal circuit condition to an open circuit condition within the first or second output circuit does not significantly affect the voltage across the first and second primary coils.