Proximity responsive device

摘要

967, 401. Detecting conductive bodies. BROOKHIRST IGRANIC Ltd. May 2, 1962 [May 25, 1961], No. 16831/62. Heading G1N. [Also in Division H1] A proximity responsive device comprises a sensing coil system in which equal and opposite alternating voltages are normally produced and which gives an alternating output voltage on the approach of a conductive member, the output voltage modulating the normally unidirectional output voltage of an amplifier to control a load, the coil system having coaxial primary and secondary coils of equal mean diameters substantially equal to the distance between successive coils. Primary coil 24 is arranged between secondary coils 26, 28 on a bored cylindrical mounting member 6 containing a fixed core 22 and a tuning slug 8. Mounting member 6 is located in a housing 2 which also contains printed circuit boards 10, 12 and potting material 5. The rear end of the unit is adapted as a connector plug and the sensing end is located in a recess in a supporting member 3. Primary coil 24 forms part of the tuned circuit of an oscillator, and the series connected secondary coils 26, 28 form a resonant circuit with capacitor C4, tuned to the oscillator frequency. In the absence of a conductive member slug 8 is adjusted so that the voltages induced in 26, 28 are equal and opposite. Coils 26, 28 are coupled through capacitor C5 to an amplifier comprising an emitter-follower stage including transistor T2, and a second stage including transistor T3. In the balanced state D.C. flows through transistor T3 and resistors R5. Transistor switch T4 is also conductive and shunts a load connected between terminals 18A and 18B, diode RT3 matching the voltage drop across transistor T4. When a conductive member approaches the device the D.C. output from the amplifier is amplitude modulated by the A.C. output from coils 26, 28. The modulation is detected in a voltage doubling detector consisting of capacitors C7, C8 and rectifiers RT1, RT2, thereby switching off transistor T4 and applying a voltage to the load. The sensitivity may be adjusted by connecting a resistor between terminals 18A and 18F. Adjacent units may operate at different frequencies to prevent interference.