Abstract: A vehicle detector installation includes a loop oscillator the loop of which is laid in the roadway and which is locked in operation to a voltage controlled oscillator (VCO). Vehicle detection is effected by a phase detector monitoring the phase difference between the oscillators. The VCO is incorporated in a phase-lock loop (PLL) that is capable of locking to a multiple of a reference frequency oscillator over a range of multiples. To achieve the locking of the loop oscillator to the VCO, means are provided for disabling the normal operation of the PLL and sweeping the VCO over its range of frequency until the phase detector indicates that the loop oscillator and VCO frequencies are equal. This indication activates the PLL to its normal operation to pull the VCO and therewith the loop oscillator to an adjacent multiple of the reference frequency. The PLL is maintained by a repeated charge/discharge cycle of the VCO capacitor that is dependent on the phase of the reference oscillator and the VCO.

Abstract: The orbital welding torch described herein has a horse-shoe shaped body arranged to engage partially around the tubes to be butt welded when inserted from one side of the tubes, and a crescent shaped table carrying a welding head which is rotatably carried by the body so that rotation of the table relative the body orbits the welding head around the region of the weld, the open mouth of the table being capable of alignment with the open mouth of the body to enable the body to be inserted from one side of the tube to engage partially around the tubes.