plew: Plew’s television picture synchronising system.

Extracted from Television Dec 1934.

Mains Synchronising

Most mains nowadays are frequency-controlled A.C., and though not interlocked with those used at the transmitter, are in themselves quite steady enough to be used to run a receiver, though one must be prepared for a slow acceleration or retardation.

Such variations will be very slow, and, of course, may happen at either the transmitting or receiving end. To overcome the difference in frequency of the two mains an ingenious system has recently been put on the market by the Plew Television Co.

It consists, see Fig. 1, of an ordinary universal motor M, which is fitted to an 8-tooth wheel and pole-pieces, S, very similar to the 30-toothed synchroniser. On the other side of the synchronising unit is a fibre bevelled wheel, F, which makes a frictional contact on D at the point P, and the movement of rotation is transferred to D, which is mounted on the same shaft as the disc or mirror drum.

Now if the diameter of F is equal to twice the radius of PC, D and F will rotate at the same speed, on the other hand, an increase or decrease of the radius of PC will either cause D to run faster or slower.

To effect the alteration of the radius PC, the driving motor is on sliders, and its position can be adjusted. Thus, though the speed of F is controlled by the A.C. mains by S, the final speed of D can be adjusted to that of the transmitter.

Of course, M could be a synchronous motor, though it is not easy to build a single-phase, self-starting motor, of small dimensions and power.

It should also be noted that there are a few makes of synchronous motor on the market in the form of gramophone mechanisms, which, though they generally run at 1,500 r.p.m., could be quite easily adapted to the system developed by the Plew Company.

Television Dec 1934, Page 534

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