Owing to the wartime shortage of X-ray tubes, any device which is likely to lead to longer tubelife will probably be of interest to other users of X-ray tubes. Tube life is dependent upon a variety of factors, of which the most important is the running voltage of the tube. Some commercial X-ray tubes at the present time seem to have very little safety margin when run at the specified voltage, and
... [Show full abstract] a small temporary over-voltage may be sufficient to break them down. We have, therefore, thought it worth while to describe the following simple over-voltage relay which experience has shown to be useful for preventing accidental over-voltages due to careless handling of the controls.
In the case of manually controlled X-ray sets, over-voltages on the tube can arise from any of the following causes:—
(a) From the operator accidentally increasing the voltage too much.
(b) From the operator accidentally reducing the tube current before the tube voltage.
(c) From fluctuations in the mains voltage which, in wartime, may be considerable.
The relay described below will protect the X-ray tube against over-voltages arising from any of the above causes. It will not protect against surge voltages as its time of response is of the order of one-fifth second.