With a phantom the thickness of the average patient, approximately 20 cm., one can adjust the phototimer circuit to give the desired density on a film in an experimentally determined time, less than the limiting time of half a second. If no impulse timer is available, the spinning top can be used for two or three spot checks.Ī distinct advantage of this impulse counter is that, for experimental work, each exposure can be individually checked, including phototimers. The accuracy of the impulse counter is easily checked by comparing it with an impulse timer. In the two counters constructed, a minimum of 120 volts A.C. The total counts should be identical with the number of dots made with a spinning top. The advantage of connecting over the primary coil is that any defect in the timer or magnetic switch is by-passed and only the actual number of impulses reaching the x-ray tube are counted. The counter can then be plugged in at any time to make a quick check. These two wires are brought out to the front control panel to terminate in a plug receptacle (B, Fig. 1) over the primary binding posts on the wiring panel. 2) is connected over the terminals of the primary coil of the high-tension transformer by placing two wires (X and Y, Fig. The total of both counts will give the total number of impulses for a given time interval. One Register will thus be activated during one half cycle and the other Register during the opposite half cycle. These two units are connected in parallel so that each bears a polarity opposite to the other. A second Register is connected to another rectifier in the same way. One Message Register (Western Electric, Type 14 E) is connected in series with a half-wave selenium rectifier (Fig.

The construction of the counter is simple. With this counter the technician or service man can obtain an immediate check on the accuracy of the timer without loss of time, while the machine is in actual use. To overcome these disadvantages, the impulse counter to be described here has been devised. Adjustment of the timer, if it is required, involves still further loss of time, during which the machine must stand idle. This method, while it is reliable, requires considerable time and film, and the results cannot be known until the film is processed. Timers used for short x-ray exposures are usually checked for accuracy with a spinning top.

Phototime in xray