US2504865A - Limit timer for protection of X-ray tubes - Google Patents

Description

Aprili 1s, 195o R. H. MORGAN I'AL LIMIT TIMER FOR PRTECTION 0F X-RAY TUBES Filed May 15, 1946 #$30k .kv @0.590,0

ANN.

nunlom Husel/ h. Morgan Hzu/ C'. Hodges machine thereby is deenergized and voltage is removed from the high-tension transformer Il of the X-ray machine and the X-ray exposure thereby terminated. The value of the resistor 7 is chosen sc that the time required for the potentials to develop on condenser 2 is equal to the exposure time Winch may be tolerated by the X-ray tube for the lowest tube currents which will be used.

Simultaneously with the charging of the condenser 2 through the resistor 'I there will also be a charging eiect through the resistor i and the rectifier by a voltage developed by the transformer B in response to a voltage developed across its primary winding when current which ows through the X-ray tube iiows through the secondary Winding of the high-tension transformer I'I and the resistor I6. This current develops a potential across the resistor I6 which is impressed upon the transformer 6. The greater the current iiowing through the X-ray tube, the greater will be the potential developed across resistor I B and applied to the transformer 6. Depending on the value of this potential, charge will be placed upon the condenser 2 by the resistor 4. The resistor 4 is adjusted so that the time at which the condenser 2 applies a suiicient voltage to the thyratron I for it to become conductive will be the maximum exposure time tolerated by the X-ray tube at the highest X-ray tube currents which are used. The rectifier tube 5 is placed in this circuit so that the current iiowing through the resistor 4 is unidirectional; the current developed by the transformer 6 is an alternating current and therefore the rectifier is needed to produce the desired unidirectional effect.

summarizing, the resistor 1 is of such value the thyratron tube I will become conductive only after the maximum exposure time which may be tolerated by the X-ray tube at the lowest X-ray tube currents employed and the resistors 4 and I6 adjusted to such values that the thyratron tube I will become conductive at the maximum exposure time tolerated by the X-ray tube when operated at the highest X-ray tube currents that are employed. At X-ray tube currents between these extremes the invention will limit the exposure time to values depending on the current owing through the X-ray tube and at such values as are Within those tolerated by the X-ray tube without causing damage.

Manifestly, many changes and modifications in the described automatic time mechanism will be apparent to those skilled in the art. For this reason the description is intended to be illustrative only and the scope of the invention is to be limited only as required by the following claims.

, Having thus described our invention what we claim as new and wish to secure by Letters Patent is:

' l. An electronic timing mechanism for controlling the exposure time .of an X-ray tube comprising in combination anormally open supply circuit, a source of potential connected with said circuit, -an X-ray tube including the electrodes thereof, a transformer embodying primary and secondary coils, the primary coil being connected with said supply circuit, the secondarycoil with the electrodes of said tube, means for closing said normally open supply circuitand initiating the exposure period of said X-ray tube and additional means in electrical relation with the secondary coill of said transformer for disrupting fili said supply circuit and terminating the exposure period of said X-ray tube at the expiration of the maximum exposure time tolerated by said tube at the lowest and at the highest tube currents used, said additional means including a control condenser, Ea pair of uni-directional charging circuits connected withrand arranged for simultaneously charging said condenser, one of said circuits being normally open and connected with a source of supply, the other of said charging circuits being connected with the secondary of said transformer, means coupled with said normally open supply circuit for closing the normally open charging circuit and simultaneously inducing current iiow in the remaining charging circuit when the exposure period of said X-ray is initiated, each of said charging circuits including resistor means, the value of the resistor means in yone of the charging circuits being such that the charging effect of such circuit with respect to said control condenser determines the maximum exposure time tolerated by said X-ray tube at the lowest tube currents used, the Value of the resistor means in the other of said charging circuits being such that the charging eiect of such circuit with respect to said control condenser determines the maximum exposure period at the highest tube currents used.

2. An electronic timing mechanism for controlling the exposure time of an X-ray tube comprising in combination a normally open supply circuit, a source of potential connected with said circuit, an X-ray tube including the electrodes thereof, a transformer embodying primary and secondary coils, the primary coil being connected with said supply circuit, the secondary coil with the electrodes of said tube, said secondary coil including a resistor, means for closing said normally open supply circuit and initiating the exposure period of said X-ray tube and additional means in electrical relation with the secondary coil of said transformer for disrupting said supply circuit and terminating the exposure period of said X-ray tube at the expiration of the maximum exposure time tolerated by said tube at the highest and at the lowest tube currents used, said additional means including a control condenser, a pair of uni-directional charging circuits connected with and effective for simultaneously charging said condenser, one of said charging circuits being normally open and connected with a source of potential, the remaining charging circuit being inductively coupled with the resistor in the secondary coil of said transformer, means coupled with said normally open supply circuit for automatically closing said normally open charging circuit and simultaneously applying the voltage drop across said last-mentioned resistor to the remaining charging circuit, resistor means in each of said charging circuits, the value of the resistor means. in one of said charging circuits being such that the charging effect of said circuit with respect to said control condenser determines the'maximum exposuretime tolerated by said X-ray tube at the lowest tube currents used, the value of the resistor means in the remaining circuit being such that its charging effect with respect to said control condenser determines the maximum exposure period at the highest tube currents used.

3. An automatic electronic timing mechanism for controlling the exposure time for an X-ray tube comprising in combination a normally open supply circuit including a pair of normally closed contacts, a'source of potential connected with' said circuit, an X-ray tube including the electrodes thereof. a transformer embodying primary and secondary coils, the primary coil being connected with said supply circuit, the secondary coil with said X-ray tube, said secondary coil including a resistor, means for closing said normal- 1y open supply circuit to initiate the exposure period of said X-ray tube, a thyratron relay system coupled to the secondary coil of said transformer and coacting with the normally closed contacts in the supply circuit, said thyratron relay system operating when said thyratron becomes conductive to open the normally closed contacts in said supply circuit, and control means in electrical relation With said thyratron relay system to render the latter conductive at the expiration of the maximum exposure time tolerated by said tube at the lowest and at the highest tube currents used, said control means including a control condenser, a pair of charging circuits connected with and effective for simultaneously charging said condenser one of said charging circuits being normally open and connected with a source of potential, the other of said charging circuits being inductively coupled with the resistor in the secondary coil of said transformer, means coupled with said normally open supply circuit for closing the normally open circuit and simultaneously applying to the remaining circuit the voltage drop across the reslstor in the secondary coil of said transformer, resistor means in each of said charging circuits, the resistor means in one of said charging circuits being such that the time at which said control condenser applies a suflicient voltage to the thyratron for it to become conductive determines the maximum exposure time tolerated by the X-ray tube at the largest X-ray tube currents used, the value of the resistor means connected with the remaining charging circuit being such that the time at which the control condenser applies a suiicient voltage to the thyratron for it to become conductive determines the maximum exposure time tolerated by the X-ray tube at the lowest X-ray currents used.

RUSSELL H. MORGAN.

PAUL C. HODGES.

REFERENCE S CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,016,147 La Pierre et .al Oct. 1, 1935 2,167,529 Scaife July 25, 1939 .2,252,530 Sweeny et al Aug. 12, 1941 2,353,980 Weisglass July 18, 1944 2,384,647 Schwarzschild Sept. 11 1945

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