GB2100892A

GB2100892A - System for controlling filament and tube current in X-ray circuit arrangement

Info

Publication number: GB2100892A
Application number: GB08214118A
Authority: GB
Inventors: Santurtun Carlos Manueco; Carmena Angel Diaz
Original assignee: ESPANOLA ELECTROMED; General Espanola de Electromedicina SA
Current assignee: ESPANOLA ELECTROMED; General Espanola de Electromedicina SA
Priority date: 1981-05-14
Filing date: 1982-05-14
Publication date: 1983-01-06
Also published as: GB2100892B; JPS5832399A; DE3217901A1; IL65771A0; IL65771A; FR2506111A1; FR2506111B1; ES8302399A1; ES502249A0; NL8201998A

Abstract

An arrangement is provided for controlling the filament current of an X-ray tube 6. A D.C.-to-D.C. converter 2 supplies power to a D.C.-to-AC. inverter 3 including an output transformer 5 which acts as the filament supply transformer for X-ray tube 6. A first feedback circuit I allows the filament current to be stabilized and a second feedback circuit 7, 8, 9 allows the X-ray tube anode-cathode current to be stabilised at a selected or desired value. <IMAGE>

Description

SPECIFICATION Static system for controlling the closed loop intensity in X-ray The present invention refers to a static system for controlling the closed loop intensity to adjust the X-ray tube filament current and, in conjunction with the high voltage applied, to produce the emission of X-rays.

The invention is essentially characterised in that a direct current/direct current converter, denominated chopper is used which, besides staticaily stabilizing the variations in the input voltage which feeds the filament, permits the intensity of the current which passes through the filament and that of the X-ray tube during exposure to be controlled.

The direct current/direct current converter used in this system controls the output voltage which is applied to the filament transformer by means of a variable frequency which is dynamically adjusted to maintain this voltage constant. On the other hand, this voltage is a linear function of the demand of the filament control loop and in fact represents a constant filament intensity.

This control circuit, functioning at a high and auto-adjustable frequency, typically from direct current to 20 KHz, operates without filter condensers at its output, the reactance of the converter being the only existing filter, permitting a high speed response in the variations of the filament intensity.

This triple conversion control system of alternating current/direct current, direct current/direct current and direct current/alternating current, represents an important improvement when compared with other conventional systems, particularly in reproducibility and speed of response, referring to control the adjustment. The advantage of this static system resides in the high impedance leakage of some filaments to others in X-ray tubes, while the leakage is slightly less in the variable filament intensity, thus remarkably reducing the range of values which is converted to a substantial simplification of the necessary control and circuitry, as well as a higher accuracy in the system due to the compression of the range.

The most important problem arising from the control of the intensity of X-rays is due to the amplification factor produced by the filament current during emission. Typically, in conventional X-ray tubes a 1% variation in the intensity of the filament can produce, under determined conditions, a variation in the intensity of the tube of up to 15%, which could cause an uncontrolled radiation excess in the patient, which is highly dangerous.

At present conventional systems use, to control the voltage of the filament, ferroresonant type stabilizers, having saturable reactances, etc, which normally function at 50/60 Hz, lowerperformance circuits, and which dissipate a large amount of energy.

The use of a voltage control system which is applied tb the filaments instead of controlling the current, implies periodical adjustments due to the high ieakages of the impedance of some filaments to others in the X-ray tubes, remarkably increasing the range of filament current values, as well as a lesser accuracy of these systems.

This amount of circuits and interconnections minimise the reliability of these systems and the mean time between failures.

On the other hand, the two filaments are maintained in operation constantly, wherefore twice as much circuitry and two simultaneous demands are necessary, shortening the life of the X-ray tube.

These systems do not furthermore compensate the evaporation of the X-ray tubes during exposure, producing an exponential intensity drop due to the intensity thermoionic emission which, when initiated, reduces the remaining mean energy.

The objects of the invention reside in proportioning a static system for controlling the intensity of a closed loop, the characteristics of which are summarized in the following points: a) Statically stabilizing the variations in the input voltage, in the range of +20% for any type of filament, adjusting the output voltage.

b) Increasing the speed of response of the system for controlling the stabilizing voltage of the filament, which can operate between direct current and 20 KHz typically, being capable of reaching 50 KHz. This chopper system minimises the dissipation of energy of the system, the stabilizing circuit reaching a performance in the range of 95%. On the other hand, there is a reduction in volume, space and cost in the range of 60% when compared with other conventional voltage stabilizing systems, such as saturable reactances, ferroresonant circuits, etc.

c) The system feeds each one of the two filaments of the X-ray tube by means of a static inverter having "push-pull" connected transistors which, in turn, feeds the filament transformer which is necessary to isolate the low voltage part of the control from the high voltage part of the Xray tube.

This transistor inverter generates a square alternating current wave with a frequency of 400 Hz and whose effective voltage value is defined by the converter output in accordance with the filament intensity demand.

d) The accuracy of the filament intensity control is greater than 0.3%, wherefore an allowance in the range of 4.5% for variation in the emission intensity of the X-ray tube is guaranteed, once the voltage in kVp applied between the cathode and the anode of the tube reaches its nominal value.

e) Dynamically compensating the evaporation of the X-ray tube during exposure, preventing the exponential intensity drop, the time constant of which, typically of 130 milliseconds, is due to the intensity of thermoionic emission which, when initiated, reduces the remaining mean energy.

This static system for controlling a closed loop reduces the number of filament current values, necessary to control the intensity of X-rays, depending on the voltage applied, wherefore, for the same accuracy in the intensity of X-rays, this reduction is higher than 80%.

The most important advantages of this type of control, when compared with conventional controls, can be summarized as follows: a) To compensate and minimize the number of components of the control and adjustment circuits, as well as the X-ray tube emission leakage, when the system operates with a closed loop having twice as much intensity, filaments and X-ray tubes.

b) An increase in the reliability and mean time between failures, since the number of components and interconnecting elements is substantially reduced, with respect to other conventional voltage stabilizing systems, such as saturable reactances, ferroresonant circuits, etc.

c) To statically control the filament intersity instead of effecting a control by voltage as in other conventional systems, in order to compensate and minimise the dimensioning of the control and adjustment circuits, due to the high impedance leakage of some filaments to others in X-ray tubes, since this leakage is slightly smaller in the variable filament intensity; and to thereby achieve a remarkable reduction in the range of filament current values, as well as a higher accuracy.

Simplification of the control and of the necessary circuitry, which is converted to a substantial reduction in cost; an increase in the reliability of the system, and a longer duration of the product.

d) To prolonge the life of the X-ray tube, as a result of the reduction of the discharging energy, when compared with conventional systems which maintain the two filaments in operation constantly.

e) There is no limitation with respect to very short exposure times, such as one or various milliseconds, in the X-ray intensity control, although the filament time constant is typically in the range of 0.7 seconds.

f) To substantially improve the reproducibility of the values obtained in the X-ray intensity, with respect to other conventional systems, in spite of the wide value spectrum and the techniques which are obtained with any X-ray generator, which depend on the kVp range, exposure time and the intensity itself; and g) To proportion a new control system to transfer the Fluoroscopic system to the Radiographic system in the approximate time of 0.8 seconds, by means of an extra-transitional demand which permits the filament to be placed close to the emitting temperature in a very short period of time, about 0.2 seconds, so that during the remaining time of up to 0.8 seconds, a stabilizing temperature corresponding to the demand required by the operator, can be reached.

In the drawings: Figure 1 is a block diagram of the static system for controlling the closed loop intensity in X-ray generators.

Figure 2 is a simplified diagram of the direct current/direct current chopper and the control system therefore.

Figure 3 is a simplified diagram of the transistor inverter which feeds the filament transformer.

Figure 4 is a diagram of the error amplifier of the X-ray tube current (mA) and of the filament current and the X-ray tube current demands.

Figure 5 is the frequency response of the filament control loop.

Figure 6 to 9 are waveforms of the filament current and the response of the system to a scaled function.

The static system for controlling the closed loop intensity in X-ray generators is comprised of the following main elements, according to the block diagram of figure 1: 1. Non-stabilized feed system 2. Direct current/direct current chopper 3. Transistor inverter 4. Logic control unit 5. Filament transformer 6. X-ray tube 7. Error amplifier of the X-ray tube current (mA) 8. Closed loop of the mA current of the X-ray tube 9. Error amplifier of the filament intensity demand 1 0. Extra-transitional demand closed loop 11. Constant demand circuit.

1. Non-stabilized feed system There is obtained from the network a low voltage (point A) by means of a transformer, which is rectified, filtered and used as a feed to the direct current/direct current chopper (See point G in figure 2).

2. Direct current/direct current chopper This circuit converts the non-stabilized direct current voltage to stabilized direct current voltage and in accordance with the desired demand, as can be seen in figure 2.

On the other hand, the output of the operational amplifier IC 54 pin 6 or TP-13, feeds through R45 the base of the transistor Q37, which operates to almost-saturation due to the combined effect of the diodes CR35-CR36. This transistor in turn controls the transistors Q1 61 and Q6 which constitute the amplification step of the direct current/direct current converter (chopper).

The swiftness in response of the direct current/direct current converter depends mainly on the cutting off and saturation system applied to the assembly of power transistors. Particularly, to reduce the storage time of bearers in the junction, there is used the system of applying an emitter-base inverse intensity at the moment of triggering off, automatically and through the inductor L20 and resistor R24, in the case of transistor Q161, and similarly L3 and R4, in the case of transistor Q6.

On the other hand, the voltage pulse modulation of the transistor Q6 is applied through the inductor L5 to the direct current/direct current converter step. The rapid diode CR19 conducts the intensity of the charging circuit through the electromagnetic energy stored in the inductor in the periods of time in which the transistor Q6 does not conduct.

The time constant of the charging circuit is of approximately L/R, wherein L is the inductance of L5 plus that of leakages of the filament transformer, and R is the equivalent resistance at the primary side of the filament.

When the ratio L/R is varied due to the intrinsic variation of the filament resistor, according to the intensity required in the X-ray tube, the direct current/direct current converter automatically adjusts the frequency to maintain an output voltage value having a constant intensity looping, through the previously described feedback.

Thus, the input voltage is stabilized by adjusting dynamically to maintain the output voltage constant. The variable frequency between direct current and 20 KHz typically, being capable of reaching 50 KHz, a performance of the stabilizing circuit in the range of 95% being obtained.

3. Transistor inverter (As illustrated in figure 3) The voltage of the direct current/direct current converter through the reactance L5 (point J) is applied to the central tap of the primary of the filament transformer, whose secondary feeds the filament itself. Thus, not only can the direct current/direct current converter be used to feed two identical direct current/alternating current converters which in turn supply the sufficient energy for the thin and the thick filaments of the X-ray tube.

The stabilized voltage applied to the central tap of the primary of the filament transformer is converted to alternating current voltage by means of a push-pull transistor power circuit Q17 1 Q1 68, whose control at a constant frequency of approximately 400 Hz is operated across a logic control unit. This frequency of 400 Hz is an approximate value to reduce the size of the filament transformer. The second transistor inverter is identical to that described and, therefore, it is not illustrated in figure 3. Thus, the two transistor inverters are fed with a single chopper, reducing the circuitry and the cost of the system.

4. Logic control unit This unit is a circuit which controls the two transistor inverters corresponding to the two filaments of the X-ray tube (See figure 3).

On the other hand, it controls the power transistors of the inverters producing the square wave for the triggering on and off thereof, and on the other hand it selects one of the two inverters, depending on whether the control of the operator has selected the thin or the thick filament.

5. Filament transformer The square wave produced in the transistor inverters is applied to the primary of a filament transformer with the purpose of isolating the control part (low voltage) from the high voltage part of the X-ray tube.

Figure 3 illustrates how one of these transformers (T1) is connected.

Thus, the secondary winding of these filament transformers feed the two filaments of the X-ray tube.

6. X-ray tube An X-ray tube is a commercial component by means of which, applying thereto a high voltage between the cathode and the anode and injecting a current to the filaments, there is produced a radiation which is capable of being recorded on a screen or a radiographic plate in order to clinically study a patient.

Due to the great variety of tubes and to the high dispersion of filaments, a system capable of automatically adjusting any filament impedance to exactly control the desired current, is necessary.

7. Error amplifier of the X-ray tube current (mA) In this circuit the current of the X-ray tube is compared with the mA demand which the operator has selected from the control console of the X-ray generator.

The error between the two demands is detected and amplified, and serves as a feedback for the closed loop of the mA current of the X-ray tube.

Figure 4 illustrates how the error signal of the intensity loop compared, corrected and treated with respect to control, constitutes the filament demand. The X-ray intensity demand signal (point E) is applied through the resistor R95 to the negative input of the operational amplifier Al and it is deducted from the real intensity of the tube (point K) through the shunt R7 1 together with the resistors R1 28-R1 27.

8. Closed loop of the mA current of the Xray tube The error signal amplified in Al constitutes the signal denominated "mA error" which is then added to the filament intensity demand (figure 4) during exposure by means of the closed loop control signal which operates on the transistor FET IC 101, permitting the passage of the "mA error" signal across the negative input of the operational amplifier A2, whose output constitutes the signal denominated "filament demand" (point H) which acts, in turn, as a demand of the direct current/direct current connection step.

The operation in the Fluoroscopic system takes place with the-transistor FET IC 10-1 in an open position, preventing the input of the error signal of the intensity loop, wherefore the filament demand coincides with that of the filament intensity.

9. Error amplifier of the filament intenstity demand Figure 2 illustrates the filament current demand circuit.

The operational amplifier IC 54 mixes the compares three signals simultaneously: the description of which is as follows: The filament demand which originates from point H at the output of operational amplifier A2, constitutes in itself the error signal of the intensity loop during exposure. This signal through resistor R42 acts on the negative input of the amplifier IC 54.

On the other hand, there is an extra-transitional demand which operates on the transistor FET (F1) during transfer of Fluoroscopy to Graphy, to permit during a variable period of time, depending on the types oftube, in the range of 0.2 seconds, the filament in a position close to the emission to have the sufficient time during the remaining 0.6 seconds, to become stabilized and to reach, at the beginning of exposure, the intensity demanded by the operator in the X-ray tube.

The third signal which acts on the negative input of the operational amplifier IC 54, through the resistors R58-R57, constitutes the filament intensity feedback signal (point 1).

Thus, the output of the operational amplifier IC 54 controls the transistors of the chopper and constitutes the error detection step and amplification of the direct current/direct current converter (chopper).

10. Closed loop of the extra-transitional demand There is an extra-transitional demand which acts on the transistor F1 (figure 2) in the transfer of Fluoroscopy to Graphy, in order to permit during a variable time, depending on the type of tube, in the range of 0.2 seconds, the filament in a position close to the emission, to have the sufficient time during the remaining 0.6 seconds, to become stabilized and to reach, when exposure commences, the intensity demanded by the operator in the X-ray tube, Point B controls F1 to open or to close this loop.

11. Constant demand circuit Figure 2 illustrates this constant demand circuit. This circuit has a fixed demand voltage and is comprised of a resistor R9 1 and a diode CR107 and is connected to the rest of the circuit when the transistor FET (F1) conducts, applying a constant voltage in the extra-transitional demand.

This circuit proportions a new control system for transferring the Fluoroscopic system to the Radiographic system, in the approximate time of 0.8 seconds, by means of an extra-transitional demand, which permits the filament to be situated close to the emitting temperature, in a very short period of time, about 0.2 seconds, wherefore it can during the remaining time of up to 0.8 seconds, reach a stablizing temperature corresponding to the demand requested by the operator.

Analysis of the gain of the filament control system The filament feedback loop has "approximately" the following gain in an open loop: Gain Operational amplifier IC 54 20,000 (d.c.) and 1780 to 20 KHz Transistor Q37 25 Transistor Q161 100 Transistor Q6 100 Total gain: 50x 108=1 94 db in d.c.

The closed loop transfer function is given by the following formula: V0 G 1 Vc 1+GH H wherein V0=output voltage Voltage demand G(s)=direct transfer function H(s)=feedback transfer function; H=1/1 0 By replacing the value of H, we obtain for a zero frequency: V0 =10 VD On the other hand, the maximum error in the amplifier IC 54 at 20 KHz is given by the following expression: 100 Maximum error= =0.056% 1780 Figure 5 illustrates the Nichols diagram, from which it is clear that the system is absolutely and relatively stable with a phase margin of approximately 127C and a gain margin which could be extrapolated in 1 26 db.

Figures 6 and 7 illustrate the behaviour of the system in a stepped function, which confirms the swiftness in response and the optimization of the overshoot.

Figures 8 and 9 illustrate the direct current voltage applied to the filament transformer.

The amplitude of the signal is of 10 volts/division and the time is of 5 milliseconds/division.

Claims

1. An arrangement for controlling the filament current of an X-ray tube, comprising D.C. to A.C.

inverter having an output transformer for connection to the X-ray tube filament, and a D.C.to-D.C. converter whose output is connected to the power supply input of the inverter.

2. An arrangement as claimed in claim 1, in which a control input of the converter is connected to a feedback loop arranged to stabilise the X-ray tube filament current at a predetermined value.

3. An arrangement as claimed in claim 1, in which a feedback loop is provided for comparing the anode-cathode current of the X-ray tube with a desired value, and is arranged to control the converter so as to stabilize the anode-cathode current at the desired value.

4. An arrangement for controlling the filament current of an X-ray tube, substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

5. An X-ray apparatus including an arrangement as claimed in any one of the preceding claims.

6. Static system for controlling the closed loop intensity in X-ray generators, essentially characteristised by a static system for controlling the X-ray intensity through a feedback closed loop control having twice the filament intensity and from that which which is generated in the X-ray tube as a result of applying a voltage, which comprises, in combination, a direct current/direct current converter to transistors which control the filament intensity directly; a transistor inverter which feeds, through the corresponding transformer, the filament of the X-ray tube; and a system for the closed loop control of the two variables, filament intensity and X-ray intensity.

7. Static system for controlling the closed loop intensity in X-ray generators according to claim 6, characterised by the triple function of the static stabilizing direct current/direct current converter, as a voltage stabilizer; controller of the filament intensity loop; and of the intensity of the X-ray tube.

8. Static system for controlling the closed loop intensity in X-ray generators according to claims 6 and 7, characterised in that it utilizes a direct current/direct current converter, here referred to as a transistor chopper, the control of which through variable frequency is dynamically adjusted to maintain a constant voltage at the output thereof, which is an approximately linear function of the demand of the filament control loop which truly represents the filament intensity.

9. Static system for controlling the closed loop intensity in X-ray generators according to claim 8, characterised in that the control circuit functions at a variable frequency between direct current and 20 KHz typically, being capable of reaching 50 KHz; the reactance of the converter being the only existing filter, which permits a higher speed of response of the system in dynamic variations in filament intensity, when compared with other conventional systems.

1 0. Static system for controlling the closed loop intensity in X-ray generators according to claim 7, characterized in that besides statically stabilizing the variations in the input voltage, it permits the filament intensity and the X-ray intensity to be controlled during exposure, constituting an important improvement in the accuracy and swiftness in response of the complete system for controlling the intensity of the X-ray tube.

11. Static system for controlling the closed loop intensity in X-ray generators according to claims 6 and 7, characterized by improving the speed of response of the system for controlling the stabilizing voltage of the filament, which can operate up to a frequency of 50 KHz, when compared with other conventional systems, such as ferroresonant circuits, saturable reactances, etc. which normally operate at 50/60 Hz.

1 2. Static system for controlling the closed loop intensity in X-ray generators according to claims 6 and 7, characterised by reducing the dissipation of power of the static system for controlling the stabilizing voltage of the filament, when compared with other conventional systems, such as ferroresonant circuits, saturable reactances, etc., reaching a performance of the stabilizing circuit in the range of 95%.

13. Static system for controlling the closed loop intensity in X-ray generators according to claims 6 and 7, characterised by a reduction in volume, space and cost in the range of 60%, when compared with other conventional systems for stabilizing voltages, such as saturable reactances, ferroresonant circuits, etc.

1 4. Static system for controlling the closed loop intensity in X-ray generators according to claims 6 and 7, characterised in that the filament of the X-ray tube is fed through an alternating current voltage generated by successive conversions of network alternating current to direct current, from direct current to direct current and through the chopper to transistors for stabilization and demand of filament intensity, and from direct current to alternating current through two transistor inverters to feed the two filaments of the X-ray tube, by individual transformers which isolate the low voltage from the high voltage.

1 5. Static system for controlling the closed loop intensity in X-ray generators according to claim 6, characterised in that each one of the two filaments of the X-ray tube is fed by means of a push-pull connected static transistor inverter, which in turn feeds the filament transformer, which is necessary in the system for isolation purposes, so that the mentioned transistor inverter generates a square alternating current wave at a frequency of 400 Hz, whose effective voltage value is defined by the output of the direct current/direct current converter, depending on the filament intensity demand.

1 6. Static system for controlling the closed loop intensity in X-ray generators according to claim 6, characterised in that the static system for controlling a closed loop considerably reduces the number of filament current values necessary to control the X-ray intensity, depending on the applied voltage, wherefore, for the same accuracy in the X-ray intensity, this reduction is greater than 80%.

1 7. Static system for controlling the closed loop intensity in X-ray generators according to claims 6, and 16, characterised by compensating and minimising the number of components of the control and adjustment circuits, as well as the dispersion of X-ray tube emission, since the system operates with a closed loop having twice as much intensity, filaments and X-ray tubes,

1 8. Static system for controlling the closed loop intensity in X-ray generators according to claim 6, 1 6 and 17, characterised by an increase in the reliability and mean time between failures, since the number of components and interconnecting elements is substantially reduced, when compared with other conventional stabilizing systems, such as saturable reactances, ferroresonant circuits, etc.

1 9. Static system for controlling the closed loop intensity in X-ray generators according to claim 6, characterised by statically controlling the filament intensity instead of effecting a control by voltage as in other conventional systems, in order to compensate and minimise the dimensioning of the control and adjustment circuits, due to the high impedance leakage of some filaments to others in X-ray tubes, since this leakage is slightly smaller in the variable filament intensity, and thereby achieving a remarkable reduction in the range of filament current values, as well as a higher accuracy.

20. Static system for controlling the closed loop intensity in X-ray generators according to claim 19, characterised by a substantial simplification of the control and the necessary circuitry, which is converted to a substantial reduction in cost; an increase in the reliablity of the system; and a longer duration of the product.

21. Static system for controlling the closed loop intensity in X-ray generators according to claims 6 and 7, characterised by operating with a single direct current/direct current converter and a single demand to control two filaments of the Xray tubes, contrary to other conventional systems which maintain the two filaments in operation constantly.

22. Static system for controlling the closed loop intensity in X-ray generators according to claim 21, characterised in that the life of the X-ray tube is prolonged as a result of the reduction of the discharging energy when compared with conventional systems which maintain the two filaments in operation constantly.

23. Static system for controlling the closed loop intensity in X-ray generators according to claims 6 to 22, characterised in that there is no limitation with respect ot very short exposure times, such as one or various milliseconds, in the X-ray intensity control, although the filament time constant is typically in the range of 0.7 seconds.

24. Static system for controlling the closed loop intensity in X-ray generators according to claims 6 to 22, characterised in that an allowance in the range of 4.5% in the intensity of the X-ray tube is guaranteed, once the voltage in kVp reaches its nominal value.

25. Static system for controlling the closed loop intensity in X-ray generators according to claims 6 to 24, characterised in that uncontrolled radiation excesses, highly dangerous for the patient, are prevented, as a result of achieving an accuracy greater than 0.3% in the control of the filament intensity, which guarantees an allowance in the range of 4.5% in the variation in the X-ray emission intensity.

26. Static system for controlling the closed loop intensity in X-ray generators according to claims 6 to 25, characterised in that the evaporation of the X-ray tubes during exposure is dynamically compensated, preventing the exponential intensity drop, whose time constant, typically of 130 milliseconds, is due to the intensity thermoionic emission which, when initiated, reduces the remaining mean energy.

27. Static system for controlling the closed loop intensity in X-ray generators according to claims 6 to 26, characterised in that the reproducibility of the values obtained in the X-ray intensity is considerably improved, when compared with other conventional systems, in spite of the wide value spectrum and the techniques which are obtained with any X-ray generator, which depend on the kVp range, exposure times and the intensity itself.

28. Static system for controlling the closed loop intensity in X-ray generators according to claims 6 to 27, characterised in that the aging of the tube is minimized, since the impedance variations produced throughout the life thereof are compensated with a double closed loop, thereby substantially reducing the maintenance of the generator and the incremental cost thereof due to this reason.

29. Static system for controlling the closed loop intensity in X-ray generators according to claims 6 to 28, characterised in that it proportions a new control system to transfer the fluoroscopic system to the radiographic system, in the approximate time of 0.8 seconds, by means of an extra-transitional demand which permits the filament to be placed close to the emitting temperature, in a very short period of time, about 0.2 seconds, so that during the remaining time of up to 0.8 seconds, a stabilizing temperature, corresponding to the demand required by the operator, can be reached.

30. Static system for controlling the closed loop intensity in X-ray generators according to claims 6 to 29, characterised in that a substantially lesser number of periodic revisions is required, when compared with other conventional systems, in order to carry out adjustments and measurements of the parameters of the generator, caused by the aging of the X-ray tube.

31. Static system for controlling the closed loop intensity in X-ray generators according to claims 6 to 30, characterised in that it proportions a substantial reduction in adjustment time during manufacture and in quality control, with respect to conventional systems with open loop, in the range of 30%.

32. Static system for controlling the closed loop intensity in X-ray generators according to claims 6 to 31, characterised in that it proportions a substantial reduction in measuring and adjustment time at the time of setting up the installation, with respect to techniques and parameters, in the range of 50% when compared with conventional systems.

33. Static system for controlling the closed loop intensity in X-ray generators according to claims 6 to 32, characterised in that it comprises a digital closed loop protecting assembly, controlled by a system of multiprocessing devices which analyze and detect errors, which could be produced as a result of an incorrect operation with the static system for controlling the closed loop intensity, in order to protect the X-ray tube from excess currents, short-circuits, opening of electrical feed circuits and failure of electronic components.

34. Static system for controlling the closed loop intensity in X-ray generators according to claim 33, characterised in that the assembly of protections takes place from control circuits, whose outputs are digitally fedback to a microprocessing assembly, herein referred to as a multiprocessing system having a radial configuration, which analyses by means of the software programs, the corresponding variations and errors between the demand signals of the filament intensity and the X-ray tube with the corresponding feedbacks thereof, prior to, during and after exposure.

35. Static system for controlling the closed loop intensity in X-ray generators according to claims 6 to 34, characterised in that it constitutes a system for controlling the intensity of X-ray tubes of a universal type, applicable to any commercial type of tube and X-ray focus, wherein the intensity adjustment takes place through a software program by a microcomputer during the adjustment process of the tube.