Method and apparatus for heating current control of a pulsed X-ray tube
View Patent ↗A method and an associated apparatus for controlling a heating current flowing through an emitter of a pulsed X-ray tube during pulse pauses are provided. The heating current is controlled by comparing a measured actual value of the heating current with a predefinable desired value of the heating current. A low-pass filtering of the actual value of the heating current is effected before the comparison. A time constant of the low-pass filtering is equal to a thermal time constant of the emitter. A correction of the actual value of the heating current is provided before the low-pass filtering by a first correction value. The first correction value is determined such that a tube current control during the pulses is not compensated for by the heating current control in the pulse pauses.
1. A method for controlling a heating current flowing through an emitter of a pulsed X-ray tube during pulse pauses, the method comprising:
comparing a measured actual value of the heating current with a predefinable desired value of the heating current;
low-pass filtering the measured actual value of the heating current before the comparison, wherein a time constant of the low-pass filtering is equal to a thermal time constant of the emitter; and
correcting the measured actual value of the heating current before the low-pass filtering by a first correction value, wherein the first correction value is determined such that a tube current control during the pulses is not compensated for by the heating current control in the pulse pauses.
2. The method of claim 1 , wherein the first correction value is determined from a difference between the measured actual value of the heating current and an actual value of the heating current at the beginning of a present pulse.
3. The method of claim 1 , further comprising subtracting the first correction value from the measured actual value of the heating current.
4. The method of claim 1 , further comprising correcting the measured actual value of the heating current before the low-pass filtering by a second correction value, the second correction value being determined from a model of electron cooling during the pulses.
5. The method of claim 4 , wherein the second correction value is determined such that thermal cooling caused by the electron cooling during the pulses is not registered.
6. The method of claim 4 , further comprising subtracting the second correction value from the measured actual value of the heating current.
7. The method of claim 4 , further comprising correcting the measured actual value of the heating current before the low-pass filtering by a third correction value, the third correction value being determined from a model of anode back heating.
8. The method of claim 7 , further comprising adding the third correction value to the measured actual value of the heating current.
9. An apparatus for controlling a heating current flowing through an emitter of a pulsed X-ray tube during pulse pauses, the apparatus comprising:
a heating current control unit configured to control the heating current by comparing a measured actual value of the heating current with a predefinable desired value;
a first low-pass filter unit that is connected upstream of the heating current control unit and comprises a time constant equal to a thermal time constant of the emitter, wherein the first low-pass filter is configured to filter the measured actual value of the heating current before the comparison; and
a first correction unit configured to:
alter the measured actual value of the heating current before the low-pass filtering by a first correction value K 1 ; and
determine the first correction value such that a tube current control during the pulses is not compensated for by the heating current control unit in the pulse pauses.
10. The apparatus of claim 9 , wherein the first correction unit is further configured to determine the first correction value from a difference between the measured actual value of the heating current and an actual value of the heating current at the beginning of a present pulse.
11. The apparatus of claim 9 , further comprising a summing unit that is connected upstream of the first low-pass filter unit and is configured to subtract the first correction value from the measured actual value of the heating current.
12. The apparatus of claim 9 , further comprising a second correction unit configured to:
alter the measured actual value of the heating current before the low-pass filtering by a second correction value; and
determine the second correction value from a model of electron cooling during the pulses.
13. The apparatus of claim 12 , wherein the second correction unit comprises a second low-pass filter unit, a time constant of the second low-pass filter unit being equal to a time constant of the electron cooling.
14. The apparatus of claim 11 , wherein the summing unit is configured to add the second correction value to the measured actual value of the heating current.
15. The apparatus of claim 12 , further comprising a third correction unit configured to:
alter the measured actual value of the heating current before the low-pass filtering by a third correction value; and
determine the third correction value from a model of anode back heating.
16. The apparatus of claim 15 , wherein the summing unit is configured to subtract the third correction value from the measured actual value of the heating current.
17. An X-ray generator comprising:
an apparatus for controlling a heating current flowing through an emitter of a pulsed X-ray tube during pulse pauses, the apparatus comprising:
a heating current control unit configured to control the heating current by comparing a measured actual value of the heating current with a predefinable desired value;
a first low-pass filter unit that is connected upstream of the heating current control unit and comprises a time constant equal to a thermal time constant of the emitter, wherein the first low-pass filter is configured to filter the measured actual value of the heating current before the comparison; and
a first correction unit configured to:
alter the measured actual value of the heating current before the low-pass filtering by a first correction value K 1 ; and
determine the first correction value such that a tube current control during the pulses is not compensated for by the heating current control unit in the pulse pauses.
18. The X-ray generator of claim 17 , wherein the first correction unit is further configured to determine the first correction value from a difference between the measured actual value of the heating current and an actual value of the heating current at the beginning of a present pulse.
19. The X-ray generator of claim 17 , wherein the apparatus further comprises a summing unit that is connected upstream of the first low-pass filter unit and is configured to subtract the first correction value from the measured actual value of the heating current.
20. The X-ray generator of claim 17 , wherein the apparatus further comprises a second correction unit configured to:
alter the measured actual value of the heating current before the low-pass filtering by a second correction value; and
determine the second correction value from a model of electron cooling during the pulses.