JPS62198095A - X-ray equipment - Google Patents

Abstract

PURPOSE:To make it possible to control tube current accurately by detecting X-ray tube current by using a sensor sensitive to the magnetic field generated by X-ray tube current around a high voltage cable, in which the X-ray tube current flows, and feedback-controlling the current in the control circuit of an X-ray tube filament by the sensor's output. CONSTITUTION:Current iP flows toward an X-ray tube 14 in a core wire 49 by the application of the positive voltage of a high voltage rectifier 11, but contains charging currents iC and iC' of the capacitances between the conductor 49 and shields 46 and 47 respectively as well as the X-ray tube current iT. Since the charging currents iC and iC' are proportional to the length of the high voltage cable, on placing the shield 47 in the neighborhood of the X-ray tube 14, the capacitance of the shield 47 is smaller than that of the shield 46 and consequently iC'<<iC. As the charging current iC does not flow to the earth point of the X-ray tube 14 side because of the existence of a cutting point of the cable, a sensor 36 does not detect iC. Furthermore, as iC'<<iT, magnetic flux detected by the sensor 36 becomes substantially that due to the X-ray tube current iT. Therefore, iT can be exactly measured.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an X-ray apparatus, and particularly to an apparatus suitable for precisely controlling an X-ray tube current.

[Background of the invention]

Conventionally, the method of measuring the tube current of an X-ray tube is as follows.

As shown in FIG. 2, a method is used in which the neutral point of a high voltage transformer is grounded and the output current of the high voltage transformer is detected as a voltage drop by a 7 Yant resistor near the ground point. The output voltage of the high voltage transformer is rectified and applied to the X-ray tube, and a high voltage cable is used for connection to the X-ray tube. This cable is usually shielded to make it safe for human contact. Therefore, there is a large amount of capacitance between the high voltage output section and the ground, and in addition to the X-ray tube current, the charging current of this high voltage cable also flows into the neutral point. Furthermore, the output winding of a high-voltage transformer has tens of thousands of turns, and the stray capacitance is large because the interlayer insulation is thick.

The charging current of this stray capacitance also flows into the current at the neutral point and becomes a large error component, causing the problem that the tube current cannot be accurately measured.

These will be explained in detail using FIG. 2.

1 is a DC power supply, 2 is a transistor, 3 is a transistor 2
4 is a smoothing reactor, 5 is a smoothing capacitor, and 2 to 5 are a DC voltage conversion circuit. The voltage across the capacitor 5 is adjusted accordingly. 6 is a DC-AC conversion circuit, 6a to 6d are transistors, and 5e to 6h are diodes. In accordance with the timer set by the timer setter 8, the timer circuit 9 outputs pulses for the set time. The drive circuit 7 outputs a signal for driving the transistors 63 to 6d for a timer period according to a preset frequency. The AC-converted voltage is input to a high-voltage transformer 10, converted to a DC voltage again by a high-voltage rectifier 11 composed of high-voltage diodes lla to lid, and applied to the X-ray tube 14 via high-voltage cables 12 and 13. Ru.

On the other hand, a DC power supply 16, a transistor 17, a drive circuit 1
8. Smoothing reactor 19 and smoothing capacitor 20 constitute a filament voltage adjustment circuit, and capacitor 2
The voltage at both ends of 0 is adjusted via a tube current control circuit 35 in accordance with a tube current reference value 33 which is an output voltage from a tube current setting device (not shown). The output voltage of the DC power supply 16 is converted into AC by a DC-AC conversion circuit 21 including transistors 21a and 21bb drive circuit 22. An alternating current voltage is applied to the filament of the x-ray tube 14 via a heating transformer 15. The neutral point of the high voltage transformer 10 is a full wave rectifier 23, an ammeter 25. Switch 24 for perspective time path. Shunt resistance 2
6 to ground.

Therefore, the current flowing through the neutral point is converted into voltage by the shunt resistor 26. The voltage across the shunt resistor 26 is the voltage across the resistor 27.
．． 28, an integrating circuit consisting of a capacitor 29 and an operational amplifier 30 outputs an output voltage proportional to the tube current time product (mA-s), and a tube current time product indicator 3 is output via a resistor 31.
2 displays the mA-s value. On the other hand, the ammeter 25 displays the tube current (average current) during fluoroscopy. Further, the output voltage of the shunt resistor 26 is compared with the tube current reference value 33 by a comparator 34, and feedback control is performed so that the voltage across the shunt resistor 26 is constant at the timer signal starting point.

As mentioned above, if the charging current for the stray capacitance is included as an error in the current at the neutral point, the errors in the ammeter 26 and tube current time product (mA-8) indicator 32 during fluoroscopy will increase. . Even in the filament control circuit that controls the tube current, it is still not possible to control the tube current to an accurate value. In this way, the error in the neutral point current poses a major hindrance to accurate control of the amount of X-ray exposure.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and provide an X-ray apparatus that can accurately measure tube current and control tube current with high precision.

[Summary of the invention]

A feature of the present invention is that the X-ray tube current is detected using a magnetic field sensitive to the magnetic field created by the X-ray tube current around the high-voltage cable through which the X-ray tube current flows, and the X-ray tube filament is controlled by the output. It is used to feedback control the current in the circuit.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIG. In all the figures, parts having the same functions are designated by the same reference numerals, and repeated explanations thereof will be omitted. High voltage cable 1
2 shield is temporarily cut near the X-ray tube 14, and
Divide into a and 12b.

A magnetically sensitive sensor 36 (hereinafter simply referred to as a sensor) is installed on the outer periphery of the shield 12b near the X-ray tube 14.

The output of an amplifier 37 that controls the sensor 36 and amplifies the output voltage is connected to an ammeter 40 via a switch 38 that is closed during fluoroscopy and a resistor 39 to display the tube current. Also, the amplifier 3
7 outputs an output voltage proportional to the tube current time product (mA-8) by an integrating circuit consisting of 27 to 30, and resistor 3
1, a tube current time product display meter 32 displays the mA-S value. On the other hand, the output of the amplifier 37 is compared with the tube current reference value 33 by a comparator 34, and feedback control is performed so that the output voltage of the amplifier 37 is always constant after the timer signal starts.

Below is the tube current control circuit 35 described above. The filament voltage adjustment circuit and the DC-AC conversion circuit 21 operate in this order to adjust the voltage applied to the heating transformer 15 and keep the X-ray tube current constant.

Details of the sensor 36 will be explained using FIGS. 3 and 4. FIG. 3 shows the high voltage cable 12a.

12b and a cross section of the sensor 36;
is a core wire of a high-voltage cable that supplies the output current of the high-voltage rectifier to the X-ray tube 14; 48 is an insulating layer that insulates the periphery of the core wire 49; 46 and 47 are shields that cover the outer periphery;
It is divided near the X-ray tube 14. 50 is shield 4
This is an insulating layer that insulates 6 and 47. shield 47
A sensor 36 is installed on the outer periphery of the sensor 36 . The shields 46 and 47 are also grounded near the connection point to the high voltage rectifier 11 or the X-ray tube 14.

The operation of the configuration shown in FIG. 3 will be explained with reference to FIG.

Due to the positive voltage of the high voltage rectifier 11, the current ip flows through the core wire 49.
The current flows toward the wire tube 14, and contains currents ip+h and ic'. The charging current i (B and lc' are proportional to the length of the high voltage cable, so the shield 47 is
If placed near the wire tube 14, the capacitance of the shield 47 will be smaller than that of the shield 46, υi c'<(i C. Also, the charging current 1c will be
It does not flow to the ground point on the wire tube 14 side, and the sensor 36 does not detect i(H. Furthermore, since Kic'((iT), the sensor 36
The magnetic flux detected by 6 is actually almost equal to the X-ray tube current IT
Therefore, it is possible to accurately measure i.

Furthermore, in this embodiment, the sensor 36 is installed on the outer periphery of the shield at ground potential, so all insulation problems for high-voltage circuits can be handled by the shield, and the sensor has a simple structure because there is no problem with high-voltage insulation. .

Reference numeral 37 is a amplifier that amplifies the sensor output, and the details can be found in the public literature Shimada, Kiwaki et al. Magnetic modulator type wide-area isolated current sensor for X-ray equipment; Materials of the Magnetics Study Group of the Institute of Electrical Engineers of Japan MAG
This can be realized with a circuit configuration as shown in FIG.

〔Effect of the invention〕

As explained above, according to the present invention, the X-ray tube current can be accurately measured without being affected by the stray capacitance of high-voltage cables or high-voltage transformers. The exposure tube current time product value (mA-3) can be displayed with high accuracy.

Furthermore, since the feedback value is accurate in tube current feedback control, the actual tube current value can be accurately controlled.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is a circuit diagram illustrating the problems of a conventional tube current amount control device,
FIG. 3 is a structural diagram for explaining the details of the sensor, and FIG. 4 is a circuit diagram for explaining the operation of FIG. 3. ■...DC power supply, 2...Transistor, 4...Reactor, 6...DC-AC conversion circuit, 10...High voltage transformer, 11...High voltage rectifier, 12...High voltage Cable, 14... X-ray tube, 36... Sensor, 37.
...Amplifier, 40...Tube ammeter, 32...in A
-S meter, 33...Tube current reference signal, 21...DC-
AC conversion circuit, 15... heating transformer. Agent: Patent attorney Katsuo Ogawa, '[j+: ':')゛\-8゛-

Claims (1)

[Claims] 1. A high voltage transformer, a high voltage rectifier that rectifies its output,
In an X-ray device comprising an X-ray tube to which a rectified high voltage is applied, a high-voltage cable connecting the high-voltage rectifier and the X-ray tube, and a heating transformer supplying power to the X-ray tube filament, A sensor is installed that is sensitive to the magnetic field created around the high voltage cable due to the current flowing through the cable.
An X-ray apparatus characterized in that this sensor output is compared with a preset tube current reference value, and the input voltage of a heating transformer is controlled based on this comparison voltage.