JPS584299A - X-ray high voltage generating device - Google Patents

Abstract

PURPOSE:To eliminate the current which flows through a floating capacity and enable the accurate tube current measuring of the captioned device to be conducted, by improving in some degree an X-ray tube current measuring circuit. CONSTITUTION:A current measuring circuit is divided into two parts 2' and 2'', the node is connected to the earth 3, and the direction of the current which flows through a floating capacity shall be the direction of IC1A. The current which flows through the floating capacity of a negative potential side is IC1A= IC2B which is to be in the direction of IC2B and the direction of the current which flows through an X-ray tube current measuring circuits 2' and 2'' is reversed to the said direction, therefore when outputs of two measuring circuits standardized by the earthing point are mutually subtracted, the final output does not appear, and the X-ray tube current can be measured without being affected by the floating capacity.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an X-ray high-voltage device, and more particularly to an X-ray high-voltage generator designed to improve the accuracy of an X@lightning current needle decoy path.

General number ζ, 0 for X-ray high voltage equipment, normally used X
This is because the line tube voltage is extremely high, reaching a maximum of 150.

The secondary winding of the high voltage generator is divided into two parts and the midpoint (neutral point) of the voltage is grounded. In addition, measurement of the X-ray tube current is also normally carried out by providing a circuit at this ground point.

On the other hand, high-voltage transformers usually have a primary winding shield plate, an insulator, and a secondary winding coaxially wound around an iron core in this order.
Next, the shield plate between the secondary windings is connected to a ground terminal for safety, and the entire high voltage transformer is housed in an oil-immersed tank. Therefore, due to its structure, the secondary winding has stray capacitance between the shield plate, core yoke, storage tank, etc. There is stray capacitance between the wholesale secondary winding and the ground point.

For this reason, when a voltage is applied to the -order winding, a charging/discharging current of this capacitance flows, and its value becomes about 1 μm at a working voltage of, for example, about 100 μm.

This current flows into the X** current measurement circuit in a single-phase device or a three-phase device in which a smoothing capacitor is connected to the high voltage side, resulting in a measurement error.

FIG. 1 is a circuit diagram of a high voltage generator including a path of current flowing from a secondary winding of a high voltage transformer of a conventional single-phase device to a stray capacitance to ground. In diagram Wi1, im is the primary winding of the high voltage transformer, 1b is one divided secondary winding of the high voltage transformer, lc is the other divided secondary winding of the high voltage transformer, and 2 is the secondary winding of the high voltage transformer. X-ray lightning current measurement circuit (resistance if you ask), 3
is grounded.

4 is the stray capacitance between the secondary winding lb and ground, 5 is the secondary winding 1
The stray capacitance between c and ground, 6 is the high voltage panel a! vessel.

7 is an X-ray tube.

At 1111ffi, the current Ic flowing through the stray capacitance 4
1 does not flow to the X-ray lightning current measurement circuit 2, but the stray capacitance 5
The current Ic2 that flows through the X-ray tube current measurement circuit 2 causes a large error, especially in the case of a small current load such as in fluoroscopy.

Figure 112 shows a conventional three-phase X-ray system in which a high-voltage capacitor is connected to the output side of a high-voltage transformer, including the path of current flowing into the stray capacitance between the secondary winding of the high-voltage transformer and the ground. FIG. 2 is a circuit diagram of a high voltage generator. High-voltage capacitors are often used for the purpose of reducing ripples in the low range of X-ray tube voltage or in high-voltage X-ray devices for pulse cine imaging devices using triode X-ray tubes.

In Figure 2, 1m is the primary winding of the high voltage transformer, I
b is 1 of the divided secondary winding of the high voltage transformer! 11
e l C is another set of the other divided secondary winding of the high voltage transformer, 2 is an X-ray lightning current measurement circuit, 3 is grounding, 4
is the stray capacitance between the high voltage transformer secondary winding l b (bl phase and ground, 5 is the same 1 c cI) and the ground, 6 is the high voltage board 11EII1.7 is X wire tube.

8.9 are high voltage capacitors, respectively. In this circuit, the electric current @Ic1a and Xcsb flowing through the stray capacitance 4 does not flow into the current measurement side path 2 due to the grounding point.

The currents Ic1a and Ic1b flowing through the stray capacitance 5 flow into the current measurement circuit 2. In this case, since the output voltages of the two sets of high voltage transformer secondary windings are each independently full-wave rectified, the current flowing through the stray capacitance takes different paths depending on the polarity of the power supply voltage. Also, X**X flowing through the current measurement circuit
The tube current (load current) is direct current, but the current flowing through all stray capacitances is alternating current. Diagram @3 schematically shows how the stray capacitance exists in the above explanation. FIG. 183 shows an example of a winding structure for one set of a three-phase high voltage transformer. In the figure, l≦, ll is the primary winding of the high voltage transformer, g, l, 1 are the secondary windings of the same, 12', 1
3' - This is a shield plate between the primary and secondary windings, and the reason why there are two sets of these in each set is to provide a positive potential side winding and a negative potential side winding to the ground on the high voltage side. It's for a reason. 10 indicates an iron core, and 11 indicates a storage tank. 4.4.4 is the stray capacitance generated between the secondary winding 1b and the storage tank 11゜shield plate 1 and the iron core IO, and 5.5.5 is the stray capacity between the secondary winding 1b and the storage tank 11. , shows the stray capacitance generated between the shield plate 15 and the iron core lO.

As is clear from this figure, stray capacitance exists extensively between the secondary winding and the ground conductor, and it is almost impossible to remove it with structural improvements to high voltage transformers. Normally, these stray capacitances are on the order of several hundred pF, but they vary depending on the assembly structure of the secondary winding and the ground conductor, and the stray capacitances 4, 4, and 4 have different values.

Additionally, the larger the capacitance value of the high-voltage capacitor, the greater the influence of the current flowing through the stray capacitance in the X-ray lightning current measuring circuit, which is inconsistent with the direction required to stabilize the tube voltage. It turns out. This error becomes a serious problem in X-ray photography, especially when measuring the maximum tube current value during short-time photography.

In view of the above, the present invention is an X-ray high voltage generator that makes it possible to remove the current flowing through the stray capacitance in the X-ray lightning current measuring circuit by slightly improving the xmtm current measuring circuit, thus making it possible to accurately measure lightning current. It provides:

Next, the present invention will be explained with reference to the embodiment shown in FIG. #!
Figure 4 shows the voltage generation circuit of a three-phase X-ray device embodying this invention, and also shows the current path flowing into the stray capacitance between the secondary winding and ground of the high voltage transformer. , and the same components as in FIG. 2 are given the same reference numerals.

The difference from Figure 112 is that the current measurement circuit is i.

i, and its connection point is connected to ground 3.

In the above configuration, if we focus on one phase of the secondary winding on the positive potential side and assume that a voltage is generated in the positive polarity indicating the voltage polarity, the current flowing through the stray capacitance 4 will be in the ICI direction.

If we pay attention to the corresponding phase on the negative potential side at this time, the stray capacitance 5
The current flowing through is Ic! The direction is b.

By the way, this kind of X-ray equipment is usually used for smoothing! 'The high voltage capacitor used is about 2 to 1/I OμF,
Compared to stray capacitance, there is a difference of about 10" to lO' times. Therefore, the current flowing through stray capacitance is an alternating current component that takes different paths and directions depending on the polarity of the voltage, but its maximum value hardly changes. This is almost the complete amount of current.

That is, even in a path passing through a high voltage capacitor, the capacitance of this capacitor is much larger than the stray capacitance, and the current value is almost determined by the stray capacitance value.

Therefore, Icl Hatake+Ic! b, and the directions of the current flowing into these X-ray tube current measurement circuits 2 and 2 are opposite, so if you subtract the outputs of the two measurement circuits with the ground point as a reference, they will cancel each other out, and the final output will be will no longer appear. This also applies to Ic5 when the polarity of the power supply voltage is reversed.
Since b + Icxa, this current is canceled out at the output of the subtraction circuit. On the other hand, since the actual X-ray tube current IL flows in the same direction through the two measurements, the result of the above subtraction appears as a sum.

Only the necessary XII lightning current IL can be extracted.

(However, the actual measurement circuit is not shown. 2'.

(i indicates only the detection part) Therefore, the xmw current can be measured without being affected by stray capacitance.

In the above description, the stray capacitances that exist in a wide range between the secondary winding and the ground conductor all have the same value.

The explanation has been made assuming that the stray capacitance current is canceled out.
・However, the stray capacitance of 4.5 in Figure 94 is the third
In the diagram, 4.4.4. and 5.5.5, and strictly speaking, they must be considered separately.

Also, due to the structure of the high voltage transformer, the stray amount t4' shown in FIG.
・Although g or 4, 5, 4, and 5 can be made equally, it is practically difficult to make g for + or 6 for Ga, etc. equally.

Therefore, if we consider the stray capacitance separately, the currents flowing through the positive potential side floating amount 4.4.4 and the load potential side floating capacitance 5.5.5 shown in FIG. 3 in FIG. 4 cancel each other out. Become. In this case, as mentioned above, the capacitance values of 4' and 4 and 5 are not equal, and it is difficult to make them equal, so the stray capacitance current will not be completely canceled.

The result is l! Although the circuit configuration shown in Figure 4 significantly improves the effect of stray capacitance compared to the conventional device shown in Figure li2,
The stray capacitance current cannot be completely canceled out, and a small amount of current due to the difference in stray capacitance flows through the current measurement circuit, resulting in a difference in current.

In view of this point, Figure 5 shows the configuration of another embodiment in which the stray capacitance current can be completely canceled out. The winding structure is such that the generated voltage polarities of the windings on the negative potential side are opposite to each other, and the other configuration is the same as that of FIG. 4.

With the above configuration, Icl member = Ic! b(Ic1b=Icz
i ), and the directions are also opposite, so if the outputs of the two current measurement circuits with respect to the ground point are subtracted, they will cancel each other out, and only the X-ray tube current will be measured.

y7 In the embodiment shown in Fig. 4, the divided secondary windings are wound in the same direction, and a transformer with the same generated voltage polarity is used. The voltage between point A to the secondary winding lb, which is connected to the positive potential side of the high voltage rectifier group, and point B, which is connected to the negative potential of the high voltage rectifier group, is low, making it a commonly used high voltage. There is an advantage that the transformer can be used as is.

In addition, in the embodiments shown in FIGS. 4 and 5, the winding connection method of the high voltage transformer is ΔIΔ−Δ, but this is not limited to fL.
For example, Δ//Y-Y connection may be used, and various wiring methods commonly used in three-phase transformer connection Y〃Δ-Δ, Y
This invention can also be applied to //YY.

Alternatively, a combination of Δ/lΔ-Y or Y//Δ-Y may be used. In this case, there is a phase difference of 30° between the positive potential side secondary winding and the negative potential side secondary winding.

Although the stray capacitance current will not completely cancel each other out,
It is clear that measurement errors due to stray capacitance can be significantly reduced compared to the conventional device shown in FIG.

Also, in a single-phase device, instead of using the method shown in Figure 1, a full-wave rectifier circuit is provided for the positive potential side and negative potential side secondary windings, and the outputs are connected in series so that the outputs are added. The present invention can be applied when a voltage capacitor is connected.

As detailed above, this invention has a simple configuration.

It is possible to provide an X-ray high voltage generator that can accurately measure X-ray tube current without being affected by stray capacitance.

[Brief explanation of the drawing]

Figures 1 and 2 are diagrams showing the direct voltage generation circuit of a conventional X-ray apparatus, and Figure 3r! g is a schematic diagram showing a one-phase winding structure of a three-phase high voltage transformer, FIG. 4 is a circuit diagram showing the configuration of one embodiment of the present invention, and FIG. 95 is a circuit diagram showing the configuration of another embodiment. It is a diagram. la: Primary winding t'lb, le: Secondary winding 2, 2:
X-ray tube current measurement circuit, 3: Ground. 4.5: Stray capacitance, 6: High voltage rectifier, 7zXli tube. Patent applicant Shimadzu Corporation Representative Patent attorney Hiko Takeishi 1'J1. :L Fortune-
'j' 楕／囃2 凯 3 fig. y+.

Claims (1)

[Claims] In a high voltage generator in which a smoothing capacitor is connected to each jumper, the load current measuring circuit is divided into two,
An X-ray high voltage generator characterized in that its intermediate point is grounded. (2) The X-ray height according to claim 1, characterized in that the two divided secondary windings have a winding structure in which the voltage polarities thereof are opposite to each other. Voltage generator.