JPS6335520Y2 - - Google Patents

Description

[Detailed description of the invention] This invention relates to a time-limiting mechanism for a three-phase X-ray device that uses a thyristor as a power switch and controls conduction to control the X-ray emission time. The aim is to obtain an X-ray apparatus having an effective continuous time-limiting function at a low cost by reducing the number of times.

Generally, an X-ray apparatus has a timer for setting the X-ray emission time. In an X-ray device that uses a thyristor as the main switch and controls the conduction state of the thyristor to control the X-ray emission time, due to the characteristics of the thyristor, an X-ray cutoff signal is provided from the thyristor's gate control circuit or phototimer. However, it was not possible to instantly shut off the X-ray radiation, and it was not possible to set an arbitrary continuous time limit. As a means to compensate for this, an X-ray cutoff signal (time limit end signal) is supplied to the gate of the thyristor as the main switch, and at the same time, it is also supplied to the gate of the thyristor as an auxiliary switch installed in parallel with the primary winding of the high voltage transformer. By supplying the X-ray cutoff signal and turning it on, the supply voltage of the main transformer is divided into the ratio of the power supply side impedance Z ₁ (voltage dividing resistor R ₁ ) and the load (voltage dividing) resistor R ₂ . The voltage supplied to the X-ray tube is reduced to below an insensitive voltage that does not substantially affect X-ray photography, etc., thereby achieving the purpose of continuous time limit.

However, in order to use this auxiliary switch in a three-phase X-ray system, it is necessary to provide one set of anti-parallel connected thyristors and one load (divider voltage) resistor for each phase. In addition, it is necessary to completely synchronize the opening and closing of the main switch for each phase with the opening and closing of the corresponding auxiliary switch thyristor for each phase, which has the disadvantage that the gate control circuit for these auxiliary switch thyristors is complicated. It was hot.

This invention solves the above-mentioned problems.In an X-ray apparatus in which an anti-parallel circuit of thyristors is connected to each line of the primary circuit of a three-phase high voltage transformer to control X-ray radiation, the thyristor A three-phase full-wave rectifier circuit is connected in parallel between the anti-parallel circuit of the transformer and the primary winding of the transformer, and an auxiliary switching thyristor is connected to the common DC output circuit of this rectifier circuit.

The drawings will be explained below. Figure 1 is a block diagram showing the circuit configuration of the present invention, Figure 2 is a waveform diagram of X-ray tube voltage and X-ray output, and Figure 3 is a circuit of a conventional three-phase X-ray device using a thyristor as the main switch. FIG. 2 is a block diagram showing the configuration. In Fig. 1, power for X-ray radiation is supplied from a general commercial three-phase power supply 1, which is composed of two thyristors connected in antiparallel, and passes through a main switch 2 inserted for each phase, and then is connected to the impedance on the power supply side. It passes through Z ₁ (voltage dividing resistor) 3 and R ₁ and reaches a three-phase transformer 4, where it is boosted and supplied to the X-ray tube 5.
When using a thyristor as the main switch, due to the characteristics of the thyristor, even if the gate of the main switch is controlled by an external timing mechanism (timer), the thyristor will not become non-conductive unless the load current falls below the holding current of the thyristor. , there are no consecutive time limits. In the conventional device shown in FIG. 3, load resistors 13, 14, 15, R' ₂ and main switching means are connected in parallel between each phase of the main circuit as auxiliary switching means for carrying out this arbitrary continuous time limit. By inserting a series connection circuit of auxiliary switches 10, 11, and 12 consisting of two thyristors connected in antiparallel in the same way as the switch, the gate of the main switch 2 is opened at the same time as the time limit end signal from a timer etc. Auxiliary switch 1
By applying this to thyristors 0, 11, and 12 and turning them on, the voltage supplied to the main transformer 4 is reduced to below the insensitive voltage determined by the voltage dividing ratio of the voltage dividing resistor _R1 and the load resistor _R'2 . It was becoming like that.
The thyristors constituting the main switches interposed in each line are turned off when the load current becomes equal to or less than the holding current, and the power supply to the main transformer 4 is cut off. FIG. 2 shows the X-ray tube voltage waveform a and the X-ray output waveform b when the supply voltage is reduced in this way. As is clear from the waveform diagram in FIG. 2, by reducing the supply voltage, the X-ray output is significantly reduced, and an effect substantially equivalent to cutting off the X-ray radiation for the time set by the timer can be obtained. In this case, the amount of reduction in the supply voltage may be set so that the resistance values of the voltage dividing resistors R ₁ and R ₂ become below the dead voltage. The auxiliary switching circuit 6 in FIG. 1 has a three-phase full-wave rectifier circuit 7 connected in parallel between the lines of each phase between the power supply side impedance Z ₁ (including the voltage dividing resistor R ₁ ) and the main transformer 4. The DC output circuit is provided with an auxiliary switch 9 (for DC) consisting of one load resistor 8R' ₂ and one thyristor. Note that the same effect can be achieved by inserting the load resistor R ₂ on the alternating current side of the full-wave rectifier circuit, but in this case, three resistors are required. 1st
In the configuration shown in the figure, at the same time the gate of the main switch 2 is opened by a time limit end signal from a timer or the like, a time limit end signal is also applied to the auxiliary switch 9 to turn it on. By turning on the auxiliary switch 9, the voltage supplied to the main transformer 4 is reduced to a dead voltage determined by the voltage division ratio between the voltage dividing resistor _R1 and the load resistor _R2 . Note that the power supply to the main transformer 4 is cut off when the load current of the thyristor constituting the main switch becomes less than the holding current and is turned off, as in FIG. 3.

As explained above, the present invention provides continuous time-limiting means for X-ray opening and closing using one auxiliary switch, which required six resistors in conventional three-phase X-ray equipment. Instead of installing an auxiliary switch between the wires to take a three-phase balanced load, it is now possible to take a three-phase balanced load via a three-phase full-wave rectifier circuit, so the auxiliary switch, which is the main active element, The device only requires 1/6 of the thyristor, which is advantageous in terms of both cost and reliability, so the improvement in commercial value is significant. Furthermore, the continuous time-limiting function achieved in conventional devices is not hindered in any way. Although this is a secondary feature, the simplification of the gate control circuit for the thyristor of the auxiliary switch has a significant effect on cost reduction and operation of practical equipment.

[Brief explanation of the drawing]

Figure 1 is a block diagram showing the circuit configuration of the present invention.
FIG. 2 is an X-ray tube voltage and X-ray output waveform diagram, and FIG. 3 is a block diagram showing the circuit configuration of the conventional device. Explanation of symbols, 1: General commercial three-phase power supply, 2: Main switch, 3: Voltage dividing resistor, 4: Three-phase transformer, 5: X-ray tube, 6: Auxiliary switching circuit, 7: Three-phase full-wave rectification circuit,
8: Load resistance, 9: Auxiliary switch thyristor.

Claims (1)

[Scope of utility model registration request] In a three-phase X-ray apparatus in which an anti-parallel connection circuit of two thyristors is connected to each line on the primary side of a three-phase high-voltage transformer to control X-ray radiation, the anti-parallel connection circuit of the thyristors and the high voltage A three-phase full-wave rectifier circuit is connected in parallel between each phase with the primary winding of the transformer, and an auxiliary switching thyristor is provided in the common output circuit of this rectifier circuit, which conducts in response to a time-limited end signal.
A three-phase
line equipment.