JPH01255200A - Overload preventing circuit for x-ray tube device - Google Patents

Abstract

PURPOSE:To accurately take hold of a stored heat energy on any radiating condition so as to enable suitable overcurrent protection by simulating the thermal behavior of an X-ray tube device by means of an overload protective circuit. CONSTITUTION:After detecting a tube voltage V and a tube current Ib, a power calculating unit 24 determines the multiplied value thereof. An integrating circuit 25, where a charge time constant and a discharge time constant simulate a thermal time constant of an X-ray tube device, converts the multipled value into a real value signal of a heat unit(HU) value corresponding to heat energy stored in the tube device. A judging circuit 26 compares the signal with an upper limit value setting signal of a heat capacity stored in the tube device so as to output a trip signal. Reception of radiation for a short time enables simulation one by one of changes at every moment in the heat energy stored in the tube device so that the output of the trip signal stops the tube current when the HU value corresponding to the stored heat energy exceeds the HU upper limit value corresponding to the heat capacity stored in the tube device. This can prevent an overload in the tube device with accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a circuit for preventing overloads exceeding the storage yt heat capacity t of an X-ray tube device in a medical or industrial XlfM tube device or the like.

[Conventional technology]

In diagnostic X-ray tubes, it is necessary to take images with a large dose in a short time in order to reduce blurring of the image due to the movement of the living body. Therefore, tube voltage and filament current are applied to the X-ray tube for a short period of time to Operation methods that emit light for a short period of time are often used. Fig. fg2 is a characteristic diagram showing the tube current-tube voltage characteristics of a large-capacity iX-ray tube device using filament flow as a parameter. In the figure, the tube current increases in proportion to the tube voltage, and the filament current changes slightly (±1
(approximately 0%) shows a tendency to change significantly depending on K. Therefore, in devices that emit X-rays for a long time, the desired tube current can be adjusted by selecting a combination of tube voltage and filament current corresponding to a predetermined tube current using the characteristics shown in Figure 2. The level can be controlled.

However, the dependence of the tube current on the filament current is caused by the filament temperature, and is difficult to understand in devices that emit short-time X-rays by passing the tube current in pulses at intervals of a short time. The effect of the thermal time constant required for the filament temperature to reach a steady state determined by the current value cannot be ignored. In addition, X-ray tubes have a fixed heat capacity for storing thermal energy generated within the tube by the filament current and tube current, and a heat radiation time constant for the stored thermal energy. It is necessary to wait until the radiation does not exceed the accumulated heat capacity and the accumulated thermal energy is sufficiently dissipated before performing the second radiation.

However, there are times when radiation is repeatedly performed for a short period of time without waiting for the entire waiting time, and in such a situation, thermal energy accumulates and the X-ray tube becomes high in temperature, so the filament temperature also increases. A much larger tube current will flow than the tube current determined based on the diagram, and an unexpected situation will occur that will damage the XM tube. In view of this situation, X-ray apparatuses are known that are equipped with an overcurrent prevention circuit that prevents excessive tube current from flowing.

FIG. 5 is a block diagram showing the conventional equipment in this building, in which the X-ray tube equipment 1 is supplied with filament current energy from a filament voltage 2, an in/+-talo, a step-up transformer 4. A pair of positive and negative rectifier bridges with a grounded midpoint 5A
, 5B is applied from the high-voltage power supply section including the high-voltage rectifier 5, the thermionic electrons emitted from the cathode filament are accelerated by the tube voltage V, and the tube current flows, increasing the daily velocity σ. Thermionic electrons are focused on a point on the anode target and collide with it, and this high-temperature focus turns into X-ray generating mud, which emits X-rays. The inverter 6 receives electric power from the commercial frequency system, first converts it to direct current, then converts it to high frequency transformed current by an inverter circuit, and supplies it to the primary side of the step-up transformer 4 . To be careful, the tube voltage V is controlled to a predetermined voltage value by phase control or pulse width modulation control of the inverter 3, and the filament current f is controlled by the power supply section 2.
The current value is adjusted to correspond to a predetermined tube current.

Also, 11 is over 1! It is a flow prevention circuit and high voltage! I flow device 5
A pair of resistors 6A connected in series to the ground side of.

The actual value of the tube current detected by the detector 6 of the tube current ■b consisting of 6B is input to the comparison 514. Also, tube current setting 6
12 output setting signals are input to the limit calculator 13,
An allowable deviation value signal from the tube current is input to the comparator 14. Therefore, when the actual tube current value exceeds the allowable deviation value signal level, the comparator 14 outputs a trip signal to the inverter 3, so that the inverter 3 throttles its output current and the tube voltage V decreases. By doing so, excess tube current is prevented from flowing.

[Problem to be solved by the invention]

Generally, the accumulated heat capacity of an X-ray tube device is expressed as the heat unit HU〆v, rb, where t is the tube current flow time.
-t, and the cooling time constant is also proportional to the rate of change in HU. However, since the conventional system Wt outputs a trip signal by comparing the actual value of the tube current with the setting,
In order to radiate the wire within the range of the accumulated heat capacity, the tube current setting 512 is set every time the tube voltage V and the twisting time t change.
There is an inconvenience in that the set value of has to be adjusted to a value corresponding to this. In particular, under conditions where short-term radiation is repeated, it is difficult to predict the cumulative value of stored thermal energy, making it nearly impossible to set the set value, and therefore, it is impossible to provide appropriate overcurrent protection. There are drawbacks.

The purpose of this invention is to use an overload circuit to simulate the thermal behavior of an X-ray tube device, so that the stored thermal energy can be accurately determined under any radiation conditions, and therefore the X-ray tube's thermal behavior can be accurately determined. The object of the present invention is to obtain a highly reliable film-retaining circuit for overload protection.

[Means to solve the problem]

In order to solve the above problems, according to the present invention, the tube voltage of the X-ray tube device is ? The tube current is controlled by an inverter controlled via a high-voltage DC power source and a filament current control power source, which emit X-rays for a short period of time. a voltage detection circuit that outputs the current value of 1g, a current detection circuit that detects the tube current and outputs a tube current actual value signal, a power calculation section that outputs the multiplication value of the output signals of both of the detection circuits; an integrating circuit that has a charging/discharging time constant corresponding to the thermal behavior of the tube device and integrates the output signal of the power calculation section to simulate changes in the accumulated thermal energy of the X-ray tube device; and this integrating circuit. and a determination circuit that outputs a trip signal when the output heat unit actual value signal exceeds the upper set value level.

[Effect]

In the above means, signals proportional to the actual values of tube current (tube current) and tube voltage V are multiplied together in a power calculation section to obtain a power value V. By integrating the value V・, calculate -t1 from the heat unit value V・, and at the same time, install a discharge circuit that simulates the cooling time constant of the X and IA tube equipment in one integration circuit, and discharge the integrated value when the flow is stopped. By configuring it to do so, the integrating circuit simulates the thermal behavior of the X-ray tube apparatus and outputs an actual value of the heat unit value that changes from moment to moment. Therefore, this actual IIM is compared with the upper limit value setting signal of the heat unit determined by the storage heat capacity set in advance in a comparison circuit as a judgment circuit, and when the actual value exceeds the set value, a trip signal is sent to the inverter or filament power supply. By outputting the output, radiation operation is maintained that does not exceed the heat capacity f of the X-ray tube device under any conditions of tube current flow or stop, and the radiation operation of the X-ray tube device that occurs when the heat capacity f exceeds the accumulated heat capacity is maintained. damage can be prevented.

〔Example〕

The present invention will be explained below based on examples.

FIG. 1 is a configuration diagram showing a device according to an embodiment of the present invention, and detailed explanations will be omitted by using the same reference numerals for the same parts as in the conventional device. In the figure, a tube current detector 6 is connected to the ground side of the high voltage rectifier 5, and a high voltage rectifier bridge 5A, 5
On the output side of B, tube voltage dividers 7A and 7B of resistance voltage divider type are provided. 21#:l: Overload prevention circuit, current detection unit 23 that receives the output current of tube current detector B and issues an actual value signal of tube current 1b, tube voltage voltage divider 7A, 7
A voltage detection section 22 receives the output voltage of the tube voltage V and generates an actual value signal of the tube voltage V, and the output actual value signals of both detection sections are multiplied together to produce an actual value signal of the power V supplied to the X-ray tube device 1. The obtained actual power value signal is input to the integrating circuit 25 via the power calculation section 24 which generates the power.

The integrating circuit 25 includes diodes D! with mutually opposite directions. .

D2, series resistors RI, R2, and an integrating capacitor C, and the power actual value signal is connected to the integrating capacitor CK with a time constant C@R during the conduction period t of the tube current rb.
It is accumulated as II air volume and the heat unit value V.
, t, and outputs an integral signal proportional to t to a judgment circuit 26 disposed on its output side. Further, during the period when the tube current is stopped, the amount of electricity stored in the capacitor C is discharged with time constants C and R2, thereby lowering the integral signal output to the judgment circuit.

Therefore, the time constants C and R1 of the integrating circuit and the discharge time constant C
, R, are set in advance to correspond to the temperature rise time constant and cooling time constant of the X-ray tube device 1, respectively.
It becomes possible to make the integrating circuit 25 simulate the thermal behavior of the Xa tube device 1, and for example, the accumulated thermal energy of the X-ray tube device fit1, which changes by repeating short-time radiation at time intervals, is sometimes stored by the integrating circuit 25. It can be simulated moment by moment. Therefore, a comparator 26 serving as a judgment circuit compares the output integral value of the integrating circuit 25 with the upper limit value of the heat unit determined by the accumulated heat capacity of the X-ray tube device 1 set in the HU value value and the membrane setting device 27 to generate a trip signal. By outputting 26S toward the inverter 23 and stopping the output current of the inverter B, overloading of the X-ray tube device and damage caused by it can be prevented.

It goes without saying that it is also possible to output the trip signal 26 to the filament power supply 2 to stop the filament current generator f, readjust the filament current, and allow a suitable cooling time. In particular, radiation of red and X-rays can be carried out.

Note that the power calculation section, the O* component circuit 2 judgment circuit, etc. may be constructed using a discrete analog IC, or may be constructed using a digital calculation circuit using a microprocessor.

〔Effect of the invention〕

As described above, the present invention is an integral circuit which detects tube voltage and tube current, calculates their multiplication value in a power calculation section, and whose charging time constant and discharging time constant completely simulates the thermal time constant of an X-ray tube device. is converted into an actual value signal of the heat unit value corresponding to the stored thermal energy of the X-ray tube device, and this signal is
It is configured to output the full trip signal by comparing it with the upper limit value setting signal of the accumulated heat capacity of the wire tube device. As a result, by returning short-term radiation that could not be detected by conventional overcurrent prevention circuits, it is possible to simulate the changes in the accumulated thermal energy of the X-ray tube device, which changes from moment to moment. X
It is possible to provide an overload prevention circuit for an X-ray tube device that can accurately prevent overload of the ray tube device. In addition, the X-ray tube device K high pressure! ! By suppressing the amount of electricity supplied through the flow device within the range determined by the accumulated heat capacity, it becomes possible to determine the capacity of the inverter and high voltage power supply based on the accumulated heat capacity. , it is possible to optimize the power supply capacity, and based on this, it is possible to achieve the advantage of miniaturization and quantification.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing a flJ device embodying the present invention;
The figure is a tube current-tube voltage characteristic diagram of an X-ray tube device, and FIG. 3 is a configuration diagram showing a conventional device. 1... X-ray tube device, 2... filament power supply, 3...
...Inverter, 4...Step-up transformer, 5...High voltage rectifier, 6...Tube current detector, 7...Tube voltage detector, 11...Overcurrent prevention circuit, 21...・Overload prevention circuit, 22... Voltage detection section, 26... Current detection section, 2
4...Power calculation unit, 25...Integrator circuit, 26...
Judgment circuit, 27...HU value upper membrane setting device ■...Tube voltage, more...Tube current, engineering f...Nino

Claims (1)

[Claims] 1) Detecting the tube voltage in an X-ray tube device in which the tube current is controlled by an inverter that controls the tube voltage via a high-voltage DC power supply and a filament current control power supply section to emit X-rays for a short time. a voltage detection circuit that detects the tube current and outputs a tube voltage actual value signal, a current detection circuit that detects the tube current and outputs the tube current actual value signal, and a power calculation unit that outputs a multiplied value of the output signals of both the detection circuits. , an integrating circuit that has a charging/discharging time constant corresponding to the thermal behavior of the X-ray tube device and integrates the output signal of the power calculation unit to simulate a change in the accumulated thermal energy of the X-ray tube device; 1. An overload prevention circuit for an X-ray tube apparatus, comprising: a determination circuit that outputs a trip signal when an output heat unit actual value signal of the circuit exceeds its upper limit set value level.