Analysis of the Development Trend of Portable Industrial X-Ray Generator

by Zhu Wen Yu (2001.05.16)

For the past five years, the domestic and international manufacturers tried very hard in the development of Industrial X-Ray Generator. The products were improved, such as the series of ICM SITE-X, the series of Andrex Smart, the new products of SEIFORT; Shenyang NDT factory, Chung Nan NDT factory, Dailin Tonghai Company also produce a new series of generators. All these developments have their own characteristics, but as a summary, it depends on the requirement of our clients.

According to our clients' requirement of the Portable Industrial X-Ray Generator, we can be simply divided into three points: weight, ability of thickness and reliability. The following are the analysis of the development trend:

I). Weight, smaller and lighter

We can find out the differences of the "Tube Head" and "Control Unit" during the 1980 to the beginning of 1990.

At that time, the 300kV Tube Head's weight is 35-38.5Kg and Control Unit is 12-25Kg. Let us compare with the current conditions.

Tube Head's weight is 27-29Kg Control Unit's weight is 7.5-14Kg
Under the same efficiency: The Tube Head's weight is reduced 20% - 23%
The Control Unit's weight is reduced 37% - 44%

Analysis on weight, we can find out the trend:

The way of reducing the Tube Head's Weight
From 1950 to 1970, Balteau of Belgium proceeded to improve their products from three directions:

- Use SF6 Gaseous Insulator to replace Oil Insulator and aluminium shell to replace iron shell

- Use one-ended ground connection to make HV coil from three units (positive high voltage, negative high voltage and filament) to become one unit.

- To reduce the size and weight of the transformer by Diverse Frequency technology.
From that time, the other manufacturers also follow the above methods to improve their products to ensure the Directional 300kV Tube Head's weight from 50Kg reduces to 35-36Kg. This improvement revolution maintained for 10 years.

At the beginning of 1990, both ANDREX and ICM started to improve the Tube:

A) X-Ray Tube
They emphasized on positive rod anode X-Ray Tube. Basically they tried to make the Tube smaller; on the other hand, they moved the window of X-Ray Emission from internal to external of the tube. Therefore it could reduce the usage of lead for X-Ray protection and made the weight lighter. We take 300kV as an example, after the experiment, the weight of ICM D3006 is 29Kg but Balteau GFD306 is 26Kg. It is because the usage of lead is reduced. Our domestic manufacturers also got the successful experiments.

B) Transformer
We have to upgrade the frequency. We can either Diverse Frequency or Constant Frequency and even through Voltage-doubler to make it as a Constant Potential system. Upgrade "f" can make the volume of iron decreased. Of course, if we increase "f", the dissipation is also high and the transformer is very hot. Therefore, many manufacturers did some experiments and consider to using the iron core material to reduce the dissipation of iron and increase the magnetic flux density. Under these circumstances, ICM is the specialist on the experiment and development of heat dissipation and cooling.

C) Control Unit
since Balteau using a Diverse Frequency technology, it influenced the design of X-Ray Generator circuit. At that time, they were using SCR and made the weight reduced to less than 20kg. That technology remained unchanged for a long time. Until the mid of 1990, ICM, ANDREX and BALTEAU were using the Dalinton Transistor for their advance directional X-Ray Generator and assembled IGBT, MOSFET accessories to be the parts of converter power. So that it could simplify the circuit and greatly reduced the heat dissipation, then the weight of Control Unit were also reduced. For instant, the series of Control Unit of ICM SITE-X were only 14kg. The Control Unit CCU186 for the crawler just weighted 4kg. Even the Control Unit made by local manufacturers also reduced to 7.5-12kg. Of course, using aluminium alloy to replace steel plate was one of the reasons to reduce weight.

II) Upgrading the thickness

The thickness of X-Ray Generator is related to the value of kV. The density of X-Ray depends of the value of kV. The ratio of the hardest X-Ray inside the X-Ray dose also depends on the waveform of the voltage. Although the ratio of Rectangle Pulse Wave is higher than Sin Wave form, the Rectangle Pulse Wave still occupied the space. We use higher kV for the total exposure time but the effect is not so good. Therefore, we need to increase the dose of kV. We can increase mA of which we can extend its time and reduce the ratio of space occupancy in order to reach 100% of Constant Potential. By using the examples of ICM SITE-X and ANDREX SMART, the first one has the higher mA, which is 6,7,8mA. It can extend the exposure time. After the enhancement of tube-end's and transformer's cooling system. We can apply only one exposure time, the Duty Cycle can reach 100%. Compare with the situation before, it has already been upgraded 50%. Just only spends 20-30 minutes in one exposure, the thickness can be upgraded to 20-30%. Also upgraded the kV value, the manufacturers develop a series of 320kV, 350-360kV. For 320kV, the thickness is 69mm Fe. 350-360kV uses voltage-doubler to become Current High Pressure. Therefore under the same exposure time can upgrade X-Ray dose in order to enhance the thickness. The power of the voltage-doubler is not strong because the current is under 3mA. The heat dissipation of the tube and high power circuit is a big problem. We are recommended to spend 10 minutes on continuous work. For 300kV, just using 10 minutes, the thickness can reach 60mm Fe. We are waiting for a good idea and improvement in this condition.

III) Good Reliability
The reliability of X-Ray Generator depends on 3 elements such as X-Ray tube, high power transformer and control system.

The reliability also decided by design, handcraft. Protection combines with mechanical protection and electric protection.

Analysis of series of ICM SITE-X, they are still using glass-casing tube. It is because glass-casing tube is more durable. The longest usage time is 100000 hours. According to the figure from the magazine, the usage time of ceramic tube, metal ceramic tube and glass-casing tube are 400 hours, 600 hours and 1000 hours respectively. Normally, people believed that the mechanical ability of metal ceramic and ceramic tubes are better than the others. Therefore the improvement of the tube's structure can upgrade the reliability of the tube.

ICM co-operated with the University of Richie in Belgium. They improved the design of the X-Ray Generator tube. The enhancement is as follows:

1) Improved the distribute of the field of Electricity inside the tube
For 300kV, the strongest power inside the tube is 25kV/mm. Reduced 16% more than before so that the ability of the tube is upgraded.

2) Improved the mechanical connection of the tube and the tube head in order to increase the ability of shock resistance.
For all the imported ICM products, we did not find any damages of X-Ray tubes caused by mechanical attack or shocking during transportation.

3) ICM is using Conical Target on all panoramic series
It is very difficult to produce this kind of tube because they have to ensure the homogentic of theX-Ray emission. Generally, the degree of the homogentic of the X-Ray emission of the local tubes are almost 0.4 which is not too bad and the imported tubes are even better, almost 0.2. ICM got the franchise of this new development of controlling the electronic beam inside the tube in order to ensure the homogentic is less than or equal to 0.1. If the users find out that the homogentic is not so good, they can easily adjust by themselves. It increases the ability of the progress of the panoramic X-Ray Generator; On the other hand, ICM also considers the protection of the electricity such as:

- X-Ray Generator can be preheated automatically (The longest preheating time is 60 minutes for ICM generator).

- To avoid over voltage, over current, lack of voltage and current.

- To avoid over temperature of the tube caused by the defect of the cooling system.

- To avoid low pressure caused by the low ability of Gaseous Insulator of SF6 when the pressure of SF6 is too low.
All these considerable factors create a protect network and increase the reliability.

With the passed experiences, high voltage coil is very easy to be damaged. The manufacturers try very hard to solve this problem especially the method of handling, quality control, the structure, the coil etc. The percentage of such kind of damage should not be exceeding 5% of the total production. It should be controlled by a good enterprise.

The ability of the control unit can be divided into two parts:

1) The ability of the whole system
All enterprises spend a lot of time to do the enhancement. The most important thing is a complete protection system to ensure the X-Ray Generator and the high voltage transformer can work properly without any damages. For instant, by using a automatically preheating, pressure protection, temperature protection, over voltage, over current, lack of voltage and current protection etc., which expand the application of voltage. Also using the surge voltage resistance method to auto adjusts the power when it is in the low voltage situation. Especially after using the microprocessor, it becomes more easily to function through the soft ware. Since then, the international manufacturers like ICM, ANDREX also using the microprocessor, automatically preheating, self-detection etc. So the reliability of the system is increased.

2) The reliability of the working performance of the control unit (includes mechanical reliability and electricity reliability)
Mechanical reliability means the ability of the shock resistance of the printing board, the density of pressurization, temperature and the indicator apparatus. They are not so easy to be damaged. Electricity reliability means the stability of the progress of circuit and the ability of elements. ICM control unit provides a very good pressurization. After ICM had two improvements on the printing board, it seldom appears the printing board loosens while under the strong vibration. Generally, there were a lot of problems about the ability of electricity on their products especially the elements. But ICM using the self-detection system, the microprocessor usually can analysis the detected messages. Once there is an error, we can easy find out what is the error and solve the problem immediately. Also it is simplify the operation procedure, the operator just only press one button, then the exposure time is finished. It avoids the big error occurred when operating the unit and increases the reliability. The reliability of electricity is mostly effected by the outdoor environment such as the change of voltage, sudden change of the external voltage, connect to unsuitable socket, change of temperature (high temperature and low temperature). Therefore the ability of electricity is a big problem of controlling the circuit. After using the microprocessor, the ability is better than before.

IX) Convenience to use

It is so easy to operate the X-Ray Generator because it uses the microprocessor and different in store elements. We can just operate the programmer, the fluorescent digital displayer or LCD displayer. It simplifies the operating procedure. We just
press one button and input some reference information, and then the exposure is finished. KV and mA can be adjusted to minimized 1kV and 0.1mA so that the users can input the accurate reference and have the best exposure result. Also it can be saved and minimized the exposure reference to kV, mA, T, density, the thickness of material, focal length, type of film, model of film etc. The users can recall the input details any time. It is convenience for the repairman to recall the information of processing file, exposure record and self-detection when they are repair the unit. Because of inserting the microprocessor and the development of the elements, it allows the X-Ray Generator control unit can be operated more easily such as the microprocessor can run faster and the memory of element becomes larger.

As a conclusion, the creative idea means upgrade the scientific technology to satisfy the demand of the users. The development of technology is unlimited; the demands of users divide into certain stages but no limit. Therefore we have creative idea and we have new development. If we do not have creative idea, business will be going down.
If we have creative idea, business will be going up. Let us co-operate together to build up our bright future.

Writer: Zhu Wen Yu

2001.05.16