DE3324759A1 - Method for determining the heat level of a rotating anode, and an electronic arrangement for carrying out the method - Google Patents

Abstract

The method for determining the heat level of a rotating anode in an X-ray tube enables the determination of the heat level (CB2), which the anode has reached at the end of a time interval ( DELTA t), on the cooling curve (40), as a function of a heat level (CB1) at the start of this time interval ( DELTA t). In this way, a sequence of n heat levels (CB2,,... CBn) can be defined which the anode reaches as a result of its cooling, the n-th level depending only on the (n-1)-th level. The invention can be used in any X-ray system having a rotating anode. <IMAGE>

Description

PRIN2, StiNkk. &. GÄRTNER

Patent Attorneys · European Patent * Attorneys J0z4 ι ÜD

Munich _o _ Stuttgart

July 8, 1983

THOMSON - CSF

173, vol. Haussmann

75008 PARIS / France

Our reference: T 3629

Method for determining the heat level of a rotating anode and electronic arrangement for Implementation of the procedure

The invention relates to a method for determining the heat level of a rotating anode in an X-ray tube; she also relates to an electronic arrangement for carrying out this method.

The method according to the invention relates in particular to the field of radiology, in particular radiodiagnostics. For these purposes, rotating anode X-ray tubes are used, which during different periods of operation depending on Type of examination must absorb high electrical power that corresponds to the load phases.

The power that is effective during the load phases generates a current of electrons that hits a small surface the anode is focused, which is called the focal point

-Λ

this surface is then called X-rays sends out. A small fraction of this energy (around 1%) is converted into X-rays, while the rest as heat is generated.

This heat can be detrimental to the life of the tube and even cause it to be disturbed. This problem is mainly due to the large amount of heat that accumulates in the anode during the load phases and their Dissipation can only be done by radiation.

A first limitation of the anode temperature results from the focal point, while a second limitation results from the temperature of the focal spot ring surface, the surface of the focal point rotating due to the rotation of the anode is formed. This creates a first zone of very high temperature, namely the focal point, and proceeding therefrom, the heat is distributed along this ring surface in order to reach a ring surface temperature and finally the entire pane is heated before the heat is dissipated by radiation. the global temperature of the disk is called the base temperature. This base temperature represents the third temperature limitation represent.

As a result, restrictions are imposed on the use of an X-ray tube with a rotating anode, which is caused by the heat capacity the anode are given.

The heat capacity of an anode is the maximum amount of heat stored in this anode of an X-ray tube can be.

During a loading phase occurs an anode heating ^ ^3, which · ungsvermögen depends on the energy applied to it and its heat ray, may be jammed in the anode being not more heat than their maximum

Corresponds to heat capacity. The heat capacity can also be exceeded during successive load phases if the time intervals between the Load phases is shorter than the time required for the anode to cool down completely.

When performing a radio diagnosis, the operator must have information that the the thermal state of the X-ray tube in question.

Give IQ. For this purpose, procedures are used in technology used with the aim of simulating the cooling of the anode. Such a procedure requires an initial one Stage in a simulation of the temperature rise of the anode on a device used as a model

IQ exists. For this purpose, an electronic circuit of the analog type is generally used, into which a current is fed which is as precisely as possible proportional to the power consumed by the X-ray tube. Such a circuit arrangement generally contains one or more capacitors, the charging and discharging of which take place analogously to the rise in temperature of the anode and its cooling.

One shortcoming of this method, however, is the imprecision of the results obtained. For one thing, they give Properties of an electronic circuit that serves as a model, the thermal properties of an anode only incomplete again, and on the other hand the current fed into this circuit arrangement is not the anode current.

The invention creates a method which makes it possible to establish a heat balance at specific times to create a rotating anode X-ray tube, in which load phases are taken into account that this Points in time ahead. A heat balance of an X-ray tube created using the method according to the invention is obtained by an accurate determination of the

Amount of the anode current to provide the operator with a sequence of indications necessary for the continuation of a radiological examination are required. Such a sequence of displays forms the basic information that is included in the rest is indispensable for any kind of automated X-ray examination.

The method according to the invention for determining the heat level of a rotating anode in an X-ray tube which is equipped with

^ O at least one load phase is operated, which determines an amount of heat stored in the anode, this anode having a known maximum heat capacity, is characterized in that a heat level is calculated at constant time intervals, which is self-cooling represents the anode during each time interval.

Further features and advantages of the invention emerge from the following description of exemplary embodiments and from the drawing referred to. In the drawing show:

1 shows a cooling curve for an anode;

2 shows a block diagram of an electronic arrangement for carrying out the method; and

3 is a diagram showing a sequence of

Operations that are carried out when performing the procedure.

As already explained, the anode is in a loading phase heated, whereby it stores an amount of heat that is proportional to the amount of energy supplied to it is. The anode is cooled down solely by radiation. That way during a given period of time The amount of heat radiated depends on the temperature of the anode, which in turn is caused by the accumulated amount of heat is determined.

* β

This stored amount of heat, which is a fraction of the Heat capacity C "corresponds to the anode, is in the

Bm

hereinafter referred to as "achieved heat level" C _R. The amount of heat radiated by the anode during the given period of time is therefore greater, the higher the heat level C_ reached at the beginning of this

Period of time at the maximum heat capacity C_ of the anode

Bm

is approximated. This determines the anode's own cooling, which also occurs during a loading phase can take place.

In the method according to the invention, a heat level C is which the anode has reached at the end of a period t after the end of a load phase, this anode has a heat level equal to the maximum heat capacity C at the beginning of this period given the following relationship:

c = ° ^Βΐα

'B 1 + at'
20th

where a is a coefficient derived from the emissivity the anode and depends on the anode surface.

This relationship enables a curve 40 shown in Fig. 1 and the cooling curve to be plotted an anode (not shown); this cooling curve 40 gives that in the anode as a function of the Time t stored heat, if there is no external heat supply, calculated starting from the end of a Load phase through which the anode is brought to its maximum heat capacity value C_.

In the exemplary embodiment described, which has no restrictive character, such an amount of heat can be accumulated in the anode during a loading phase that the anode has a heat level at the end of the loading phase which is equal to C _x,. and lower than that

B I

maximum heat capacity C is. The value of this heat level C ₁ can be determined by a conventional calculation from the energy which was supplied to the anode during the loading phase. At the beginning of this load phase, for example, the anode has a temperature which is close to the ambient temperature, so that the effect of self-cooling is negligible. Since the amount of heat stored is equal to the amount of heat accumulated, this heat level C ₁ corresponds to the total energy that was supplied during the load phase.

Starting from this heat level C _R1 , which is reached at a point in time ti, a heat level C_ ", which the anode has at a point in time t2, is given by the following relationship in the method according to the invention:

r r

Bm ^- B1

B2 aC _Br At ₊ C _Bm *

Herein, At = t2 - ti.
20th

The difference between the heat level C .. at time ti and the heat level C _ß2 at time t2 is the amount of heat that was radiated through the anode.

It is thus possible to determine a number η of heat levels C - .., ... C_ to determine which the anode has due to its cooling (outside of the load phases).

According to a further step of the method, the heat level C., C _2, ... C _SS as variables X1, X2, ... Xn words, corresponding to a percentage of anode heating reached by its maximum heat capacity C _R and are determined so that applies:

^C B1 ^C B2

Λ I - -ρ, Λ.Δ - ρ

Bm Bm

By inserting these values X1, X2 into the formula given above to determine C _{ß2, the} result is:

X1

X2 =

a.Xi.

where X1 is known, so that the only variable parameter is At, but that in the method according to the invention is made constant.

^ O This is an essential feature of the Invention, i.e. the sizes X1, X2, ... Xn, which the anode reaches during its cooling, are set at time intervals At, At1, ... Atn, which are constant, where X2 becomes a function of X1.

The anode can be cooled in this way by a

Sequence of η values X1, X2, ... Xn, which is such that Xn is a function of Xn-1, such as is demonstrated by the following formula: 20

"a.Xn-1.At + 1

In the described, non-limiting embodiment, the constant time intervals At have a duration of 1 second. They allow the development of the heat level C _n reached by the anode, even during loading

Jd

to track load phases, the duration of which is greater than the time intervals At. The one through the anode at the end of each Interval At, the heat level reached taking into account any stored in the anode during this interval The amount of heat is then referred to as the "global heat level Cp" designated.

In the exemplary embodiment given above, in which the anode _{stores an amount of heat C F1 during a load phase and has a heat level C B1} at the end of a first time interval At1, the following applies:

\ If the load phase lasts until the end of a second time interval At2, when determining the global heat level achieved by the anode, the amount of heat that was radiated during this second time interval is taken into account, as well as the amount of heat C stored during this same second time interval _ . A global heat level C "is reached by the anode at the end of the second time interval At2

GZ

then the sum of the IQ heat level C_2 given by the self-cooling ^and the stored amount of heat C ".

From the global heat level C _G2 , the heat level C _ can be determined, which is reached at the end of the following interval At3, depending on the self-cooling of the anode, whereby two cases have to be distinguished:

1. The stress phase is at the end of the second time interval At2 ended: the heat level C is then the heat level reached by the anode and becomes as follows calculated:

_c Bm ^U G2

B3 a - C "" · At + C _n G2 Bm

2. The load phase is continued during the third time interval t3, and the amount of heat C _ must be taken into account, which is stored in the anode during this third interval; the global heat level C _3, to the anode reached, is equal to: CC

_c ^ Bm ^U G2 . "■

G3 a. C "_. At + C ₁₃ e3 G ^ Bm

Since the global heat levels reached by the anode also represent a fraction of the maximum heat capacity C _R , they can also be expressed as the percentage X
will.

also a fraction of the maximum heat capacity C _R

Theorem X of this maximum heat capacity C is expressed

Fig. 2 shows schematically in one embodiment an X-ray tube 1, to which an electronic arrangement 2 is assigned, which is controlled by functional blocks inside a dashed frame is shown. The performing

§ ment of the components of the X-ray tube 1 is on the limited to the description of the most necessary elements, in particular the cathode 3 and the anode 4.

A supply block 5 applies the stabilized high voltage required for the operation of the 2Q X-ray tube 1 between cathode 3 and anode 4. This voltage is generated by a winding S of a transformer, not shown generated. The end of the winding S marked + KV is connected to the anode 4 via a line, in which one current marked + mA, i.e. the anode current, flows, while the other, marked -KV End is connected to the cathode 3 via a line labeled -mA. The level of the anode current is adjustable and is determined before each load phase, as is the level of the high voltage KV.

The anode current labeled mA, which can vary during a load phase, must during the duration be known during this stress phase. The accuracy of the measurement of the anode current is a basic requirement, and this measurement must be made on the high voltage circuit. This leads to difficulties through that which cause very high levels of high voltage. In the described, non-restrictive exemplary embodiment is an anode current transducer formed by a Hall probe 6, which at any point with -mA designated line or the line designated + mA can be arranged. With the one described Embodiment, this Hall probe 6 is coupled to the connection labeled + mA and gives to their two connections 9, 10 to a scanning circuit 7 one electrical signal level that is proportional to the anode current mA. In such a transducer is

m <n <Λ 4 * · ·

advantageous that it is isolated from the high voltage circuit, which by the secondary winding S, the Anode 4 and the cathode 3 is formed.

The sampling circuit 7 applies signals at the frequency F1 to an analog-to-digital converter A / N under the control of signals the electrical signal supplied by the Hall probe 6, whereby this converter outputs digital information in AN, which corresponds to the anode current. In this way, the anode current inA can be sampled with the frequency F1 during the entire duration of the load phase of the X-ray tube 1 will.

The digitized values mAN are applied to a data acquisition and processing arrangement 12. This arrangement In particular, in the embodiment described, 12 contains a microprocessor 20, a first Program memory formed by a ROM circuit 21, a second program memory formed by a second ROM circuit 22, a work memory constituted by a RAM circuit 23 is, as well as an interface function block 24, which is labeled E / S and parallel inputs / outputs having. The microprocessor 20 is controlled by the signals <p1 and φ2 is synchronized from a clock generator 25 to which it is connected via lines 26,27. Further is the microprocessor 20 to the above-mentioned functional blocks

21, 22, 23 and 24 via an address bus 28, a data bus 30 and control and command lines 31 connected.

The microprocessor 20 and all function blocks 21,

22, 23, 24 are connected to the positive pole (VCC) via a line 32 and to the negative pole (VSS) via a line 33 Power supply connected.

The signals with the frequency F1, which ^{are intended to control the scanning circuit n} , are emitted by the arrangement 12, which is suitable for this purpose

Program contains. This frequency F1 must be relatively high, so that the sampling of the anode current mA possible fluctuations of this stream taken into account. In the exemplary embodiment described, the sampling frequency is F1 10 kHz, which corresponds to time increments it1, it2, itN of 200 microseconds, each corresponding to η samples, known from the η values mA1, mA2, ... mAN of the anode current occurring at the anode during a time interval At. The digitized values mAN of the aenode current mA are fed to the arrangement 12 via the input / output circuit 24, which also has a signal from the Frequency FT to the sampling circuit 7 outputs.

The high-voltage supply block 5 is an electrical Voltage NKV, the level of which is proportional to the value of KV. is high voltage applied to the X-ray tube 1. This Voltage level NKV is applied to a second analog / digital converter 14, which digitized it into a Information KVN converts the arrangement 12 on the Input / output circuit 24 is supplied.

The arrangement 12 is further provided with a display device 35 connected via a display control bus CA.

A preparatory phase of the method according to the invention can consist in inputting data into the arrangement 12 belonging to the X-ray tube 1 and its anode 4. This can be done by inserting the second information memory 22 can be reached, which contains this information, while the first memory circuit 21 the commands of the operating program.

The above information applies to a non-limiting exemplary embodiment of an organization of the means for Implementation of the method according to the invention.

Referring to Figure 3, there is shown a diagram showing the: Operations reproduces that in the implementation of the procedure

to be executed; this process begins with the exemplary embodiment with a loading phase, while the anode 4, as in the example considered above, is on the ambient temperature.

The following applies at time tO:

- (a): Beginning of a stress phase that occurs during the

Time span TC lasts;

- (b): Detection and storage of the value of the digitized high voltage KVN by the arrangement 12;

- (c): beginning of a first, constant time interval ti, ^ g that is given by the arrangement 12.

The following applies at time ti:

- (d): sampling and digitization of a first value of the anode current nA.

The following applies at time t2:

- (f): Storage of the digitized value mAN des Anode current mA through assembly 12;

- (g): counting a first time increment it1.

The following applies at time t3: 30

- (d): sampling and storage of a second value

of the anode current mA.

The following applies at time t4: 35

- (f): Storage of the second digitized value mAN

the anode current mA;

68 ff ■ £.

- (g): counting a second time increment it2. The following applies at time t5:

- (d): Sampling and storage of the η-th value of the anode current nA.

The following applies at time t6:

- (a): end of the load phase at the end of the period TC, which is equal to the first time interval At1 (and the start of cooling of the anode 4);

- (c): End of the first time interval At1 and start of a second time interval At2.

The following applies at time t7:

- (h): Calculation of an average power that is dependent on the Tube was recorded during the loading phase, from the product of the high voltage KV and the averaged anode current; this is divided by the sum of the samples of the anode current inA obtained by the number η of samples it, namely:

man

Y ~ mA

mA1

nit The following applies at time t8:

- (j): Determination of the amount of heat C .. that is in the anode

is stored.

The following applies at time t9:

- (k): Determination of the heat level C ₁ .

The following applies at time t10:

- (1): Calculation and storage of the percentage X1. The following applies at time ti 1:

- (m): display of the percentage X1 by the display device 35.

IQ At time ti 2, the following applies:

- (c) :: End of the second time interval At2 and start

a third time interval At3;

- (1): Calculation of the percentage X2 as a function of X1 and storage of X1.

The following applies at time t13:

~ ( ^m ) ^: display of the percentage X2 by the device 35 by replacing X1.

The following applies at time t14:

~ (c): End of the third time interval At3 and start a fourth time interval At4;

- (1): Calculation of X3 as a function of X2 as well as

Storage of X3. 30th

The following applies at time t15:

- (m): display the percentage X3 while X2 replaces

will.
35

I O «O ft Λ Λ β β ·

As described above, the display device can at constant time intervals At a sequence of values X1, X2, X3, ... indicate Xn, where Xn is a function of Xn-1 is. As previously explained, the value X is a percentage of the maximum heat capacity achieved by the anode C ". This percentage can also be used during a Bm

Heating phase of the anode can be specified.

If it is assumed that a stress phase occurs at a point in time t14, which is not shown, then the percentage X4 ^{1 of} the maximum heat capacity C that the anode 4 has reached at the end of the fourth time interval At4 is determined from:

15 - the amount of stored heat C ₄ ,

- the heat level C ₅₃ reached by the anode at the beginning of the interval At4 or its equivalent in the form of the percentage X3,

- the consideration of the self-cooling of the anode 4.

This is expressed by the following formula:

X3. ^C e4

25 χ4 =

a. At. X3 + 1 C_

Bm

This description shows that the method according to the invention provides accurate information at constant time intervals can be obtained via the thermal state of an X-ray tube, both during heating as well as during the cooling of the anode.

This information is displayed and enables the operator to make the most of the X-ray diagnostics Conditions to execute.

Λο

-W-

This information is also the necessary basis for any programming of the possible number of Load phases, the anode output and, in general, the best use of an X-ray system as a function of a given radiological examination.

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Claims (6)

PRIN £ ,: B-U.NKE- &. PARTNER Patent Attorneys * "European Patent Attorneys 3 3? 4 · 7 S Munich Stuttgart July 8, 1983 THOMSON - CSF 173, vol. Haussmann 75008 PARIS / France Our reference: T 3629 Claims Method for determining the heat level of a rotating anode an X-ray tube (1) under the effect of at least one load phase through which an amount of heat (C) is determined, which stores the anode (4), which has a known maximum heat capacity (C_.), around characterized in that at constant time intervals (At1, At2, ... Atn) a heat level (C _n . C ₀₀ , ... ■ Cg) is calculated, which is the self-cooling of the anode (4). during each respective time interval (At1, At2, ... Atn). 2. The method according to claim 1, characterized in that the heat levels (C "., C" _o , ... C ₀ ) outside the loading phases form the heat levels reached by the anode (4) during its cooling, each heat level (C ₁₃₀ , ... C _n ) is linked to the previous heat level by the following relationship: r c
_c Bm 'B1 'B2 C _n1 * a. t + C ₁₁ 20 1 ■ where a is a coefficient given by the emissivity and the surface of the anode (4) is determined. 3. The method according to claim 1, characterized in that the sum is formed in the case of a stress phase from an amount of heat (C., C -, ... C) and from a heat level (C - .., C ₁₃₀ ... C _n ), Q /, en α ι az , on which is obtained at the end of this interval by self-cooling, so that a global heat level (C ₁ , C ^ _n , ... C ") is determined, which the anode (4) effectively Kj ^ i ^ n has reached. 4. The method according to any one of the preceding claims, characterized in that the heat level (C _ß1 , C _ß2 , ... C _D ) which has reached the anode are expressed in terms (X1, X2, ... Xn), which correspond to the percentage of the maximum heat capacity (C _o ") achieved by the anode (4) and form a sequence of η values, Dili which are determined such that the n-th quantity (Xn) is a function of the (n-1) th quantity (Xn-1), respectively of the following formula: 25 Xn = ^Xn " ¹ a · At. Xn - 1 + 1 5. Electronic arrangement for carrying out the procedure according to one of claims 1 to 4, characterized in that it has a transducer (6) for measurement of the anode current (mA) and that this transducer (6) from the high-voltage circuit (5, 3, 4) is isolated. 6. Electronic arrangement according to claim 5, characterized in that the transducer (6) by a Hall probe (6) is formed.