CA1122330A - X-ray tube filament current predicting circuit - Google Patents
X-ray tube filament current predicting circuitInfo
- Publication number
- CA1122330A CA1122330A CA325,809A CA325809A CA1122330A CA 1122330 A CA1122330 A CA 1122330A CA 325809 A CA325809 A CA 325809A CA 1122330 A CA1122330 A CA 1122330A
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- ray tube
- voltage
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- 238000004364 calculation method Methods 0.000 claims description 10
- 230000000694 effects Effects 0.000 claims description 9
- 238000010586 diagram Methods 0.000 description 2
- 238000005259 measurement Methods 0.000 description 2
- 101100382321 Caenorhabditis elegans cal-1 gene Proteins 0.000 description 1
- 241000617482 Kiwa Species 0.000 description 1
- VREFGVBLTWBCJP-UHFFFAOYSA-N alprazolam Chemical compound C12=CC(Cl)=CC=C2N2C(C)=NN=C2CN=C1C1=CC=CC=C1 VREFGVBLTWBCJP-UHFFFAOYSA-N 0.000 description 1
- 230000001276 controlling effect Effects 0.000 description 1
- 238000009434 installation Methods 0.000 description 1
- 238000007620 mathematical function Methods 0.000 description 1
- 238000000034 method Methods 0.000 description 1
- 230000000737 periodic effect Effects 0.000 description 1
- 230000001105 regulatory effect Effects 0.000 description 1
- 230000006641 stabilisation Effects 0.000 description 1
- 238000011105 stabilization Methods 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05G—X-RAY TECHNIQUE
- H05G1/00—X-ray apparatus involving X-ray tubes; Circuits therefor
- H05G1/08—Electrical details
- H05G1/26—Measuring, controlling or protecting
- H05G1/30—Controlling
- H05G1/34—Anode current, heater current or heater voltage of X-ray tube
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- General Health & Medical Sciences (AREA)
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- X-Ray Techniques (AREA)
Abstract
An X-ray generator circuit includes a feedback regulator which adjusts X-ray tube filament current to regulate anode current. A predictor circuit is connected to calculate an appropriate filament voltage from preoset values of anode current and anode voltage; it functions to control the filament current during a period immediately following application of the anode voltage and when the feedback regulator is ineffective.
Description
ll~Z;~3~3 "X-ray tube filament current predicting circuit".
This invention relates to electric circuits for X-ray generators. More specifically, this invention relates to circuits for determini~g the filament current in X-ray tubes.
BACKGROUND OF THE INVENTION.
Power supply circuits utilized with X-ray tubes generally include controls for independently presetting anode kilovoltage and anode current flow prior to tube operation. Anode current flow is generally adjusted by presetting filament current to a predetermined value which is known to provide the required anode current flow at a selected anode kilovoltage. During application of the anode kilovoltage a feedback regulator may be utilized to control filament current in response to anode current.
Such feedback regulators `are, however, gsnerally limited by the thermal time constants of the X-ray tube filament structure and do not, therefore, provide adequate regula~n during the period immediately following the application of anode voltageto the tube.
Prior art X-ray generators included c~rcuits for presetting the X-ray tube filament current to a value which had been determined, by previous measurement, to provide the preset anode current flow at the preset anode voltage.
These r,rior art generators included a large num~er of cali-bration controls. During initial set up of the gellerator a 112~33(~
separate control was adjusted to provide the necessary filament current for each of a large number of separate combinations of preset anode current and anode kilovoltage. Periodic readjustments of these controls were required as X-ray tubes aged or were replaced.
Many modern X-ray facilities include multiple X-ray tubes which are selectively powered from a common X-ray generator. X-ray generators which are operated in this mode required a separate set of filament current adjusting controls for each X-ray tube utilized.
Prior art circuits and methods which attempted to calculate filament current as a mathematical function of anode voltage, preset anode current, and operating time are known, for example, from United States Patent No.
3,983,396, and need numerous adjustments due to the use of a function generator, which should approximate the X-ray tube filament current - emission current characteristics.
SUMMARY OF THE INVENTION
X-ray generators of the present invention include a circuit which predicts and controls X-ray tube filament current, during the time period following turn on and prior to stabilization of the feedback current regulator circuit, as a function of preset kilovoltage and anode current values. The filament current is calculated on the basis of a three term equation of the form:
If = s ~u+ kIa + cIY + KV + Z] (1) wherein the first term, u, represents the preemission point of the X-ray tube;
the second term.
kIwa (2) represents the tube emission characteristic in the absence of space charge effects (that is: on the assumption that emission is not a function of anode voltage) and the third term ~r cI + KV + z accounts for space charge effects in the tube. In practice, it has been ~ - 2 -llZ~330 determined that most X-ray tube emission characteristics can be accurately characterized by equation ~1) with the constants u, w, x, y, and z sub-stantially equal, respectively, to 1.38, 0.16, 1.5, -0.667, and -2.4. Only two individual calibration measurements and adjustments must be made for each individual X-ray tube. The value of k which characterizes the tube in the absence of space charge effects is measured and adjusted at a single high kilovoltage-low current value and the value of c, which characterizes the space charge effects in the tube, is measured and adjusted at a single low kilovoltage-high current value. If, as is commonly the case, there are multiple filaments in each X-ray tube separate calibrations must of course be performed for each filament. A typical X-ray generator which may, for example, power three X-ray tubes with two filaments in each tube will thus require only twelve separate calibration adjustments in contrast with hundreds of adjustments which were required in prior art X-ray generator equipment of a similar type.
According to one broad aspect of the invention there is provided a circuit for predicting filament current for producing a predetermined anode current in an X-ray tube operating with a known anode kilovoltage, comprising electronic calculation circuits having input connections for receiving a first input voltage (KV) representative of the X-ray tube anode voltage and a second input voltage (la) representative of the predetermined anode current, the electronic calculation circuits comprising first circuit means receiving the second input signal for generation of a first and a second output signal (kIaW, cIaY), which show an exponential relation with respect to the input signal, second circuit means for generating a third output signal, which is proportional to the sum of the first input signal (KV) the second output signal (cIa ) and a first constant signal (Z), third circuit means for generation of a fourth output signal, which is proportional to the quotients of a second constant signal (X) and the third output signal, and fourth circuit means for adding the first output signal, a third constant signal (U) and the . .
llZ~330 fourth output signal thereby generating a signal proportional to the filament control voltage.
According to another broad aspect of the invention there is provided a circuit for predicting filament current for producing a predetermined anode current in an X-ray tube operating with a known anode kilovoltage, comprising electronic calculation circuits having input connections for receiving a first input voltage (KV) representative of the X-ray tube anode voltage and a second input voltage (Ia) representative of the predetermined anode current, the electronic calculation circuits receiving the second input signal for genera-tion of a first and a second output signal ~kIaW, cIaY), which show an exponential relation with respect to the input signal, generating a third output signal, which is proportional to the sum of the first input signal (KV), the second output signal (cIa ) and a first constant signal (Z), generating a fourth output signal, which is proportional to the quotient of a second constant signal (X) and the third output signal, and adding the first output signal, a third constant signal (U) and the fourth output signal thereby generating a signal proportional to the filament control voltage.
BRIEF DESCRIPTION OF THE DRAWINGS
The preferred embodiments of the invention may be best understood by reference to the attached drawings in which:
Figure 1 is a block diagram of an X-ray generator of the present invention and Figure 2 is a schematic diagram of a predictor circuit of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Figure 1 is an X-ray generator of the present invention. Although a typical X-ray generator might be connected to power three separate X-ray tubes with two filaments in each tube the embodiment of Figure 1 includes, for clarity of illustration, only two X-ray tubes 10 and 11 each containing a single filament. The extension of the principles illustrated herein to a - 3a -~.
Z~30 greater number of X-ray tubes and filaments will be apparent to those skilled in the art. The anodes of the X-ray tubes are, in conventional fashion, connected to a high voltage power supply 12 which - 3b -llZ'Z330 18-12-1978 ' -4- - PHA 20795 includes means for switching the high voltage between the anodes of the tubes 10 and 11 in response to a signal from a tube selector 13. The filaments of the X-ray tubes 10 and 11 are connected to a filament current control 14, which may, by way of example, be similar to the filament current control illustrated in the above referencedpatent 3,983,386 or similar circuits which are well known in the prior art. The filament controller receives electrical signals from a feedback current regulator 15 and a filament current predictor circuit 16 as well as from the tube selector 13 and adjusts filament current in the operating X-ray tube in response thereto. Controls, which may for example be selec'tor switches, 17 and 18 are disposed on an operators console where they may be utilized to presèt, respectively, anode kilovoltage and anode current prior tg operation of an X-ray tube. The tube selector 13 typically is also included in the console to allow preselection of a particular X-ray tube for a given exposure.
The anode kilovoltage control 17 provides a signal to the high voltage power supply 12 which varies the anode voltage in a conventional manner. The anode current control 18 similarly provides a conventional signal to the feedback current regulator 15. The feedback current regulator 15 is well known in the prior art and comprises means for sensing the anode current flow *hrough the X-ray tube, for exarnple within the high voltage power supply 12, and for adjusting the filament current, via the filament current 'controller 14, to stabilize the tube anode current.
The time constant of the feedback current regulator 15, which is su'bstantially determined by the thermal inertia of the X-ray tube filament structure, precludes that cir-cuit from effcctively regulating tu'oe current during the first approximately 20 mil;seconds following application of anode voltage. During that i~tial 20 milisecond period filament current is determined by a predictor circuit 16 ~` which, on the basis of analog signals, KV and ~, derived respectively from controls 17 and 18, predicts and cal-- -- - - -- - - -1~ 2233~) culates an appropriate filament c-urrent value to re~ulate anode curr0nt i~ $he operating X-ray tube.
It has been ~etermined that the filament current - which is required to produce a known anode current flow, Ia, at a known anode voltage, KV, for a large number of X-ray tubes may be effectively predicted by an analog computer which calculates the value of a filament current controlling voltage If from the equation:
10 I = s~1.38 + kl o 16 , 66 ~ ( 4 ) The first term of equation (4) represents the pre-emission point of the X-ray tube filament. In a typical X-ray tube Model SR0 31/100 marketed by Philips Medical 15-Systems, Inc., Shelton, Connecticut approximately 0.33 amperes of primary filament current were required to initia-te emission.
The second term determines the base line value of filament current, on the assumption that there is no 20 .space-charge effect in the X-ray tube; that is, that emission is not a function of the anode voltage.
The third t~rm represents the effects of space charge in the X-ray tube.-The constant, s, is a scale factor which represen~
25 the transfer function of the filament current control 14.In a preferred embodiment the constant, s, e~uals 2 amps of filament current per volt output from the filament current predictor circuit.
Fig. 2 is a preferred embodiment of the filament 30 current predictor circuit 16. The tube selector 13 (Fig. 1) alternately applies logical "true" levels to~the inputs 20 or 21 to indicate the particular X-ray tube (10 or 11 6~ Fig. 1) in operation. The signals at inputs 20 and 21 are, respectively, applied to the logic inputs of analog 35 switctles 22 and 23 or 24 and 25 to respect~ely connect potentiometers RA and R~ or RC and RD which are preset, in a manner described below, t`o progam the values of constan~s c alld ~ for eacll particular X--ray tube.
, , , , . , . , . . ~. ~ ..... .. . .. . ... .. . .
112i~;~30 Amplifier Al is connected, via resistors R34 and R36, to a 9 volt reference voltage VREF and is programmed by feedback resistor 33 and *nput resistors R34 and R36a to provide a -2,l~ volt reference level at its output. Ampli-fier A2 is similarly programmed to provide a 1,0 volt outputlevel.
The first term of equation (4) is generated by amplifier A6 which is programmed by resistors R56 and R68 to produce a constant 1.38 v-~lt signal at its output.
The second term of equation (4) is generated by circuit Ml which is a multi-function device whose output voltage Va is defined as V
Va = 9 tVy) (V- ) (5) 15 where m is a programmable exponent. Multi-function devices having the indicated transfer function are, for example, manufactured by Analog Devices of Norwood, Massachusstts~
as part no. AD433J and by others. The transfer fun^tion of module Ml may be characterized as k(Ia)m ~ (6) where k equals Vy, Ia equals Vz~ and Vx equals ~(VREF).The exponent m is programmed by resistors R29 and R30:
25 m = R2g ~ R30 , (7) ~c~ . . .
B The input ~ from the anode current preset switch 18 (Fig.
1) is applied to the input Vz o~ the multifunction device Ml. The constant k is determined by the setting of poten-30 tiometers RA or RC which are selected by analog switches 22 or 2'~ in response to signals from the tube selector 13 and is connected co the input Vv of Ml.
The constant k is programmed for each tube by adjusting the appropriate potentiometer (RA or Rc) at a 35 high anod~ kilovoltage (typically 120 kilovolts) and a low anode current (typically 50 milliamps). Selection of a particular tube closes one of the analog switches (22 or llZZ330 18-12-19,8 -7- PHA 2O-79;
24) which connects one of the potentiometers to Ml. The output of Ml, which represents the second term of equation (4), is summed into amplifier A5 and then into amplifier A6 which provides the filament current predictor output to the filamen-t current controller 14.
The third term of equation (4) represents the effects of space charge in the X-ray tube. The first term in the denominator i0 cI -O.667 (8) is generated by a multi-function device M2 wherein the -~`1 exponent m is programmed to the value O.667 b~ resistors R35 and R36 The anode current preset signal ~ is applied to input Vx of multi-function circuit M2 and the constant c is determined for each tube by the potentiometers RB and RD which are switchably connected to the input V of M2 via the analog switches 23 and 25. The constant c is adjust-ed for each tube at a low anode voltage (approximately 5O icilovolts and a ~igh operating current where space-charge effects are significant.
The output of M2 is aummed in aplifier A3 withthe constant -2.4 produced at the output of Al and with a signal KV representing preset anode voltage which is derived ~om control 17 (Fig.l). This sum can be negative, however, rectifier CR2 at the output of A3 limits the signal to non-negative values. This signal is inverted in amplifisr A4 and is f~d to the Vx input of multi-function circuit M3 ~hich is connected as a divider and serves to calculate the indicated reciprocal. The output of M3 is connected to the input of amplifier A5 and is multiplied therein by a scale ~actor, 0.15, determined by resistors R48 and R45.
~ The combination of amplifiers A5 and A6 is used to sum the three terms of equation (43 and to apply the appropriate scale factor is to achieve the predictor output ~hich is applied to the fllament current controller.
llle circuit of F:ig. 2 thus allows prediction and control of X-ray tube filament current d~ring the interval immediate~y followil-g the application of anode voltage, . . .
~ ~ - - -.
.....
18-12-~978 -8- PHA 2O-795 during which feedback control is ~nadequa.te. The circuit may be easily constructed using standard multi-function analog modules. Only two calibration adjustments (one performed at high voltage and low current, the other at low current and high voltag~e) are required for each X-ray tube; a feature which greatly simplifies installation and maintainence of generator apparatus.
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This invention relates to electric circuits for X-ray generators. More specifically, this invention relates to circuits for determini~g the filament current in X-ray tubes.
BACKGROUND OF THE INVENTION.
Power supply circuits utilized with X-ray tubes generally include controls for independently presetting anode kilovoltage and anode current flow prior to tube operation. Anode current flow is generally adjusted by presetting filament current to a predetermined value which is known to provide the required anode current flow at a selected anode kilovoltage. During application of the anode kilovoltage a feedback regulator may be utilized to control filament current in response to anode current.
Such feedback regulators `are, however, gsnerally limited by the thermal time constants of the X-ray tube filament structure and do not, therefore, provide adequate regula~n during the period immediately following the application of anode voltageto the tube.
Prior art X-ray generators included c~rcuits for presetting the X-ray tube filament current to a value which had been determined, by previous measurement, to provide the preset anode current flow at the preset anode voltage.
These r,rior art generators included a large num~er of cali-bration controls. During initial set up of the gellerator a 112~33(~
separate control was adjusted to provide the necessary filament current for each of a large number of separate combinations of preset anode current and anode kilovoltage. Periodic readjustments of these controls were required as X-ray tubes aged or were replaced.
Many modern X-ray facilities include multiple X-ray tubes which are selectively powered from a common X-ray generator. X-ray generators which are operated in this mode required a separate set of filament current adjusting controls for each X-ray tube utilized.
Prior art circuits and methods which attempted to calculate filament current as a mathematical function of anode voltage, preset anode current, and operating time are known, for example, from United States Patent No.
3,983,396, and need numerous adjustments due to the use of a function generator, which should approximate the X-ray tube filament current - emission current characteristics.
SUMMARY OF THE INVENTION
X-ray generators of the present invention include a circuit which predicts and controls X-ray tube filament current, during the time period following turn on and prior to stabilization of the feedback current regulator circuit, as a function of preset kilovoltage and anode current values. The filament current is calculated on the basis of a three term equation of the form:
If = s ~u+ kIa + cIY + KV + Z] (1) wherein the first term, u, represents the preemission point of the X-ray tube;
the second term.
kIwa (2) represents the tube emission characteristic in the absence of space charge effects (that is: on the assumption that emission is not a function of anode voltage) and the third term ~r cI + KV + z accounts for space charge effects in the tube. In practice, it has been ~ - 2 -llZ~330 determined that most X-ray tube emission characteristics can be accurately characterized by equation ~1) with the constants u, w, x, y, and z sub-stantially equal, respectively, to 1.38, 0.16, 1.5, -0.667, and -2.4. Only two individual calibration measurements and adjustments must be made for each individual X-ray tube. The value of k which characterizes the tube in the absence of space charge effects is measured and adjusted at a single high kilovoltage-low current value and the value of c, which characterizes the space charge effects in the tube, is measured and adjusted at a single low kilovoltage-high current value. If, as is commonly the case, there are multiple filaments in each X-ray tube separate calibrations must of course be performed for each filament. A typical X-ray generator which may, for example, power three X-ray tubes with two filaments in each tube will thus require only twelve separate calibration adjustments in contrast with hundreds of adjustments which were required in prior art X-ray generator equipment of a similar type.
According to one broad aspect of the invention there is provided a circuit for predicting filament current for producing a predetermined anode current in an X-ray tube operating with a known anode kilovoltage, comprising electronic calculation circuits having input connections for receiving a first input voltage (KV) representative of the X-ray tube anode voltage and a second input voltage (la) representative of the predetermined anode current, the electronic calculation circuits comprising first circuit means receiving the second input signal for generation of a first and a second output signal (kIaW, cIaY), which show an exponential relation with respect to the input signal, second circuit means for generating a third output signal, which is proportional to the sum of the first input signal (KV) the second output signal (cIa ) and a first constant signal (Z), third circuit means for generation of a fourth output signal, which is proportional to the quotients of a second constant signal (X) and the third output signal, and fourth circuit means for adding the first output signal, a third constant signal (U) and the . .
llZ~330 fourth output signal thereby generating a signal proportional to the filament control voltage.
According to another broad aspect of the invention there is provided a circuit for predicting filament current for producing a predetermined anode current in an X-ray tube operating with a known anode kilovoltage, comprising electronic calculation circuits having input connections for receiving a first input voltage (KV) representative of the X-ray tube anode voltage and a second input voltage (Ia) representative of the predetermined anode current, the electronic calculation circuits receiving the second input signal for genera-tion of a first and a second output signal ~kIaW, cIaY), which show an exponential relation with respect to the input signal, generating a third output signal, which is proportional to the sum of the first input signal (KV), the second output signal (cIa ) and a first constant signal (Z), generating a fourth output signal, which is proportional to the quotient of a second constant signal (X) and the third output signal, and adding the first output signal, a third constant signal (U) and the fourth output signal thereby generating a signal proportional to the filament control voltage.
BRIEF DESCRIPTION OF THE DRAWINGS
The preferred embodiments of the invention may be best understood by reference to the attached drawings in which:
Figure 1 is a block diagram of an X-ray generator of the present invention and Figure 2 is a schematic diagram of a predictor circuit of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Figure 1 is an X-ray generator of the present invention. Although a typical X-ray generator might be connected to power three separate X-ray tubes with two filaments in each tube the embodiment of Figure 1 includes, for clarity of illustration, only two X-ray tubes 10 and 11 each containing a single filament. The extension of the principles illustrated herein to a - 3a -~.
Z~30 greater number of X-ray tubes and filaments will be apparent to those skilled in the art. The anodes of the X-ray tubes are, in conventional fashion, connected to a high voltage power supply 12 which - 3b -llZ'Z330 18-12-1978 ' -4- - PHA 20795 includes means for switching the high voltage between the anodes of the tubes 10 and 11 in response to a signal from a tube selector 13. The filaments of the X-ray tubes 10 and 11 are connected to a filament current control 14, which may, by way of example, be similar to the filament current control illustrated in the above referencedpatent 3,983,386 or similar circuits which are well known in the prior art. The filament controller receives electrical signals from a feedback current regulator 15 and a filament current predictor circuit 16 as well as from the tube selector 13 and adjusts filament current in the operating X-ray tube in response thereto. Controls, which may for example be selec'tor switches, 17 and 18 are disposed on an operators console where they may be utilized to presèt, respectively, anode kilovoltage and anode current prior tg operation of an X-ray tube. The tube selector 13 typically is also included in the console to allow preselection of a particular X-ray tube for a given exposure.
The anode kilovoltage control 17 provides a signal to the high voltage power supply 12 which varies the anode voltage in a conventional manner. The anode current control 18 similarly provides a conventional signal to the feedback current regulator 15. The feedback current regulator 15 is well known in the prior art and comprises means for sensing the anode current flow *hrough the X-ray tube, for exarnple within the high voltage power supply 12, and for adjusting the filament current, via the filament current 'controller 14, to stabilize the tube anode current.
The time constant of the feedback current regulator 15, which is su'bstantially determined by the thermal inertia of the X-ray tube filament structure, precludes that cir-cuit from effcctively regulating tu'oe current during the first approximately 20 mil;seconds following application of anode voltage. During that i~tial 20 milisecond period filament current is determined by a predictor circuit 16 ~` which, on the basis of analog signals, KV and ~, derived respectively from controls 17 and 18, predicts and cal-- -- - - -- - - -1~ 2233~) culates an appropriate filament c-urrent value to re~ulate anode curr0nt i~ $he operating X-ray tube.
It has been ~etermined that the filament current - which is required to produce a known anode current flow, Ia, at a known anode voltage, KV, for a large number of X-ray tubes may be effectively predicted by an analog computer which calculates the value of a filament current controlling voltage If from the equation:
10 I = s~1.38 + kl o 16 , 66 ~ ( 4 ) The first term of equation (4) represents the pre-emission point of the X-ray tube filament. In a typical X-ray tube Model SR0 31/100 marketed by Philips Medical 15-Systems, Inc., Shelton, Connecticut approximately 0.33 amperes of primary filament current were required to initia-te emission.
The second term determines the base line value of filament current, on the assumption that there is no 20 .space-charge effect in the X-ray tube; that is, that emission is not a function of the anode voltage.
The third t~rm represents the effects of space charge in the X-ray tube.-The constant, s, is a scale factor which represen~
25 the transfer function of the filament current control 14.In a preferred embodiment the constant, s, e~uals 2 amps of filament current per volt output from the filament current predictor circuit.
Fig. 2 is a preferred embodiment of the filament 30 current predictor circuit 16. The tube selector 13 (Fig. 1) alternately applies logical "true" levels to~the inputs 20 or 21 to indicate the particular X-ray tube (10 or 11 6~ Fig. 1) in operation. The signals at inputs 20 and 21 are, respectively, applied to the logic inputs of analog 35 switctles 22 and 23 or 24 and 25 to respect~ely connect potentiometers RA and R~ or RC and RD which are preset, in a manner described below, t`o progam the values of constan~s c alld ~ for eacll particular X--ray tube.
, , , , . , . , . . ~. ~ ..... .. . .. . ... .. . .
112i~;~30 Amplifier Al is connected, via resistors R34 and R36, to a 9 volt reference voltage VREF and is programmed by feedback resistor 33 and *nput resistors R34 and R36a to provide a -2,l~ volt reference level at its output. Ampli-fier A2 is similarly programmed to provide a 1,0 volt outputlevel.
The first term of equation (4) is generated by amplifier A6 which is programmed by resistors R56 and R68 to produce a constant 1.38 v-~lt signal at its output.
The second term of equation (4) is generated by circuit Ml which is a multi-function device whose output voltage Va is defined as V
Va = 9 tVy) (V- ) (5) 15 where m is a programmable exponent. Multi-function devices having the indicated transfer function are, for example, manufactured by Analog Devices of Norwood, Massachusstts~
as part no. AD433J and by others. The transfer fun^tion of module Ml may be characterized as k(Ia)m ~ (6) where k equals Vy, Ia equals Vz~ and Vx equals ~(VREF).The exponent m is programmed by resistors R29 and R30:
25 m = R2g ~ R30 , (7) ~c~ . . .
B The input ~ from the anode current preset switch 18 (Fig.
1) is applied to the input Vz o~ the multifunction device Ml. The constant k is determined by the setting of poten-30 tiometers RA or RC which are selected by analog switches 22 or 2'~ in response to signals from the tube selector 13 and is connected co the input Vv of Ml.
The constant k is programmed for each tube by adjusting the appropriate potentiometer (RA or Rc) at a 35 high anod~ kilovoltage (typically 120 kilovolts) and a low anode current (typically 50 milliamps). Selection of a particular tube closes one of the analog switches (22 or llZZ330 18-12-19,8 -7- PHA 2O-79;
24) which connects one of the potentiometers to Ml. The output of Ml, which represents the second term of equation (4), is summed into amplifier A5 and then into amplifier A6 which provides the filament current predictor output to the filamen-t current controller 14.
The third term of equation (4) represents the effects of space charge in the X-ray tube. The first term in the denominator i0 cI -O.667 (8) is generated by a multi-function device M2 wherein the -~`1 exponent m is programmed to the value O.667 b~ resistors R35 and R36 The anode current preset signal ~ is applied to input Vx of multi-function circuit M2 and the constant c is determined for each tube by the potentiometers RB and RD which are switchably connected to the input V of M2 via the analog switches 23 and 25. The constant c is adjust-ed for each tube at a low anode voltage (approximately 5O icilovolts and a ~igh operating current where space-charge effects are significant.
The output of M2 is aummed in aplifier A3 withthe constant -2.4 produced at the output of Al and with a signal KV representing preset anode voltage which is derived ~om control 17 (Fig.l). This sum can be negative, however, rectifier CR2 at the output of A3 limits the signal to non-negative values. This signal is inverted in amplifisr A4 and is f~d to the Vx input of multi-function circuit M3 ~hich is connected as a divider and serves to calculate the indicated reciprocal. The output of M3 is connected to the input of amplifier A5 and is multiplied therein by a scale ~actor, 0.15, determined by resistors R48 and R45.
~ The combination of amplifiers A5 and A6 is used to sum the three terms of equation (43 and to apply the appropriate scale factor is to achieve the predictor output ~hich is applied to the fllament current controller.
llle circuit of F:ig. 2 thus allows prediction and control of X-ray tube filament current d~ring the interval immediate~y followil-g the application of anode voltage, . . .
~ ~ - - -.
.....
18-12-~978 -8- PHA 2O-795 during which feedback control is ~nadequa.te. The circuit may be easily constructed using standard multi-function analog modules. Only two calibration adjustments (one performed at high voltage and low current, the other at low current and high voltag~e) are required for each X-ray tube; a feature which greatly simplifies installation and maintainence of generator apparatus.
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Claims (6)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A circuit for predicting filament current for producing a predeter-mined anode current in an X-ray tube operating with a known anode kilo-voltage, comprising electronic calculation circuits having input connections for receiving a first input voltage (KV) representative of the X-ray tube anode voltage and a second input voltage (Ia) representative of the predeter-mined anode current, the electronic calculation circuits comprising first circuit means receiving the second input signal for generation of a first and a second output signal (kIaW, cIaY), which show an exponential relation with respect to the input signal, second circuit means for generating a third output signal, which is proportional to the sum of the first input signal (KV) the second output signal (cIaY) and a first constant signal (Z), third circuit means for generation of a fourth output signal, which is proportional to the quotients of a second constant signal (X) and the third output signal, and fourth circuit means for adding the first output signal, a third constant signal (U) and the fourth output signal thereby generating a signal proportio-nal to the filament control voltage.
2. A circuit as claimed in claim 1, wherein the second and fourth cir-cuit means are analog adding circuits comprising linear amplifiers.
3. A circuit as claimed in claim 1, wherein the first and third cir-cuit means are analog multi-function circuits comprising logarithmic-and antilogarithmic amplifiers.
4. A circuit as claimed in claim 1, wherein the first, second and third constant signals are respectively -2.4, 1.5 and 1.38 Volt and exponents of the first and second output signals are respectively 0.16 and -0.667.
5. A circuit as claimed in claim 1 or 3, including for each X-ray tube filament two control means for supplying third and fourth input signals (k, c) to the electronic calculation circuits, the first and second output signals of which being proportional to respectively the third and fourth input signals, which depend on respectively the emission characteristic and the space charge effects of the corresponding X-ray tube, and switching means for receiving a signal indicative of the fact that a particular X-ray tube is to be operated and connecting the two corresponding control means to the electronic calculation circuits.
6. A circuit for predicting filament current for producing a pre-determined anode current in an X-ray tube operating with a known anode kilo-voltage, comprising electronic calculation circuits having input connections for receiving a first input voltage (KV) representative of the X-ray tube anode voltage and a second input voltage (Ia) representative of the predeter-mined anode current, the electronic calculation circuits receiving the second input signal for generation of a first and a second output signal (kIaw , cIaY), which show an exponential relation with respect to the input signal, generating a third output signal, which is proportional to the sum of the first input signal (KV), the second output signal (cIaY) and a first constant signal (Z), generating a fourth output signal, which is proportional to the quotient of a second constant signal (X) and the third output signal, and adding the first output signal, a third constant signal (U) and the fourth output signal thereby generating a signal proportional to the filament control voltage.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US89773178A | 1978-04-19 | 1978-04-19 | |
| US897,731 | 1978-04-19 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1122330A true CA1122330A (en) | 1982-04-20 |
Family
ID=25408330
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA325,809A Expired CA1122330A (en) | 1978-04-19 | 1979-04-12 | X-ray tube filament current predicting circuit |
Country Status (7)
| Country | Link |
|---|---|
| JP (1) | JPS54158893A (en) |
| BE (1) | BE875641A (en) |
| CA (1) | CA1122330A (en) |
| DE (1) | DE2915548A1 (en) |
| FR (1) | FR2423950A1 (en) |
| GB (1) | GB2021810B (en) |
| IT (1) | IT1120109B (en) |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3001118A1 (en) * | 1980-01-14 | 1981-07-16 | Siemens AG, 1000 Berlin und 8000 München | X-RAY DIAGNOSTIC GENERATOR FOR AN X-RAY TUBE WITH SEVERAL FIRE SPOTS |
| GB2174492A (en) * | 1985-04-29 | 1986-11-05 | Philips Nv | X-ray examination system and method of controlling an exposure therein |
| CN110793981B (en) * | 2019-10-30 | 2022-03-22 | 新鸿电子有限公司 | Time-sharing multiplexing control device and system |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3521067A (en) * | 1968-04-15 | 1970-07-21 | Picker Corp | X-ray tube current stabilization |
| NL7314036A (en) * | 1973-10-12 | 1975-04-15 | Philips Nv | GLOW CURRENT SUPPLY FOR A HIGH VOLTAGE ELECTRON TUBE. |
| DE2422844C3 (en) * | 1974-05-10 | 1978-10-19 | Siemens Ag, 1000 Berlin Und 8000 Muenchen | X-ray diagnostic apparatus in which the X-ray tube voltage is regulated via the X-ray tube heating current |
| DE2539898C2 (en) * | 1975-09-08 | 1982-06-03 | Siemens AG, 1000 Berlin und 8000 München | X-ray diagnostic apparatus with an adjusting means for the control circuit containing the X-ray tube heating current for a recording parameter dependent on the X-ray tube current |
| DE2542016A1 (en) * | 1975-09-20 | 1977-03-24 | Philips Patentverwaltung | Control circuit for X-ray tube exposure current - has resistor switched between two HV generators with voltage drop proportional to actual value of exposure current |
| US4072865A (en) * | 1976-06-24 | 1978-02-07 | American Radiologic Systems, Inc. | Automatic control system |
| DE2754920A1 (en) * | 1977-12-09 | 1979-06-13 | Koch & Sterzel Kg | PROCEDURE AND CIRCUIT ARRANGEMENT FOR THE HEATING POWER SUPPLY OF A ROENTINE PIPE |
-
1979
- 1979-04-12 GB GB7912913A patent/GB2021810B/en not_active Expired
- 1979-04-12 CA CA325,809A patent/CA1122330A/en not_active Expired
- 1979-04-13 IT IT21884/79A patent/IT1120109B/en active
- 1979-04-17 BE BE0/194658A patent/BE875641A/en unknown
- 1979-04-17 FR FR7909637A patent/FR2423950A1/en active Granted
- 1979-04-17 JP JP4612679A patent/JPS54158893A/en active Granted
- 1979-04-18 DE DE19792915548 patent/DE2915548A1/en not_active Ceased
Also Published As
| Publication number | Publication date |
|---|---|
| GB2021810A (en) | 1979-12-05 |
| IT7921884A0 (en) | 1979-04-13 |
| IT1120109B (en) | 1986-03-19 |
| JPS54158893A (en) | 1979-12-15 |
| DE2915548A1 (en) | 1979-10-25 |
| FR2423950A1 (en) | 1979-11-16 |
| JPS638598B2 (en) | 1988-02-23 |
| GB2021810B (en) | 1982-08-04 |
| BE875641A (en) | 1979-10-17 |
| FR2423950B1 (en) | 1983-12-09 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |
