JPS6346944B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for baking a thermionic filament used, for example, in an X-ray source such as an electron spectrometer.

In an X-ray generation source such as an electron spectrometer, a thermionic filament and an
A line generation target is placed. After evacuating the housing, a heating current is supplied to the filament to generate thermoelectrons from the filament, and a high voltage is applied between the filament and the target to cause the generated thermoelectrons to collide with the target. In this way, X-rays are generated from the target. However, when the filament is heated, outgassing occurs from the filament and the degree of vacuum within the housing decreases, which may lead to dielectric breakdown and discharge, which may damage the device.

Therefore, conventionally, after a filament is installed in a housing, a baking current is first applied to the filament to heat the filament and degas the filament. At this time, the supply time of the baking current was either a fixed time determined empirically by the handler, or a time determined on a case-by-case basis by the handler being present and monitoring the progress of degassing. .

However, since the amount of gas contained in each filament differs from filament to filament, the baking current supply time is too short in the former method.
Or it may be too long. If the baking time is too short and the baking is insufficient, heating the filament under high pressure to generate the X-rays will result in continued outgassing and thus the electrical discharge described above. Put it away. Furthermore, if the baking time is too long, power will be wasted. On the other hand, according to the latter method,
Although the baking time is neither too short nor too long, it has the disadvantage that it is troublesome because the operator must be present all the time and monitor the progress of degassing using a vacuum gauge or the like.

The present invention has been made to solve these drawbacks of the prior art, and one embodiment of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention. In the figure, 1 is a vacuum casing, and the vacuum casing 1 is connected to a vacuum pump (not shown) via an exhaust pipe 2. has been done. An X-ray generating target 3 is arranged within the vacuum housing 1. Further, a filament 4 is provided opposite the X-ray generating target 3.
is grounded and installed within the housing. By closing the switch 5, a high positive voltage is applied to the target 3 by the DC power supply 6. Reference numeral 7 denotes a heating power source that supplies a heating current for generating thermoelectrons from the filament 4.
8 is a detection resistor for detecting the current flowing through the target 3, and the detection signal of the detection resistor 8 is supplied to the heating power source 7, and the heating power source 7 ensures that the detection signal always matches the reference value. The heating current supplied to the filament 4 is controlled accordingly. When the changeover switch 9 is connected to the a terminal, the filament 4 is connected to the heating power source 7, but when it is connected to the b terminal, the filament 4 can be connected to the baking power source 10. 11 is a switch circuit for making the baking power supply 10 and the b terminal conductive or non-conductive;
1 is periodically brought into conduction by an on/off signal as shown in FIG. 2a supplied from the A terminal of the control circuit 12.
It becomes non-conductive. The on period of this signal corresponding to the period during which the baking current flows is, for example, 7 minutes;
The off period of this signal, which corresponds to the period during which no baking current flows, is, for example, 10 minutes. 13 is housing 1
The vacuum gauge 13 is a vacuum gauge that generates a signal according to the degree of vacuum inside the oven, and the vacuum gauge 13 is connected to a baking completion determination circuit 14.
The first and second sample and hold circuits 15a, 1 of
5b. The control circuit 12 has B and C
Sampling pulses as shown in FIG. 2b and c are generated from the terminals, respectively, and are supplied to the first and second sample and hold circuits 15a and 15b, respectively. The baking completion determination circuit 14 includes the first and second sample and hold circuits 15a and 15b, and both circuits 1.
The subtraction circuit 16 includes a subtraction circuit 16 for obtaining a difference signal between the output signals of the subtraction circuits 5a and 15b, and a comparator 17 that generates a response signal when the output signal of the subtraction circuit 16 becomes less than or equal to a reference signal from a reference power supply 18. The response signal of the comparator 17 is supplied to a buzzer 19,
A buzzer 19 generates a sound to notify completion of baking.

In such a configuration, after the filament 4 is installed in the housing 1 with the switch 5 turned off, the interior of the housing is evacuated. After evacuation has progressed to a certain extent, the changeover switch 9 is connected to the b terminal. Therefore, the control circuit 12 supplies an on/off signal as shown in FIG. 2a to the switch circuit 11.
In FIG. 2a, the switch circuit 11 is in a conductive state during a period when a high level signal is supplied, and becomes nonconductive during a period when a low level signal is supplied. Therefore, a baking current of a constant level flows periodically through the filament 4 from the baking power supply 10. While the baking current is flowing, the filament 4 is heated, and the filament 4
If it contains gas, degassing occurs and the degree of vacuum decreases, and the pressure inside the casing reaches, for example, about 5×10 ⁻² Pa at the beginning of baking. On the other hand, when baking is stopped, degassing is not performed, so the degree of vacuum is improved, and the pressure inside the housing becomes, for example, about 1×10 ^-3 Pa at the beginning of baking.
Therefore, in the initial stage of baking, there is a considerable difference in the output signal of the vacuum gauge 13 between immediately before supplying the baking current and immediately after supplying it for one cycle, as shown in Fig. 2(d), but in the advanced stage of baking, The degree of vacuum inside the housing immediately before starting supply of baking current and immediately after supplying it for one cycle varies only slightly, for example, by a value of about 0.7 × 10 ^-3 Pa, so the output signal of the vacuum gauge There is not much difference between before and after the baking current is supplied. The signal from the vacuum gauge 13 is transmitted to first and second sample and hold circuits 15, which are supplied with the sampling signals shown in FIG. 2d and c, respectively.
a, 15b, the output signals of the first and second sample and hold circuits 15a, 15b become as shown in FIG. 2, e and f, respectively. Therefore, the output signal of the subtraction circuit 16 is as shown in FIG. 2g. Therefore, if the level of the reference signal supplied to the comparator 17 is set to a level as shown by the dotted line in FIG. Therefore, at time T, the comparator 17
Generates a response pulse as shown in . Note that an extremely large signal is held in the sample-and-hold circuit 15b before the first sampling pulse is supplied to prevent the comparator 17 from malfunctioning. The output signal of the comparator 17 is supplied to a buzzer 19, and the buzzer 19 notifies completion of baking. Therefore, the operator can connect the switch 9 to the a terminal to stop the supply of baking current to the filament 4.

As described above, according to the present invention, it is possible to conduct baking by passing a sufficient and necessary baking current through the filament without constantly monitoring baking, and in addition to eliminating waste, baking can be performed without constantly monitoring baking. If X-rays are generated by electrons from the filament, discharge due to insufficient baking will not occur.

Furthermore, in the present invention, a baking current is automatically and repeatedly supplied to the filament intermittently, and in each period of supplying the baking current, a vacuum gauge is provided immediately before the supply of the baking current is started and immediately after supplying the baking current for a certain period of time. A difference signal between the output signals of the circuit is obtained, and a response signal is generated when the signal from the circuit falls below a certain level. Therefore, the following effects are achieved.

(1) Determine whether the vacuum level is decreasing due to air entrapment due to insufficient vacuum sealing of the casing, or whether the vacuum level is decreasing periodically due to insufficient baking that is synchronized with the timing of energizing the filament. ,
It is possible to reliably determine when baking has been sufficiently performed and to stop baking without being affected by the decrease in vacuum level due to insufficient sealing.

(2) Considering the tolerance to thermal deformation and oxidation of the filament and its surrounding parts, intermittent energization allows a larger current to be supplied to the filament at once compared to continuous energization, reducing bakeout time. can do.

In the above embodiment, the buzzer 19 is sounded by the output of the comparator 17, but the switch 9 may be changed from the b terminal to the a terminal by the response pulse of the comparator 17.

Further, in the above-described embodiment, the baking power source and the heating power source are provided separately, but it is also possible to provide a single power source that serves both purposes.

Furthermore, in the embodiments described above, the baking current is supplied completely periodically.
If it is supplied intermittently, it does not have to be completely periodic.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of one embodiment of the present invention, and FIG. 2 is a diagram illustrating output signals from each circuit element in FIG. 1. 1: Vacuum housing, 2: Exhaust pipe, 3: Target,
4: Filament, 5: Switch, 6: DC power supply, 7: Heating power supply, 8: Detection resistor, 9: Selector switch, 10: Baking power supply, 11: Switch circuit, 12: Control circuit, 13: Vacuum gauge, 14 : baking completion determination circuit, 15a, 15b: sample hold circuit, 16: subtraction circuit, 17: comparator, 18: reference power supply, 19: buzzer.

Claims (1)

[Claims] 1. A filament placed in a casing to be evacuated, a vacuum gauge that generates a signal according to the degree of vacuum inside the casing, and means for automatically and intermittently repeatedly supplying baking current to the filament. , a circuit that calculates the difference signal between the output signal of the vacuum gauge immediately before the supply of baking current starts and immediately after supplying the baking current for a certain period in each period of supplying the baking current, and when the signal from the circuit becomes below a certain level. A filament baking device for an open type X-ray source comprising a circuit for generating a response signal.