DE3105909A1 - Measurement tube for a glow-cathode ionisation manometer - Google Patents

Abstract

The invention relates to a measurement tube for a glow-cathode ionisation manometer having a wide measurement range for measuring total pressures in the range from 10<-8> Pa to 10<3> Pa. The invention has the aim of simplifying the construction of the measurement tube by means of an additional ion trap, in the form of a grid, in order to extend the measurement range. According to the invention, a Bayard-Alpert measurement tube, which has an electron reflector on the glow cathode, and the electrode, which is arranged concentrically with respect to the ion collector and is in the form of a grid, are connected in such a manner that the Bayard-Alpert circuit is used with an electron reflector in order to measure low pressures and the electron reflector is connected as an anode and the electrode (which is in the form of a grid) is connected as an additional ion collector in order to measure high pressures, the ratio of the ion flows from the ion collector and the electrode in the form of a grid or the sum of the ion flows being evaluated to determine the pressure. <IMAGE>

Description

Gauge for a hot cathode ionization manometer

Field of application of the invention The invention relates to a measuring tube for a hot cathode ionization manometer with a wide measuring range for measuring total pressures in the range from 1018 Pa to i03 Pa.

Characteristics of the known technical solutions for total pressure measurement Incandescent cathode ionization manometers are known in the high and ultra-high vacuum area (R. T.

Bayard, D. Alpert, Rev. Sci. Instr. 1950), in which a wire-shaped Ion collector concentric from a cylindrical grid electrode - the anode - is surrounded.

Outside this grid electrode are one or more hot cathodes arranged parallel to the ion collector. During the ion collector approximately on Earth potential, the cathodes have a positive potential with respect to earth and the grid-shaped electrode is even more positive compared to the cathodes. Between the electron current 1 flowing from a hot cathode to the grid and that to the ion collector flowing ion current 1+ there is the relationship I + = CpI where C in the measuring range of this Ionization manometer3 (approx up to 10 8 Pa) is a constant, that of the potentials of the electrodes and their dimensions and distances is determined. This constant is commonly referred to as sensitivity.

It is also known that in hot cathode ionization manometers from Bayard-Alpert-yp behind the cathodes electrode sheets on the one facing away from the grid Can be arranged side by side (Krishnamurthy), whose fixed potential approximates equal to the cathode potential or slightly negative compared to the cathode potential Under these conditions, these electrodes reflect those emitted by the cathode Electrons and increase the sensitivity of the ionization manometer.

Both with the one given by Bayard and Alpert and with the Ionization manometers described by Krishnamurthy can show pressures above Do not measure 0.1 Pa any more, because then the sensitivity becomes pressure-dependent.

For measuring such pressures ionization manometers are known a large-area ionon collector and cinc large-area, no longer grid-shaped Anode blan-parallel plates or concentric sheet-metal cylinders, which are in a a small distance of 2 ... 3 mm from each other), with in the middle between these two electrodes the hot cathode parallel to these electrodes is arranged (Schulz and Phelps). Due to the flat anode and the small one Distance between cathode and anode, these pressure gauges have a low sensitivity, because here the electron paths become short and almost straight. As a result, these are Devices that also have a relatively high Have photoelectron current, unable to produce very small pressures (about p c 10 3 Pa). At high pressures (p to 100 Pa) there are deviations from the given equation, where the ion current passes through a maximum and finally Becomes zero. This means that the pressure display of this ionization manometer is at high Pressures ambiguous and above 100 Pa no longer proportional to pressure. These Disadvantages are the patent @@@@ ldung Wl 'lt Oil J / 201 326 thereby eliminates that between the ion collector and cathode on the one facing away from the anode Side of the Schulz-Phelps manometer a grid is arranged, which is approximately ion collector potential is maintained, so that the ion current is directed to the grid electrode and Dividing ion collector. The ratio of these two ion currents is higher Pressing in a unique way is pressure dependent and can be used to create a to get a clear statement about the pressure and the ion current-pressure characteristic linearize above 1 Torr. According to this construction, pressure values below 0.01 Pa the grid-shaped electrode on in relation to the ion collector negative potential so that the photoelectrons generated at the ion collector be forced to repent. This allows the lower limit pressure of this ionization manometer compared to the Schulz-Phelps ionization manometer by 1 ... 2 powers of ten. However, the disadvantage of this operating mode is the low sensitivity and the fact that the measuring range is not far enough into the UHV area (p> 10- 6 Pa) is sufficient, so that the lower limit pressure of the Bayard-Alpert ionization manometer is not achieved.

OBJECT OF THE INVENTION The invention aims at the construction of the measuring tube a hot cathode ionization manometer with additional grid-shaped ion trap to simplify the expansion of the measuring range.

Statement of the essence of the invention The invention is the task based on developing a measuring tube that is constructed concentrically and one Measuring range from 10 -8 to 103 Pa.

According to the invention, this object is achieved in such a way that a Bayard-Alpert ionization manometer is used with electron reflector. The reflector has a lower effect on the measurement Press an increase in sensitivity. Usually it is at a potential in the order of magnitude of the cathode potential or slightly negative compared to the cathode potential.

The grid is used in the usual way as an anode to accelerate the Electrons used and the axially arranged wire-shaped electrode is located on a negative potential compared to the cathode - usually earth potential - and serves together with a highly sensitive one arranged in the external circuit Amplifier for measuring the ion current, which is a measure of the pressure.

According to the invention, the reflector is used when measuring high pressures (p 0.1 Pa) behind the hot cathode used as an anode and the grid-shaped electrode is on placed a potential which is similar to that of the ion collector, so that part of the ion flow flows onto this electrode and with an amplifier connected to this electrode can be measured.

The ratio is in the range of very high pressure t103 Pa up to approx. 1 Pa) both currents approximate a power of pressure with an exponent of about 1 The sum of both currents is proportional to the pressure and in the range below approx. 1 Pa proportional. A suitable switchover takes place at the transition point between the two proportionality ranges.

With this circuit is achieved according to the invention that in the area high pressures over several powers of ten the relationship between the ratio of the ion currents measured at the two electrodes and the pressure is linear.

Exemplary embodiment The invention is based on an exemplary embodiment below are explained in more detail.

The associated drawing shows in Fig. 1: the structure of the coaxial Measuring tube Fig. 2: the circuit of the measuring tube according to Fig. 1 for low pressures Fig. 3: the circuit of the measuring tube according to FIG. 1 for high pressures.

In Fig. 1 the structure of a measuring tube with a cathode and a electron reflector arranged close behind. In the practical Execution can also be 2, 3 or 4 cathodes with reflector.

The individual elements are designated as follows in FIG. 1: 1 is a cylindrical grid, 2 an axially arranged wire-shaped electrode, 3 the cathode stretched outside the grid, 4 an angled electrode sheet and 5 the cathode holder. This basic structure is well known. According to the invention is the new circuit of these tube elements.

In Fig. 2 the circuit for measuring low pressures is - (p c 0.1 Pa).

The cathode 3, as a hot cathode, is directly heated and has to earth positive potential. The cylindrical grid 1 is positive compared to the cathode 3 Potential. The electrode sheet 4 acting as an electron reflector has approximately Cathode potential or with respect to the cathode 3 a weakly negative potential.

The wire-shaped electrode 2 is grounded through an amplifier. With The ion current is measured with the aid of the amplifier.

The following applies here: I + = CpI-.

(C = sensitivity of the measuring probe) The lower limit pressure is known in Way caused by the photo effect on the ion collector and lies, depending on the sensitivity of the measuring tube and the dimensions of the wire-shaped electrode between 10-6 and 10 -8 Pa.

In Fig. 3 is the circuit of the measuring tube of Fig. 1 for the measurement high pressures (0.1 to 103 Pa).

The corresponding switchover is expediently carried out within of the measuring device automatically.

In this circuit, the electrode sheet 4 is connected as an anode. The electron current flows from the cathode 3 to the one which is at positive potential Electrode sheet 4.

The cylindrical grid 1 and the wire-shaped electrode 2 are over Amplifier grounded. The two ion currents I + 1 and 1 + 2 are measured in one large pressure range is 1 + 1/1 + 2 r C2p (C2 ~ sensitivity of the circuit).

This special type of circuit makes it possible to use a measuring tube, while maintaining the lower detection range of the Bayard-Alpert measuring tube, the Significantly increase the detection range for high pressures, up to 103 Pa.

Blank page

Claims (1)

Patent claim measuring tube for a hot cathode ionization manometer with one ion collector in the form of a wire-shaped electrode (2), one on the ion collector connected ammeter, one the ion collector as a cylindrical grid (1) surrounding electrode, one or more incandescent cathodes, which are outside the cylindrical Grid (1) run parallel to the cylinder axis and an electrode sheet (4) close behind each of the cathodes (3) on the side facing away from the ion collector, in the case of the measurement of low pressures - approximately between 10 7 Pa and 10 1 Pa - the cylindrical one Grid (1) is connected as anode by being positive with respect to the cathodes (3) Has potential, and the electrode sheets (4) connected as electron reflectors are characterized by having a negative potential with respect to the cathodes (3) in that the electrode plates are used to measure high pressures - for example between i01i and 103 Pa (4) are connected as anodes by having positive potential with respect to the cathodes (3) and the cylindrical grid (1) connected as an additional ion collector is by having the same or approximately the same potential as this and is switched on via a separate ammeter, the ratio of the ion currents of ion collector and cylindrical grid (1) or the sum of the ion currents for Determination of the pressure can be evaluated.