FR2511152A1 - METHOD OF USING APPROPRIATE PIRANI VACUOMETER RULE AND APPROPRIATE PIRANI VACUOMETER - Google Patents

Abstract

PROCESS FOR USING A THERMAL CONDUCTIVITY VACUOMETER OF PIRANI RULE AND VACUOMETER OF PIRANI APPROPRIATE FOR THE IMPLEMENTATION OF THE SAID PROCESS AND INCLUDING A FILAMENT INSERTED IN A BRIDGE 6. THE SUPPLY CURRENT OF THE BRIDGE THAT THE SUPPLY VOLTAGE CIRCULATED IS USED AS A MEASURE FOR PRESSURE INDICATION.

Description

The present invention relates to a method of using a vacuum gauge to

  thermal conductivity of Pirani It also concerns a

  Pirani vacuum gauge suitable for carrying out this method of use.

  tion. In the thermal conductivity vacuometers of Pirani set,

  a filament is inserted into a Wheatstone bridge The power supply

  tation applied to this bridge is set so that the resistance and consequently the filament temperature are constant regardless of the heat released In other words, the bridge is still balanced This regulation has a time constant of a few milliseconds, so

  that devices respond very quickly to pressure changes.

  The voltage applied to the bridge is a measure of the pressure because the trans-

  Thermal mission of the gas filament increases with the pressure In addition to a short response time, the thermal conductivity vacuometers of

  Pirani have the advantage of a relatively large measuring range.

  As a result of these advantages, thermally conductive vacuometers

  of this type are preferably used for the control or monitoring of

  It is often necessary to provide

  measure relatively long and different depending on local conditions -

  between the pressure probe (the measuring bridge with the measuring tube) and

  the power supply apparatus, which includes the amplifier

  setting voltage of the bridge.

  This results in a risk of false pressure indication, since this indication is not distorted only when the line resistance is

  low compared to the total resistance of the measuring bridge.

  This disadvantage is well known and has already been

  laying two extra lines for high resistance measurement

  voltage applied directly to the measuring system.

  However, this arrangement is sensitive to disturbances. It is also possible to

  compensate for cable length using a voltage divider dis-

  posed upstream of the indicating apparatus This solution presents the incon-

  next: the balancing can only be done after the

  in use of the measuring device with a specific cable, which

  poses the presence of qualified personnel at each local modification.

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  The subject of the present invention is a method of using a thermo-thermal vacuometer of Pirani set and a vacuometer suitable for the implementation of said method and in which the size

  measured is independent of line and contact resistances.

  According to an essential characteristic of the invention, the current

  the regulated supply voltage circulates in the bridge is used

  for the pressure indication. Such a measured quantity is inde-

  line resistance and contact resistance This solution does not pre-

  Moreover, it does not suffer from the disadvantages of the known solutions mentioned above for

  the suppression of a distorted pressure indication.

  According to another characteristic of the invention, the supply of a pressure sensor, comprising at least the measuring tube and the components of the Wheatstone bridge and an amplifier, is also provided by the bridge supply circuit. It is thus possible to give up a

  cable with four separate conductors between the pressure probe and a

  Power supply and indication Two drivers are sufficient for this often very long target in surveillance or

pressure control.

  In a Pirani vacuum gauge suitable for the implementation of the

  assigned to use according to the invention, an ammeter or resistor, to which is assigned an apparatus indicating the voltage drop across its terminals, is inserted into the part of the supply circuit of the bridge located

  in the feeding and indicating apparatus.

  Other features and advantages of the invention will be better

  understood using the detailed description below of examples of

  embodiment and the accompanying drawing in which Figure 1 shows a Pirani vacuometer with a separate amplifier;

  FIG. 2 represents a Pirani vacuometer in which the amplification

  is part of the pressure sensor; and

  FIG. 3 represents a Pirani vacuometer in which the amplification

  The transmitter is also part of the pressure sensor and uses a

  two-wire cable only.

  All highly schematized figures each represent the pressure sensor 1 on the left and the supply-indication device 2

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  on the right (framed in dashed form) The two parts are united by a

  cable 3, variable length depending on the application.

  In the exemplary embodiment according to FIG. 1, the pressure probe

  1 comprises the measuring tube 4, whose inner chamber is connected to a container not shown, in which the pressure must

  be controlled or monitored for example.

  Inside the measuring tube 4 is the filament 5, inserted into the Wheatstone bridge 6 with the other resistors 7, 8, 9. The line sections 11 and 12 located in the pressure sensor 1 are part of the circuit. supply of the bridge The line sections 13 and 14 transmit the voltage fluctuations of the bridge to the amplifier 15.

  Amplifier 15 (amplifier-regulator) is part of the

  same supply-indication 2 in the embodiment according to

  This is why the connecting cable 3 has 4 conductors.

  The line sections 16 and 17 form the part of the feed circuit

  the bridge located in the power-indicating device. An ampere-

  meter 10 is inserted in line section 17 Variations of pressure

  The inside of the measuring tube 4 varies the current flowing in the supply circuit of the bridge, is indicated by the ammeter 10 and is a direct measurement of the pressure in the measuring tube. The exemplary embodiment according to FIG. 2 differs from that according to FIG. 1 in that the amplifier 15 is part of the pressure sensor 1. It is certainly no longer necessary then to transmit the voltage fluctuations of the bridge outside the probe. However, the cable 3 is again constituted by four conductors, since the power supply of the amplifier 15 (voltage source 21) is in the device

  The voltage source 21 is connected to the ampli-

  15 by the cable 3 and the line sections 22 and 23 Another difference with respect to FIG. 1 is the replacement of

  the ammeter 10 by the resistor 18 with a voltmeter 19 bypass.

  The apparatus 19 indicates the voltage drop across the resistor 18.

  This indication also corresponds to the current flowing in

  Con line 17 and can therefore be used as a measure of pressure.

  In the exemplary embodiment according to FIG. 3, the amplifier 15 is also part of the pressure sensor 1. In order to be able to use a connection cable 3 with only two conductors, at least parts

  of the bridge supply circuit and the supply circuit are

ticks.

  In the exemplary embodiment according to FIG. 3, the feeding apparatus

  tion-indication 2 contains a circuit 25 in which are inserted the resistor 18 and the supply voltage source 21 This circuit is

  extends in the pressure probe 1 by the line sections 26 and 27.

  These are shunted by a voltage stabilizer 28 whose output is connected by the line section 29 to the amplifier 15 and it

delivers a constant voltage.

  The exemplary embodiment according to FIG. 3 further comprises a tran-

  sistor 31 inserted in the power supply circuit of the bridge and whose base is connected by line 32 to the output of the amplifier 15 The transistor 31 constitutes the variable resistor in the power supply circuit of the bridge, allowing permanent balancing Wheatstone bridge 6 Fluctuations in current that different pressures inside the measuring tube 4 show in the bridge supply circuit, consisting of the

  line sections 25, 26 and 27 produce different voltage drops.

  rents across the resistor 18, so that the desired pressure can

  read on the indicator 19 This can obviously be replaced by.

  electronic means producing any commands or regulations.

  In the embodiment according to FIG. 3, the feed circuit

  The bridge structure also contains protection barriers 33 and 34, which are also part of the pressure sensor 1.

  protection against the explosion of the pressure sensor in service These ele-

  protection leads can be constituted for example by diodes

  Zener who have the property of limiting upward any fluctuation

  Power generation, sparking It is also possible to mount these protection elements 33 and 34 in the part of the supply circuit of the outer bridge to the pressure sensor 1, for example

in the camera 2.

  Of course, various modifications may be made by those skilled in the art to the principle and to the devices that have just been described as non-limiting examples, without going out

of the scope of the invention.

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Claims (6)

claims   A method of using a Pirani thermal conductivity vacuometer, comprising a filament placed in a bridge and a regulation of the bridge supply voltage such that the resistance and therefore the temperature of the filament are constant, independently of the heat released (Pirani vacuum gauge set), said method being characterized by   the use of the current that the regulated supply voltage circulates   in the bridge supply circuit as a measure for the indication pressio '.   Process according to Claim 1, characterized in that the feed   of a pressure sensor, comprising at least the measuring tube and the   Wheatstone bridge and amplifier speakers, is also provided   by the bridge supply circuit.   3 Pirani vacuum gauge suitable for the implementation of the method of   the use according to one of claims 1 or 2, comprising a probe of   pressure and a feeding apparatus-indication, and characterized in that a resistor, to which is assigned a device indicating the fall   voltage at its terminals, is inserted in the part of the power supply circuit.   the bridge located in the power-indicating device.   4 Vacuum gauge according to claim 3, characterized in that the pressure sensor contains, in a known manner, the components of the Wheatstone bridge,   including the measuring tube, and further the components of an amplifier.   Vacuum gauge according to claim 4 for carrying out the method according to claim 2, characterized in that the pressure probe contains   electronic means that keep the power supply voltage constant amplifier.   6 Vacuum gauge according to one of claims 4 or 5, characterized in that   that the output of the amplifier is connected to the base of an inserted transistor   in the bridge supply circuit.   Vacuum gauge according to one of Claims 3 to 6, characterized   in that protective barriers are inserted in the feed circuit. the bridge.