FR2520107A1 - PROBE FOR DETERMINING THE LEVEL OF LIQUID GASES - Google Patents

Abstract

LEVEL PROBES SYSTEM. THROUGH TERMINALS 1, 2, 3, 4, FOUR AMPLIFIERS 1, 2, 3, 4 ARRIVE THE SIGNALS FROM RESISTORS SEPARATED FROM ONE OF THE OTHER AND IMMERSION IN AN EXTERNAL ENVIRONMENT BY BEING ISOLATED IN A HERMETICALLY SEALED MANNER. DETECTION OF THE LEVEL OF LIQUID NITROGEN IN A CONTAINER.

Description

Liquid gas level determination probe The present invention is

relates to a

  liquid gas level determination probe, com-

  liquid nitrogen or liquid oxygen, wherein the electrical signal indicative of the liquid level is formed by means of a temperature-dependent resistor The invention further relates to a system of probes made of

several probes.

  Probes are known for determining

  the level of liquid gases'.

  a general rule of semiconductors,

  Negative temperature coefficient ducts, conductors with positive temperature coefficient

  or temperature sensitive diodes.

  The field of application of probes of this type is, for example, the determination of the level of liquid gases in gas purification traps which are used, for example, in the metal test field gas circuit: The electrical signal obtained by means of the probe can be used, especially when using multiple probes,

  input quantity to control the supply of liquid

of.

  Unambiguous determination of the level of liquidity

  presents difficulties, however, because the temperature

  of gas directly above the free surface

  of the liquid gas is barely above the temperature

liquid gas.

  The invention therefore aims at a determination probe

  nation of the liquid gas level through which it is possible to unequivocally determine the level of

liquid gas.

  According to the invention, the probe which is of the recalled type

  at the head of the present memory, is characterized in that it

  door in addition to the first resistance, which varies

  the temperature, which is used to indicate the level, another electrical resistance, which is galvanically separated from the first one.

  resistance and which is intended for the application of an electrical

  and that the two resistors are encapsulated in a hermetically sealed manner with respect to the external medium. In the design of the probe according to the invention, use is made of the fact that the probe in the

  liquid gas is in a medium with a good

  conductivity, whereas when it is in the gas above it is in a medium of poor conductivity If one provides to the probe, which can be done from the second resistance,

  electrical energy of the order of magnitude of some

  wattages, in the case where the probe is immersed in the liquid, a variation of

  signal because of the warm-up, which is more

  If in the case where the probe is outside the liquid Car, when the probe is immersed, the energy

  supplied is dissipated not only by the probe but also

  by the liquid, while, when the probe is

  above the liquid, the dissipation of energy

  provided is only through the intermediary of

  the probe and hardly through the surrounding gas

  The electrical energy supplied to the probe thus causes, in the case where the level of the liquid

  falls below the wave, a sharp variation

  signal and gives an indication accordingly

  that the probe is no longer in the free gas

  quide. According to an advantageous embodiment of the probe, it is provided as a pair of resistors a 2 x PT 100 The use of a 2 x PT 100 in a common steel sheath is advantageous because this embodiment of the probe according to the invention allows heating of the probe up to 400 'C. This

  is absolutely necessary, especially when using

  is probing it in gas purification traps.

  In addition, a sound system is

  in which the probes, rigidly mechanically connected to one another, are arranged with such

  offset from each other) only when

  that the probe system is arranged vertically

  in a container containing the liquid, the refere-

  trantle lower in the container serves to provide the

  general filling of the container with liquid and the lowest penetrating probe in the container serves to provide the signal to terminate the filling of the container with liquid As the probes provide an unequivocal determination of the liquid level, it is

  possible without further difficulty with the sound system.

  In order to prevent undesirable disturbances, it is furthermore advantageous, according to an improvement of the probe system, to provide two other probes and to arrange them by shifting them with respect to the first two probes. so that the first another

  probe designed to monitor the filling process

  take, when the probe system is

  tically, the lowest position, and so

  that the second other probe provided for the over-

  monitoring of the interruption process take the

highest level.

  The mode of operation of a particular variant of the probe according to the invention is described in more detail below,

  while an embodiment of the sound system

This is schematically indicated.

  Drawing, given only as an example

  FIG. 1 gives the curve of the measurement resistance of the probe when it is used for liquid nitrogen,

  Figure 2 shows the curve of the elec-

  of the heating resistance of the probe when

  that it is used for liquid nitrogen,

  FIG. 3 is a diagram of a mode of realization

  of a probe system 5 having additional warning stages, FIG. 4 is a diagram of an amplifier

  for the step-up probe system.

you extra.

  The curve of the value of the measuring resistor, which is reproduced in figure 1, is the curve of one of the two resistors of a thermometer with two resistors 2 x PT 100 (designation according to standard DIJ 4376 C) and conforms to IEC document B-Secretariat-33 in a stainless steel sheath The length of the measuring socket is 20 mm, the probe diameter is 6 nmm The probe is used

  to determine the level of liquid nitrogen (temperature

  -1960 C), which is shown as a hatch at the bottom of

gure 1.

  A constant DC voltage of 8 volts

  is applied to the heating resistance of the sound-

  This gives the curve of the electric current

  heating, shown in Figure 2.

  As can be seen in FIG. 1, the ohmic value of the measuring resistor is, in the case where the probe is immersed in liquid nitrogen over the entire length of the measurement socket, at 40 ohms (corresponds to at 500 ° C) If the probe is above the liquid nitrogen, at a distance of 2 mm above the surface

  of the liquid, the value of the resistance value of the resistance

  Measurement range is 85 ohms (corresponds to -380 C).

  In Figure 3 is shown schematically

  a probe system consisting of four probes of the type

  pe 2 x PT 100 At each of the resistors of the probes is applied a voltage of 8 volts The supply conductors 1 to 5 are, in operation, connected to the

  terminals 1 to 5 of the switching amplifier

in Figure 4.

  The switching amplifier consists of four operational amplifiers p A 741 with the reference numerals 1 'to 4' mounted in the circuit shown in FIG. 4. As an input variable, the resistance characteristic of the probe is used. measurement according to the graph of Figure 1, which is introduced into a branch of the input bridge arrangement The operating point of 60 ohms is set with the potentiometer 5 K The compensation of

  offset with the 10 K potentiometer.

  holds the abrupt transition of the transistor stage and therefore the supply of the relay by a Zener diode mounted in reverse direction The relay contacts can be used for any mounting, for example as a four-way indication device points of

  filling level of the container and as a

  input tacts for a command that can be programmed

  freely, as in the case of present use.

  When the probe system shown in Figure 3 operates without disturbance, the liquid level oscillates between the positions of the two probes

  intermediates "full" and "filling" (see Figure 3).

  The other two probes serve as a warning indication

  in case of overflow and when the container is empty.

Claims (4)

  1 Probe for determining the gas level   liquids, such as liquid nitrogen or oxygen   in which the electrical signal indicating the level of the liquid is formed by means of a resistance   which varies according to the temperature,   characterized in that the probe comprises, in addition to the first resistance which varies with the temperature and which serves to indicate the level, a   another electrical resistance, which is galvanically separated   only the first resistor and which is intended for the application of a voltage, and in that the two resistors are encapsulated in a hermetically sealed manner with respect to the outer bilge   Probe according to claim 1, characterized   characterized in that it is intended as a resistive torque a 2 x PT 100.   Probe according to claim 1, characterized   characterized in that it is intended as a resistive torque   a 2 x PT 100 in a stainless steel common sheath.   4 Probe system composed of probes   according to claims 1 to 3, characterized in that   that the probes mechanically connected to each other rigidly, are arranged with an offset between them which is such that when the probe system is disposed vertically in a 252010?   container containing the liquid, the lowest engaged probe in the container serves to provide the signal for   the filling of the container with liquid and the sound   the lowest in the container is used to   signal to terminate the filling of the pies in liquid.   Probe system according to claim   4, characterized in that two other probes are   views and are arranged with such a relative offset   first two probes that the first   Another probe, intended to monitor the filling process, will, when the probe system is arranged vertically, the lowest position, and the second other probe intended for the monitoring of the interruption process take the same position. highest position.