WO1981002062A1

WO1981002062A1 - Fluid pressure monitoring device

Info

Publication number: WO1981002062A1
Application number: PCT/AU1981/000002
Authority: WO
Inventors: L Adam
Original assignee: Varian Techtron Pty Ltd; L Adam
Priority date: 1980-01-08
Filing date: 1981-01-08
Publication date: 1981-07-23

Abstract

Fluid pressure monitoring device, particularly for controlling a solenoid valve in the gas feed of a spectrophotometer is described. The device has a housing (10) with a pressure chamber (11) having a diaphragm (16) which moves a plunger (17) between a radiation source (26) and detector (27). The detector (27) is connected to a switching circuit (28) which adopts one of two states depending on the position of the plunger (17). The source (26) and detector (27) are adjustable so as to enable variation of the fluid pressure at which the switching circuit (28) changes state.

Description

FLUID PRESSURE MONITORING DEVICE

This invention relates to devices for monitoring pressure within a fluid system. Such devices have many possible uses but it will be convenient to hereinafter describe the invention with reference to use in relation to spectrophotometers.

One pressurized fluid system of a spectrophometer is the air supply to the sample nebulizer and that supply should be at a particular pressure, or within a predetermined pressure range, for optimum results. Devices as previously used for that purpose have not been sufficiently sensitive.

It is an object of the present invention to provide a relatively simple but sensitive fluid pressure monitoring device.

According to the present invention there is provided a fluid pressure monitoring device including, a chamber connectable to a fluid system, means responsive to the pressure within said chamber and including a member which moves in either of two directions in response to variation in said pressure, a switching circuit operable to switch between two different states, a radiation source, a detector coupled to said switching circuit and arranged to receive radiation from said radiation source, said detector being responsive to said radiation to cause said switching circuit to adopt one of said states, a space existing between said radiation source and said detector, and said member being movable into said space to interrupt the path of said radiation and to thereby cause said switching circuit to adopt the other said state.

The device preferably includes adjusting means operable to enable variation of the pressure at which the member interrupts the radiation path. The adjusting means may comprise a support on which the radiation

detector are both mounted, the support being adjustably movable relative to the pressure responsive means.

The device according to the invention may be used in a spectrophotometer including a nebulizer for receiving a sample to be analysed, a gas supply line for supplying pressurized gas to the nebulizer, a solenoid operated valve in the gas supply line and operable to control the pressure of gas in the supply line, the chamber being connected to the gas supply line so that the member is movable in response to a change in gas pressure in the line, the switching circuit being coupled to the solenoid operated valve so as to control the operation thereof and thereby control the pressure of gas in the gas supply line.

When designed for use in a spectrophotometer, the device can be preset to perform the switching function at any pressure within a range of pressures such as 1 psi to 60 psi, for example.

A particular embodiment of the device which can be used with spectrophotometers will now be described with reference to the accompanying drawings, in which:

Fig. 1 is a cross sectional view of one embodi¬ ment of the present invention.

Fig. 2 is a cross sectional view of a second embodiment of the present invention.

Fig. 3 is circuit diagram for the electrical components of the device, and

Fig. 4 is schematic fluid circuit diagram of a spectrophotometer incorporating the device of the present invention.

In the Fig. 1 embodiment, the device includes a housing 10 having a pressure chamber 11 in one part connectable to a fluid system and containing the opto¬ electronic system in another part. The housing 10 comprises a hollow body section 20 having front and back covers 12 and 13 respectively. The front cover 12 is removable to expose the pressure chamber 11 and fluid under pressure may be fed into the chamber 11 through an inlet port 14 provided in a wall of the front cover 12. The back cover 13 is secured to the body section 20 so as to resist separation for_a. reason hereinafter explained. . Pressure responsive means 15 is located within the housing 10 so as to be exposed to the pressure chamber 11. In the illustrated arrangement, the pressure responsive means 15 comprises a flexible diaphragm 16 and a member 17, shown as a plunger, which moves in either of two directions in response to variation of fluid pressure in the chamber 11. The diaphragm 16 may be composed of any suitable elastomeric material and defines one wall of the chamber 11 by forming a division between the pressure chamber 11 and a compartment 18 of the housing 10 which contains part of the plunger. The diaphragm 16 may also function as a gasket between the housing body section 20 and the front cover 12, in which event it is convenient to form the pressure chamber 11 within the front cover 12.

The plunger 17 may comprise a stem 19 and an enlarged head portion 21 at one end of that stem 19. The head portion 21 is located within the housing compartment 18 and the stem- 17 is slidable within an open ended bore 22 of the housing which is arranged substantially coincident with the central axis of the diaphragm 16. A biasing spring 23 acts between the plunger head portion 21 and an internal transverse wall of the housing 10 so as to maintain engage¬ ment between the head portion 21 and the diaphragm 16. The housing bore 22 contains a bush 24 of PTFE or other appropriate material. An end portion of the plunger 17 projects beyond the housing bore 22 into a control compart¬ ment 25 of the housing 10 which contains at least part of the optoelectronic system.

The device of Fig. 1 also includes a radiation source 26 and a detector 27 which is coupled to a switching circuit 28, such as is shown in Fig. 3, and which is operable to switch between two different states. The detector 27 is arranged to receive radiation from the source 26 and is responsive to the radiation to cause the switching circuit 28 to adopt one of its two states. The plunger 17 is movable into the space 29 between the radiation source 26 and the detector 27 to interrupt the path of the radiation to thereby cause the switching circuit 28 to switch from one state to the other.

As shown in Fig. 3, the radiation source 26_is_a

OMPI

4&mτioi$ light emitting diode 30 and the detector 27 is a photo¬ transistor 31 and the switching circuit 28 includes a switching transistor 32 coupled to the phototransistor 31 so as to be switched on and off depending on the .amount of light reaching the phototransistor 31 from the diode 30. The light need not be in the visible part of the spectrum but may be any suitable wavelength such as in the infra-red region and a suitable optoelectronic switch is the OPTRON DPB 8135/814.

The device also includes adjusting means 33 operable to enable variation of the pressure at which the member 17 interrupts the radiation path. The adjusting means

33 is operable by enabling variation of the position of the radiation path along the straight line of travel of the member 17. The adjusting means 33 comprises a support 34 on which the radiation source 26 and detector 27 are both mounted so that the source 26 and detector 27 are arranged on opposite sides of the line of travel of the member 17. In Fig. 1 the adjusting means 33 includes the back cover 13 to which the support 34 is mounted and the back cover 13 is adjustably movable relative to the housing 10 to thereby provide the adjustability of the support 34 for calibration purposes. ^• The back cover 13 includes a cylinderical wall 35 having an internal screw thread which cooperatively engages with an external thread of the body portion 20. Rotation of the back cover 13 relative to the body portion 29 thereby adjusts the position of the support

34 relative to the body portion 20 in the axial direction of the plunger 17.

It will be appreciated that a change in the switching circuit function will occur when the plunger 17 is positioned to break the beam between the source 26 and detector 27. The plunger 17 is arranged to be located forwardly of the beam path when the fluid pressure in the pressure chamber 11 is not above atmospheric pressure. However, when the pressure in the chamber 11 is increased, the diaphragm 16 is caused to deflect away from the front cover 12 and as a consequence the plunger 17 is moved towards the rear cover 13. Assuming the switch function is to be changed at 20 psi, the back cover 13 will be adjusted relative to .the body portion 20 to position tl _^ beam path at the location adopted by the end of the plunger 17 at 20 psi. Once that calibration step has been completed, the back cover 13 may be locked against movement from the selected position and that may be achieved in any suitable manner. In one form, a screw 36 carried by the cylindrical wall 35 of the back cover 13 is adjusted to bite into the body portion thread and distort part of that thread to create a lock between the back cover 13 and body portion 20.

In the alternative construction of the device shown'in Fig. 2, the same reference numerals to those used in Fig. 1 have been used to designate corresponding components. The housing 10 has front and back covers 12 and 13 which are spaced by plunger guide 37 and annular spacer block 38 which also serve to define compartment 18. The radiation source and detector (not shown) are mounted on support 34 similarly to Fig. 1, and support 34 is pivotally mounted relative to the plunger guide 37 so as to be adjustably movable relative to the pressure responsive means 15. The support 34 is adjustably movable by means of adjustment screw 39 between the support 34 and plunger guide 37. This is achieved by pivotally mounting support 34 to apertured block 40. on plunger guide 37 by means of pivot pin 41. The support 34 is biased away from plunger guide 37 by spring 42 so that adjustment of screw 39, such as during calibration, sets the pressure at which the plunger 17 will interrupt the radiation path.

Also in Fig. 2, there is shown a circuit board 43 mounted on posts 44 (only one of which is shown) and which may be used to mount the switching transistor 32 and associated electronic components shown in Fig. 3 as parts of the switching circuit 28.

The electronic components (Fig. 3) can be powered from a suitable external source 45 and may be electrically connected to means operable to control the pressure system being monitored. For example, the change in state of switching transistor 32 may cause a solenoid valve 46 to open or close according to requirements. Alternatively, the change in state may cause a response in a control system which in turn causes operation of a valve or other pressure regulating means. For example, in Fig. 4 there is shown diagrammatically how a device according to the invention might be used in a spectrophotometer and in particular in controlling the fluid supplied to the nebulizer of a spectrophotometer. In the Fig. 4 example, three separate devices according to the invention are included in the nebulizer system and they are respectively identified as pressure switches 50, 51 and 52. A solenoid operated valve 53, 54 is associated with each of the switches 50 and 51 and it is preferred that both of those solenoid valves 53, 54 are connected to the main electronics of the spectrophoto¬ meter through appropriate feedbacks so as to indicate when fuel or air flow respectively is available. The switch 52 is a safety switch to ensure that there is not concurrent flow of air and N₂0. The oxident selector 55 responds to operation of switch 52 so that either air or N₂0, not both, will be passed to the nebulizer 56. The other fluid circuit components are labelled with their names and will be understood by those skilled in the art. The solenoid valves 53, 54 are operable to control the pressure of gas in the associated gas supply line. The devices 50 and 51 would each have its chamber 11 in communication with its associated gas line and each switching circuit 28 would be coupled to the respective solenoid valve 53 and 54 so as to control the operation thereof and thereby control the pressure of gas in the associated gas supply line.

Claims

s:

1. A fluid pressure monitoring device including, a chamber connectable to a fluid system, means responsive to the pressure within said chamber and including a member which moves in either of two directions in response to variation in said pressure, a switching circuit operable to switch between two different states, a radiation source, a detector coupled to said switching circuit and arranged to receive radiation from said radiation source, said detector being responsive to said radiation to cause said switching circuit to adopt one of said states, a space existing between said radiation source and said detector, and said member being movable into said space to interrupt the path of said radiation and to thereby cause said switching circuit to adopt the other said state.

2. A fluid pressure monitoring device according to claim 1_r including adjusting means operable to enable variation of the said pressure at which said member interrupts said radiation path.

3. A fluid pressure monitoring device according to claim 2, wherein said member is movable along a substantially straight line of travel which intersects said radiation path, and said adjusting means is operable to enable variation of the position of said radiation path along said line of travel.

4. A fluid pressure monitoring device according to claim 3 wherein said adjusting means comprises a support on which said radiation source and detector are both mounted so that the source and detector are arranged on opposite sides of the line of travel of said member.

5. A fluid pressure monitoring device according to claim 4 and including a housing, said pressure responsive means and said support being mounted in said housing, said adjusting means including a cover member to which said support is mounted and which is adjustably movable relative . to said housing to thereby provide the adjustability of said support.

6. A fluid pressure monitoring device according to claim 4 and including a housing, said pressure

means and said support being mounted in said housing, said support being pivotally mounted relative to a portion of said housing so as to be adjustably movable relative to the pressure responsive means.

7. A fluid pressure monitoring device according to claim 6 wherein said support is adjustably movable by means of an adjustment screw between said support and said housing portion.

8. A fluid pressure monitoring device according to claim 1 wherein said pressure responsive means comprises a diaphragm defining one wall of said chamber and said member comprises a plunger in contact with said diaphragm and movable in response to deformation and relaxation of said diaphragm.

9. A fluid pressure monitoring device according to claim 1 wherein said radiation source is a light emitting diode and said detector is a phototransistor, said switching circuit including a switching transistor coupled to said phototransistor so as to be switched on and off depending on the amount of light reaching said phototransistor from said diode.

10. A spectrophotometer including a nebulizer for receiving a sample to be analyzed, a gas supply line for supplying pressurized gas to said nebulizer, a solenoid operated valve in said gas supply line and operable to control the pressure of gas in said line, and a fluid pressure monitoring device according to claim 1, said chamber being connected to said gas supply line so that said member is movable in response to a change in gas pressure in the line, said switching circuit being coupled to said solenoid operated valve so as to control the operation thereof and thereby control the pressure of gas in the gas supply line.