GB2425599A

GB2425599A - Apparatus and method for testing a pressure sensor

Info

Publication number: GB2425599A
Application number: GB0508394A
Authority: GB
Inventors: Nigel Vaughan Allen; Roger John Hicks
Original assignee: Hycontrol Ltd
Current assignee: Hycontrol Ltd
Priority date: 2005-04-26
Filing date: 2005-04-26
Publication date: 2006-11-01
Anticipated expiration: 2025-04-26
Also published as: GB0508394D0; GB2425599B

Abstract

A pressure sensor adapted to monitor, and provide a signal output as a function of, air pressure developed in an interior of a container during charging of the container with air-fluidised particulate material is tested remotely by providing an enclosed chamber (16) communicating with the pressure sensor (18) and adapted to communicate with an upper region of the interior of the container (2) by means of a porous element (22). The porous element is adapted to permit two-way pressurised air flow thereacross between the interior of the container and the enclosed chamber at a predetermined restricted flow rate while substantially preventing transfer of the particulate material thereacross. A test pulse of air is injected at a predetermined pressure into the enclosed chamber (16) for sensing by the pressure sensor (18). Functional operability of the pressure sensor is verified if the resultant signal output therefrom is representative of a pressure higher than atmospheric pressure and less than the predetermined pressure.

Description

APPARATUS AND METHOD FOR TESTING OF A PRESSURE SENSOR

This invention relates to an apparatus and a method for testing of a pressure sensor, particularly at a remote location. Such a pressure sensor is adapted to monitor, and provide a signal output as a function of, air pressure developed in an interior of a storage silo or the like during charging of the silo with air-fluidised particulate material.

Silos are well known for the storage of particulate material until such material is required to be used. The particulate material may, for example, be in the form of powder, flakes, pellets or granules.

Silos may be high and of large volume and are generally charged (i.e. filled) with the particulate material through an inlet at an upper region thereof, subsequent discharge of the material being effected, as required, by way of a controlled outlet means at a bottom region thereof.

It is common practice to deliver particulate material into a silo, such as from a road tanker, by air- fluidising the material and blowing it into the silo.

Such a process is known as pneumatic conveying. The air used to carry the material is vented from the top of the silo, usually through filtering means.

If the air entering the silo is not vented adequately, delivery in this manner may result in over-pressurisation of the silo, with a possible consequence of rupture or other damage to the silo. Pressures above about 70 mbar may be sufficient to cause damage to the silo.

It is known to provide a pressure sensor communicating with an upper internal region of the silo and adapted to provide a signal output as a function of the air pressure within the silo. Such signal output may be electrical and may be adapted to operate indicating means providing a visual indication of the air pressure inside the silo and/or to activate a warning device when a critical pressure level is reached. The indicating means is suitably provided at a location remote from the pressure sensor, for convenience of an operator charging material into the silo.

In addition to providing a pressure sensor, one or more level sensors is or are usually provided whereby an indication of the level of the material inside the silo can be provided.

Requirements exist for a means of testing functionality of the pressure sensor prior to charging the silo with the particulate material. Such a pressure sensor may generally be provided with associated electronic circuitry. It is known to provide an electronic test circuit which operates to provide verification that the pressure sensor is properly electrically connected for the purposes of pressure measurement. However, such a test circuit is unable to determine whether the pressure sensor is properly able to monitor pressure changes. For example, mechanical damage or failure may occur to or of a pressure-responsive component of the sensor, or blockage of air-inlet means thereof may occur.

Difficulties further occur in that the pressure sensor is located at a somewhat inaccessible high level region of the silo and it is desirable that testing means provided for the sensor should be operable from a convenient remote location, such as at the position where the pressure indicating means is provided.

It is an object of the present invention to overcome or minimise these problems.

According to one aspect of the present invention there is provided apparatus for remote testing of a pressure sensor adapted to monitor, and provide a signal output as a function of, air pressure developed in an interior of a container during charging of the container with airfluidised particulate material, the apparatus comprising: an enclosed chamber communicating with the pressure sensor and adapted to communicate with an upper region of the interior of the container by means of a porous element, the porous element being adapted to permit two- way pressurised air flow thereacross between the interior of the container and the enclosed chamber at a predetermined restricted flow rate while substantially preventing transfer of the particulate material thereacross; and air-injection means adapted to inject a test pulse of air at a predetermined pressure into the enclosed chamber for sensing by the pressure sensor, functional operability of the pressure sensor being verified if the resultant signal output therefrom is representative of a pressure higher than atmospheric pressure and less than the predetermined pressure.

According to another aspect of the present invention there is provided a method of remote testing of a pressure sensor adapted to monitor, and provide a signal output as a function of, air pressure developed in an interior of a container during charging of the container with airfluidised particulate material, the method comprising: providing an enclosed chamber communicating with the pressure sensor and adapted to communicate with an upper region of the interior of the container by means of a porous element, the porous element being adapted to permit two- way pressurised air flow thereacross between the interior of the container and the enclosed chamber at a predetermined restricted flow rate while substantially preventing transfer of the particulate material thereacross; injecting a test pulse of air at a predetermined pressure into the enclosed chamber for sensing by the pressure sensor; and verifying functional operability of the pressure sensor if the resultant signal output therefrom is representative of a pressure higher than atmospheric pressure and less than the predetermined pressure.

The invention also provides a way of testing whether or not the porous element is blocked. Blockage can be determined if the pressure within the enclosed chamber exceeds a further predetermined pressure higher than the pressure for verifying functional operability of the pressure sensor and less than the first-mentioned predetermined pressure.

The pressures for verifying functional operability and for determining blockage will depend upon the specific system and will depend, for example, upon the pressure sensing range of the pressure sensor and upon the predetermined pressure of the air providing the test pulse.

Where the predetermined pressure is not greater than the pressure sensing range of the pressure sensor, the determining factor is the predetermined pressure of the air providing the test pulse. In this case, for example, the pressure for verifying functional operability may be in the range from 5 to 50 percent, preferably substantially 20 percent, of the predetermined pressure of the air providing the test pulse. Similarly, the pressure for determining blockage may be in the range from 25 to 75 percent, preferably substantially 30 percent, of the predetermined pressure of the air providing the test pulse.

However, in the event the predetermined pressure is greater than the pressure sensing range of the pressure sensor, then the pressure sensing range of the pressure sensor is the determining factor. In this case, for example, the pressure for verifying functional operability may be in the range from 5 to 80 percent, preferably substantially 65 percent, of the upper pressure sensing capability of the pressure sensor.

Similarly, the pressure for determining blockage may be in the range from 50 to 100 percent, preferably 65 to 100 percent, of the upper pressure sensing capability of the pressure sensor.

The signal output from the pressure sensor may be an electrical signal.

The porous element is suitably adapted whereby it restricts passage of air therethrough to an extent that injection of the pulse of air results in an adequate build-up of pressure within the enclosed chamber for sensing by the pressure sensor for testing thereof, while ensuring adequate flow rate of air thereacross from the container into the enclosed chamber, during charging of the container with the particulate material, such that rising air pressure within the container is sufficiently rapidly sensed by the pressure sensor.

The porous element may be of membrane form.

The porous element may have pores having a size of from about 50 to about 250 microns and preferably of from about 100 to about 250 microns.

The porous element may have a thickness of from about 0.5 mm to about 50 mm.

The porous element may have an exposed area of at least 4 square centimetres and preferably of about 5 square centimetres.

The porous element may comprise a disc of porous polymeric plastics material and may comprise polyethylene or polypropylene material, particularly of sintered high- density form.

The disc of sintered porous high-density polyethylene material may have a diameter of about 25 mm.

The disc of sintered porous high-density polyethylene material may have a thickness of about 4.5 mm.

The disc of sintered porous high-density polyethylene material may have an average pore size of at least 100 microns and may have a maximum pore size of about 150 microns.

The disc of sintered porous high-density polyethylene material may have an apparent density of about 0.47 g/cm3 and may have an air permeability of from about 6.1 to - 10 - about 7.9 m3/min/m2 (measured at a pressure difference of about 0.1 mbar) Alternatively, the porous element may comprise a disc of fibre material. Such fibre material may be natural or synthetic fibre material and may, for example, comprise cellulose (wood) fibres, glass fibres and/or fibres of plastics material.

The disc of fibre material may have a diameter of about mm.

The disc of fibre material may have a thickness of about mm.

The disc of fibre material may have an average pore size of about 250 microns.

Alternatively still, the porous element may comprise porous foam, porous paper, porous metal, porous glass or porous ceramic material.

- 11 - The enclosed chamber may have a volume of from about 10 to about 125 cubic centimetres.

The test pulse of air may be injected by way of a remotely controlled valve means, such as an electrically controlled solenoid valve, which may be of normally closed form and may be provided adjacent to or incorporated with the enclosed chamber.

Operation of the remotely controlled valve means may be effected from a location where indicating means is also provided, such indicating means being connected to the pressure sensor and providing an indication of the pressure sensed by the pressure sensor and resulting from the signal output from the pressure sensor.

Air for the test pulse of air may be provided by a compressed air source provided with a pressure regulator whereby the predetermined pressure for the injected test pulse of air is obtained.

- 12 - The regulated predetermined pressure of the injected test pulse of air may be from about 200 to 700 mbar, preferably substantially 350 mbar.

The test pulse of air may also serve to purge any accumulated particulate material from the porous element.

The air-fluidised particulate material for charging of the container may comprise powder, flake, pellet or granular material and/or may be of fine particulate form.

For a better understanding of the present invention and to show more clearly how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings in which: Figure 1 is a representation of a container in the form of a storage silo provided with apparatus according to the present invention; and Figure 2 is a schematic representation of an embodiment of apparatus according to the present invention for use with the storage silo of Figure 1.

- 13 - Referring to Figure 1, a silo 2 is provided for storage of particulate material 4 which is charged or delivered thereto through a feed pipe 6 and discharged therefrom, as required, by way of a controlled outlet means 8 at a bottom region of the silo 2. The particulate material 4 may be in the form of powder, flakes, pellets or granules and/or may be of fine particulate form. The silo 2 is charged with the particulate material 4, such as from a road tanker, charging being effected by airfluidising the material 4 and blowing it into the silo 2. Such a process is known as pneumatic conveying. The air used to carry the material 4 is vented from the top of the silo 2, such as through filtering means 10.

If the air entering the silo 2 is not vented adequately, overpressurisation of the silo could occur, with a possible consequence of rupture or other damage to the silo 2. Pressures above about 70 mbar may result in damage to the silo 2.

Risk of over-pressurisation and damage to the silo 2 is minimised by providing a pressure sensing arrangement 12 communicating with an upper internal region of the silo 2 - 14 - and adapted to provide an electrical signal output as a function of, the air pressure within the silo 2. The pressure sensing arrangement 12 is electrically connected to a remote indicating and control unit 14, where output signals from a pressure sensor in the pressure sensing arrangement 12 are processed and a display of the sensed air pressure provided. Appropriate preventative or remedial action can be taken by an operator, involved in charging the silo 2 with the particulate material 4, if the air pressure in the silo 2, sensed by the pressure sensing arrangement 12 and indicated at the indicating and control unit 14, reaches or exceeds a predetermined safe limit value. Audible and/or visual warning means may alternatively or additionally be provided for activation in such an event.

Great reliance is placed on the pressure sensing arrangement 12 functioning properly. The pressure sensing arrangement 12 is located at a high level on the silo 2 and safe accessibility thereto is difficult.

In the present invention, a remote test facility is provided for the pressure sensing arrangement 12 and - 15 - which operates to indicate departure from correct functional operability of the pressure sensor in the pressure sensing arrangement 12. Such departure from correct functional operability could result, for example, from mechanical damage to or failure of a pressure- responsive component of the pressure sensor in the pressure sensing arrangement 12. Blockage of an air- inlet means of the pressure sensor may also occur.

The pressure sensing arrangement 12, with its remote test facility, is shown in detail in Figure 2. An enclosed chamber 16 communicates with a pressure sensor 18 of the pressure sensing arrangement 12 by way of a communication port 20 and is also arranged to communicate with the upper region of the interior of the silo 2 by means of a porous element 22. The porous element 22 is adapted to permit two-way pressurised air flow across it between the interior of the silo 2 and the enclosed chamber 16 at a predetermined restricted flow rate, while substantially preventing or minimising transfer across it of the particulate material 4 when the particulate material 4 is being blown into the silo 2. While the particulate material 4 is being blown into the silo 2, air pressure - 16 building up in the silo 2 also builds up in the enclosed chamber 16 by way of the porous element 22 and is sensed by the pressure sensor 18. Output signals from the pressure sensor 18 are transmitted to the remote indicating and control unit 14 where they are processed and an indication of the sensed pressure provided.

In order to test functional operability of the pressure sensor 18, prior to an operation for charging the silo 2 with the particulate material 4, air-injection means 24 is arranged to inject a test pulse of air 26 at a predetermined pressure of, say, about 350 mbar into the enclosed chamber 16 by way of a connecting port 28. Such test pulse of air 26 at the predetermined pressure is sensed by the pressure sensor 18, which may have a pressure sensing range of, for example, up to about 100 mbar. If the pressure sensor 18 is functioning correctly, an indication of pressure of, say, about 35 mbar (dependent upon the predetermined pressure provided by the test pulse of air 26 and upon the pressure sensing range of the pressure sensor 18) will be provided at the remote indicating and control unit 14.

- 17 - The test pulse of air 26 will also serve to purge accumulated particulate material 4 from the porous element 22 and will therefore, at least to some extent, serve to clean and maintain the porous element free of blockage.

Nevertheless, in an unlikely event that the porous element 22 becomes blocked with particulate material and is not cleared by the action of the test pulse of air 26, the test pulse of air will additionally determine whether or not the porous element is blocked. That is, the resulting pressure characteristic of the test pulse of air 26 sensed by the pressure sensor 18 can be used to provide an alarm signal to the operator. In such a situation, air from the test pulse 26 will not permeate through the porous element 22 with the result that the pressure in the enclosed chamber 16 will build up towards the predetermined pressure and no decay, or only a slow decay, of the predetermined air pressure from the test pulse 26 will occur in the enclosed chamber 16. In practice, for a predetermined pressure of about 350 mbar, blockage can be determined if the indicated pressure exceeds about 35 mbar by a significant amount (for - 18 - example if the indicated pressure reaches about 100 mbar) . This will be sensed by the pressure sensor 18 and will provide a corresponding indication at the remote indicating and control unit 14. Such blockages can generally be cleared simply by performing the test procedure two or three times.

Having verified functional operability of the pressure sensor 18 and confirmed that the porous element 22 is not blocked, an operator can then safely proceed to charge the silo 2 with the particulate material 4.

The test pulse of air 26 is suitably injected into the enclosed chamber 16 by means of a remotely controlled valve means 30, such as an electrically controlled solenoid valve, preferably of normally closed form, which may be provided adjacent to or incorporated with the enclosed chamber 16. The valve means is suitably remotely controlled from the indicating and control unit 14.

Air for the test pulse of air 26 is suitably provided by a compressed air source 32 provided with a pressure - 19 - regulator 34, whereby the predetermined pressure for the injected test pulse of air 26 is obtained. The regulated predetermined pressure of the injected test pulse of air 26 is suitably from about 200 to about 700 mbar. The pressure sensor 18 is able to be tested over its full operating range.

The porous element 22 is adapted by way of surface area, thickness and porosity, whereby it restricts passage of air through it to an extent that injection of the test pulse of air 26 results in an adequate build- up of pressure within the enclosed chamber 16 for sensing by the pressure sensor 18 for testing thereof. At the same time, the porous element 22 is adapted to ensure that adequate flow rate of air can occur across it from the silo 2 into the enclosed chamber 16, during subsequent charging of the silo 2 with the particulate material 4, such that rapidly rising air pressure within the silo 2 is sufficiently rapidly responded to by the pressure sensor 18.

The porous element 22 is suitably of membrane form and is suitably arranged with pores having a size of from about - 20 - to about 250 microns and preferably of from about 100 to about 250 microns. The porous element 22 suitably has a thickness of from about 0.5 mm to about 50 mm and suitably has an exposed area of at least 4 square centimetres and preferably of about 5 square centimetres.

The porous element 22 may particularly comprise a disc of sintered highdensity polyethylene material, which may have a diameter of about 25 mm, a thickness of about 4.5 mm, an average pore size of at least 100 microns and a maximum pore size of about 150 microns. Such a disc of the polyethylene material suitably has an apparent density of about 0.47 g/cm3 and an air permeability of from about 6.1 to about 7.9 m3/min/m2 (measured at a pressure difference of about 0.1 mbar) . A suitable porous polyethylene material is available from SPC Technologies under Product Code No. SP-049.

Alternatively, the porous element 22 could comprise a disc of other polymeric plastics materials, such as polypropylene, or a disc of natural or synthetic fibre material such as, for example, cellulose (wood) fibres, glass fibres and/or fibres of plastics material. Such a - 21 - disc of natural or synthetic fibre material may suitably have a diameter of about 75 mm, a thickness of about 30 mm and an average pore size of about 250 microns.

Other porous materials could be used for the porous element 22, such as porous foam, porous paper, porous metal, porous glass or porous ceramic materials.

The enclosed chamber 16 suitably has a volume of from about 10 to about 125 cubic centimetres.

A further advantage of the porous element 22 is that it protects the pressure sensor 18 from contamination by the particulate material 4 in the silo 2.

The pressure sensor 18 can be arranged with the air- injection means 24 and associated processing circuitry to execute various emergency triggering or tripping functions, such as operating means to automatically prohibit charging of the silo 2 with the material 4.

Instead of providing separate communication ports 20, 28 in the enclosed chamber 16 for connection to the pressure - 22 - sensor 18 and the air-injection means 24, a single communication port could be provided in the enclosed chamber 16 and connected by way of a T- piece to the pressure sensor 18 and the air-injection means 24.

Claims

- 23 - CLAIMS

1. Apparatus for remote testing of a pressure sensor adapted to monitor, and provide a signal output as a function of, air pressure developed in an interior of a container during charging of the container with airfluidised particulate material, the apparatus comprising: an enclosed chamber communicating with the pressure sensor and adapted to communicate with an upper region of the interior of the container by means of a porous element, the porous element being adapted to permit two- way pressurised air flow thereacross between the interior of the container and the enclosed chamber at a predetermined restricted flow rate while substantially preventing transfer of the particulate material thereacross; and air-injection means adapted to inject a test pulse of air at a predetermined pressure into the enclosed chamber for sensing by the pressure sensor, functional operability of the pressure sensor being verified if the resultant signal output therefrom is representative of a pressure higher than atmospheric pressure and less than the predetermined pressure.

2. Apparatus as claimed in claim 1, wherein the porous element is of membrane form.

- 24 -

3. Apparatus as claimed in claim 1 or 2, wherein the porous element has pores having a size of from about 50 to about 250 microns.

4. Apparatus as claimed in claim 3, wherein the porous element has pores having a size of from about 100 to about 250 microns.

5. Apparatus as claimed in any preceding claim, wherein the porous element has a thickness of from about 0.5 mm to about 50 mm.

6. Apparatus as claimed in any preceding claim, wherein the porous element has an exposed area of at least 4 square centimetres.

7. Apparatus as claimed in claim 6, wherein the porous element has an exposed area of about 5 square centimetres.

8. Apparatus as claimed in any preceding claim, wherein the porous element comprises a disc of porous polymeric plastics material.

- 25 -

9. Apparatus as claimed in claim 8, wherein the porous element comprises a disc of sintered porous high-density polyethylene material having a diameter of about 25 mm.

10. Apparatus as claimed in claim 8 or 9, wherein the porous element comprises a disc of sintered porous high- density polyethylene material having a thickness of about 4.5 mm.

11. Apparatus as claimed in any one of claims 8 to 10, wherein the porous element comprises a disc of sintered porous high-density polyethylene material having an average pore size of at least 100 microns.

12. Apparatus as claimed in any one of claims 8 to 11, wherein the porous element comprises a disc of sintered porous high-density polyethylene material having an apparent density of about 0.47 g/cm3.

13. Apparatus as claimed in any one of claims 8 to 12, wherein the porous element comprises a disc of sintered porous high-density polyethylene material having an air permeability of from about 6.1 to about 7.9 m3/min/m2 (measured at a pressure difference of about 0.1 mbar) - 26 -

14. Apparatus as claimed in any one of claims 1 to 7, wherein the porous element comprises a disc of fibre material.

15. Apparatus as claimed in claim 14, wherein the disc of fibre material has a diameter of about 75 mm.

16. Apparatus as claimed in claim 14 or 15, wherein the disc of fibre material has a thickness of about 30 mm.

17. Apparatus as claimed in any one of claims 14 to 16, wherein the disc of fibre material has an average pore size of about 250 microns.

18. Apparatus as claimed in any preceding claim, wherein the enclosed chamber has a volume of from about 10 to about 125 cubic centimetres.

19. Apparatus as claimed in any preceding claim and including a source of compressed air for providing air for the test pulse of air, the source being provided with a pressure regulator whereby the predetermined pressure for the injected test pulse of air is obtained.

20. Apparatus for remote testing of a pressure sensor adapted to monitor, and provide a signal output as a - 27 - function of, air pressure developed in an interior of a container during charging of the container with air- fluidised particulate material substantially as hereinbefore described with reference to, and as shown in! the accompanying drawings.

21. A method of remote testing of a pressure sensor adapted to monitor, and provide a signal output as a function of, air pressure developed in an interior of a container during charging of the container with airfluidised particulate material, the method comprising: providing an enclosed chamber communicating with the pressure sensor and adapted to communicate with an upper region of the interior of the container by means of a porous element, the porous element being adapted to permit two- way pressurised air flow thereacross between the interior of the container and the enclosed chamber at a predetermined restricted flow rate while substantially preventing transfer of the particulate material thereacross; injecting a test pulse of air at a predetermined pressure into the enclosed chamber for sensing by the pressure sensor; and verifying functional operability of the pressure sensor if the resultant signal output therefrom is representative of a pressure higher than atmospheric pressure and less than the predetermined pressure.

- 28 -

22. A method according to claim 21, wherein the pressure for verifying functional operability is in the range from to 50 percent of the predetermined pressure of the air providing the test pulse.

23. A method according to claim 22, wherein the pressure for verifying functional operability is substantially 20 percent of the predetermined pressure of the air providing the test pulse.

24. A method according to claim 21, wherein the pressure for verifying functional operability is in the range from to 80 percent of the upper pressure sensing capability of the pressure sensor.

25. A method according to claim 24, wherein the pressure for verifying functional operability is substantially 65 percent of the upper pressure sensing capability of the pressure sensor.

26. A method according to any one of claims 21 to 25 and including the further step of testing whether or not the porous element is blocked by determining whether the pressure within the enclosed chamber exceeds a further predetermined pressure higher than the pressure for - 29 verifying functional operability of the pressure sensor and less than the first-mentioned predetermined pressure.

27. A method according to claim 26, wherein the pressure for determining blockage is in the range from 25 to 75 percent of the predetermined pressure of the air providing the test pulse.

28. A method according to claim 27, wherein the pressure for determining blockage is substantially 30 percent of the predetermined pressure of the air providing the test pulse.

29. A method according to claim 26, wherein the pressure for determining blockage is in the range from 50 to 100 percent of the upper pressure sensing capability of the pressure sensor.

30. A method according to claim 29, wherein the pressure for determining blockage is in the range from 65 to 100 percent of the upper pressure sensing capability of the pressure sensor.

31. A method according to any one of claims 21 to 30 and including the step of injecting the test pulse of air by way of a remotely controlled valve means.

- 30 -

32. A method according to claim 31, wherein operation of the remotely controlled valve means is effected from a location where indicating means is also provided, such indicating means being connected to the pressure sensor and providing an indication of the pressure sensed by the pressure sensor and resulting from the signal output from the pressure sensor.

33. A method according to any one of claims 21 to 32 and including the step of providing air for the test pulse of air by a compressed air source provided with a pressure regulator whereby the predetermined pressure for the injected test pulse of air is obtained.

34. A method according to claim 33, wherein the regulated predetermined pressure of the injected test pulse of air is from about 200 to 700 mbar.

35. A method according to claim 34, wherein the regulated predetermined pressure of the injected test pulse of air is substantially 350 mbar.

36. A method according to any one of claims 21 to 35, wherein the test pulse of air also serves to purge any accumulated particulate material from the porous element. 31 -

37. A method of remote testing of a pressure sensor adapted to monitor, and provide a signal output as a function of, air pressure developed in an interior of a container during charging of the container with airfluidised particulate material substantially as hereinbefore described with reference to the accompanying drawings.