WO2006090251A1

WO2006090251A1 - Measuring conditions in a rotational moulding process

Info

Publication number: WO2006090251A1
Application number: PCT/IB2006/000381
Authority: WO
Inventors: Gary Lategan
Original assignee: Gary Lategan
Priority date: 2005-02-24
Filing date: 2006-02-24
Publication date: 2006-08-31

Abstract

The invention provides a method of measuring moulding conditions in a rotational moulding process, and to a telemetry device (10) for measuring and reporting ambient conditions in a high temperature environment, such as in a rotational mould. The method includes mounting the telemetry device (10) on a rotational moulding apparatus such that the device (10) moves with an associated mould into a moulding oven. The device (10) has a casing (30) which houses electronic equipment (34, 36, 46) providing a transmission means for transmitting wireless signals indicative of measured ambient conditions outside of the casing (30). The device (10) further includes a cooling arrangement for cooling the interior of the casing (30) by channelling pressurised cooling fluid through the casing (30). Typically, the device (10) includes a cooler (70) for cooling air before entry of the air into the casing (30).

Description

MEASURING CONDITIONS IN A ROTATIONAL MOULDING PROCESS

THIS INVENTION relates to a telemetry method and system in rotational moulding operations. In particular, the invention relates to a method of measuring moulding conditions in a rotational moulding process. The invention extends to a telemetry device for measuring and reporting ambient conditions in a high temperature environment. The invention extends to a control system for a rotational moulding apparatus.

The remote monitoring of physical variables, such as temperature, pressure, and the like, in high temperature environments is normally done by exposing only transducers to the high temperature environment, while avoiding exposure of electronic monitoring equipment to the high temperatures. For example, the electronic monitoring equipment can be positioned remote from the transducers with signal guides, such as electrical leads or fibre optic cables, . connecting the transducers to the_. electronic monitoring equipment.

However, in certain applications, such as rotational moulding machines, it is not possible to connect the transducers to electronic monitoring equipment via signal guides. In such instances, telemetry transmitters are often used to transmit signals to remote monitoring stations. These telemetry transmitters typically contain electronic equipment which is sensitive to exposure to high temperatures.

The invention provides a method of measuring moulding conditions in a rotational moulding process, which method includes: mounting a telemetry device such that the device moves with an associated mould into a moulding oven, the telemetry device having a casing which houses electronic equipment providing a transmission means for transmitting wireless signals representative of condition measurements to a monitoring station; and cooling the electronic equipment in the casing by passing a cooling fluid through the casing.

The telemetry device typically includes at least one temperature sensor for providing temperature measurements of air inside a moulding cavity, and for relaying the temperature measurements to the transmission means inside the casing.

The method may include pre-cooling the cooling fluid before passing it through the casing, the fluid being pre-cooled to at least -5⁰C, preferably to about -1 O⁰C. It will be appreciated that the electronic equipment inside the casing is optimally cooled to about -10⁰C₁ and that pre-cooled air of about -2O⁰C can be used for this purpose.

In a preferred embodiment, the fluid is pre-cooled by passing pressurised fluid through a cooler which is mounted upstream of the casing, the cooler preferably being a vortex tube. The method may include attaching the cooler to the telemetry device before insertion of the device into a moulding oven, passing cooling fluid through the cooler and through the casing to cool the interior of the casing, and removing the cooler before movement of the casing into the oven. The method may include passing the cooling fluid through a moisture trap before entry of the cooling fluid into the casing, to remove moisture from the fluid before entry into the casing.

The cooling fluid is typically air, optionally supplied by an industrial air supply system, but the fluid may instead be any other suitable gas, for instance carbon dioxide.

Cooling fluid may be passed through the casing before and/or after movement of the casing into the moulding oven, so that the interior of the casing is cooled intermittently. In one example, passing cooling fluid through the casing includes placing a cylinder of pressurised gas in fluid flow connection with the casing.

Instead, the method may include passing the cooling fluid through the casing while the telemetry device is positioned in the moulding oven. In a particular embodiment of the invention, the casing may be continuously connected to a supply of air under pressure, for continuous cooling of the interior of the casing.

The method may include providing an insulating jacket around the electronic equipment inside the casing. The insulating jacket may be spaced from the electronic equipment by an annular space, or instead, in the insulating jacket more or less completely fill a space around the electronic equipment. The method optionally include cooling a thermal storage mass in an interior of the casing, while the thermal storage mass is located in the casing, by passing the cooling fluid through the casing in heat transfer relationship with the thermal storage mass, the thermal storage mass, in turn, being in heat transfer relationship with the electronic equipment.

By thermal storage mass is meant a body of material for absorbing heat, the thermal storage mass, as a unit, having a heat capacity which is higher than the heat capacity of a body of air occupying the same volume. Differently defined, the thermal storage mass provides a heat sink for absorbing and storing heat, thus retarding the rise of internal temperature in the casing or enclosure when heat passes through peripheral walls of the enclosure, by absorbing the heat to raise the temperature of the thermal storage mass.

The thermal storage mass will typically be of a material having a relatively high specific heat capacity, preferably having a specific heat capacity of at least 400 J/kg.K, most preferably more than 600 J/kg.K.

Preferably, the thermal storage mass in the form of a particulate material which permits the passage of cooling fluid through it to allow heat transfer between the fluid and particles of the thermal storage mass, the thermal storage mass for instance being provided by tightly packed glass beads. The beads may have an average diameter of about 1 mm. The thermal storage mass may be a resident thermal storage mass, by which is meant that the thermal storage mass is permanently or semi-permanently enclosed in the enclosure and is not intended for frequent removal and replacement.

Pre-cooling of the thermal storage mass is thus performed while the thermal storage mass is located in the interior of the enclosure.

The method may include covering or encasing the electronic equipment with a synthetic material, for instance by dipping the electronic equipment in an epoxy resin.

The method may include powering the electronic equipment with a main battery which is removably connected to the electronic equipment, and removing the main battery for recharging when the device is outside of the oven, the method in such case preferably including powering the electronic equipment with a backup battery while the main battery is removed for recharging. The main battery and the backup battery of preferably connected during use, to recharge the backup battery.

The invention also provides a telemetry device for measuring and reporting ambient conditions in a high temperature environment, which device includes: a casing having a hollow interior; electronic equipment housed in the interior of the casing, the electronic equipment including a transmission means for transmitting wireless signals indicative of measured ambient conditions outside of the casing; and a cooling arrangement for cooling the interior of the casing, the cooling arrangement including a fluid flow path through the casing for channelling pressurised cooling fluid supplied to the casing, in use, through the casing in heat transfer relationship with the electronic equipment.

The device may include at least one temperature sensor for measuring ambient temperature outside of the casing, each temperature sensor being operatively connected to the electronic equipment inside the casing. At least part of the casing's peripheral walls is typically non-metallic, to permit the transmission of signals from inside the casing. At least part of a wall of the casing may also be of a thermal insulating material, such as non-woven glass-reinforced plastic, or the like.

At least part of an outside wall of the enclosure may be of a non-metallic or synthetic material, such as polytetrafluoroethylene (PTFE), or the like, which can withstand a high temperature environment of about 275^aC to 350^aC.

The cooling arrangement may include an inlet port for receiving the cooling fluid into the casing, and an outlet port for discharging the cooling fluid from the casing, so that the fluid flow path is formed between the inlet port and the outlet port, one-way valves preferably being mounted respectively in the inlet port and the outlet port.

The device may include a jacket of insulating material which is positioned inside the casing around the electronic equipment. In one embodiment of the invention, a cavity immediately surrounding the electronic equipment is substantially fully occupied by insulating material. In another embodiment of the invention, the cavity around the electronic equipment is filled with a thermal storage mass which is, in turn, surrounded by an insulating jacket.

The device preferably includes a cooler which is connected or connectable to the fluid flow path for supplying cooled fluid to the fluid flow path, the cooler typically being arranged to receive air under pressure and to supply cooled and pressurised air to the fluid flow path. The cooler may thus be in the form of a so-called vortex tube.

The cooler may be integral with the enclosure or may be located remote from it, in which case it may be connected to the enclosure by means of a fluid guide.

In a particular embodiment of the invention, the device includes a canister or vessel of pressurised fluid which is connectable to the cooler or to the casing for providing a limited supply of pressurised fluid to the fluid flow path.

The device preferably includes a moisture trap in the fluid flow path between the cooler and the electronic equipment, for reducing the amount of liquid vapour carried by the cooling fluid. Instead, or in addition, a desiccant material may be provided in the casing to absorb moisture carried by the cooling fluid. In instances where the device includes a thermal storage mass in the form of a particulate material, the desiccant material may itself be particulate and may be mixed with the particulate thermal storage material.

The device preferably includes a thermal storage mass located in the interior of the casing in heat transfer relationship with the electronic equipment, the thermal storage mass preferably being in the form of a particulate material through which the cooling fluid can pass. The thermal storage mass may be in the form of glass beads.

The device may include a removable and rechargeable battery, the battery being connected to the electronic equipment in the casing for providing electrical power thereto. An auxiliary battery may be connected to the electronic equipment in the casing, the auxiliary battery being arranged for providing electrical power to the electronic equipment when the removable battery is disconnected from the electronic equipment, and for being recharged by the removable battery when the removable battery is connected to the electronic equipment.

The casing may be of composite construction, comprising an electronics unit and a battery unit which are releasably connectable together, the electronic equipment being housed in the interior of the electronics unit and the removable battery being housed in the battery unit for powering the electronic equipment when the units are connected together. In such case, a peripheral wall of the battery unit may provide a fluid inlet port, while the electronics unit provides an outlet port, the units being constructed such that the interiors of the units are in fluid flow communication when the units are connected together, the composite interior of the composite casing being airtight. It will be appreciated that, in such case, the fluid flow path extends through the interiors of both the battery unit and the electronics unit, so that the battery unit serves as a liquid trap for condensing water vapour in air which is, in use, passed through the composite enclosure. Typically, the thermal storage mass is provided in the interior of the electronics unit, but not in the interior of the battery unit. In another embodiment of the invention, the device may include a sub- casing located within the casing, the electronic equipment being housed inside the sub- casing and the fluid flow path passing through the sub-casing in heat transfer relationship with the electronic equipment. The casing optionally has a lid which is removable to expose the interior of the casing and permit removal of a rechargeable battery which is connected to the electronic equipment but which is located outside of the sub-casing.

The device preferably includes an insulating material inside the sub- casing, optionally filling the interior of the sub-casing, or, alternatively, surrounding a thermal storage mass located in the sub-casing.

The device may thus include a thermal storage mass inside the sub- casing, the thermal storage mass being in heat transfer relationship with the electronic equipment.

The invention extends further to a control system for a rotational moulding apparatus, which system includes at least one telemetry device as defined above.

The control system typically includes a control station for receiving and interpreting signals transmitted by a plurality of the telemetry devices in accordance with the invention. The invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a longitudinal section through a telemetry device in accordance with the invention for measuring operating conditions inside a rotational mould; Figure 2 is a view corresponding to Figure 1 of another embodiment of a telemetry device in accordance with the invention, electronic equipment forming part of the device being surrounded by insulating wool;

Figure 3 is a view corresponding to Figure 2 of a further embodiment of a telemetry device in accordance with the invention, the electronic equipment being surrounded by glass beads and an insulating jacket of wool;

Figure 4 is a view corresponding to Figure 2 of yet another embodiment of a telemetry device in accordance with the invention, the electronic equipment being surrounded by glass beads only; and

Figure 5 is a schematic view of another embodiment of a telemetry device in accordance with the invention, the device having a CO₂ cylinder for providing cooling air to a casing in which electronic equipment is housed.

In Figure 1 of the drawings, reference numeral 10 indicates a telemetry device for measuring operating conditions, particularly temperature, in a rotational mould, and for transmitting data indicative of the operating conditions to a remote monitoring station. The device 10 includes an electronics unit 12 which houses electronic measurement and transmission equipment. The electronics unit 12 has a casing having a hollow interior 13 in which the electronic equipment is located. The casing defines an inlet port 14 in the form of a cluster of perforations for receiving a cooling fluid, in this example air, into the interior 13 of the electronics unit 12, and an outlet port 16 for discharging the fluid from the electronics unit 12. The inlet port 14 and the outlet port 16 are at opposite ends of the casing, so that the interior 13 of the electronics unit 12 effectively forms a fluid flow passage connecting the inlet port 14 and the outlet port 16.

A thermal storage mass 18 is provided in the interior 13 of the casing, the thermal storage mass being in the form of a multitude of glass beads filling the interior 13, each bead having a diameter of about 1 mm. It will be appreciated that the glass beads or granules have a relatively high specific heat capacity of about 700 J/kg.K, so that substantial heat is required to raise the temperature of the beads 18 if they have been pre-cooled. The beads 18 are more or less spherical, so that they define interconnected interstitial spaces, thus permitting the flow of air through the mass of beads 18. A silica gel is mixed with the glass beads 18 in a ratio of 1 :4 by volume, to act as a desiccant.

As can be seen from the drawings, the electronic equipment 34, 36 is positioned centrally in the interior 13, so that the beads 18 fill an annular space surrounding the equipment 34, 36 and spacing the equipment from peripheral walls of the casing.

The casing of the electronics unit 12 is provided by an outer cylindrical wall 30 of a non-metallic material, in this case being of polytetrafluoroethylene, and two discshaped end walls 42, 44 of polytetrafluoroethylene closing off the cylindrical wall 30. The radially inner surface of the cylindrical wall 30 is lined with a layer of insulation material 32, in this case glass-reinforced plastic. One of the end walls 44 has a series of axially extending openings, thus providing the inlet port 14. The inlet port 14 is covered inside the casing by a retaining means 20 in the form a mesh with a diameter of less than 1mm. The retaining means prevents spillage of glass beads 18 from the casing through the inlet port 14.

The casing of the electronics unit 12 is sealed, in that the end walls 42, 44 are semi-permanently connected to the cylindrical wall 30. By semi-permanently is meant that the end walls 42, 44 are not intended for frequent removal from the cylindrical wall 30, to open the unit 12. In other words, the end walls 42, 44 are not constructed for disengagement from the cylindrical wall 30 every time that the glass beads 18 are to be cooled. The connection between the cylindrical wall 30 and the end walls 42, 44 is air tight.

The electronic equipment installed inside the electronics unit 12 includes a telemetry transmitter 34. The telemetry transmitter 34 is connected to thermally insulated sensor leads 38 passing through the cylindrical wall 30. The sensor leads 38 connect the transmitter 34 to measurement devices such as thermo-couples (not shown), for instance a K-Type thermo-couple, for measuring the operational conditions in a rotational mould in the mould oven, or in walls of the mould, thus relaying signals indicative of the measurements to the transmitter 34. The telemetry transmitter 34 includes an antenna 36 for transmission of radio frequency signals to a remote monitoring station. It will be appreciated that transmission of signals by the antenna 36 from the interior of the unit 12 is made possible by the non-metallic casing 30. A non-return valve 40 is provided at the outlet port 16 in the other end wall 42. The non-return valve 40 permits flow of air from the inside of the unit 12 to the outside, but not in the opposite direction.

The device 10 further includes a battery unit 50 which is removably connected to the telemetry unit 12. The battery unit 50 has a radially outer cylindrical wall 54 of polytetrafluoroethylene and insulation material 56 arranged inside the cylindrical wall 54. Two disc-shaped end walls 58, 60 which are of a polytetrafluoroethylene material are provided at the ends of the cylindrical wall 54. It is to be appreciated that, although the interior 51 of the battery unit 50 is empty in this example, a thermal storage mass, such as the glass beads 18, can also be provided in the interior 51 of the of the battery unit 50.

It is further to be appreciated that the construction of the electronics unit 12 and the battery unit 50 can be simplified by moulding the cylindrical walls 30 and 54 integral with the end walls 42 and 60, or by manufacturing the end walls 44, 58 in one unit.

An inlet port 62 is defined in the one end wall 60, a non-return valve 66 being provided in the inlet port 62. The nonreturn valve 66 permits the passage of air into the battery unit 50 only. The other end wail 58 of the battery unit 50 defines an outlet port

64 which is in flow communication with the inlet port 14 of the electronics unit 12, when the units 12, 50 are connected together. Although not shown in detail in the drawing, the device 10 includes quick release clamps for releasably locking together the battery unit 50 and the electronics unit 12 such that the cylindrical walls 30, 54 are aligned end- to-end and the inlet port 14 of the electronics unit 12 is in fluid flow communication with the outlet port 64 of the battery unit 50. It will be appreciated that when the units 12, 50 are connected together, it forms a composite device 10 having a hollow interior which is airtight under conditions typically experienced in moulding ovens. The non-return or one-way valves 66, 40 permit the passage of pressurised air through the interior of the composite device, but no ambient air can enter the battery unit 50 or the electronics unit 12. In other embodiments of the invention, the one-way valves 66, 40 can be replaced by removable plugs which are removed when the device is to be cooled, but which is engaged with the ports, to plug the casing, before entry of the device 10 into the oven.

A lead-acid rechargeable battery 52 is installed in the battery unit 50, while a backup battery 46 is housed in the electronics unit 46. The abutting end walls 58, 44 have co-operating connection means for electrically connecting the transmitter 34 and the back-up battery 46 to the battery 52 when the units 12, 50 are connected together. When thus connected, the main battery 52 powers the telemetry unit 34 and re-charges the backup battery 46. The back-up battery 46 is arranged to power the telemetry unit 34 when the battery unit 50 is disconnected from the electronics unit 12.

The device further includes a removable connectable cooler 70 in the form of so-called vortex tube 72 having a compressed air inlet 76 which is connectable to a compressor (not shown), a hot air outlet 78 through which hot air is expelled, and a cold air outlet 80 which is removably connected to the disc-shaped side wall 60 at the inlet port 62. Although, in this example, the cooler 70 is removable, the cooler 70 can be fast with the casing. An advantage of such an arrangement is that it prevents a user from blowing into the casing air which is not cooled to the desired temperature.

Additionally, a moisture trap can be connected in-line between the cooler 70 and the casing, to ensure the supply of cooled, clean air to the casing.

In this example, the device 10 is used to measure the operational conditions inside a rotational mould during the entire moulding process. To this end, the device 10 is mounted on a moulding station at an outer end of one arm of a moulding machine (not shown), so that the device 10 rotates with the moulding station which is to be monitored about a pair of orthogonal axes. Electrical connection of the data readers mounted on such machines to stationary monitoring stations is problematic, and telemetry is thus employed. It will be appreciated, though, that the device 10 can be used with similar efficacy in other applications, and that some aspects of the invention are not limited to use in rotational or moving moulds.

In use, the air inlet 76 is connected to a supply of compressed air, typically the compressor (not shown), before the following station on which the device 10 is mounted is moved into an oven for heating of the mould. When air is passed through the air inlet 76, the vortex tube 72 expels hot air from the hot air outlet 78 and expels cold air through the cold air outlet 80 into the battery unit 50. The cold air cools the interior 51 of the battery unit 50 and passes to the interior of the electronics unit 12 via the ports 64 and 14. This cold air passes through interstitial spaces between the glass beads 18 and out of the non-return valve 40 at the outlet port 16. The passage of cold air through the composite device 10 thus cools the interior of both the electronics unit 12 and the battery unit 50.

The majority of water vapour in the cold air condenses in the interior of the battery unit 50, so that the battery unit 50 serves as a water trap. Any remaining vapour is absorbed by silica gel mixed with the glass beads 18.

Heat transfer occurs between the cold air and the glass beads 18 through which it passes, so that glass beads 18 are cooled and act as a thermal storage mass. As the glass beads 18 have a relatively high specific heat capacity (about 700 J/kg.K) and have a high density relative to air, the heat capacity of the glass beads 18 is considerably greater than the heat capacity of air occupying the same space. The longer cold air is passed through the device 10, thus pre-cooling the beads 18, the colder the beads 18 become, and the more energy will be required, in use, to raise the temperature of the beads 18 and therefore the interior of the electronics unit 12 to unacceptably high levels.

In an experiment, the inventor used a vortex tube 72 model number V10008, manufactured by Arizona Vortex. The vortex tube 72 was connected to a compressed air supply of 3 KPa, which then produced cold air at a temperature of about -20²C at the inlet port 62. By passing the cold air through the units 50 and 12 long enough, the thermal storage mass 18 was cooled down to a temperature of -10⁰C.

It is to be appreciated that all the electrical components, including the batteries 52, 46 and the telemetry transmitter 34, still operate at a temperature of -10°C. After cooling the thermal storage mass 18, the cooler 70 is disconnected from the port 62 and the non-return valves 40, 66 seal the units 12, 50 air tight, the units being connected together. The device 10, excluding the cooler 70, is then moved into a high temperature environment of the moulding oven, together with moulds which are to be monitored. If desired, the cooler 70 can be left in connection with the rest of the device 10 for the duration of the process.

In the oven, signals gathered by the temperature sensing device and relayed by the sensor leads 38 are processed by the telemetry transmitter 34, and are then transmitted by the telemetry transmitter 34, via the antenna 36, to a remote receiver (not shown).

In the oven, the outer walls 30, 54 are exposed to the heat but the layers of insulation 32, 56 shield the inside of the composite device 10, from external heat. The glass beads 18, which have been pre-cooled to a temperature -10⁰C, retards or slows down heating of the space around the telemetry transmitter 34, as heat that passes through the outer walls 30, 54 and the layers of insulation 32, 56 has to raise the temperature of the glass beads 18 which together, as a thermal storage mass, has a relatively high heat capacity. In laymen's terms, the glass beads 18 provide the interior of the device 10 with greater thermal inertia.

When the device 10 has passed through the oven and is in a cooling or a de- moulding phase, the cooler can again be connected to the inlet port 62, to cool the interior of the device 10. The electronics unit 12 remains mounted on the moulding station during all the phases of a moulding cycle and through a plurality of successive cycles, the interior 13 of the device 10 being pre-cooled, heated, and cooled down cyclically. During these successive phases, the telemetry transmitter produces a continuous radio frequency signal which is received and logged at the remote monitoring station.

When the main battery 52 is depleted, the battery unit 50 is disconnected from the electronics unit 12 and is plugged into a recharger (not shown) for recharging the battery 52. In a preferred arrangement, the battery unit 50 is removed from the electronics unit 12 and replaced with a charged battery. During such recharging/replacement, the telemetry transmitter 34 is powered by the back-up battery 36 in the electronics unit 12. Naturally, the battery unit 50 will be removed only during a de-moulding phase, as the electronics unit 12 in isolation can not be exposed to a high temperature enviroment, bearing in mind that the inlet port 14 will then permit hot air to enter the interior 13 of the electronics unit 12.

In an example of another aspect of the invention, which is not illustrated, the thermal storage mass 18 in the interior of the electronics device 12 can be dispensed with, so that the electronic equipment 34, 36 in the electonics device is surrounded by an air-filled space. In this construction, cold air is passed through the battery unit 50 and through the electronics unit 12 even while the device 10 is exposed to the high temperature environment. The cooler 70 is thus not removed before entry of the device 10 into an oven or the like, but remains connected to the device 10, the cooler 70 being continuously connected to a source of air under pressure. In Figures 2 -- 4 reference numerals 100, 200, and 300 respectively indicate further embodiments of a telemetry device in accordance with the invention. Like reference numerals indicate like parts in Figure 1 and in Figures 2 - 4, unless otherwise indicated.

The device 100 of Figure 2 is broadly similar in function to the device 10 of Figure 1 , with two major distinctions being that the casing 102 is not of composite construction, and that there is no thermal storage mass surrounding the electronic equipment 34, 36.

The casing 102 is in the form of a container which is cylindrical in shape, with a removable or lid 104 at an open end of the casing 102. The entire casing 102 and lid 104 are of PTFE. A sub-casing 106 is located inside the hollow interior 13 of the casing 102, the sub-casing 106 also being a hollow unit of a polymeric plastics material.

The sub-casing 106 is a sealed container in which telemetry equipment and insulating material are held. The electronic equipment 34, 36 is located inside the sub- casing 106, so that a peripheral space is formed between the electronic equipment 34, 36 and the wall of the sub-casing 106.

In the embodiment of the device 100 shown in Figure 2, the peripheral space inside the sub-casing 106 is completely filled with a jacket 112 of insulating material, in this case being in the form of high temperature fibreglass wool. The device 100 also includes a rechargeable battery 54 which is removably connectable to the electronic equipment inside the sub-casing 106. As can be seen in Figure 2, the battery 54 remains outside of the sub-casing 106, but is located inside the casing 102. The battery 54 is on the side of the sub-casing 106 closest to the open end of the casing 102, so that the battery 54 is easily accessible when the lid 104 is removed. In this example, the electronic equipment does not include a backup battery

In use, the interior of the sub-casing 106 is cooled before the device 100 is moved into the oven by passing cooled air through the casing 102 in a manner similar to that described with reference to Figure 1. Cold air moving through the casing 102 moves into the casing through the inlet port 62, over the battery 54, axially along an annular peripheral space between the sub-casing 106 and the cylindrical wall of the casing 102, and out of the casing 102 through the outlet port 40, as indicated by the air flow lines in Figure 2. Air inside the casing 102 is thus pre-cooled before the device 100 is exposed to high temperatures. Movement of the cooled air past the sub-casing 106 also results in some cooling of the contents of the sub-casing 106.

It will be appreciated that the cold air is blown over the battery 54 first, as cooling of the battery 54 is of critical importance. The upstream part of the interior of the casing 102 thus again serves as a moisture trap.

After cooling, the device 100 is then placed inside a box (not shown) of carbon silica board wrapped with insulating wool. Spaces between the outside of the casing 12 and the inner surfaces of the box are filled with pyrosol blanket. The box is removably mounted on the moulding station for movement therewith into the oven, the thermal sensors connected to the device 100 leading out of the box and into a moulding cavity where temperature is to be measured.

As the device 100 moves through various cycles of heating when the moulding station on which it is mounted moves into and out of the oven, the temperature inside the sub-casing 106 increases until it reaches a level at which re- cooling is required. The device 100 is then removed from the box and is connected to a vortex tube 72 supplied with pressurised air, to cool the device 100.

The rechargeable battery 54 is easily accessible for removal and recharging or replacement when the lid 104 is removed.

The devices 200, 300 Of Figures 3 and 4 are largely similar to the device 100 of Figure 2, the main difference being in the construction and contents of the sub-casing 106. In the device 200 of Figure 3, the peripheral space around the electronic equipment 34, 36 is filled by glass beads 18 surrounded by a jacket 202 of insulating wool lining the peripheral walls of the sub-casing 106.

The sub-casing 106 in figures 3 and 4 also have an inlet 108 and an outlet 110 at opposite ends of the sub-casing 106, so that the fluid flow path along which air flows through the casing 102, passes through the sub-casing 106.

In use, air passing through the sub-casing 106 during cooling of the device 200 cools the thermal storage mass provided by the beads 18. When the device 200 is exposed to high temperature environments, heating of the beads 18 is retarded by insulation provided by the jacket 202.

It will be appreciated that the sub-casing 106 serves as a retainer for holding the beads 18 captive in position around the electronic equipment, so that there is no risk of spillage of the beads 18 when the lid 104 is opened for recharging of the battery 54.

In the device of 300 of figure 4, the insulating jacket 202 is omitted, so that the sub-casing is filled with glass beads 18.

As explained above, air can be passed through the telemetry device either continuously or intermittently. In Figure 5 of the drawings, an arrangement is shown for facilitating intermittent cooling of the device 200 by the supply of a pressurised gas to the device 200. A removable and replaceable gas canister filled with carbon dioxide is mounted close to the device 200, and is connected to the inlet port 62 of the device by a flexible conduit 402.

When the device 200 is to be cooled, pressurised gas in the canister is released and is discharged through the conduit 402 into the interior of the casing 102.

It is an advantage of the telemetry device in accordance with the invention, as described with reference to the drawings, that its construction increases thermal protection of telemetry devices which are exposed to high temperature, enabling continuous monitoring of high temperature devices better than existing methods.

Claims

CLAIMS:

1. A method of measuring moulding conditions in a rotational moulding process, which method includes: mounting a telemetry device such that the device moves with an associated mould into a moulding oven, the telemetry device having a casing which houses electronic equipment providing a transmission means for transmitting wireless signals representative of condition measurements to a monitoring station; and cooling the electronic equipment in the casing by passing a cooling fluid through the casing.

2. A method as claimed in claim 1 , in which the telemetry device includes at least one temperature sensor for providing temperature measurements of air inside a moulding cavity, and for relaying the temperature measurements to the transmission means inside the casing.

3. A method as claimed in claim 2, which includes pre-cooling the cooling fluid before passing it through the casing.

4. A method as claimed in claim 3, in which the fluid is pre-cooled to at least

-5⁰C.

5. A method as claimed in claim 3, in which the fluid is pre-cooled to about -

1O⁰C.

6. A method as claimed in claim 3, in which the fluid is pre-cooled by passing pressurised fluid through a cooler which is mounted upstream of the casing.

7. A method as claimed in claim 6, in which the cooler is a vortex tube.

8. A method as claimed in claim 6 or claim 7, which includes attaching the cooler to the telemetry device before insertion of the device into a moulding oven, passing cooling fluid through the cooler and through the casing to cool the interior of the casing, and removing the cooler before movement of the casing into the oven.

9. A method as claimed in any one of claims 6 to 8, which includes passing the cooling fluid through a moisture trap before entry of the cooling fluid into the casing.

10. A method as claimed in any one of the preceding claims, in which the cooling fluid is air.

11. A method as claimed in any one of the preceding claims, which includes passing cooling fluid through the casing before and/or after movement of the casing into the moulding oven, so that the interior of the casing is cooled intermittently.

12. A method as claimed in claim 11 , in which passing cooling fluid through the casing comprises placing a cylinder of pressurised gas in fluid flow connection with the casing.

13. A method as claimed in any one of claims 1 to 10, which includes passing the cooling fluid through the casing while the telemetry device is positioned in the moulding oven.

14. A method as claimed in any one of the preceding claims, which includes providing an insulating jacket around the electronic equipment inside the casing.

15. A method as claimed in any one of the preceding claims, which includes cooling a thermal storage mass in an interior of the casing, while the thermal storage mass is located in the casing, by passing the cooling fluid through the casing in heat transfer relationship with the thermal storage mass, the thermal storage mass, in turn, being in heat transfer relationship with the electronic equipment.

16. A method as claimed in claim 15, which includes cooling a thermal storage mass in the form of a particulate material which permits the passage of cooling fluid through it to allow heat transfer between the fluid and particles of the thermal storage mass.

17. A method as claimed in any one of the preceding claims, which includes powering the electronic equipment with a main battery which is removably connected to the electronic equipment, and removing the main battery for recharging when the device is outside of the oven.

18. A method as claimed in claim 17, which includes powering the electronic equipment with a backup battery while the main battery is removed for recharging.

19. A method as claimed in claim 18, which includes connecting the main battery and the backup battery, to recharge the backup battery.

20. A telemetry device for measuring and reporting ambient conditions in a high temperature environment, which device includes: A casing having a hollow interior; electronic equipment housed in the interior of the casing, the electronic equipment including a transmission means for transmitting wireless signals indicative of measured ambient conditions outside of the casing; and a cooling arrangement for cooling the interior of the casing, the cooling arrangement including a fluid flow path through the casing for channelling pressurised cooling fluid supplied to the casing, in use, through the casing.

21. A telemetry device as claimed in claim 20, which includes at least one temperature sensor for measuring ambient temperature outside of the casing, each temperature sensor being operatively connected to the electronic equipment inside the casing.

22. A telemetry device as claimed in claim 21 , in which at least part of the casing's peripheral walls is non-metallic.

23. A telemetry device as claimed in any one of claims 20 to 22, in which the cooling arrangement includes an inlet port for receiving the cooling fluid into the casing, and an outlet port for discharging the cooling fluid from the casing, so that the fluid flow path is formed between the inlet port and the outlet port.

24. A telemetry device as claimed in claim 23, or which includes one-way valves mounted respectively in the inlet port and the outlet port.

25. A telemetry device as claimed in claim 23 or 24, which includes a jacket of insulating material which is positioned inside the casing around the electronic equipment.

26. A telemetry device as claimed in claim 25, in which a cavity immediately surrounding the electronic equipment is substantially fully occupied by insulating material.

27. A telemetry device as claimed in any one of claims 20 to 26, in which the cooling arrangement includes a cooler which is connected or connectable to the fluid flow path for supplying cooled fluid to the fluid flow path.

28. A telemetry device as claimed in claim 27, in which is the cooler is arranged to receive air under pressure and to supply cooled and pressurised air to the fluid flow path.

29. A telemetry device as claimed in claim 28, in which the cooler is in the form of a vortex tube.

30. A telemetry device as claimed in claim 28, which includes a canister of pressurised fluid which is connectable to the cooler or to the casing for providing a limited supply of pressurised fluid to the fluid flow path.

31. A telemetry device as claimed in any one of claims 27 to 30 inclusive, which includes a moisture trap in the fluid flow path between the cooler and the electronic equipment, for reducing the amount of liquid vapour carried by the cooling fluid.

32. A telemetry device as claimed in any one of claims 27 to 31 inclusive, in which a desiccant material is provided in the casing to absorb moisture carried by the cooling fluid.

33. A telemetry device as claimed in any one of claims 20 to 32 inclusive, which includes a thermal storage mass located in the interior of the casing in heat transfer relationship with the electronic equipment.

34. A telemetry device as claimed in claim 33, in which the thermal storage mass is in the form of a particulate material through which the cooling fluid can pass.

35. A telemetry device as claimed in claim 34, in which the thermal storage mass is in the form of glass beads.

36. A telemetry device as claimed in any one of claims 20 to 35 inclusive, which includes a removable and rechargeable battery, the battery being connected to the electronic equipment in the casing for providing electrical power thereto.

37. A telemetry device as claimed in claim 36, which includes an auxiliary battery connected to the electronic equipment in the casing, the auxiliary battery being arranged for providing electrical power to the electronic equipment when the removable battery is disconnected from the electronic equipment, and for being recharged by the removable battery when the removable battery is connected to the electronic equipment.

38. A telemetry device as claimed in claim 36, in which the casing is of composite construction, comprising an electronics unit and a battery unit which are releasably connectable together, the electronic equipment being housed in the interior of the electronics unit and the removable battery being housed in the battery unit for powering the electronic equipment when the units are connected together.

39. A telemetry device as claimed in claim 38, in which a peripheral wall of the battery unit provides a fluid inlet port, while the electronics unit provides an outlet port, the units being constructed such that the interiors of the units are in fluid flow communication when the units are connected together, the composite interior of the composite casing being air-tight.

40. A telemetry device as claimed in any one of claims 20 to 37 inclusive, which includes a sub-casing located within the casing, the electronic equipment being housed inside the sub-casing and the fluid flow path passing through the sub-casing in heat transfer relationship with the electronic equipment.

41. A telemetry device as claimed in claim 40, in which the casing has a lid which is removable to expose the interior of the casing and permit removal of a rechargeable battery which is connected to the electronic equipment but which is located outside of the sub-casing.

42. A telemetry device as claimed in claim 40 or claim 41 , which includes an insulating material inside the sub-casing.

43. A telemetry device as claimed in any one of claims 40 to 42 inclusive, which includes a thermal storage mass inside the sub-casing, the thermal storage mass being in heat transfer relationship with the electronic equipment.

44. A control system for a rotational moulding apparatus, which system includes at least one telemetry device as claimed in any one of claims 20 to 43 inclusive.