|Title of Invention||
"IMPROVED MERCURY-IN-GLASS THERMOSTAT AND HOLDER ASSEMBLY"
|Abstract||An improved mercury- in -glass thermostat and holder assembly comprising a base plate, one or more plugs and a thermostat is disclosed. The base plate is with at least one pair of sockets for each of the said plugs. The plug is provided with at least one pair of connection pins, and the sockets of base plate are adapted to receive the connection pins of the plug. Side holder pins are provided on the side of the said base plate to enable mounting of the base plate on the mounting plate of the location where the mercury-in-glass thermostat and holder assembly is to be mounted.|
|Full Text||Field of the invention
The present invention relates to improved mercury- in- glass thermostat and holder assembly useful for precise temperature control in several applications. More particularly, the present invention relates to improved mercury-in-glass thermostats used for precise temperature control in coaches, buildings, any mobile environment such as automobiles. The present invention also relates to improvements in the holder assembly used for fixing contact type mercury-in-glass thermostats.
Background of the invention
Mercury-in-glass thermostats find use in several applications where the level of temperature control required is very precise. It is a cost-effective solution giving a high degree of reliability and repeatability as well as accuracy for its price point. Among the various areas where such thermostats are required to maintain a control over temperature are coaches of the air conditioned type, buildings with central heating and central cooling systems, mobile environments such as air conditioned automobiles for instance caravans, buses, charabancs, cars, aircrafts and other vehicles. Such thermostats also find application in static environments such as factories manufacturing electronics, food processing industries where a precise temperature level is required for optimization of the manufacturing process as well as in ordinary office environment.
Two types of mercury -in-glass thermostats are in wide
spread use in the art—fixed contact type thermostats
and variable contact thermostats. Mercury - in glass
thermostats work on the principle of expansion of mercury
in response to a temperature rise. A glass capillary is cut at two points and platinum wire is fused across the bore at both the points to act as probes. The segments thus formed are reconnected by melting and fusing over a flame. Thereafter, conductive leads are attached to the platinum probes. The mercury is stored in a bulb attached to the bottom of the capillary. The mercury column is subjected to a gas pressure over it.
Fixed point thermostats are pre set at a particular temperature from the place of manufacture itself. The temperature range of a fixed point thermostat is therefore rigid and cannot be altered during use to suit the specific application. Thus, if there is a wide variance of temperature, or if multiple points of temperature control are required, multiplicity of fixed point thermostats are required. For example, in air conditioned coaches, six temperature points are used at a time. The first is the heating range with three thermostats of ranges 19°C, 19°C and 21°C. The second is the cooling range of 24°C, 24°C and 26°C. Thus one set of thermostats is used to control the heating system and one set is used to control the cooling system of the air conditioned coaches.
The prior art mercury - in - glass thermostats suffer from the disadvantage of being unstable and unable to withstand high levels of vibration. In the art, each set of thermostats is held together physically in order to give thermostats pertaining to each temperature setting physical support as well as a wiring interface. The thermostats are generally held together by a mounting assembly which functions as a holder assembly.
Prior art holder assemblies used for example in air conditioned coaches are made of Bakelite and can accommodate three thermostats. The
three fundamental elements of the prior art holding assembly comprise of a holder, a base plate and a steel mounting plate. The thermostats are secured on to the holder by means of rubber bushes. Each thermostat is also wired to the holder. One lead of each thermostat is shorted by screwing to a single point. The other lead is screwed to each of the other three points. These four points extend as plug-in pins on the other face of the holder.
The holder was then plugged in to the base plate which was provided with a similar wiring interface with the air conditioning system. The base plate was provided with four pins, one corresponding to the common point and the other three to the second point of each of the thermostats. The base plate and the holder assembly was then mounted on to the steel mounting plate which was physically secured to the air conditioning plant by any conventional means such as welding.
While installing the thermostats into the holder assembly plug, the rubber bushes have to be pushed into the corresponding slots on the holder to secure the same. It is observed that the prior art thermostats suffer from the problem of being physically not durable and subject to easy breakage. More particularly, it is observed that the thermostats being made of glass would break at the point where the platinum probe was fused into the capillary tube. It is observed that users of the thermostats would be push the thermostats in at points where the glass has been cut and platinum probes fused across the bore, while applying excessive pressure, resulting in breakage at these weak points in the construction.
It is also observed that the rubber bushes used in the art to secure the thermostats to the holder assembly function only as holders and do not
provide adequate support to the glass itself, thereby resulting in breakage during use due to use conditions. Additionally, the prior art thermostats and holder assemblies suffer from the disadvantage of not being able to with stand vibrations beyond a certain limit. In fact, the vibration tolerance levels of prior art thermostats and holder assemblies have not been measured or paid enough attention to. It is observed that while the vibration tolerance of the holder assembly and the thermostat is adequate in conditions of low vibration, the assembly is unstable and could be damaged in conditions of high vibration. Since in actual use, the vibration levels could be quite high depending on, for example, on the motion of the air conditioned coaches where the thermostat and holder assembly is installed, the stability and shock-proofness of the assembly is quite important.
Another problem associated with prior art mercury - in - glass thermostats and holder assemblies is that the gaps between the rubber
bushes on each thermostat is set by hand. As a result the gap is not always uniform and equal to the spacing between the slots in the holder. This results in the development of stress when improperly adjusted rubber bushes are pushed into the slots of the holder plug of the holder assembly. It is observed that the stress levels increase during high frequency vibrations often resulting in breakage of the thermostat.
Another problem associated with prior art mercury - in - glass thermostats is that to remove one component, the entire assembly has to be dismantled. This is because the common lead has to be detached from the common point, which is located below the thermostats on the holder. The possibility of damage occurring during dismantling increases with the
number of times the thermostat is wired into and wired out of the nolder
US Patent 5,419,489 discloses a mobile thermostat in order to control the space temperature in a building. The disclosure sought to improve the level of temperature control in a static environment by providing a mobile thermostat in addition to the existing fixed thermostat in order to monitor temperature gradients across the entire building.
US Patent 5, 279, 264 relates to a viewable thermostat device and discloses a transparent thermoplastic thermostat housing for the thermostat to enable a visual indication of the precise operation of the engine thermostat in all phases of the engine operation. The emphasis of this invention was on improving the visibility of the thermostat itself rather than improving other important factors such as stability, shock-proofness, etc. The invention also related only to thermostats for internal combustion engines.
US Patent 3, 941, 310 relates to a thermostatic control for use in variable air distribution systems. The patent discloses a method of regulating the flow of conditioned air in order to maintain the temperature levels of the air conditioned environment. The entire focus of the patent is on static and stable environments such as buildings with heating and cooling systems.
The applicant is unaware of prior art relating to any method or system for ensuring that thermostats of the mercury-in-glass type are rendered stable and substantially break proof during use particularly in mobile
operation such as in air conditioned coaches which are subject to high variation in frequency levels.
It is therefore clear that there is a definite need for an improved mercury-in-glass thermostat and a holder assembly that overcomes the problems associated with the prior art listed above. Objects of the invention
It is therefore one object of the invention to provide improved mercury-in-glass thermostat, which obviates the disadvantages of the prior art listed above.
It is another object of the invention to provide improved mercury-in-glass thermostat and holder assembly that minimises the need for wiring and rewiring during repair.
It is another object of the invention to provide mercury-in-glass thermostat and holder assembly that is capable of withstanding the shock of high frequency vibrations.
It is a further object of the invention to provide improved mercury-in -glass thermostat that does not require complete dismantling for repair.
It is a further object of the invention to allow easy maintenance, inspection and servicing.
It is another object of the invention to provide improved mercury-in-glass thermostat and holder assembly that is capable of withstanding high levels of stress during operation.
It is yet another object of the invention to provide a holder assembly for a mercury- in- glass thermostat that supports the thermostat while minimising the chances of damage during actual use.
It is a further object of the invention to provide an improved mercury-in-glass thermostat and holder assembly without requiring structural alterations in the site where the assembly is to be located. Summary of the invention
Accordingly, the present invention provides an improved mercury-in-
glass-thermostat and holder assembly comprising a base plate, one or more
plugs and a thermostat, wherein said base plate is provided with at least one pair
of sockets for each of said plugs, said plug is provided with one pair of
connection pins, said sockets of said base plate are adapted to receive the
said connection pins of said at least one plug, side holder pins are provided on the side of the said base plate to enable mounting of the base
plate on the mounting plate of the location wherein the mercury-in-glass
thermostat and holder assembly is to be mounted, said plug is bush-
free, the thermostat is cordless and comprises of at least two platinum probes connected to a glass capillary and soldered on to the face of said connection pins by means of lead tags.
In one embodiment of the invention, one socket of each said pair of sockets adapted to receive the connection pins of at least one plug is smaller in diameter than the other socket in order to prevent wrong insertion of the plug into the socket.
In another embodiment of the invention, the plug comprises of connection pins connected to the plug casing by means of insert molding.
In another embodiment of the invention, bulb of said thermostat is free of the casing of the plug, to prevent interference from the specific heat of the casing.
In a further embodiment of the invention, the probes on said at least one thermostat are connected to said connection pins on the said at least one plug. Brief description of the accompanying drawings
Figure 1is illustrates the mercury in glass thermostat and holder
apparatus of the invention.
Figure 2 illustrates the positioning and connection between the
thermostat and plug of the invention.
Figure 3 illustrates the construction of the base plate of the apparatus
of the invention.
Figure 4, further illustrates the construction of the novel plug of the invention. Detailed description of the invention
The base plate is a Bakelite molding and serves as the socket base for
three individual plugs. The sockets are generally made of brass. There is one
pair of sockets 7 and 8 (Figure 1) for each plug. Thus three pairs of sockets are required to accommodate the pins as can be seen in Figure 3. As can be
seen socket (7) has a smaller hole as compared to socket (81) This is to avoid
wrong insertion of plug into the socket.
Additionally, side holder pins are inserted on both the sides (4,5 and 6, Figure 1). The two pins together act as the mounting mechanism for the steel mounting plate.
The plug is modified over conventional prior art plugs and incorporates several constructional features to counter the problems that were faced earlier. Protection to the instrument is ensured by making the casing of
Ryton-R4. The plug is designed so as to give the thermostat support at all points. Thus, a wrongful pressure at the weak points will not lead to breakage. Thus breakage due to mishandling during installation into the base plate is avoided. Being physically protected from all sides and more resilient to shock, vibration breakage due to mishandling will become lesser. The thermostat is connected to the plug in such a manner that a normal finger pressure while plugging it into the plate and plugging it out will not break the thermostat. At the same time, the bulb is exposed on all sides to air flow to ensure a quick response to temperature change and to avoid specific heat of the encasing to interfere with the response.
In the mercury-in-glass thermostat and holder assembly of the invention, the thermostat is held to the encasing by means of an RTV adhesive (Filling in Figure 2). The adhesive is chosen for its shock-absorbent characteristics. The encasing and the instrument is thus one entity. Rubber bush mounting of the older design has been done away with. Thus, the issue of inappropriately aligned bush and slot of the plug does not arise. An inappropriate alignment is understood to be the cause of major breakages. In high vibration environments like mobile cooling plants, such a misalignment can lead to stress developing at the joints and consequently leads to damage of the thermostat. The improvements in the casing support and the substantial reduction if not total absence of stress at the points T-1 and T-2 (Figure 2) due to the lack of stress-causing causing bushes leads to lesser breakages.
The thermostat in this system is cordless in nature. The platinum probes from glass capillary are connected to tags (9 in Figure 1) as long as 5
mm and soldered to the face of the pins (10 and 11 in Figure 1). The pins are insert molded into the casing. Thus, the pins P-l and P2 work as the primary connection points for the thermostats through which the signal
flows to the base plate socket (7,8 in Figure 1). The sockets in turn are
connected to the air conditioning plant's wiring through screws (12 and 13
in Figure 1) at detail 'c' in Figure 3.
Since all the circuitry wiring is done behind the base plate in the socket of the holder assembly, if only one piece needs to be removed for the purpose of replacement or repair, only the piece to be repaired or replaced needs to be pulled out or dismantled. This ensures that the remainder of the mercury-in-glass thermostat and holder assembly is left intact thus minimizing possibility of damage and wear and tear. A new piece fitted in a new plug can be inserted while disposing the old piece along with the plug. This makes that the thermostat assembly absolutely cordless in nature and no screwing and unscrewing needs to be done to service the thermostats. If one thermostat needs to be replaced it can be simply plugged out and a new one can be plugged in its place without disturbing the other pieces.
In prior art thermostats, on the other hand, one lead (10cm long) from each of the thermostats was screwed to the common point on holder plug and one each to the other three points. This meant replacing one thermostat would require removing all the three and inserting them back after due replacement of the defective thermostat.
The above improvements in the construction ensures that modularity is also introduced. Modularity and cordless character together ensure in
turn that the thermostats require lesser handling during servicing and leads to lesser breakage due to mishandling.
Regular maintenance check of the plant includes checking the continuity of the thermostat. In the prior art thermostat assemblies, to check the continuity of the thermostat, the thermostats had to be removed from the assembly to access the wiring hidden beneath them. The thermostat and holder assembly of the invention makes available the contact points on the face itself and thus the thermostat does not have to be removed form the assembly. An added advantage is that the plug is so constructed that it exposes the mercury column all over the thermostat. Thus, presence of a breakage in mercury column can be easily detected.
Thus, the new plug is an innovative design as it merges the desirable features of support and protection, modularity, cordlessness, easier maintenance and servicing all into one design.
The material for construction can be conventional. However, in one embodiment of the invention, the material is chosen such that the fumes in case of a fire are minimized and inflammability was low. The base plate design is simple and is covered by Bakelite. The plug is constructed using injection molding with insert-molded pins for efficient production and accuracy of fitment. Ryton-R-4 is preferred since the plastic has negligible shrinkage like Bakelite, is not inflammable and is a strong plastic with good tensile strength.
1. An improved mercury-in-glass thermostat and holder assembly comprising a
base plate, one or more plugs and a thermostat, at least one pair of sockets
located on said base plate for each of said plugs, where said plug is provided
with one pair of conneotor pins for engaging with said sockets; characterised
in that side holder pins are provided on the side of the said base plate to
enable mounting of the base plate on the mounting plate of the location wherein the mercury-in-glass thermostat and holder assembly is to be
mounted, said plug bush free, the thermostat is cordless and
comprises of at least two platinum probes connected to a glass capillary
and soldered on to the face of connec pins by means of tags.
2. An improved mercury-in-glass thermostat and holder assembly as claimed in
claim 1 wherein one socket of each said pair of sockets is smaller in
diameter than the other socket.
3. An improved mercury-in-glass thermostat and holder assembly as claimed in
claim 1 wherein said connection, pins are connected to the plug casing by
means of insert cleing molding.
4. An improved mercury-in-glass thermostat and holder assembly as claimed in
claim 1 wherein the bulb of said thermostat is free of the casing of the plug.
5. An improved mercury-in-glass thermostat and holder assembly substantially as described hereinbefore and with reference to the accompanying drawings.
|Indian Patent Application Number||504/DEL/2000|
|PG Journal Number||30/2008|
|Date of Filing||11-May-2000|
|Name of Patentee||PAWANDEEP SINGH BAHL|
|PCT International Classification Number||G01K 5/00|
|PCT International Application Number||N/A|
|PCT International Filing date|