DE202004000585U1 - Explosion safe temperature gage with a sensor enclosed in a protective metal tube with flex wires passing thru a connecting cable useful for measuring temperature under explosion sensitive conditions - Google Patents

Abstract

A explosion safe temperature gage with a sensor (1) enclosed in a protective metal tube (2) with at least a first and second flex wire (5.1, 5.2) passing thru a connecting cable on tube (2), and insulated from each other, and electrically connected to the sensor, with a third flex wire (5.3) fed and connected to base (4) of tube (2).

Description

The invention relates to a temperature sensor a temperature sensor arranged in a metallic protective tube and with at least a first and at least a second cable strand, the run in a connection cable attached to the protective tube and are isolated from each other, is conductively connected.

The invention is preferably used for Temperature measurement in potentially explosive areas.

In such applications, electrical Connection cable preferred with Teflon due to the material properties executed.

The following is used as a temperature sensor both a single such sensor and an electrical one Group of several such sensors in series and parallel connection considered.

Cable resistance thermometers are in the prior art known, generally the temperature sensors on cable leads connected and encased in a hermetic encapsulation metallic protective tube can be inserted and for strain relief the cable leads are squeezed or crimped.

The connection of the sensor with the Leads can be done in two ways: first, that the sensor directly to the bottom of the metallic protective tube or shows that the Sensor lies flat on the strands of the connection cable and to the cable outlet shows and only the free solder joints to Pointing to the bottom, so-called inverse soldering. The potting agents used consist of epoxy resins or silicone potting compounds. For insulation among other things, shrink tube solutions are known accordingly.

DD 267 790 describes a temperature sensor which has a metal layer sensor, connection lines and a housing, that filled with insulating compound and is closed, with the connecting line up to approximately the bottom of the case is enough and the metal layer sensor in the opposite direction and lying on the insulation of the connection cable contacted with it is.

The DE 16 48 188 describes an interchangeable sensor for contact thermometers with a semiconductor as a transmitter, in which the semiconductor is embedded in a rounded metal tip at one end, the other end of which is in a PVC tube of the same outside diameter and which integrally merges into the PVC tube , thin PVC layer is covered.

DD 301 124 describes a method for Manufacture of a cable resistance thermometer described, consisting from platinum thin-film sensor, Insulation compound and sheathed cable, in which the sensor is flat is placed on the cable and the connection wires in the direction of the stripped Point the end of the cable, with the prepared cable assembly in one with fine grain PVC paste filled form is immersed and with the shape in a three-stage annealing process heated and the PVC paste is pre-gelled in the mold and then the pre-gelled demolded and cooled Cable assembly with hot air a temperature above 165 ° C for a short time annealed and covered with a continuous protective skin becomes.

Through the DE 44 24 384 A1 becomes a temperature sensor with fast response time with a temperature-dependent sensor, which is arranged in a sleeve-shaped measuring tip in the end region of an elongated protective tube, while the protective tube has an opening at its other end for the passage of a connecting line for the sensor, the measuring tip in its end facing the measurement has a flat taper.

In the DE 44 24 630 C1 is a temperature sensor with a sleeve closed at one end by a bottom and open at the other end and a support body inserted into the sleeve in the direction of the sleeve axis, on which a measuring resistor is fixedly arranged, which is a ceramic substrate and two towards the open end of the sleeve Sleeve protruding connecting leads, and with two connecting leads inserted into the open end and aligned with the floor, the supporting body having a central web running in the direction of the sleeve axis, on both sides of which the connecting leads are laid with their connecting points in between, and the one with the connecting leads and the Connection points on at least part of its length is surrounded by a fixing, insulating sheath.

The known solutions each have at least one of the following disadvantages:

• - Becomes If a casting compound is used, the required Ti value is clear below 200 ° C and the use of the temperature sensor is restricted. Furthermore the potting technology is complex.
• - Becomes the connection cable strongly bent, affect the copper souls of the Different tensile forces, which continue to the sensor. These tensile forces can also be caused by twisting or can only be intercepted incompletely by the encapsulation. The So far, different tension on the connecting wires of the sensor is only through a feedthrough device, the squeezable or solderable is complete caught, this solution however extremely costly is and accordingly requires space in the interior of the sensor, so that small arrangements cannot be realized.
• - At the use of casting compounds - extraordinary expansion forces occur from 150 ° C, which to pressure loads on the sensor and thus to falsification of the measurement result.
• - By Strain reliefs on the cable have so far been used for simple crushing only incomplete when using Teflon cable. After prolonged thermal cycling is a for larger forces It is possible to pull out the entire cable sensor assembly.

The invention is based on the object a temperature sensor to specify the inexpensive to manufacture, versatile and in the sense of general explosion protection elevated is safe and can also have small dimensions.

According to the invention, the object is achieved with an arrangement which contains the features specified in claim 1, solved.

Advantageous configurations are in the subclaims specified.

The arrangement according to the invention has the advantage that they're in potentially explosive atmospheres clear can be used. The risk of explosion can result from Exposure to gas or dust. That is advantageous Execution according to the invention also because Teflon cables for the realization can be used.

A cable strand leading to the bottom of the protective tube, which is connected to this, provides a heavy-duty strain relief of the connection cable, which is very easy to manufacture and only extremely little space required. This minimizes the risk of cable pulling out.

When the temperature sensor is axially bonded leads has, which is conductive on the first and second connection cable strands are attached, with the connecting cable strands varying in extend the interior of the protective tube and the length difference between the cable strands connected to the temperature sensor Length of Temperature sensor with its connecting wires can be cast on can be dispensed with, since all the required distances are maintained even without casting be, and thus an extremely inexpensive manufacture possible is. In addition, the sensor is against different tensile forces in the strands stored insensitive.

The axial orientation of the connecting wires relates on the longitudinal axis of the protective tube.

By making the connection wires consist of a stable material with a Ni component and together are firmly cemented or glued into a ceramic sleeve with the temperature sensor, which is positioned parallel to the protective tube axis is another Tension relief of the sensor and the connecting wires possible.

Forms the ceramic sleeve a wire array running parallel to the cable strands is positioned in a metallic inner protective tube, each one or two cable strands, each connected to a sensor connection wire, depending on the type of connection are, the sensor is also protected against lateral forces.

A series-parallel circuit from four identical resistance sensors, the total resistance of which with Resistance value of a single temperature sensor matches, allows an integral capture over four discrete points. This sensor configuration also allows the Dispensing with potting agents, as all the necessary ones without potting distances be complied with, and thus an extremely cost-effective production is possible.

Because in the course of each the first and second lead strands in a particular one Distance from each other two resistance sensors arranged in series are, with the distances, in which the resistance sensors of the first connection cable are arranged by the distances in which the resistance sensors of the second connection cable are arranged, differentiate and electrically between each two resistance sensors of a connecting cable strand a piece of the respective Connection cable strand is arranged and the two resistance sensors electrically connects, and that a fourth lead wire without Interruption is also led to the protective tube sheet, this before Protective tube sheet electrically with the first and second connection cable strands is connected and opposite the thermowell base and thermowell are electrically insulated, is a series-parallel connection in a simple manner and space-saving possible.

Are the electrical connections of the cable strands with the temperature sensor covered with insulating materials and show these insulation pieces along the Tube, with remaining creepage distances to bare solder joints longer than 8 mm, the electrical functionality is simple Means ensured, while also the stability of the arrangement is improved.

A multiple squeeze of the Cable with the protective tube, the squeeze from two double roll beads between which there is a hexagon crimp, and the distance between the double roller beads and the distance between the hexagon crimp and the adjacent double roll surround are of the same order of magnitude; allows a very high tensile load on the connection cable and the strands the inside of it even with warping of the cable.

There are connection cable strands with Teflon insulation weatherproof and have a small footprint.

The invention is explained below of an embodiment explained in more detail.

Show this

1 the outside view of a temperature sensor,

2 a section through a temperature sensor with a single resistance sensor

and 3 a section of a temperature sensor with series-parallel network of resistance sensors.

In 1 is the connection cable 7 with Teflon insulation through crushing 6 , consisting of two double roller beads 6.1 and a hexagon crimp 6.2 , tensile with the protective tube 2 connected.

In 2 is in the metallic protective tube 2 the connection cable 7 with four insulated strands 5.1 . 5.2 . 5.3 and outer teflon cover 7.1 guided. The strand 5.3 is down to the ground 4 of the protective tube 2 guided. The thermowell base contains a central hole 4.1 into which the strand 5.3 introduced and with the floor 4 is cohesive and tightly welded. The strand 5.1 is shorter and ends approximately 10 mm from the floor 4 , The strands 5.2 are again opposite the strand 5.1 made shorter, the length difference between the strands 5.1 and 5.2 by the length of the sensor 1 including its connecting wires. The strands 5.2 are soldered overlapping with the connecting wire of the sensor, as well as the wire 5.1 with the connecting wire of the sensor facing the floor. The end of the strand 5.2 and the free wire end of the sensor are covered with an insulating tube. Over the entire bandage from the end of the outer insulating hose of the cable to the soldering point of the strand 5.2 is a shrink tube shrunk. The shrink tube protrudes 8 mm over the end of the soldering point of the strand 5.2 , The cable is inserted deep enough into the protective sleeve so that three bruises can be exerted on the cable. First, two beads are made with a double roller and finally a hexagonal pinch is carried out. The hexagon bruise 6.2 lies between the double roller beads 6.1 ,

The following dimensions are within an uncertainty of ± 1 mm equal:

• - distance between the protective tube end and the first rolling bead
• - distance between the double rollers of the double roller bead
• - distance from the bead to the hexagon crushing
• - length of Allen pinch

The temperature sensor is connected in a 3-wire circuit and for hazardous Rooms after Dust-Ex and Gas-Ex can be used.

Finally shows 3 a variant of the temperature sensor with a series-parallel circuit network of resistance sensors 1 , which preferably has the same total resistance as a single one of the sensors 1 , Other resistance distributions are also possible. A strand 5.4 runs to the ground 4 of the protective tube 2 , is there with the strands 5.1 and 5.2 contacted, but further through a Teflon shrink tube opposite the protective tube 2 and the floor 4 electrically isolated. The resistance network consists of the strands 5.1 and 5.2 that are interrupted and in interruptions with the sensors 1 are soldered.

1

temperature sensor

2

thermowell

3

interior insulation

4

ground

4.1

bottom hole

4.2

welding

5

strands

5.1

First braid

5.2

Second braid

5.3

third braid

5.4

Fourth braid

6

bruise

6.1

roll Beading

6.2

Hexagonal crimping

7

connection cable

7.1

External teflon insulation

8th

ceramic sleeve

9

leads

Claims (10)

Temperature sensor with a temperature sensor ( 1 ) in a metallic protective tube ( 2 ) arranged and with at least a first and at least a second cable strand ( 5.1 . 5.2 ) in a on the protective tube ( 2 ) attached connection cable ( 7 ) run and are insulated from each other, is connected in an electrically conductive manner, characterized in that at least one third cable strand ( 5.3 ) to the protective tube bottom ( 4 ) is guided and connected to it there. Temperature sensor according to claim 1, characterized in that the temperature sensor ( 1 ) axially bonded connecting wires ( 9 ) on the first and second connection cable strands ( 5.1 . 5.2 ) are attached in an electrically conductive manner, with the connecting cable strands ( 5.1 . 5.2 ) to different degrees in the interior of the protective tube ( 2 ) and the length difference between the temperature sensor ( 1 ) connected cable strands the length of the temperature sensor ( 1 ) with its connection wires ( 9 ) corresponds. Temperature sensor according to claim 2, characterized in that the connecting wires ( 9 ) consist of a stable material with a Ni component and together with the temperature sensor ( 1 ) firmly in a ceramic sleeve ( 8th ) are cemented or glued in, which is positioned parallel to the protective tube axis. Temperature sensor according to claim 3, characterized in that the ceramic sleeve ( 8th ) with the parallel to the cable strands ( 5 ) form a sensor assembly, which is in a metallic inner protective tube ( 10 ) is positioned, depending on the type of connection one or two cable strands ( 5.1 . 5.2 ) with one sensor connection wire each ( 9 ) are connected. Temperature sensor according to claim 1, characterized in that the temperature sensor ( 1 ) consists of a series-parallel connection of four identical resistance sensors, the total resistance of which corresponds to the resistance value of a single temperature sensor ( 1 ) matches. Temperature sensor according to claim 5, characterized in that in the course of the first and second connection cable strands ( 5.1 . 5.2 ) two resistance sensors are arranged in series at a certain distance from each other, the distances at which the resistance sensors of the first connection cable strand ( 5.1 ) are arranged from the distances at which the resistance sensors of the second connection cable strand ( 5.2 ) are arranged, differentiate and electrically between the two resistance sensors of a connecting cable strand ( 5.1 . 5.2 ) a piece of the respective connection cable strand ( 5.1 . 5.2 ) is arranged and electrically connects the two resistance sensors, and that a fourth connection cable strand ( 5.4 ) also to the protective tube bottom without interruption ( 4 ), which is electrically connected to the first and second connecting cable strands ( 5.1 . 5.2 ) is connected and opposite the thermowell base ( 4 ) and the protective tube ( 2 ) are electrically insulated. temperature sensor according to claim 6, characterized in that the fourth lead wire through an insulation hose is insulated. Temperature sensor according to one of the preceding claims, characterized in that the electrical connections of the cable strands ( 5 ) with the temperature sensor ( 1 ) are covered with insulating materials, these insulating pieces pointing along the pipe and the remaining creepage distances to bare solder joints are longer than 8 mm. Temperature sensor according to one of the preceding claims, characterized in that the cable ( 7 ) several times with the protective tube ( 2 ) is squeezed, the bruise ( 6 ) from two double roller beads ( 6.1 ) between which there is a hexagon crimp ( 6.2 ) and the distance between the double roller beads ( 6.1 ) and the distance between the hexagon crimp ( 6.3 ) and the neighboring double roll surround ( 6.1 ) are of the same order of magnitude. Temperature sensor according to one of the preceding claims, characterized in that the connecting cable strands ( 5.1 . 5.2 . 5.3 . 5.4 ) are insulated by a Teflon cover.