DE7136616U - Strain gauges of variable electrical resistance - Google Patents

Description

Patent attorney

Dr. J, Staff9ns
8032 Lochham / Mffcn., Mozartstr. 24

Tel. (0811) 372551

September 27, 1971 A-104

Reuter Maschinen- und Werkzeugbau GmbH 2844 lemfördj, Hageweder Strasse 219

Strain gauges of variable electrical resistance »e-ae — a — ooag-

The invention relates to a strain gauge of variable electrical resistance for relatively large expansions in the millimeter and centimeter range, which electrically conductive particles, especially in the form of soot or graphite, as well as highly elastic material, especially highly elastic silicone and polyurethane elasollers, contains as essential components.

There are already strain the type ^ l form mentioned known a strip of rubber, in which soot particles embedded. US Pat. No. 2,492,429 and British Pat. No. 720,602 should be mentioned as prior art.

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With such a "known measuring strip made of mixtures of rubber and soot, the soot chains are grounded, and the elec-

torn or destroyed, so that "in a subsequent Relaxation of the chess strip no reproducible Value is achievable, with the fact that the strip has an irreversible leaning and is strong is temperature dependent. The well-known hot strips are therefore if at all, only suitable for a single measurement process.

The object of the invention is to create a strain gauge which is improved in comparison and which, when stretched has reproducible resistance values within a permissible range, essentially temperature-independent and can be used for a variety of measurement processes. This is achieved through a well-known one Structure corresponding to an elastic textile cord with elastic warp thread consisting of the highly stretchable material as well as inelastic weft threads interwoven with it, in which only the weft threads with one the electrical conductive particles containing layer are coated.

Since the strain gauge according to the invention only the weft threads are coated can tear apart or a destruction of the part of the electrically conductive Particle-formed chains do not take place. Rather, when the elastic warp threads stretch, the originally, parallel to each other, in line approach weft threads located with each other more or less largely out of contact, so that in a white Range results in a proportional increase in resistance, which, however, after letting the warp thread relax

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agitation of the weft threads is returned to the original value. Because the warp thread "when stretching are subject to a cross-control, the in the relaxed state of the warp thread under slight pre-tension weft threads are slightly loosened so that In any case, overloading of the inelastic weft threads cannot occur during the stretching process. Self when the warp threads begin to flow in the tensioned state due to unfavorable rheological properties, The weft thread spacing is not affected. The rheological properties of the warp thread, the temperature coefficient the electrical resistance and the modulus of elasticity have only a very minor effect the end.

A strain gauge according to the invention can be particularly simple and cheap to manufacture if according to a particular embodiment of a method for manufacturing a strain gauge according to the invention of a ready-made, non-electrically conductive 'light containing textile cord is assumed. According to this In a process, the textile braid is electrically connected to a die conductive particles as well as a binder-containing dispersion well soaked and then during the subsequent The drying process is periodically stretched to a certain length and relaxed until the binding agent hardens calmly. By such a process it is achieved that the dried or hardened binder from the warp threads due to the periodic expansion and relaxation of which drops while it adheres to the weft threads, so that im The result, in turn, is a strain gauge according to the invention in which only the weft threads are electrically connected conductive particles are coated.

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The invention is explained in more detail below with reference to the drawing. Show it:

Fig. 1 shows an embodiment of a according to the invention Strain gauge in the relaxed state (solid lines) or in the tensioned state (dashed lines), each in a perspective top view,

Pig. 2 shows a section from the strain gauge according to Pig. 1 in greatly enlarged Top view,

Pig. 3 the characteristic of the strain gauge according to Pig. 1 in a diagram with a stripe enlru: ^ of 80 mm and a stripe width of 12 mm.

The one in Pig. 1 is designed for relatively large expansions in the millimeter and centimeter range and comprises an elastic textile cord 1, which is coated with precious metals in a manner to be described below with electrically conductive particles, in particular in the form of carbon black or graphite or precious metals other metals or other materials, as well as an electrode 2, 3 at each end. The electrodes 2, 3 are designed as clamps for the firm mechanical anchoring of the warp and weft threads forming the textile braid. The electrodes 2, 3 are provided at their outer ends with a projection 4 and 5 , respectively, in order to connect a connection in a measuring

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Stromiareis heraxellen to Icönnen. In the present embodiment the electrodes 2, 3 are connected to the 'üextilband 1 by means of rivets b, 7, whereby through the Rivets 6, 7 at the same time an expansion limiter thread 8 essentially inelastic. limaterial clamped is held. This strain limiting thread 8 is at in a relaxed state of the textile cord 1 in a slack, in a relaxed state illustrated in solid lines maximum permissible elongation of the textile cord 1, however, in a tightly stretched state. In a relaxed state the textile cord 1 has the strain gauge a resistance value R1, while the stretching corresponding to a maximum expansion path S a dementspre-; sets a higher resistance value R2.

From 3? Ig. 2 results in the structure known per se

ι Textile cord 1 made of warp thread 8 and weft threads 9

\ Fig. 2 illustrates a twill weave. The warp thread

• they are preferably made of monofilament, highly elastic

! Silicone or polyurethane threads, while the weft threads 9

\ from a practically inelastic compared to the warp threads 8

Shem material exist, only the weft threads 9 are covered with a conductive layer containing carbon black particles, which is described in Pig. 2 by a dark tint of the weft threads 9 is indicated. The warp threads can also be made of high quality rubber.

Pig. 2 shows the state of the textile tape 1 in the stretched state State of the warp threads 8, in this stretched state the weft threads 9, which in the relaxed state in Line contact against each other, lie slightly loosened on the warp thread 8 and the line contact between the weft is more or less canceled.

For the production of a strain gauge according to the invention two different methods can be used.

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The first exemplary embodiment of an inventive The process starts with the ron fabrics, i.e. the warp thread S and the weft threads 9 from. The weft threads 9 are before weaving with the warp threads 8 with a die Treated soot particles and a binder containing dispersion and dried. Which in this way Weft threads 9 provided with a carbon black layer are then woven with the warp threads 8.

According to the second embodiment of an inventive The procedure is based on a ready-made textile heald (in common parlance also with Rubber band), which is impregnated with a dispersion containing carbon black particles. During that the following drying process until the binding agent has hardened, the textile cord is periodically adjusted to a certain level Length stretched and allowed to relax, with the stretching and relaxing periods each about three Seconds. During the drying process, this leads to the binding agent and the binding agent flaking off Soot particles from the warp threads 8, as these are subjected to constant stretching and relaxation, while a layer of soot can form on the weft threads 9, and it was such that neighboring Weft threads 9 is reliably prevented. For treating the textile cord 1, preference is given to using it an aqueous plastic dispersion with soot particles, the viscosity of which is less than 50 centipoise, and one for example from a commercially available aqueous 25% carbon black dispersion and an aqueous $ 50 plastic dispersion based on a copolymer made of acrylic, vinyl acetate and acrylic

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acid produces. The viscosity is preferably
such a dispersion 20 centipoise.

Pig. 3 gives the resistance characteristics for a textile strand of 80 mm length and T2 mm width again, whereby the electrical expansion resistance in kilo-ohms as a puncture the expansion path is given in millimeters. One obtains within a range of about 20 kilo-ohms here an almost strictly linear range of characteristics, while with additional stretching, the stretching resistance strives for a limit value.

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Claims (1)

Ρ — a— I ΰ Ii ~ ϋ epnsprüche ^ Strain gauges of variable electrical Resistance / for relatively large expansions in the millimeter and centimeter range, which is electrical conductive particles, in particular in the form of carbon black or graphite, and highly ductile material, in particular Contains silicone or polyurethane elastomers, labeled by a structure known per se corresponding to an elastic textile cord (1) mix the highly stretchable material existing elastic warp threads (8) and herewith woven inelastic Weft threads (9), in which only the weft threads (9) with one containing the electrically conductive particles Layer are coated. S according to Claim 1, characterized in that the weft threads are tied with the warp threads before being woven a dispersion containing the electrically conductive particles s-0w * ie a binder. 3. A method for producing a strain gauge according to claim 1, characterized in that a ready-made,! its electrically conductive particles containing ^ textile braid with one that electrically containing conductive particles and a binder Soaked in dispersion and during the subsequent drying process until the binder hardens Periodically stretched and released to a certain length - Sdutaspr. 2i Ά \, sheet ^ deleted 7136616 06/03/76