DE2842190C2 - Strain gauges in thick film technology - Google Patents

Description

the same resistance value is 3 to 12 percent by weight Provide graphite and 0 to 30 percent by weight silver. To adjust the viscosity were found the use of 10 to 30 percent by weight «terpineol and from 5 to 10 percent by weight ethyl cellulose with about 60 percent benzyl alcohol as particularly favorable. With the specified formulation, on the one hand, a high K value and, on the other hand, a low temperature dependency of the strain gauge can be determined. The resistance value is essentially influenced by the pigmentation. A high proportion of silver is reduced the resistance value while made up by the mere use of graphite instead of a mixture Graphite and silver the resistance value can be increased. Depending on the proportion and composition of the rest The thickening agents - terpineol and ethyl cellulose are to be added to the components.

The coated base material is then dried, fired and cured. The known treatment methods of thick-film technology can be used here. Favorable results have been achieved in Versucn at a drying period of about 10 minutes at about 100 ° C Firing is advantageously at 300 ⁰ C hold temperature and low air flow. The firing conditions can be varied over a wide range depending on the layer. The burning time can be between 30 and 90 minutes, the holding temperature can be varied between 200 ° C and 350 ° C. Curing is in about 20 hours at a temperature of about 200 ° C. Due to the possible choice of relatively low firing temperatures i "* it possible to coat elastic base material without Zwischenbclag" tirekt 7 ". Therefore As a base material, optionally, the The test object itself can be used. The duration and duration of the heat treatment make it possible to influence the resistance value of the layer. After hardening, the now completed strain gauge can be contacted with almost all known conductive layers. It can therefore be inserted into both thin and thick layer circuits as well as with conductive adhesives or pressure contacts.

The use of non-conductive substances with conductive inclusions is a substantial increase the sensitivity and thus the / C factor. This is done by changing the specific Resistance when changing the conductor length

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Claims (2)

Patent claims: 1. Strain gauges for measuring mechanical deformation due to changes in electrical deformation Resistance - a base material which is subjected to mechanical deformation ' Resistance layer, which contains graphite and / or silver as electrically conductive particles, thereby characterized in that the resistance layer is applied in the form of a paste, apart from the electrically conductive particles as a carrier material for setting one for processing suitable consistency isophthalic acid with styrene. Λ-terpineol and ethyl cellulose with benzyl alcohol contains. 2. Strain gauge according to claim 1, characterized in that the to be applied to the base material paste 25-48% by weight 10-30% by weight
5-10% by weight 3-12% by weight
0-30% by weight Isophthalic acid with
20% styrene,
dr-terpineol,
Ethyl cellulose with
approx. 60% benzyl alcohol,
Graphite as well
Contains silver. The invention relates to a strain gauge for measuring mechanical deformation due to change the electrical resistance according to the preamble of claim 1. Strain gauges have long been known and in the Literature has already been described in detail. In F. X. Eder, Modern Measurement Methods in Physics, VEB Verlag der Wissenschaften, Berlin 1968, part 1, page 329 it is proposed to produce strain gauges from the thinnest manganine wire, which meanders between thin paper is glued as the base material. It is also proposed on an acrylic or phenyl resin base embed a measuring wire made of constants. As explained in detail in this reference, the sensitivity of the strain gauge is determined by the so-called K-factor. With the usual With strain gauges, the K-factor is on the order of two. Furthermore, it is already known to take place Gluing measuring wires to the base material, evaporating thin metal films onto a base material (DE-OS 27 41 055). From US-PS 24 92 429 it is known to produce a strain gauge graphite as Resistance material on an elastic plastic base material to be applied, the thickness of the graphite layer only due to the electrical power to be achieved Resistance is defined. In order to apply the graphite to the base material, it is in a liquid suspended, which is able to loosen the flexible plastic material, in order to adhere in this way To achieve graphite on the base material. The base material is then dipped into the suspension several times and dried in between to achieve a sufficient thickness of the graphite layer. This is a very cumbersome one and certainly a process that is difficult to reproduce. All known strain gauges there is also the disadvantage that their sensitivity is not significantly higher than the / f factor of two Furthermore, its meander-like design is fixed, because only in this way can it be higher Resistance value can be generated. If the resistor is vapor-deposited onto the base material, either to make special masks or to carry out special photo masking and etching processes. The object of the present invention is to develop a strain gauge of the type mentioned, in which the resistive layer in a single ίο Work step in the required thickness preferably hn screen printing process can be applied to the base material in a simple manner, and the ii values has, which are between 4 and 10 and thus has a much higher sensitivity than them is known so far, so that downstream measuring devices greatly simplify or the resolution of the Measurement can be increased. This problem is solved with the characterizing features of claim 1. Strain gauges made with the specified thick-film paste show very high K values and, in addition, only a low temperature dependence of the resistance, and excellent adhesion is achieved on almost any surface. By varying the composition of the paste and its geometric dimensions on the base material; 1 a large resistance variation is possible. As a result of the greater layer thickness, differences in the surface roughness of the base material do not play a role, which is particularly noticeable in the case of strain gauges with a vapor-deposited conductive layer. Resistors of the aforementioned type can also easily be contacted in the most varied of ways.
It is also advantageous that the thick-film paste can be applied to the base material in a simple manner by means of screen printing. Once the thick-film paste has been applied, it can be dried, burned and hardened. The finished strain gauge can then be calibrated by scratching with a laser or by sandblasting. The thick film paste is applied to a base material, for example a plastic or a metal such as spring steel or spring bronze with intermediate insulation is applied Screen printing process. It is also possible to stamp, roll or spray the thick film paste. The thick-film paste to be applied consists of an organic carrier material to impart Adhesion and internal cohesion, from a pigmentation with electrically conductive particles and from ei-η em adjusting agent to adjust the viscosity. Depending on the task and application, these are three Ingredients can be combined with one another in order to ensure that the paste is easy to process and that it adheres well the corresponding base material and a suitable conductivity of the measuring resistor. try have shown that the organic carrier material is isophthalic acid with styrene, ground for pigmentation Graphite and silver with a particle size of about 1 micrometer and as an adjusting agent for adjusting the so viscosity a-terpineo! and ethyl cellulose with benzyl alcohol is to be used. The composition of the substances depends on the intended use. Tests have shown that particularly good results are then achieved. when 25 to 48 percent by weight Isophthalic acid with approx. 20% styrene can be used as the basic organic substance. For pigmentation with electrically conductive particles, ground graphite and silver are particularly suitable, depending on the