The quality of a measurement made with a strain gauge essentially depends on the type of installation and design of the measuring point. A thorough preparation of the installation surface, correct connection, and protective covering are important factors for problem-free results.
Immediately after completing the installation of a strain gauge, the measuring point on the surface of the component must be carefully protected from environmental influences by a covering material. In the selection of the covering material, the following factors are to be considered:
The measuring point must be covered directly after installation. Only the covering materials recommended by strain gauge manufacturers should be used to protect the strain gauge and adhesive layer.
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Viscous putty Ord. no.: 1-AK22 |
Aluminum foil with kneading cmpd Ord. no.: 1-ABM75 |
Nitrile rubber Ord. no.: 1-NG120 |
Transparent Silicone rubber Ord. no.: 1-SG250 |
Polyurethane paint Ord. no.: 1-PU140 |
Transparent silicone resin Ord. no.: 1-SL450 |
Temperature range of resistance in air in °C | -30°C...+75°C [-22°F ... +167°F] | -196°C … +75°C [-321°F … +167°F] | -40°C ... +120°C [-40°F … +248°F] | -70°C … +200°C [-94°F … +392°F] | -40°C … +140°C [-40°F … +284°F] | -50°C … +450°C [-58°F … +842°F] |
Package contents | 1 kg | 11 pcs. 205 mm x 100 mm | Tube with 150 g | Tube with 85 g | 3 bottles each with 30 ml | 3 bottles with 25 g each |
One Package sufficient for approx. | 30 SG | 200 SG | 200 SG | 20 SG | 250 SG | 90 SG |
Application method | Kneading by hand | Pressing on by hand | Application from tube | Application from tube | Brush application | Brush application |
Curing conditions | – | – | Air drying at room temperature | Room temperature | Room temperature … + 80°C | In temperature levels from 95°C - 315°C |
Storage life at room temperature | 2 years | 2 years | 15 months | 6 months | 9 months | 6 months |
Ingredients | Viscous, kneadable, sticky putty | 0.05 mm thick aluminum foil coated with 3 mm thick kneading cmpd. | Brown, solvent one-component silicone rubber | Transparent, solvent free one-component silicone rubber | Solvent-containing one component polyurethane paint | Transparent, solvent-containing silicone resin |
Weather | yes | yes | yes | yes | yes | yes |
Water:
Pressurized water Condensation Tropical climate Water vapor | yes - - - no | yes - - - condtl. | yes - - - no | yes - - - no | yes - yes yes no | yes - - - no |
Oil:
Engine oil (RT/70°C) Mineral oil (RT/70°C) Hydraulic oil (RT/70°C) | no - - - | no - - - | yes yes yes yes | yes - - - | yes - - - | - - - - |
Greases | - | - | - | - | yes | - |
Solvents in general | no | condtl. | condtl. | no | - | condtl. |
Fuels:
Gasoline Kerosene | no no – | no no – | yes yes yes | no no – | – – – | – – – |
Aromatic / Aliphatic mixtures | – | – | condtl. | – | – | – |
Aromatics:
Benzene Toluene Xylene | no – no no | no – no no | condtl. no condtl. condtl. | no – no no | no – – no | no – no no |
Chlorinated solvents:
Dichloromethane Carbon tetrachloride Perchloroethylene 1.2-Dichloroethane o-Dichlorobenzene | no no – – – – | no no – – – – | no no no no no no | no no – – – – | no no – – – – | no no – – – – |
Alcohols:
Ethyl alcohol Methyl glycol Butyl alcohol Isopropyl alcohol Ethylene glycol | condtl. condtl. – – – – | yes yes – – – – | condtl. condtl. no condtl. condtl. yes | condtl. condtl. – – – – | no no – – – – | yes yes – – – – |
Ketones:
Acetone Methyl ethyl ketone | condtl. condtl. no | condtl. condtl. no | no no no | no no no | no no no | condtl. yes condtl. |
Terpenes:
Dipentenes Turpentine | – – – | – – – | condtl. condtl. yes | – – – | – – – | – – – |
Acids:
Hydrochloric acid conc. Sulfuric acid 50 % Acetic acid 50 % Nitric acid 50 % Oleic acid conc. Lactic acid conc. Air containing acids | no no no no no – – – | condtl.(1)
– – – – – – – | condtl. condtl. – no no – condtl. – | yes yes yes yes yes – – – | no no no no no – – yes | yes yes yes condtl. yes – – – |
Alkalis:
Sodium hydroxide 10 % Potassium hydroxide 10 % Ammonia 28 % Air containing alkalis | condtl. condtl. – – – | condtl.(1)
– – – – | condtl. no no condtl. – | no no – – – | condtl. no – – yes | yes yes – – – |
Liquefied gases (excluding oxygen) | - | - | yes | - | - | - |
UV resistance | yes | yes | yes | yes | yes | - |
(1) Up to 5 % (destruction of aluminum foil!).
condtl. = Conditionally resistant (at least 10 days at RT)
A single covering agent is often not enough for sufficient measuring point protection. Examples for combinations of several agents are given by the AK22 and ABM75 (plastic mass plus aluminum foil).
Multi-layer protection is absolutely essential for indefinable media such as seawater. The top layers that do not come into contact with the strain gauge can be made of other materials from those mentioned here, e.g., asphalt. These materials must, however, not dissolve or chemically change the underlying layers. Apart from that, their electrical insulation resistance is not relevant.
Absolute protection for an unlimited period of time is only possible with a hermetically sealed metallic enclosure. This type of protection can be implemented for standard commercial transducers. However, hermetically enclosing strain gauges for experimental purposes can only be implemented with extremely high overhead or not at all.
This will bring together HBM, Brüel & Kjær, nCode, ReliaSoft, and Discom brands, helping you innovate faster for a cleaner, healthier, and more productive world.
This will bring together HBM, Brüel & Kjær, nCode, ReliaSoft, and Discom brands, helping you innovate faster for a cleaner, healthier, and more productive world.
This will bring together HBM, Brüel & Kjær, nCode, ReliaSoft, and Discom brands, helping you innovate faster for a cleaner, healthier, and more productive world.
This will bring together HBM, Brüel & Kjær, nCode, ReliaSoft, and Discom brands, helping you innovate faster for a cleaner, healthier, and more productive world.
This will bring together HBM, Brüel & Kjær, nCode, ReliaSoft, and Discom brands, helping you innovate faster for a cleaner, healthier, and more productive world.