Selection and Overview of Covering Materials

The quality of a measurement with strain gauges depends essentially 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 complete installation of the SG, the measuring point on the surface of the component must be carefully protected from environmental influences by a covering material.

Selecting the Covering Material

When selecting the covering material, important considerations should be taken:

  • environmental conditions during the measurement
  • duration of the measurement
  • required service life
  • measuring accuracy
  • measuring object must not be stiffened in an impermissible manner
  • material that comes in contact with the measuring point, including the connection cable, must also have a very high insulation resistance and must not be capable of triggering any chemical reactions or corrosion.

Condition of measuring point

The measuring point must be in flawless condition before a sufficiently large cover is spread on it, meaning it is free of dirt, moisture, perspiration from hands, and solder residue. All cable entries must also be very carefully sealed off. In addition, only covering materials recommended by SG manufacturers may be used to protect the SG and adhesive layer.

Commonly used covering materials include:

  • a permanently plastic putty with or without diffusion barrier (AK 22 and ABM 75), which is resistant against oil and gasoline,
  • air-drying nitrile rubber (NG 150), and
  • transparent, solvent-free silicone rubber (SG250) to protect against moisture and water.

Polyurethane lacquer (PU140) is ideally suited for several purposes, including as a primer layer for a multi-coat covering.

Click here to get to HBM's range of covering materials

Absolute protection for an unlimited period of time?

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 gages for experimental purposes can only be implemented with extremely high overhead or not at all.

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