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Environmental Protection

Strain gage performance is easily degraded by the effects of moisture, chemical attack, or mechanical damage.  As a result, gages require varying degrees of protection according to the severity of the environment in which they must operate.   Strain gages should be covered with a suitable coating as soon as possible after the installation because the coating will protect the strain gages as well as the adhesive layer. 

 

The M-Coat Protective Coatings have been formulated specifically for use in protecting strain gage installations from destabilizing and damaging environmental conditions.  The range of materials offered will cover a majority of gage protection requirements.  In the benign atmosphere of an air-conditioned laboratory, for instance, a single layer of the M-Coat A will ordinarily provide sufficient protection against the humidity, fingerprints, and other degrading contaminants.  When the strain gage must operate in a more severe environment, alternate coatings or combinations of coatings can be employed and you will find these coatings within this section of our web site. 

 

The following Selection Chart is intended to be preliminary guide for a variety of typical environments.  The effectiveness of these materials and procedures have been experimentally validated on numerous occasions.  However, application technique is also an important factor of any strain gage protection system.  It is therefor good practice, particularly in the case of long-term installations, to verify by test that the coating system performs as required.  

 

Coating Selection Guide

 

ENVIRONMENT   PREFERRED   ALTERNATE
         
 > Typical Laboratory        

 

50%, or lower, relative humidity

 

  M-Coat A   M-Coat C, or M-Coat D, or M-Coat F, or GageKote #1
 > Field Applications        

 

Outdoor installations, shield from rain or snow

 

  M-Coat F, or Barrier E   M-Coat JA or Gagekote #5
 > High Humidity, Water Splash        

 

Laboratory and field applications under damp or wet conditions

 

  Short Term:3140-RTV Long Term: M-Coat W-1 Wax   Short Term:3145-RTV Long Term: M-Coat F
 > Water Immersion        

 

Short-term, fresh water or salt water

 

  Etched Teflon + M-Coat B (on vinyl insulated leadwires) + M-Coat JA   M-Coat W-1 Wax or Barrier WD

Long-term, fresh water

 

  M-Coat W-1 Wax or Barrier WD   M-Coat F or Barrier E

Long-term, salt water

 

  M-Coat W-1 Wax combined with M-Coat JA   None

High-pressure water

 

  M-Coat W-1 Wax, M-Coat JA, M-Coat FA-2, followed by M-Coat B   M-Coat F, or M-Coat W-1 Wax for short-term
 > Steam        

 

+212 F (+100 C), long term installation

 

  Hermetically sealed metal cap, conduit for leadwires   None
 > Concrete Surfaces        

 

Long-term

 

  M-Coat JA or Gagekote #5   M-Bond GA-61 to seal the concrete surface
 > Oils and Fuel        

 

Commerical oils, to +180 F(+80 C), gasoline, and kerosene 

 

  M-Coat JA, or M-Coat D + two or three layers of M-Coat B   3145-RTV + M-Coat B

 

Synthetic oils, to +200 F (+95C)

 

  Two or three layers of M-Bond 43B   M-Bond GA-61
 > High Temperature Air        

 

To +500 F (+260 C), with good mechanical protection

 

  Short Term: M-Bond GA-61 or Epoxylite #813   3145-RTV

Above +500 F( +260 C) when using free filament gages

 

  Gagekote #11   None

 

 

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