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Our 1.5LTE-1000MM Low Thermal Expansion Length Reference Bar provides a stable length for use during laser tracker or scanner jobs.  Its unique design uses specially designed end caps which counteract length changes in the bar due to thermal growth.  This provides a virtually constant length through a wide working temperature range.  Testing has shown that the 1.5LTE-1000MM has a thermal stability 40% better than invar.

The target holders on each end are positioned off-axis, and allow 360° rotation of the SMR, adding application flexibility.  You can place the reference bar in relevant positions in the measurement volume for scaling, consistency, and stability checks during a job.  Or, you can align the bar with your tracker's beam, and use the interferometer alone to compare against the bar's length (with no Az or El encoder contributions to error)

The 1.5LTE-1000MM consists of a single length of invar tubing with two permanently mounted aluminum end caps, each with a 1.5INV magnetic SMR nest (SMRs not included). 

This item is available in a 1 meter length (target center to target center).  Actual length will be within ±1/32" (0.79mm) of  1 meter, but our calibration laboratory will provide a certificate with NIST-traceability indicating the actual length of the assembly within ±0.0001" (0.003mm). Patent pending.
 

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How does it work?

The LTE bar maintains a very low coefficient of expansion by virtue of its unique design.  Invar, already a very thermally stable material, is used as the main component.  Aluminum end caps are permanently mounted to the ends of the invar bar, with an SMR target nest situated inboard from the end of the bar.  The bar and the end cap both expand/contract with temperature increases/decreases.  However, when the bar lengthens and moves the target nests further apart, the end caps also expand, moving the target nests back together again.  The location of the nests is precisely calculated so that the change in invar and changes in the end cap lengths tend to cancel each other out.