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Tribrach Basics: How Tribrachs Influence Measurement Accuracy

Leica Tribrach

Almost every total station, GNSS antenna, laser scanner, or laser plummet is mounted and secured with a tribrach. Tribrachs are an integral part of surveying procedures and are important to the overall accuracy of your measurements.

Special applications like forced traverses and other applications based on pillar setups cannot be performed without using a forced centering system provided by tribrachs.

Torsional rigidity (hysteresis) – the accuracy with which a tribrach returns to its starting position once the instrument has stopped moving – is the most important criterion of a tribrach and is constantly controlled and tested during production. It is critical that your instrument remains secured in the tribrach throughout the entire measuring process.

You should rely on the initial orientation of the tribrach to achieve accurate horizontal (and vertical) angle measurements to guarantee the instrument’s overall orientation. The below figure illustrates an example of hysteresis.

Every instrument setup must undergo a leveling process in order to guarantee the operation of your compensator and to refer your measurement to the horizon, respectively. The remaining tilt after tripod setup is usually compensated through your tribrach’s footscrews.

tribrach hysteresis

To achieve the highest measurement accuracy:

  • Use tribrachs with adequate specifications to fulfill required measurement accuracy
  • Use a tribrach model that provides required features (like an optical plummet, for example)
  • Ensure periodic maintenance

For additional guidance in using or choosing a tribrach, please contact us.