The Vector Gauge Length is Wrong and Keeps Changing

Description of the Issue

Each time Vector enters measuring, Vector automatically sets the precise gauge, or gauges. The precise gauge length is reported in the Interface App.

• The gauge length changes every time.

• When using speckles the gauge length does not match the Target Gauge Length.

• The Gauge Length differs by too much.

Gauge length variation is not a fault.

Rationale

Vector automatically positions the gauge algorithmically using user preferences and presented markings. The extensometer gauge length can vary slightly between scans, irrespective of the presented markings, based on the instantaneous appearance.

Every measurement instance relates directly to that positioned gauge, not to any specific feature on the specimen. As such, the outputted strain and extension values are not affected by extensometer gauge length error.

With traditional contacting extensometers there is also a variation in gauge length between measurements. However, for contacting extensometers the true gauge length is not known. Therefore, a nominal length must be assumed, an extensometer gauge length error must be accepted, and the variability of the gauge length from a nominal must be assessed at calibration.

Solutions

• When testing using strain from Vector, the nominal gauge length is sufficient for record keeping and Vector will increase the efficiency and productivity of testing.

  Recording the precise gauge length is not required to produce accurate results.

• When testing using extension from Vector, record the precise gauge length used during the test for best results.

  The additional information of a precise gauge length provided in the Interface App is beneficial in producing a test or verification of higher quality.

  For example, deploying the precise listed gauge length for calculating elongation at fracture improves the repeatability and accuracy of the batch.

Information - Extensometer as an extension device

Vector outputs strain directly.

Switching to strain removes the requirement to input the gauge length and extension to compute strain.

• When calibrating, record the precise gauge length used during the test.

  Vector may be outputting strain, but the extensometer gauge length must be known to compute the equivalent strain of the verification device displacement.