Datasheet

1550A
Vishay Micro-Measurements
www.vishaymg.com [e-mail] Document Number: 11313
54 Revision: 08-Jun-06
Strain Indicator Calibrator
FEATURES
• True Wheatstone bridge circuitry
• Simulates quarter, half &full bridge - both 120Ω/350Ω
• Three decades of push buttons
• Strain range direct reading: ±99 900µε. . .
increments of 100µε
• Transducer range: ±49.95mV/V. . . increments of
0.05mV/V
• Reversing switch for plus and minus calibration
• High precision Vishay resistors used throughout to ensure
excellent stability
• Accuracy 0.025 percent - traceable to the U.S. National
Institute of Standards and Technology
A laboratory standard for verifying the calibration of strain
and transducer indicators.
DESCRIPTION
Sound engineering and laboratory practices require that the
instrumentation used to make critical strain measurements
be periodically calibrated to verify that it is within the
manufacturer’s original specifications. Additionally, each
type of strain indicator exhibits some degree of nonlinearity,
especially for large strains during quarter-bridge operation.
Since this is the most common stress analysis application of
strain gages, it is important that the strain indicator be
calibrated in this mode. Instrumentation span should also be
checked at a number of points before each important test to
avoid inaccurate data.
The Model 1550A calibrator is a Wheatstone bridge and
generates a true change of resistance in one or two arms of
the bridge. It simulates the actual behavior of a strain gage in
both positive and negative strain.
The ‘star network’ used in certain other commercial
calibrators provides a substantially lower cost instrument
design, because component specifications are less critical,
and fewer components are required.
However, the ‘star network’ cannot simulate quarter-bridge
strain gage behavior, and cannot simulate positive strain.
Another serious problem with this circuit is that the bridge
input and output resistances change in an abnormal manner,
leading to inaccuracies in calibration under some conditions.
A calibrator based on the Wheatstone bridge principle
requires stable components. A total of 66 ultra-stable Vishay
precision resistors are used in the Model 1550A calibrator to
provide the stability, repeatability, accuracy and incremental
steps required in a laboratory standards instrument.
WHEATSTONE BRIDGE / STAR NETWORK