Abstract
This paper describes a validation of a combinatorial calibration technique based calibration procedure for strain-gauge amplifier calibration. The deviation between two strain-gauge amplifiers at calibration using the combinatorial technique is compared to the deviation between the same two amplifiers at calibration on a force calibration machine as a transducer-amplifier chain under unchanged conditions, serving as an amplifier linearity comparator. This enables the validation to be confirmed with a suitable expanded measurement uncertainty of 3 nV/V.
Highlights
IntroductionThe calibration of strain-gauge amplifiers (bridge amplifiers) used in measuring chains for force, torque and pressure measurements is potentially subjected to large measurement uncertainties when calibrated with traditional voltage ratio (mV/V) standards – bridge standards
The calibration of strain-gauge amplifiers used in measuring chains for force, torque and pressure measurements is potentially subjected to large measurement uncertainties when calibrated with traditional voltage ratio standards – bridge standards
In previous publication [1] we presented an alternative calibration procedure which reduces the calibration uncertainty to a more acceptable level by calibrating the bridge amplifier at a single reference point with a traditional bridge standard and performing linearity evaluation between the relative 0 mV/V and the calibrated reference point using the ZAG LinCheck combinatorial system [2]
Summary
The calibration of strain-gauge amplifiers (bridge amplifiers) used in measuring chains for force, torque and pressure measurements is potentially subjected to large measurement uncertainties when calibrated with traditional voltage ratio (mV/V) standards – bridge standards. In previous publication [1] we presented an alternative calibration procedure which reduces the calibration uncertainty to a more acceptable level by calibrating the bridge amplifier at a single reference point with a traditional bridge standard and performing linearity evaluation between the relative 0 mV/V and the calibrated reference point using the ZAG LinCheck combinatorial system [2] This procedure has already been offered to customers as a calibration service within ISO/IEC 17025 accredited scope with an expanded relative measurement uncertainty of 3 nV/V or 0.003 % (whichever is higher) in the range from 0.05 mV/V to 2.5 mV/V for positive and negative voltage ratios, covering the typically required range, Figure 1. Lower uncertainties for linearity evaluation were not possible until recently, when a cascaded inductive voltage divider setup was presented for bridge amplifier linearity evaluation, achieving expanded uncertainty of 2 nV/V [5] and offering 107 steps within the ±5 mV/V range
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