A self-calibrating instrument current transformer

This paper presents the development of a self-calibrating transformer for using as a primary standard in the Uruguayan National Metrology Institute. Nominal ratios go from 5 A/5 A to 2000 A/5 A. The primary windings are divided in groups to allow different ratios by changing their combinations in series–parallel connections, so that the errors remain the same. In ratio 1 (5 A/5 A) the transformer can be calibrated without any external standard, and a step-up procedure is proposed. Low errors are achieved by using a modified zero-flux technique.     

Shielded electronic current transformer

A current transformer with nominal ratio 10 A to 10 mA, intended for low-frequency applications, was developed. It includes an electronic device to reduce the magnetizing current, and a continuous shield in the secondary winding (coaxial cable) in order to eliminate the effect of stray capacitances. No guard-source is connected to the shield. It is proposed in this paper to leave the cable-shield-potential floating. This leads to high-accuracy results (ratio errors and phase-displacements in the order of few parts in 10/sup 6/ from 50 Hz to 1 kHz).     

Electronic error reduction system for clamp-on probes and measuringcurrent transformers

An original electronic device for compensating ratio and phase-displacement errors, of measuring current transformers and clamp-on probes, is proposed. It is intended for low-frequency applications (power frequency and its harmonic components), where the magnetizing current is the main cause of measuring errors. This system reduces the magnetic flux in the transformer core, reducing in this way the magnetizing current. The proposed system even reduces the influence of the error produced by the variation of the burden connected to the secondary winding. Large values of burden can be used without effects on the transformer measuring errors. This device can be directly applied to conventional current transformers, connecting the device to the secondary terminals. It is not necessary to use any auxiliary winding or auxiliary core, or any modification of those transformers     

Electronic based high-voltage measuring transformers

A new electronic system to assist high-voltage measuring transformers is proposed. This system compensates the voltage drops in the series impedances of the transformer, which are the main cause of errors at power frequency. The nonlinear behavior of the magnetizing branch has no influence on the results. The proposed compensator also reduces the influence of the burden impedance on the transformer errors. Any auxiliary winding or core is not necessary so that conventional units can be compensated     

Electronic compensation of inductive voltage dividers and standardvoltage transformers

A new compensating system is proposed to reduce the ratio error and the phase error of inductive voltage dividers and standard voltage transformers, operating at no load. An electronic amplifier reduces the input current, which is the main cause of error in low-frequency applications, while at the same time the input impedance is greatly increased     

Validation of a hand-held lactate device in determination of blood lactate in critically injured patients

OBJECTIVES: Admission blood lactate is an accurate predictor of injury severity and mortality in trauma patients. The purpose of this study was to evaluate a portable lactate analyzer in a clinical setting by patient care staff. DESIGN: A prospective, single-operator control solution and patient sample study, using two test devices and a reference device. SETTING: An urban Level I trauma center. PATIENTS: A convenience sample of 47 trauma patients. INTERVENTIONS: Intra-assay precision was demonstrated by performance of consecutive analyses of two lactate control solutions (high and low lactate control concentrations) by medical students and physicians. Split sample, simultaneous testing of the portable lactate analyzer was then performed on 66 whole blood specimens from a convenience sample of 47 trauma patients admitted to an urban Level 1 trauma center over 4 mos. Samples were tested simultaneously tested on two portable lactate analyzers and a reference instrument. MEASUREMENTS AND MAIN RESULTS: Acceptable intra-assay precision was achieved. Regression analysis for two test instruments demonstrated a slope of 0.920, an intercept of 0.323, an r2 of .982, and an SEM of 0.496. Regression analysis for test instrument "A" vs. the reference instrument showed a slope of 0.861, an intercept of 0.209, an r2 of .977, and an SEM of 0.598. Regression analysis for test instrument "B" vs. the reference instrument demonstrated a slope of 0.929, an intercept of -0.095, an r2 of .983, and an SEM of 0.506. CONCLUSIONS: Good correlation with a low SEM was obtained over a wide range of clinically relevant lactate values. Use of point of care lactate analysis will decrease analytic time, making an important diagnostic parameter immediately available in the critical care setting.