Measuring SPRTs and PRTs with high levels of precision and low uncertainties requires the performance only found in resistance bridge systems. Such bridges also must include the critical capabilities that link resistance measurement technologies with temperature sensor measurement capabilities. This offers users the best basis for unmatched resistance thermometer metrology.
Core to primary level use of resistance bridges is the AccuBridge Direct Current Comparator (or ADCC) measurement system. Based on the principal of a transformer’s ampere turn ratios, a superior ratio measurement accuracy is specified over the full ratio range. Measurement International’s 6xxx series of temperature bridges operate at ratios where the accuracy can be easily verified.
Confidence in performance
All of the ADCC Bridges have a built in calibration routine to calibrate and verify the linearity and accuracy of the bridges. This information is stored to a file for providing the necessary documentation and history files for audits. All three bridges are stable and do not drift with time. Compliment or interchange measurements can be used to verify the ratio accuracy. Only the reference resistors need calibrating providing traceability for the measurement. No special equipment is required for calibrating the bridges.
Measurement speed and throughput
The ADCC Series of temperature bridge makes fast sub ppm measurements at a rate of ~2s with the 1st reading been displayed in ~20 seconds. All bridges are supplied with a USB interface for saving data or IEEE488 for remote computer control.
The ADCC design obsolete’s the end for AC bridges
AC bridges were designed to minimize the effect of errors caused by thermal voltages. These thermal EMFs are generated as the result of dissimilar metals and temperature gradients. These are eliminated by reversing the test stimulus in successive measurements.
This process of current reversal and averaging, together with true 4-wire resistance measurement has the effect of eliminating thermal EMFs and of ensuring an intrinsically stable zero with time and temperature. The 6242T and 6020T have the option of either ramping the currents or providing a true square wave reversal.
Both √2 and 1/√2 currents can be initiated at any time during the measurement.
Also the ADCC measurement processes inherently reject unwanted noise and provide a better quality bridge measurement, where AC bridges have difficulties in this area.
Temperature bridge measurement specifications
- Thermometers: 0.25Ω, 2.5Ω, 25.5Ω, 100Ω or any value 0.1Ω to 10kΩ
- Standard Resistor Range: 0.1Ω to 1,000Ω
- Measurement ratio range: 6020T: 0 to 4:1 6010D/6242T: 0 to 14:1
- Accuracy: 6020T:
- Reversal Rates: 2, 3, 4 to 1000 seconds
- External Standard: AC/DC or DC Standard Resistor
- Sensor current: 0.01, to 100 mA or √2 or 1√2 times any value
- Sensor current frequency: Switched DC
- Bridge balancing modes: Automatic to 0.01 ppm
- Self Check Modes: CAL (Verifies linearity of Bridge to < 0.005 ppm)
- Lead Connections: True Four Wire Connections
- USB: Stores all measurement Data
- IEEE488: Input / Output
- Measurement Time: 20/60 seconds to full balance, 2/5 seconds incremental
- balance (6020T/6010D,6242T)
- Warm up time: 5 minutes
- Operating Conditions: 10°C to 35°C, 10% to 90% RH non-condensing
- Power Requirements: 100, 120, 220, 240 VAC ±10% 50/60 Hz
All bridge accuracies are stated at the k=2 (95% confidence) level.
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