Model 370 AC Resistance Bridge Model 370 AC Resistance Bridge Resistance measurement ranges from 2 mΩ to 2 MΩ 21 excitation levels from 3.16 pA to 31.6 mA Displays real-time sensor excitation power One sensor input (up to 8 or 16 with scanner) PID temperature control IEEE-488 and RS-232C interfaces, alarms, relays, and analog outputs Unique noise-reduction elements: Patented* current source preserves common mode noise rejection Optically isolated measurement electronics eliminates the potential for ground loops Model 3716 scanner is optimized for low DC bias current Model 3716L scanner is optimized for low noise 8-channel preamp/scanner: Model 3708 scanner is optimized for ultra-low noise AC resistance measurements * .S. Patent #6,501,255, Dec., 2002, “Differential current source with active U common mode reduction,” Lake Shore Cryotronics, Inc. Lake Shore Cryotronics, Inc. 77 with Temperature Control Resistance Measurement With the same attention to precision and detail that helped Lake Shore become the world leader in subkelvin temperature sensors, the Model 370 AC resistance bridge combines a full range of design strategies which optimize resolution and minimize measurement uncertainty in low power resistance measurement. Two 16-channel scanners: www.lakeshore.com Instruments Introduction The Model 370 AC resistance bridge is designed for precise, accurate, low noise, low excitation power AC resistance measurements. Its primary application is the measurement of resistive materials in cryogenic environments from 20 mK to 1 K. Fully integrated, the Model 370 includes features to reduce and control noise at every step of the resistance measurement process. A unique, patented, matched impedance current source and active common mode reduction circuitry minimize noise and self-heating errors. With up to 16 channels, IEEE‑488 and serial interfaces, and closed loop temperature control, the Model 370 offers seamless integration with existing cryogenic systems and is the most complete package on the market today. Used with Lake Shore calibrated subkelvin resistance temperature sensors, it not only measures and displays, but also controls temperature for dilution refrigerators and other cryogenic systems. Model 370 Features The Model 370 uses 4-lead AC measurement for the best possible accuracy with the lowest possible excitation current. AC coupling at each amplifier stage reduces offsets for higher gain and greater sensitivity than DC techniques allow. Phase sensitive detection, an AC filtering technique used in lock-in amplifiers, reclaims small measurement signals from environmental noise. A low excitation frequency of 13.7 Hz reduces the effect of lead capacitance on measurement. These features, in conjunction with innovative lead shielding and active noise reduction circuitry, significantly reduce measurement noise and resistor self-heating. (614) 891-2244 fax: (614) 818-1600 e-mail: [email protected]

78 Instruments Model 370 AC Resistance Bridge The Model 370 current excitation source provides stable, reliable, low power excitation current. Twenty-one AC current levels from 3.16 pA to 31.6 mA RMS offer low noise with no significant DC component to contribute to sensor self-heating. Two operating modes provide excitation control options to meet user and application needs. Performance Enhancement Innovative features enhance the performance of the Model 370 from excitation to output. Common mode voltage can come from many sources, including external noise coupling into the lead wires. The Model...

Model 370 AC Resistance Bridge Manual range selection provides the option of full user control. With manual range selection, the user selects excitation as well as resistance range; ranges do not change automatically. If input resistance exceeds the range, an overload message appears. With both autorange and manual range selection, the excitation current source is shorted inside the Model 370 during range changes to minimize transients. Temperature Conversion The temperature conversion function of the Model 370 converts measured resistance to temperature for calibrated resistance thermometers....

80 Model 370 AC Resistance Bridge Instruments Scanners for the Model 370 Three custom scanners are available with the Model 370, the Model 3716, 3716L, and the 3708. These are designed specifically to increase the Model 370 input capability from 1 to either 8 or up to 16 resistors without sacrificing measurement performance. Each scanner is housed in a separate enclosure and can be mounted directly on the cryostat so leads carrying the most sensitive low voltage signals are as short as possible. The scanner also allows extension of the Model 370 shield to all resistor leads. A preamplifier in...

Model 370 AC Resistance Bridge Instruments 81 Sensor Performance Lake Shore Germanium GR-50-AA Sensor properties Excitation and instrumentation Temperature Resistance dR/dT Thermal resistance 0.05 K 35 kΩ -3.6 MΩ/K 200 mK/nW 0.1 K 2 kΩ -72 kΩ/K 20 mK/nW 0.3 K 164 Ω -964 Ω/K 4 mK/nW 1K 34 Ω -31 Ω/K 0.1 mK/nW Instrument performance Temperature Resistance range Excitation voltage limit Excitation current Power 63.2 kΩ 20 µV 0.316 nA 3.5 fW 6.32 kΩ 63 µV 10 nA 232 fW 200 kΩ 63 µV 316 nA 16.4 pW 63 kΩ 200 µV 1 µA 33.5 pW Calibration accuracy Self-heating errors Interpolation error Overall accuracy...

370/3716 Performance Specification Table 82 Voltage Range 31.6 mA 10 mA 3.16 mA 1.0 mA 316 µA 100 µA 31.6 µA 10 µA 3.16 µA Current Excitation 1.0 µA 316 nA 100 nA 31.6 nA 10 nA 3.16 nA 1.0 nA 316 pA 100 pA 31.6 pA 10 pA 3.16 pA 1.0 pA 632 mV 200 mV 63.2 mV 20 mV 6.32 mV 2.0 mV 632 µV 200 µV 63.2 µV 20 µV 6.32 µV 2.0 µV 20 Ω 20 µΩ 10 mW 6.32 Ω 6.0 µΩ 3.2 mW 2.0 Ω 2.0 µΩ 1.0 mW 632 mΩ 1.3 µΩ 320 µW 200 mΩ 400 nΩ 100 µW 63.2 mΩ 130 nΩ 32 µW 20 mΩ 100 nΩ 10 µW 6.32 mΩ 100 nΩ 3.2 µW 2.0 mΩ 100 nΩ 1.0 µW * * * 63.2 Ω 60 µΩ 3.2 mW 20 Ω 20 µΩ 1.0 mW 6.32 Ω 6.0 µΩ 320 µW 2.0 Ω 4.0 µΩ 100 µW 632 mΩ 1.3...