1OUTLINE1. Thermometry2. Temperature Ranges of Application3. Constant Volume Thermometer4. Thermocouples5. Thermometer Time Response Data6. 4 Terminal Resistance Measurement8. Pt (pure metal) Thermometer9. Typical Resistive Thermal Sensor10. Typical Resistance and Sensitivity Curves11. Thermal Regulation12. Data Collection/Wheatstone BridgeCryogenic Instrumentation IThermometryTemperature Ranges of ApplicationConstant Volume Thermometer•Named after Sir Fancis Simon•Helium is an ideal gas down to 5 K•Modern versions use in situ pressure gauges at low T with electrical read-out (no gas line from RT to Low T)Low TRTHeliumgasGas lineThermocouplesFigure adapted from Cryogenic Engineering by Thomas M. Flynn, Dekker:NY (1997), p. 530Wires of 2 different metals (pure or alloy) when joined and connected to a volt meter produce a voltage related to temperature.At right is the sensitivity of various common thermocouples, perhaps the simplest, least expensive, and most common thermometer in use. Usually a reference junction in an ice bath is used to make the measurement absolute.Calibrations are tabulated (e.g. type K)Thermometer Time Response DataDifferences between wet and dry can be exploited for level detectionFigure adapted from Cryogenic Engineering by Thomas M. Flynn, Dekker:NY (1997), p. 49524 Terminal Resistance MeasurementThermometerat low TLeads from RT toLow T must havelow heat leak (alloy)Meter at RT must have high input impedanceCurrent source must be stable and reversible. Average of readings with current flowing in opposite directions gives correct voltage drop, canceling thermal emfs. Often, low frequency ac source is used, with lock-in detector as volt meter, to improve sensitivity.Pt (pure metal) thermometer•Resistance thermometer—use 4 terminal set-up•R is almost proportional to T:Callender-VanDusen Equation: R(T)=R0[1+AT+BT2+C(T-10)T3](0 K<T<300K)Other calibrations available down to 20 K•Purity determines calibration (A, B, C)-no individual calibration required•Transfer standard used by NISTFigure adapted from Cryogenic Engineering by Thomas M. Flynn, Dekker:NY (1997), p. 512Typical Resistive Thermal SensorCross-section:Details of construction showing strain-freemounting of chip (#4) inside hermetically sealed containerPhoto of sensor with leads0.01 0.1 1 10 100101102103104105106TTR-DTTR-G Resistance ()Temperature (K)0.01 0.1 1 10 1000123TTR-GTTR-D Dimensionless Sensitivity (S)Temperature (K)Typical Resistance and Sensitivity CurvesGe on GaAs substratesProduced in development ofMaximum sensitivity at 20 K(liquid hydrogen)TemperatureInput-set pointPID HeaterResponseTemp. MonitorThermometerDewarThermal RegulationHeaterComputer data acquisitionboard may be used for allelectronicsComputerwith dataacquisitionboardInput-CurrentlevelTemperatureComputer boardBreak-out boxResistorDecadeResistorTemperaturesensorResistorRResistorRsourcedetectorData Collection/Wheatstone BridgeTemperature measurementand control is easily automated3OUTLINE1. Pressure Measurements2. Pressure Transducers Characteristics3. Thermal Conductivity Measurements4. Example: Ortho-Para Ratiometer5. Level Detection-Point6. Level Detection-Continuous7. Thermometer Time Response Data-again8. Flow MeteringCryogenic Instrumentation IIPressure Measurement at Low Temperature•Pressure is a force applied to an area, so its measure involves the conversion of a force measurement to some measurable parameter•Converters, or transducers may be: Electrical: Capacitive-diaphragm Inductive-reluctive Resistive-strain gauge Mechanical-spring Piezoelectric-quartz crystal•These devices may often be connected to low temperature volumes using small tubes, avoiding cooling the transducer•Most transducers operate at low temperature, although sensitivity and calibration are usually changed•Low temperature devices often work better than at room temperature because the environment is more controlledTypical Pressure TransducersBourdon TubeCapacitiveInductivePiezoelectricFigure adapted from Cryogenic Engineering by Thomas M. Flynn, Dekker:NY (1997), p. 457Mechanical Pressure GaugeCharacteristics of TransducersFigure adapted from Cryogenic Engineering by Thomas M. Flynn, Dekker:NY (1997), p. 458Temperature Dependence of Transducer OutputFigure adapted from Cryogenic Engineering by Thomas M. Flynn, Dekker:NY (1997), p. 4594DifferentialPressure GaugeScreenPush RodSupports25 cmMaximumVo l u m edisplaced~1.3 litersC10 cmDeveloped strain-type (similar to UF“Straty-Adams” gauge) in situ capacitive probe with resolution of 1 PaRequires at least 15 J for 1 measurement(cap(capacitor plate moves 0.01 Å))Pressure Transducer Test ApparatusTested in liquid nitrogenand liquid heliumUltra-sensitive/Low TemperaturePressure TransducerCapacitive ManometerCTest Port Reference PortConnections to Capacitance BridgeMembrane which FlexesUnder PressureCapacitor PlatesMEMS Technology for Sensor ConstructionblockkkkkkPerfect size rangeDesign Of Piezo-resistive Pressure Sensors Typical design: 4 piezo-resistors in Wheatstone bridge on a diaphragm diaphragm deflects from applied pressure causing the deformation of the piezo-resistors mounted on the surfaceWheatstone bridgePiezo-resistive Pressure Sensor SM5108Manufactured by Silicon Microstructures, Inc.Semiconductor resistors joined by aluminum conductors in bridge configurationResistors placed on diaphragmTwo strained parallel to ITwo strained perpendicular to IPiezo-resistive Pressure Sensor SM51085Drawbacks of Piezo-resistive Pressure Sensors-Results Relatively low sensitivity Large temperature dependence temperature compensation necessary0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.40510152025303540455055 300 K 91.2 K - 94.6 K 64.4 K - 66.0 K 49.8 K - 51.0 K 40.4 K - 43.5 K 29.9 K - 30.4 K 22.9 K - 26.0 K 26.2 KVoltage vs Pressure for Piezoresistive Transducer at varying temperaturesVoltage (mV)Pressure (Bar)Principle of Gas Thermal Conductivity MeasurementRegulate the temperature of a pure metal film separated by the H2gas from a constant T heat-sinkMetal film is both heater and thermometerQtotal=QH2 conduction+Qconvection+Qradiation+Qstructural supportsDesign makes the hydrogen conduction dominatePlanar design—linear heat conductionQTTT=constantH2gas:ortho-paramixtureQbfjlL N 2 Cold Cu PlatePure Ni heater & Thermo-meterQuartz Spacer (Low Ther. Ex.& low ThermoconductivitySecond ThermalInsulation LayerIn SealIS.S. Cap Outlet Needle