A New Coaxial Flow Calorimeter for Accurate RF Power Measurements up to 100 Watts and 1 GHz Andrew S. Brush Jefferson D. Lexa

Transcription

1 Slide 1 A New Coaxial Flow Calorimeter for Accurate RF Power Measurements up to 100 Watts and 1 GHz Andrew S. Brush Jefferson D. Lexa

2 Motivation Slide 2 Decrease uncertainty of working standards at 100 Watts from 1 MHz to 1 GHz, from 2% to 1% Decrease labor involved in maintaining working standards.

3 Bramall Cascaded Couplers Slide 3

4 Existing Method Slide 4 Uncertainty of approximately 1.5% Uses banded couplers or manually tuned couplers. Tedious steps of stepping to 50 db coupling ratio.

5 Calorimeter Block Diagram Slide 5

6 Error Sources Slide 6 Effective Efficiency Reflection vs. Frequency Thermal leaks Thermopile nonlinearity Flow Meter Error Coolant Properties Instrumentation error Time shifting errors

7 RF efficiency model Slide 7 Note: Enter "0" for line length if section not used Section 1 Section 2 Section 3 Section 4 Section 5 Section 6 Section 7 Section 8 dielectric constant E E E E E E E E-13 Farads/in Farads/in Farads/in Farads/in Farads/in Farads/in Farads/in Farads/in permeability E E E E E E E E-08 Henries/in Henries/in Henries/in Henries/in Henries/in Henries/in Henries/in Henries/in conductivity of metal 6.29E+07 mhos/m 6.29E+07 mhos/m 6.29E+07 mhos/m 6.29E+07 mhos/m 6.29E+07 mhos/m 6.29E+07 mhos/m 6.29E+07 mhos/m 6.29E+07 mhos/m 1.60E+06 mhos/in 1.60E+06 mhos/in 1.60E+06 mhos/in 1.60E+06 mhos/in 1.60E+06 mhos/in 1.60E+06 mhos/in 1.60E+06 mhos/in 1.60E+06 mhos/in inner conductor radius in 0.09 in in 0.25 in in in in in outer conductor radius 0.39 in in in in in in in in input line length 0.4 in in in 0.75 in 0 in 0 in 0 in 0 in loss tangent of dielectric alpha0 4.76E E E E E E E E-10 Power at input Power at calorimeter higher than calorimeter lower than section 1 section 2 section 3 section 4 section 5 section 6 section 7 section 8 alpha total alpha total RF efficiency measured input meas. frequency (MHz) frequency (Hz) rad/sec alphat (db) alphat (db) alphat (db) alphat (db) alphat (db) alphat (db) alphat (db) alphat (db) (db) % % factor factor E E E E % % E E E E % % E E E E % % E % % E % % E % % E % % E % % E % % E % % E % % E % % E % % E % % E % % E % % E % % E % % E % % % % Enables assessment of RF losses in load that do not heat the water Allows up to 8 geometrical configurations We are using a constant =.9995 for 1 GHz currently based on best guess of RF load geometry Significant factor for > 1GHz

8 RF Load VSWR characterization Slide 8 RF load characterized to determine trans. coefficient Data embedded in firmware for RF calibration Models developed for VSWR assessment 60 Hz Surface Current Density EXPIRATION DATE: 03/12/13 DATA FILE TYPE: SENSOR Corrections data for load # SIGMA FREQUENCY(MHZ) CALFACTOR % UNCERTAINTY(%) S11MAG(RHO) S11PHASE(DEG)

9 Thermopile characterization Slide 9 Thermopile characterized to determine Seebeck coefficient (Volts/deg K) needed for system algorithm Flow and thermal models utilized to determine pressure loss and heat distribution parameters

10 Ambient s Role in offset power Slide 10

11 Calibration standard & AC source Slide 11 Agilent 6811B Radian RD-23 Cal standard and AC source procured Extremely steady & repeatable Fully programmable for phase 3 tasks

12 Phase 1 Modified Block Diagram Slide 12 Max RF mismatch +120 VAC NMB 4715MS- 12TB10 Fan +24 VDC Temp Control Push to reset PID Controller Omega #CN DC Temp Sensor Drain Coolant Reservoir +120 VAC Flow adjust Min See through Level Meter Temp sensor Lines either physically shortened or compensated for thermal losses Liquid Cooled RF Load Bird #5710 constants Liquid temp sensor (RTD) RF POWER TO BE MEASURED Flow constriction Emerson Motor #S55JXNSR-7299 ProCon Pump #101A125F11BB130 Temp Switch indicator +24 VDC New flowmeter Facility water inlet ASCO Solenoid Value Facility water outlet Heat Exchanger SWEP #B5H Compensated Flowmeter Low flow indicator Thermopile module Power Supply Push to reset Interlock connector 120 VAC +5 VDC New signal proc. PCB +24 VDC Relay Acopian 24WB210 Power Supply A AC ON/OFF Switch Polyscience Chiller model # VAC Signal Processor delta T & algorithms absolute T RF Power Display +5 VDC Relay Relays Tyco #K10P-11DT5-24 Acopian 5EB50 Power Supply ma Tegam, Inc 120 VAC 60 Hz Proposed new block diagram 12/1/2011 Rev 1.0 Thursday, 12/1/11

13 Calorimetric System Algorithm Slide 13 Thermistor ADC output ADC counts vs. Temp Table T ADC counts Calculate absolute T of ambient air (C ) 1 3 Thermopile ADC output Air temp vs. Water Temp Table 28 ADC counts vs. voltage Table V ADC counts Calculate voltage output from thermopile (V) 12 Seebeck Coefficient Table T V Calculate delta T (C ) (Calibration Procedure) Measure DC resistance of RF load (ohms) 17 (Calibration Procedure) p 16 p vs. frequency Table Convert to trans. loss factor 18 (dimensionless) trans loss vs. freq Table trans loss f RF trans. loss factor of RF load vs. freq (dimensionless) 23 T f New RTD ADC output ADC ref output ADC counts vs. Temp Table T ADC counts Calculate absolute T of heated water (C ) 2 A s.g. T analytic estimatecalculate waterflow temp loss (C ) Specific Heat vs. Water Temp Table s.h. T Calculate specific heat of water (J/g-C ) 5 Specific gravity vs. Water Temp Table T Calculate specific gravity of water (g/cm 3 ) Viscosity vs. Water Temp Table 4 6 T pivot Power K Air temp vs. Power P T Calculate power offset from Ambient reading (watts) 29 Load efficiency factor 15 Calculate input power Serial number of RF load (watts) frictional watts Measure ref. coef. vs. freq of RF load (rho) (Calibration Procedure) Read 19 Calibrated AC power from Radian Calculate cal factor + Offset 20 (dimensionless) (watts) cal factor vs. power Table cal P Store cal factors vs. power level 21 eff. Number of segments RF eff. vs. freq Table f Analytic estimate- RF efficiency factor of RF load vs. freq (dimensionless) Display AC calibrated power (watts) Calculate RF calibrated power (watts) Display RF calibrated power (watts) User defined frequency input variable u analytic estimate (dimensionless) analytic estimate (watts) 8 Apply K factor f(u) T Calculate viscosity of water (mpa-sec) Denotes future capability Denotes calibration procedure items 7 (pulses/liter) Flowmeter frequency output measure pulses/sec Calculate flowrate Convert to flow volume Convert to mass flowrate Tegam, Inc (GPM) (cm 3 /sec) (g/sec) Calorimetric Algorithm 7/12/2012 Rev 1.1 Friday, 7/13/12 A

14 Auto AC Calibration Block Diagram Slide 14

15 Calibration Algorithm Slide 15 Y 100 Linear regression best fit line n = 1, s = 1 Segment n Calorimeter Power in watts Dataset x 10, y 10 Segment 3 Linear regression best fit line n = 10, s = Segment 4 Segment 1 Y = m ns x + b ns (during calibration) Segment 2 X = (y b ns )/ m ns (during measurement) Offset = b ns 0 Radian Power Readings in Watts 100 Reference standard X

16 System.ini files Slide 16 [ReflectiveCoef] 50= = = = = = = = = = = = = = = = = = = = = = = = = Relection.ini [Version] =1.1, [RFLoadSerialNumber] =5710 [UserDefinedFreq] =1000 [DCLoadResistance] =47.6 [SeebeckCoef] At this time a table can not be used since the calculation uses 1/SeebeckCoef = [LoadEfficiencyFactor] =0.995 [RFPressureDrop] = [TotalPressureDrop] =17.83 [WaterFlowTempLoss] = [Viscosity] =1.0 [KFactor] =8000 [RFEfficiencyFactor] Characterization.ini = [DF_FLOWMETER] =7.0 [DF_THERMISTOR] =4.0 [DF_RTD_PRE] =4.0 [DF_RTD_POST] =4.0 [DF_THERMOPILE] =6.0 [T_PIVOT] =26.11 [T_POWER] = [CalibrationFactor] 12.8=1.008, =1.009, =1.008, =1.011, =1.013, =1.013, =1.005, =1.016, =1.013, =1.015,2.329 Calibration.ini

17 Calorimeter Error Budget Slide 17 Sources of Uncertainty Calorimeter Uncertainty Type Estimate (in %) Probability Distribution Divisor Standard Uncertainty (in %) waterflow heat loss Type B 0.05 Normal temperature uncertainty Type B 0.10 Normal AC Source stability Type B 0.30 Rectangular calibration standard Type B 0.01 Normal Flowmeter repeatability Type B 0.10 Normal waterflow friction heating Type B 0.20 Normal pump flow instability Type B 0.01 Rectangular RF Load Mismatch between AC and RF (reflection losses) Type B 0.05 U-shaped Load efficiency Type B 0.01 Rectangular RF efficiency Type B 0.05 Rectangular Measurement Repeatability due to connector wear Type B 0.01 Normal Measurement Uncertainty Combined Uncertainty (%) Root Sum Squared Expanded Uncertainty (%) Coverage Factor (K) 2 Measured Value ± 0.44 Expanded Uncertainty (db) Coverage Factor (K)

18 Model 1311 Slide 18