Continuous Resistance Temperature Detector Calibration Using Johnson Noise Thermometry

1. Continuous Resistance Temperature Detector Calibration Using Johnson Noise Thermometry Presented as part of the IAEA Technical Meeting on Increasing Instrument Calibration Interval Through On-line Monitoring Technologies This presentation conveys the status of Subtask 2.2 � Johnson Noise Thermometer (JNT) Development. David Holcomb is the manager for all subtasks of this DOE International Nuclear Energy Research Initiative project. I am Roger Kisner, the subtask technical leader. Thank you for this opportunity. It is a privilege to be speaking to this group.This presentation conveys the status of Subtask 2.2 � Johnson Noise Thermometer (JNT) Development. David Holcomb is the manager for all subtasks of this DOE International Nuclear Energy Research Initiative project. I am Roger Kisner, the subtask technical leader. Thank you for this opportunity. It is a privilege to be speaking to this group.

2. Why Johnson Noise Thermometry (JNT)? Accurate temperature measurement is required for both control and safety All available temperature measurement technologies drift unacceptably under the harsh reactor environment Periodic calibration is required to operate with acceptable temperature uncertainty Temperature sensor recalibration costs time & money Recalibration process stresses the sensor and introduces possibility of reconnection error Johnson noise thermometry is quasi-first principles and consequently is immune to sensor drift Continuous calibration prevents measurement uncertainty from increasing over time

3. Physics Behind the Measurement: a Resistance Generates Thermal Noise Johnson noise is thermal noise (Nyquist relation) � occurs in all conducting materials and is a consequence of random motion of electrons through a conductor. Each free flight of an electron, between collisions, constitutes a minute current. The sum of all these currents taken over a long period of time must be equal to zero. But their AC component is Johnson noise.

4. History of Johnson Noise Thermometry For Reactor Temperature Measurement Brixy introduced concept in 1971 ORNL began work for fuel centerline temperature measurement in 1972 U.S., German, and Japanese researchers have implemented JNT in nuclear power plants during the 1980�s & 1990�s Sensor recalibration & innovative measurement concepts NASA space reactor program sponsored a �Tuned-Circuit� implementation of JNT at ORNL 1987-91 Cross correlation technique and digital spectrum identification technique initially conceived in early 1990s as part of ORNL SP-100 program Ongoing International Nuclear Energy Research Initiative (I-NERI) program to develop demonstration version of digital version of JNT incorporating best features of prior work

5. The project participants are from three organizations . The Korean Atomic Energy Research Institute, Ohio State University, and Oak Ridge National Laboratory. The project participants are from three organizations . The Korean Atomic Energy Research Institute, Ohio State University, and Oak Ridge National Laboratory.

6. System Combines Traditional Resistance Thermometry With Noise Measurement Accurate temperature value is obtained by Johnson noise: Requires long term integration. RTD resistance must be accurately measured. Transfer function produces fast response but subject to drift Periodically calibrate R/T transfer function with JNT

7. Dual Mode JNT Approach Incorporates Resistance Thermometry A standard industrial RTD is the JNT sensor Resistance measurement performed using a standard bridge circuit Resistance temperature measurement is essentially prompt Allows fast response to temperature change Measurement of any stochastic process takes time with longer times required for more precise measurements Johnson noise signal from resistance element provides continuous calibration of RTD value � removes drift Compensation by continuous AC calibration signal eliminates amplifier gain non-linearity and overall spectral response variation � stability assured from preamp input to A/D converter Small electronics packages � easy mounting, low power consumption, low cost, and high reliability Digital signal processing � removes environment, electronics, and interconnect noise and monitors instrument status

8. JNT System�s Major Components

9. Why Hasn�t JNT Already Been Widely Adopted? Long, high-capacitance cables alter the transmitted noise Short cables with local 1st stage amplifier (radiation tolerant electronics may be required) Periodically measure cable transfer function The charge thermal motion (Johnson noise) produces a small signal is easily contaminated with other noises Notably electromagnetic interference and microphonics Digital signal processing to reject band limited noise was prohibitively expensive until recently The electronics implementation is challenging High gain, wide band-width, highly stable devices Implementing a through-channel in-band calibration check method

10. I-NERI Implementation of Instrument Head

11. Analog Signal Transmission Method Selected To Minimize Radiation Sensitive Technologies In First Stage Amplifier Box Analog signal path Employs simple front-end electronics Uses 50 Ohm coaxial cables two per channel (may use twisted pair style) Noise channels are at base-band frequency (10MHz BW) RTD DC resistance is converted to AC signal Minimizes signal degradation from cable attenuation Cable attenuation effects compensated by sweep calibration Amplitude variation effects from cable are cancelled by phase locked loop Digital signal path configuration rejected because of susceptibility to radiation damage

12. Built and Tested Circuit Board for Dual High-Frequency Preamplifier Channels

13. Built and Tested Circuit Board for DC Resistance, Volt/Freq Converter, and Noise Channel Calibrator

14. Cross Power Spectral Density Employed to Remove Uncorrelated Amplifier Noise Amplifier noise is essentially uncorrelated and increases measurement uncertainty

15. Knowledge of Distribution of Johnson Noise in Frequency Domain Allows Deglitching and Distortion Correction Johnson noise is white while electromagnetic interference tends to be narrowband Microphonic noise removed by high pass filtering

16. Long Runs of Coaxial Cable Misshapes HF Spectrum

17. Receiver Digitizes, Filters, and Processes The JNT Signals

18. Receiver Subsystem Contains High-Frequency and DC Circuits Johnson Noise Channels Two wideband amplifier channels Anti-alias and low frequency rejection filtering (bandpass) Additional gain (as needed for A/D input) Analog-to-digital converter DC Resistance Channel Noise filtering Phase-locked loop detector to recover DC signal from frequency encoding Gain (as needed for A/D input) A/D Converters (three channels may be card in VME bus) Power Supply

19. Digital Signal Processing Implemented on Dedicated Hardware at KAERI

20. Digital Signal Processing Calibrate Johnson noise channel Extract continuous calibration signal Apply non-linear gain correction to each noise channel using amplitude and harmonic spectral content of calibration signal Remove unrelated electromagnetic interference signals from Johnson noise signals Cut spikes Filter semi-periodic exogenous carriers Remove amplifier noise from resistance noise by cross-correlation Calculate absolute reference temperature from processed spectrum Periodically correct DC resistance measurement by applying absolute reference temperature

21. Conceptual Block Diagram of Digital System Receiver Function

22. Where Do We Go From Here? Plant demonstration Radiation and temperature hardened system design Quality control Testing & more testing Commercialization