TECHNION — ISRAEL INSTITUTE OF TECHNOLOGY Department

TECHNION - ISRAEL INSTITUTE OF TECHNOLOGY Department of Electrical Engineering Control And Robotics Laboratory UNCOOLED IR DETECTOR TEMPERATURE CONTROL Performed by : Shimon Amir Yogev Ben-Simon Instructor : Arie Nakhmani Control And Robotics Laboratory 1

PRESENTATION OUTLINE • • PROBLEM SYSTEM STRUCTURE PROJECT GOALS & OPTIONAL SOLUTIONS CHOSEN SOLUTION RESULTS FINDINGS SUMMARY CONCLUSIONS Control And Robotics Laboratory 2

PROBLEM • Detector “BIRD 384” is IR detector type uncooled. • This kind of detector requires stable substrate temperature. • The requirement for temperature deviation is +/- 10 m. K. • During the characterization after manufacture the detectors pass series of tests , which include settling to several set points. This procedure takes a lot of time , therefore we need to reduce the detector settling time. • The initial tests showed that there is variance between the time response of the detectors. Control And Robotics Laboratory 3

SYSTEM STRUCTURE Detector Controller & Acquisition Mechanical Stand active element: TEC Microcontroller embedded on FPGA Heat sink Measurement : RTD PT 100 24 bit ADC Thermal Coupling 20 bit DAC linear power amplifier Control And Robotics Laboratory 4

Uncooled IR Detector Alumina RTD TEC Control And Robotics Laboratory 5

Thermoelectric Cooler (TEC) Control And Robotics Laboratory 6

PT 100 RTD Platinum RTDs ( Resistance Temperature Detectors ) are recognized as the most reliable standard available for temperature measurement. The PT 100 RTD is described by the following generic equation , which makes a obvious nonlinear relationship between temperature and resistance: Since the B and C coefficients are relatively small, the resistance changes almost linearly with the temperature. Control And Robotics Laboratory 7

Mechanical Stand Gap Filler For Thermal coupling Electronic card & Detector Control And Robotics Laboratory 8

Control loop Control And Robotics Laboratory 9

PROJECT GOALS & OPTIONAL SOLUTIONS The project goals : 1. 2. 3. To reduce settling time. To improve the robustness. Identify the reasons for the variance between the settling time of detectors. Optional solutions : 1. 2. To improve the control algorithm. To improve the physical parameters of the system/detector such as : – Thermal impedance between detector package and the heat sink. – Heat sink. – “Inside of the package”, e. g. internal PT 100 sensor location. Control And Robotics Laboratory 10

CHOSEN SOLUTION • System modeling. • Algorithm : PID + switch mode - full power until getting to set-point area , initializing the integral with a desired value , and then continue with closed loop to convention. • PID tuning using software tool and manual adjustment. • Mechanics : improve thermal coupling to the heat sink. Control And Robotics Laboratory 11

System Modeling • The chosen model is second order system : one pole for the TEC and another one for the temperature sensor. • Even though we know that there is delay in thermal system , in our system the delay can be neglected. Temperature [ o. C ] • Initial system modeling using step response of the open loop system , and set the system parameters using software tool. Time [ sec ] Control And Robotics Laboratory 12

Plant Simulink Model Control And Robotics Laboratory 13

Modeling Results The results for the second order estimation : • DET 1(OK) : • DET 2 (SLOW): HIGH VARIANCE Control And Robotics Laboratory 14

PID tuning using sisotool Control And Robotics Laboratory 15

RESULTS The results of the PID tuning using sisotool : • P = 15 • I = 0. 008 and after manual adjustment : • P = 7 • I = 0. 02 Control And Robotics Laboratory 16

SETTLING TIME RESULTS Measurements were taken from 8 detectors that tested in 3 configurations : 1. 2. 3. Original system - “Old”. Improved controller and manually PID tuning – “New” Improved controller , heat sink and thermal impedance - “New +Pad” Control And Robotics Laboratory 17

IMPROVEMENTS Old New + pad New vs Old New + pad vs Old Avg time [sec] improvement [%] improvement [sec] improvement [%] 60 25 82. 5 60 47. 2 22. 5 27. 3 35. 3 42. 8 25 60 101. 8 67. 2 37. 5 34. 7 34 64. 3 63. 2 35 25 62. 5 36. 5 35 26 41. 6 27. 5 44 25 35 76. 3 48. 7 34. 2 27. 7 36. 2 42. 2 55. 2 15 25 91. 7 61. 3 34. 8 30. 3 33. 1 56. 8 62 25 15 76. 7 35. 3 36. 2 41. 3 53. 9 40. 5 52. 8 5 25 73. 7 53 33. 8 20. 7 28. 1 39. 8 54. 1 25 5 64. 2 32. 2 33. 7 32 49. 9 30. 5 47. 5 Control And Robotics Laboratory 18

Comparison Between Detector #1 Results For The Jump 25 60 Det 1 “Old” fig. 1 : Det 1 “old” settling time to +/-10 m. K Det 1 “New” fig. 3 : Det 1 “New” settling time to +/-10 m. K Det 1 “New+Pad” fig. 5 : Det 1 “New+Pad” settling time to +/-10 m. K 19 fig. 2 : zoom on the relevant area in fig. 1 fig. 4 : zoom on the relevant area in fig. 3 fig. 6 : zoom on the relevant area in fig. 5

MEASUREMENT QUALITY • Temperature sense readout circuits accuracy and quality is very important. • Testing the accuracy and noise of the temperature sense circuits was done by replacing the RTD with a regular resistor of 118. 2 ohm [~ 46. 5 deg’]. • Readout circuits noise is ~10 m. K pk-pk. • Impact of readout circuits temperature drift is less then 20 m. K for 10 deg’ change of surroundings. ~10 m. K Control And Robotics Laboratory 20

FINDINGS • There are two main kinds of temperature stability problems: 1. “Detector slow response” 2. “Detector can’t cool down” • • Slow response : the problem is mainly TECalumina and alumina-RTD contacts. Not cooling : the problem is mainly TEC-package contact. Control And Robotics Laboratory 21

RTD ASSEMBLY Control And Robotics Laboratory 22

GLUINGS TEC - PACKAGE ALUMINA-TEC Control And Robotics Laboratory RTD SURFACE 23

MECHANICS • The current design includes a gap filler pad as thermal coupling to the heat sink. • It has a thermal conductivity of 2 . and with 2 mm thickness it’s thermal impedance is 1. 3 . • Compression achieved using material elasticity and socket friction. • Possible improvement can be achieved by using a thermal pad with a better thermal impedance and a copper heat sink. – will require mechanical adjustments. • Tested – 0. 3 mm thermal pad with aluminum film to avoid pull-out (pad stick to the detector’s package) effect, thermal conductivity of 17 and thermal resistance of 0. 06 , copper heat sink. Control And Robotics Laboratory 24

SUMMARY • Settling time improvement of 30%-40% has been achieved. • Reasons for variance has been identified. • Manufacturing process is being modified. Control And Robotics Laboratory 25

CONCLUSIONS Points of view for future work : • To build a better model , linear or non-linear , and check the influence of adding derivative. • To explore robust control methods. • To explore adaptive control methods. • Check the influence of adding derivative. • Change the location of the temperature sensor. • Thermal coupling improvement. • Thermal mass reduction. • Better heat sink. Control And Robotics Laboratory 26