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

2 OUTLINE PRESENTATION PROBLEM SYSTEM STRUCTURE PROJECT GOALS & OPTIONAL SOLUTIONS CHOSEN SOLUTION RESULTS FINDINGS SUMMARY CONCLUSIONS

Control And Robotics Laboratory3 PROBLEM Detector “BIRD 384” is IR detector type uncooled. This kind of detector requires stable substrate temperature. The requirement for temperature deviation is +/- 10mK. 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 Laboratory4 SYSTEM STRUCTURE Detector Controller & Acquisition Mechanical Stand active element: TEC Measurement : RTD PT100 Microcontroller embedded on FPGA 24 bit ADC 20 bit DAC linear power amplifier Heat sink Thermal Coupling

Uncooled IR Detector Control And Robotics Laboratory5 TEC Alumina RTD

Thermoelectric Cooler (TEC) Control And Robotics Laboratory6

PT100 RTD Platinum RTDs ( Resistance Temperature Detectors ) are recognized as the most reliable standard available for temperature measurement. The PT100 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. 7Control And Robotics Laboratory

8 Mechanical Stand Gap Filler For Thermal coupling Electronic card & Detector

Control loop 9Control And Robotics Laboratory

PROJECT GOALS & OPTIONAL SOLUTIONS The project goals : 1.To reduce settling time. 2.To improve the robustness. 3.Identify the reasons for the variance between the settling time of detectors. Optional solutions : 1.To improve the control algorithm. 2.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 PT100 sensor location. 10Control And Robotics Laboratory

11 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 the thermal coupling to the heat sink.

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. Initial system modeling using step response of the open loop system, and set the system parameters using software tool. 12Control And Robotics Laboratory Temperature [ oC ] Time [ sec ]

Plant Simulink Model 13Control And Robotics Laboratory

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

PID tuning using sisotool Control And Robotics Laboratory15

RESULTS 16Control And Robotics Laboratory The results of the PID tuning using sisotool : P = 15 I = and after manual adjustment : P = 7 I = 0.02

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

IMPROVEMENTS New + pad vs Old New + pad vs OldNew vs Old New + padNewOld improvement [%] improvement [sec] improvement [%] improvement [sec] Avg time [sec] Avg time [sec] Avg time [sec]         25 18Control And Robotics Laboratory

Comparison Between Detector #1 Results For The Jump 25  60 Det 1 “Old” Det 1 “New+Pad” 19 Det 1 “New” 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 fig. 1 : Det 1 “old” settling time to +/-10mK fig. 3 : Det 1 “New” settling time to +/-10mK fig. 5 : Det 1 “New+Pad” settling time to +/-10mK

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 ohm [~ 46.5 deg’]. Readout circuits noise is ~10mK pk-pk. Impact of readout circuits temperature drift is less then 20mK for 10 deg’ change of surroundings. 20Control And Robotics Laboratory ~10mK

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 TEC- alumina and alumina-RTD contacts. Not cooling : the problem is mainly TEC-package contact. 21Control And Robotics Laboratory

22 RTD ASSEMBLY

23Control And Robotics Laboratory RTD SURFACEALUMINA-TECTEC - PACKAGE GLUINGS

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 2mm 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. 24Control And Robotics Laboratory

SUMMARY Control And Robotics Laboratory25 Settling time improvement of 30%-40% has been achieved. Reasons for variance has been identified. Manufacturing process is being modified.

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 Laboratory26