Thermoelectric Life Cycler Performance Improvement
Polymerase Chain Reaction Devices (PCR) are used to cycle DNA samples in order to break the DNA and allow primers to bond to the base pairs. Our TEC’s are used in these machines and customers want to know how long they will last when designing a new cooler. Depending on the cooler construction cycle life could be anywhere from 50k to 1million cycles. Typically smaller modules last much longer and have the ability to cycle much quicker, however our dated PID control system could not handle these fast speeds. Ramping from 15C to 90C in about 0.75 seconds. I led the team in coming up with the new architecture for the tester and programed the first proof of concept prototype. Developed an improved control algorithm that did not rely on PID control but rather looked back at previous cycles using a highspeed agilent digitizing DAQ. When it knew how the system performed in the past it would make changes to its cycling control (heat and cool times) to get closer to the target set point. After a few minute startup sequence the module would cycle 15C-90C until the test was stopped or the TEC failed. A microcontroller (ESP32) would control an H-bridge to switch heating and cooling while a python program would control multiple units cycling at one time. The python program would gather data from the DAQ, determine adjustments to be made by the algorithm I wrote and then send the updated cycle rates to the ESP32. This resulted in being able to power the TEC’s 100% of the time at full power whereas PID tends to dial back power as you approach a set point. These modules cycled so fast and are so small that even mounting a tiny thermocouple could interfere with commanded and actual temperature achieved. To mitigate this we went with an IR sensor that looked at the module instead of thermally contacting it. End result was a cycling test stand that performed 7-14 times faster than our existing PID control system and took test times for our million cycle TEC’s down from over a year to less than a month!