Adaptive thermal block temperature control method and system
Aspects of the present teachings describe a method and apparatus for automatically controlling a block temperature to reduce undershooting and overshooting of the temperatures of a sample contained in the block and participating in a polymerase chain reaction (PCR). The adaptive thermal block temperature control begins when a sample temperature enters a sample window region between a preliminary setpoint temperature and a target setpoint temperature for the sample. Based on thermodynamic behavior of the sample and the predetermined phase of PCR, predicting a time period measured subsequent to the preliminary setpoint temperature when the sample will reach the target setpoint suitable for the predetermined phase of PCR. During this time period, varying the block temperature ramp rate with a series of cooling and heating changes to ensure the block temperature reaches the target setpoint temperature at approximately the same time as the sample reaches the same. Synchronizing the block temperature and sample temperature to the target setpoint temperature reduces undershooting and overshooting of the sample temperature and increases the speed and efficiency of the overall PCR process as it relates to the thermal cycling operations.
1. A non-transitory computer-readable storage medium encoded with instructions, executable by a processor, for controlled automated performance of a polymerase chain reaction (PCR) thermal protocol, the instructions comprising instructions for:
calculating a current temperature ramp rate for a sample comprising a PCR mixture to be amplified and contained in a sample vessel whose temperature is varied by association with a thermal block of variable temperature, wherein calculating the current temperature ramp rate is based on temperature readings received from a plurality of temperature sensors;
calculating an expected time interval for the sample to reach a target setpoint temperature based upon the current temperature ramp rate for the sample;
operating the thermal block at a thermal block ramp rate according to the calculated time interval for the sample to reach the target setpoint temperature, wherein operating the thermal block is done by varying an amount of power sent to a cooling control system and a heating control system associated with the thermal block;
repeating calculation of the current temperature ramp rate for the sample as the PCR thermal protocol is performed;
determining whether the predicted time interval for the sample to reach the target setpoint temperature has changed based on the current temperature ramp rate; and
modifying the predicted time interval and the thermal block ramp rate such that the thermal block and the sample reach the target setpoint temperature at approximately a same time.
2. The non-transitory computer-readable storage medium of claim 1 wherein repeating the calculation of the current temperature ramp rate occurs at a frequency corresponding to a control loop time interval.
3. The non-transitory computer-readable storage medium of claim 2 wherein said frequency is approximately 20 times per second.
4. The non-transitory computer-readable storage medium of claim 1 wherein modifying the predicted time interval occurs during an adaptive window for adjusting the thermal block ramp rate.
5. The non-transitory computer-readable storage medium of claim 4 wherein the adaptive window designates approximately where the sample temperature is predicted to reach the target setpoint temperature and wherein the target block ramp rate is modified to achieve substantially the same sample temperature and block temperature within the range of the adaptive window.