Precise Set-Point Control of Temperature for Coral Bleaching Experiments

Experimental research into the upper thermal limits of corals is underpinned by the need for precise control of water temperature in the testing environment, with evidence that temperature differences of as little as 0.1°C can be a significant factor in whether coral bleaches or not. Off-the-shelf temperature control equipment is generally unsuitable for high precision temperature experiment because the realized accuracy of temperature control is typically less than 0.5°C, even from state-of-the-art proportional, integral, derivative (PID) control technology. However, high temperature resolution and accuracy is achievable using simple control technology. This paper reviews the principles behind two temperature control technologies and describes a system capable of controlling temperature in actual experimental conditions to better than ±0.05°C over a 24-hr period and typically better than ±0.1°C over a 12-day period. This result is obtained through appropriate design of the experimental tank set-up and the use of “on-off” temperature control technology with very small hysteresis. Accuracy of set-point temperature is maintained by calibration against a reference temperature. Sensor drift, resulting from ambient temperature fluctuations, is avoided by immersing the circuitry in the temperature-controlled water.