- The energy balance of small temperature sensors was modelled to illustrate the effects of sensor characteristics, particularly size, on the accuracy of readings in the presence of strong shortwave or longwave radiant loads. For all but extremely small sensors, radiant exchange may lead to unacceptable errors. The common practice of using passively ventilated instrument screens was evaluated in a series of comparative measurements. The differences resulting from the use of different models of shields may be an order of magnitude greater than the error resulting from sensor calibration. In the absence of technological innovation capable of reducing the error due to radiant exchange to negligible proportions, it is suggested that a standard methodology for calibrating and labelling the error resulting from the characteristics of the screens be adopted, to allow comparison of new data with long-established records.