This paper demonstrates the capability of the 'Smart' sphere to measure a temperature which varies with axial length and time in a non-stationary system such as a rotary drum mixer. The 'Smart' sphere is a low-cost, low-power, small, wireless (infrared), self-equipped data logger with a built-in temperature sensor, which moves freely when introduced inside the process and measures the surrounding temperature and subsequently stores measured data in its internal memory. This data is subsequently transferred by wireless means to the computer once the sphere is recovered at the end of the process. The `Smart' sphere, when introduced into the rotary drum mixer, moves with the bulk particles and measures high resolution longitudinal (axial) temperature data. Thus, the capability of free moving measurements by a `Smart' temperature sphere in rotary drum mixers has been experimentally demonstrated and found satisfactory. Moreover, the `Smart' sphere measurement has been compared with the fixed point measurements taken at an instant in the drum. Axial temperature variation measured by the sphere in the rotary drum experiment is in good agreement with the reference temperature measured by the temperature probe. Thus, the `Smart' sphere measurement fills the gaps between the fixed point measurements and provides high resolution temperature data which could be further used for modelling and prediction of such processes. (C) 2007 Elsevier B.V. All rights reserved.