A review

It is widely known that defrosting operation on commercial refrigerators is one of the main causes of inefficiency on these systems. Several defrosting methods are used nowadays, but the most commonly used are still time-controlled defrosting, usually by either electric resistive heating or reverse cycle, as most demand defrost methods are usually complex, expensive or unreliable. Demand defrost can work by either predicting frost formation by processing measured conditions (fin surface temperature, air humidity and air velocity) and/or frost accumulation symptoms such as pressure drop and refrigerant properties. Other way of knowing when to defrost is to directly measure the frost formation using sensors such as photoelectric, capacitive or resistive. This review gathers some of the methods that can be used for directly measuring frost accumulation on the evaporator fin surface.info:eu-repo/semantics/publishedVersio

A simple interface circuit for digital readout of lossy capacitive sensors

Direct Interface Circuits (DICs) allow straightforward digital reading from a range of sensors. Their architecture consists of a few passive components that help a digital processor (DP) perform a series of charge and discharge processes that provide time measurements to determine the sensor's resistive, capacitive, or inductive magnitudes. This article presents a new DIC that only requires two resistors for the digital readout of a group of sensors with a wide range of applications, namely lossy capacitive sensors. The DP does not need any analog element in its architecture, and the arithmetic operations involved are simple additions and multiplications. Apart from its simplicity, the new circuit brings significant improvements compared to other DICs proposed in the literature for the same type of sensors. Thus, the systematic errors in the capacitance estimates are only 0.30% for a wider range (100 pF − 95.92 nF), and the measurement time is 34% shorter.Funding for open access charge: Universidad de Málaga / CBU

Experimental Validation of a Sensor Monitoring Ice Formation over a Road Surface

The reliable detection of ice over road surfaces is an important issue for reducing maintenance costs and improving traffic safety. An innovative capacitive sensor was developed to detect the presence of ice on its surface, and its repeatability, stability and reliability were assessed in simulations and experiments described in previous papers. The indications of the sensor are compared in this paper with the objective identification of ice formation or melting over a road surface in laboratory, under dynamic or stationary conditions, using tap water or a solution with 5 % of salt concentration. The sensor provides indications which are in line with the condition of the road surface, with a mean error in the identification of the time instants of ice-wet and wet-ice transitions lower than about 10 and 40 minutes in the case of tap water and salt water, respectively, both under different temperature gradients or in stationary conditions. Moreover, the indication provided by the sensor always anticipates the formation of ice over the road surface