Design and implementation of a low-cost multi-channel temperature measurement system for photovoltaic modules Rustu Eke ⇑ , A. Sertap Kavasoglu, Nese Kavasoglu Mugla University, Clean Energy Research & Development Centre, 48120 Kotekli, Mugla, Turkey Mugla University, Faculty of Sciences, Department of Physics, Photovoltaic Material and Device Laboratory, 48120 Kotekli, Mugla, Turkey article info Article history: Received 3 October 2011 Received in revised form 7 February 2012 Accepted 25 February 2012 Available online 8 March 2012 Keywords: NTC 12-bit A/D Temperature measurements Solar cell temperature PC-controlled switch Sensor amplifier abstract An efficient and low-cost temperature logging system with a 16-channel input was devel- oped for measurements of photovoltaic module temperature. This paper reports the prin- ciple of operation, design aspects, as well as the experimentation and performance of the simultaneous temperature measurement of 16 solar cells/modules. The system consists of a 16 channel multiplexer, a 12 bit A/D, a differential amplifier and NTC temperature sen- sors. The temperature range of the sensor is from 20 °C to 120 °C. The simplistic design requires no large internal memory to store data but incorporates a high degree of sensitiv- ity and dynamic range (according to climate condition), thus the cost of the design remains low and makes it suitable for field applications. The system was successfully tested for the operating temperature of a 40-cell mono crystalline Si photovoltaic module under realistic outdoor conditions during a summer and a winter day. The temperature Instrumentation developed for avoidance of special interface card use enabled the successful collection of data from long distances with negligible level of noise. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Controlling and monitoring of accurate and reliable measurement of temperature is particularly essential in various fields, including the environmental, industrial, food, agricultural, clinical and biotechnology sectors. In addition research labs, clean rooms and nuclear reactors are all environments that are highly affected by tempera- ture levels and require constant monitoring. It is crucial to understand the role of sensors in a circuit and what er- ror they may introduce into the measurement. We will, therefore, point out the advantage and disadvantage of the two most common industrial temperature sensors: thermocouples and NTC’s. The sensor choice may play a large role in how cost effective the system becomes. Every temperature measurement application has different per- formance requirements and it is important to know exactly how your resolution is being affected by noise. The issue of the noise and the presence of measurement errors are not investigated in details for this work. However the issue of the error analysis has been discussed in some publication and the theories behind these analyses are well explained in literature [1–7]. Thermocouples are the most widely used type of tem- perature sensor in industry. Extremely rugged, they can be used from sub-zero temperatures to temperatures over 4000 °F. A thermocouple takes advantage of the voltage in- duced between two different metals as they are heated. A technology known as cold junction compensation (CJC) is used to remove unwanted junction voltage. CJC essentially uses a direct-reading temperature sensor to measure the cold-junction temperature, and then adds the appropriate value to the measured voltage to eliminate these ‘parasitic’ thermocouple effects but the error introduced by your CJC sensor compounds any error already existent in measure- ment [8]. Especially at long range remote temperature measurement requires very long length thermocouple extension wire. This disadvantage brings together high cost and high noise amplitude during the measurement. When 0263-2241/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.measurement.2012.02.029 ⇑ Corresponding author. E-mail address: erustu@mu.edu.tr (R. Eke). Measurement 45 (2012) 1499–1509 Contents lists available at SciVerse ScienceDirect Measurement journal homepage: www.elsevier.com/locate/measurement