Module 3: CLIMATE MANAGEMENT

[Audio] Hi, I'm Jorge Sanchez, professor at the University of Alme-ria and member of the Automatics, Robotics and Mechatronics research group. I am responsible for Lesson 1, which deals with the basic principles of greenhouse climate variable measurements using sensors. This first theme focuses on studying the fundamental of measurement.

[Audio] The contributors to this section are Professors Manuel Berenguel and Francisco Rodríguez, both of whom work at the University of Almeria..

[Audio] In this topic, we will cover the following points: We will begin by discussing the concepts relating to sensors and their most basic definitions. Then, we will look at the steps in the measurement process and the materials needed to carry it out. We will finish with some conclusions..

[Audio] In order to manage the climate in a greenhouse, it is essential to measure the internal variables that directly influence crop growth: air temperature, radiation hitting the canopy, CO2 concentration and relative humidity. As will be described in the next module, the control of these internal variables also depends on the external climate, and it is therefore advisable to measure these external variables as well. In addition, there are other variables, such as the opening of vents or the water temperature in the heating system pipes that should be measured. On the other hand, all the internal climate variables must be controlled simultaneously, so it is necessary to measure all variables that come into play at the same time. Signals from all the systems measuring the above variables must reach the controller. For this purpose, a data acquisition system is used to collect these signals so that the controller can work with them. This topic describes the fundamentals of the systems that make up the measurement process..

[Audio] Sensors are instruments that are used to estimate the average reality of a measurement. Digital sensors are responsible for converting the physical signal to be measured into an electrical signal. Among the different variables that can be measured, in this case in a greenhouse, we have on the one hand the climatic variables, which are those we are going to discuss in this topic: namely, temperature, relative humidity, radiation, and wind speed etc ... And, on the other hand, the many other measurements that can be taken, both in the soil and in the plant or water, for example, electrical conductivity, pH, soil temperature, stem thickness, condensation on the leaf, and so on..

[Audio] Given the number of sensors available on the market, the problem is which to choose. When we want to buy one, we must consider certain basic concepts to avoid making a mistake because this can increase the acquisition or mean you end up with one that lacks the minimum required characteristics. One of the most basic concepts to consider is accuracy, since this is a characteristic of the sensor that makes it very expensive. Its accuracy is defined as the difference between the measurement taken and the measurement that should be the standard. In the table, you can see an example of a temperature and relative humidity sensor, and how the accuracy of the Vapour Pressure measurement varies depending on the ambient temperature and humidity values; in our case, this would be in a greenhouse. One can observe how they are between a maximum of 2.3kPa and minimum of 0.03 kPa. In the next example, we can see the accuracy of the temperature variable as a function of the ambient temperature itself, and this accuracy is between -4 and 4 ºC. The question is whether such precision in the temperature and humidity sensor values are acceptable for a greenhouse. Is an accuracy level of 0.5 ºC in temperature or 5% in relative humidity adequate for a greenhouse? I think so because, in my opinion, half a degree in temperature and 7% humidity will not substantially change our climate management decision..

[Audio] Another parameter to analyse when selecting a sensor is the "measuring range". This refers to the environmental conditions under which the sensor is expected to perform. It is usually given as a range with a maximum and a minimum value. For example, for this temperature and humidity sensor, a temperature range between 0 and 60 °C is given. The manufacturer assures us that any measurement provided by the sensor in this range will be correct. To control a greenhouse climate in a Mediterranean environment, it could therefore be used, as it would be unlikely for conditions outside this range to occur..

[Audio] To understand how the measurement process works, we have taken a Telemecanique pressure sensor as an example. This can be used in an irrigation system pipe to measure the pipe's pressure in Bars..

[Audio] This sensor will have a series of characteristics such as maximum or minimum pressure, precision, and operating conditions etc....

[Audio] To transform this analog sensor into a digital sensor, we need a transducer, the function of which is to convert the physical signal into a low-quality electrical signal, for example, into millivolts..

[Audio] This signal can be changed as needed, using a signal conditioner, which is available with different characteristics, for example, to amplify the signal so as to improve its quality, from millivolts to volts..

[Audio] Once transformed, this signal can be sent to a monitor where the transformed value can be viewed directly..

[Audio] or sent to a data logger for storage and subsequent analysis to help understand the systems..

[Audio] Finally, the trend over recent years has been for sensors to send information to the cloud, known as the Internet of Things. This can be done in several ways: the sensor can send data directly to the cloud. On the other hand, the sensor can be connected to an acquisition system or data logger, which is responsible for sending the data, or the logger can be connected to a monitoring system and this system is responsible for sending the data. In addition, this sensor can have a local monitor if necessary. As an example, the climate IoT station of the company Libelium is shown. For more information on these trends, see Module 6. Digitalization..

[Audio] To conclude, I would like to point out that: In order to control a variable, one must be able to measure it - that is what sensors are used for. The sensor is a system that converts the physical, chemical or biological variable to be measured into an electrical signal that can be processed by electronic control systems. To transmit the measured variable, one needs a system that improves the electrical signal produced by the sensor, eliminating noise and amplifying the signal. One must be aware of the features of the sensors because not all of them are suitable for all applications. For example, in a Mediterranean greenhouse, temperatures of 60 ºC and 100% relative humidity , so it is necessary to use sensors that can withstand these conditions. In addition, the price of the sensors increases depending on the measurement quality (the accuracy) . A sensor that is able to measure 0.01 °C provides higher quality than one with an accuracy of 0.1ºC, but is it necessary to have such highly accurate sensors for these applications? A price/performance ratio has to be decided upon. In the next lesson, we will review the different sensors required for optimal indoor greenhouse climate management..

[Audio] Thank you for your attention. If you have any questions or comments, please write them down and send them to this contact email address..