Sensors and measurement, a review

Greenhouse management implies making decisions at different levels. These decisions are related to the daily control of the greenhouse climate, the requirements for the development of the crop during the next few weeks and the strategy to be chosen to timely produce a high quality product to the requirements of the market at minimum cost. Present developments are towards the use of automated systems for both control and management. These can range from classical temperature control systems to expert systems for strategic planning based on growth models and economic outlooks. These systems require as an input a continuous flow of quantitative data. Most of these data result from measurements of physical, chemical or physiological phenomena in and around the greenhouse. The continuous measurement of an increasing number of quantities implies the use of sensors with an electrical output, connected to an automatic data acquisition system. Many existing sensors have to be modified and new sensors have to be developed to suit these new requirements. Improved methods of measurement and newly emerging semiconductor technologies not only result in more and better sensors, but also provide opportunities to adapt sensors to specific requirements for horticulture. Opportunities are found in improvements in classical measurement methods with extra features and options like digital output, smaller dimensions, lower cost and higher reliability, as well as in the development of hitherto not existing sensors.