A CONTROL OF AN IRRIGATION SYSTEM IN A GREENHOUSE

Abstract: In order to ensure that the greenhouse plants receive a sufficient supply of water it is suggested to integrate the atmospheric moisture within the greenhouse and control the supply of water as a function of the integrated atmospheric moisture. The moisture control is preferably combined with a control according to the solar radiation. An apparatus for controlling the irrigation may comprise a moisture sensor (12) and a light- and heat sensor (14) transmitting signals via an AD-converter to a microcomputer which is adapted to calculate the size of the amounts of water supplied through irrigation and which is capable of activiting the supply by transmitting a suitable number of pulses to a relay (R) controlling a solenid valve (16) controlling the supply of water.

Description: Title: A Control of an Irrigation System in a Greenhouse- Technical Field The invention relates to a method of controlling a system for irrigation in a greenhouse, said system comprising one or several controlled valves for regulating the supply of water to the growth substratum or to the earth in the growth bed of the greenhouse, said method comprising a determination of the moisture inside the greenhouse. Background Art Automatic irrigation systems are wellknown in connection with greenhouses. Such irrigation systems may be adjusted to submit a constant waterflow or constant water portions at regular intervals, but as the need of w.ater of the plants varies, it is also known to provide for important factors, such as solar radiation and the evaporation of the plant. However, until now the attempt of providing a satisfactory method of this k-ind has not been successful. The known apparatuses, such as solar integrators for con- >trol according to the solar radiation alone is encumbered with the drawback, that in the winter period when the sun is low in the sky, they lose their significance concur¬ rently with the heat radiation from the pipe systems of the heating plant in the greenhouse increasingly influen¬ cing the water evaporation of the plants and consequently the consumption of water in the earth. Apparatuses are admittedly known providing for the evapo¬ ration of the plants by comprising an atmometer registering the evaporation from the surface of a liquid. Such a sur¬ face of a liguid has, however, a tendency to be covered completely or partly with impurities, such as dust. This reduces the evaporation considerably and gives thus an incorrect evaluation of the actual evaporation. Description of the Invention It is the object of the present invention to provide a simple and reliable method and an apparatus, which par- ticularly in the winter period is better than the appa¬ ratuses hitherto known for controlling an irrigation sys¬ tem. ;" The evaporation which occurs partly from the surfaces of the plants and partly from the surface of the earth in the growth beds will depend on the relative atmospheric moisture. According to the invention it is thus suggested to integrate the atmospheric moisture within the greenhouse and control the supply of water as a function of the in¬ tegrated atmospheric moisture. The atmospheric moisture may be measured by means of existing measuring instruments in a considerably more reliable manner than the evapora¬ tion, and as it will be obvious the evaporation will depend on the atmosperic moisture in a predictable manner, viz. in such a manner that the evaporation decreases when the atmospheric moisture increases and vice versa. Special conditions will admittedly apply if the atmospheric mois¬ ture reaches an extremely low level, because the plants themselves will then react by closing all stomata in the leaves and thereby reduce the evaporation drastically. This condition will, however, seldom apply in a greenhouse, as the climatic regulation should always be adapted to avoid such a low atmosperhic moisture, the growth of the plants being stopped under such conditions. When evaluating the connection between amospheric moisture and evaporation it can consequently be assumed that the atmospheric mois¬ ture has a value advantageous to the plants, normally between about 60 - 90% and at any rate above about 40% relative atmospheric moisture. The measurings of the atmospheric moisture are preferably integrated during a given period of time, and an average value of the atmospheric moisture is calculated at regular intervals, and the supply of water is controlled as a function of the latest calculated average value. As a result a reliable expression of the atmospheric moisture is obtained, and by a suitable choice of the period of time a fairly quick regulation of the supply of water is obtained. • in periods with strong solar radiation, namely especially in the spring and summer, a control as function of the atmospheric moisture is not sufficient. The solar radiation causes heating of the plant leaves, and the plant attempts to counteract this heating by a corresponding evaporation. Besides, the solar radiation has an effect on the growth function of the plants, which is .closely connected to the supply of nourishment, which is also contingent on a suf- ficent irrigation." As it is known, the plants receive nourishment for their growth from the water which is sucked by the roots and rises through the stems and leaves of the plants and is evaporated through the stomata of the leaves. As a consequence, the supply of water is preferably controlled both as a function of the integrated atmospheric moisture and dependent on the solar radiation. The measuring of the solar radiation is preferably a mea¬ suring of the heat radiation, as the heat radiation pre¬ sumably has the greatest influence on the consumption of water of the plants . In the method according to the invention the radiation may optionally be measured in such a manner that the heat radiation from the heat pipes of the greenhouse is com¬ prised by the measuring, and in such a manner that the water supply is controlled as a function of the atmospheric moisture, the influx of light as well as of the heat radi- ation . An apparatus according to the invention for controlling an irrigation system may comprise a sensor for measuring the atmospheric moisture and a radiation-sensitive detector for measuring the solar radiation, the signal processing means for determining an evaporation and/or the corres¬ ponding amount of water substitution to be supplied by the irrigation and output circuits connected therewith for controlling the regulating valves of the irrigation system. The sensor for measuring the atmospheric moisture may be a hygrometer or a psycrometer. In its most simple form the sensor is a hair hygrometer. The sensor has, however, to be of the kind capable of transmitting an electric signal corresponding to the moisture. Brief Description of the Drawing The invention will be described below with reference to the accompanying drawing, in which Fig. 1 illustrates an example of an apparatus according to the invention, Fig. 2 illustrates a second embodiment, and Fig. 3 is a flow chart. Description of the Preferred Embodiments of the Invention The apparatus according to the invention comprises a con- trol unit 10 connected with a number of sensors. Among the sensors is at least one sensor 12 for determining the atmospheric moisture and at least one sensor 14 for deter¬ mining the solar radiation. The sensor 12 may be a hygrometer or a psycrometer for dry/wet measuring, for example two electric thermosensors , one wet thermosensor and one dry thermosensor. The sensor 14 may be of the kind comprising a photocell registering the radiation intensity, especially of the sunlight, and is preferably particularly sensitive to infra-red radiation, as the heat radiation is of consider¬ able importance to the velocity of evaporation of the plants and consequently to the consumption of water. The sensor 14 is preferably a socalled thermal cell and pre¬ ferably located at a high level inside or outside the greenhouse, so that nothing shades the sensor. An addi¬ tional sensor 14 may optionally be located in such a manner that the heat radiation from the heat pipes of the green- house is measured, too. The apparatus is on its outlet connected to one or several controlled valves 16 for regulating the supply of water to the growth beds of the greenhouse. The valve 16 may be a solenoid valve, but it is within the scope of the inven- tion to use other kinds of controlled valves. In one embodiment according to the invention the apparatus 10 integrates the reciprocal value of the integrated atmos¬ pheric moisture, and the integrated signal is used for adjusting the supply of water. In a preferred embodiment of the apparatus 10 according to the invention the input signals from the sensors 12, 14 are converted into digital signals transmitted to a microcomputer adapted to process the sizes measured and convert them into adjusting factors. The apparatus pre- ferably calculates an average atmospheric moisture during a certain period, and this value is converted into a cor¬ recting factor or a moisture factor, which is used on a corresponding light factor calculated by integration of the solar radiation during the corresponding period. The regulation according to the invention is particularly advantageous in the winter period, in which the sunlight is relatively weak and consequently of less importance to the evaporation of the plants than in the summer period. An operator, normally a gardener, can adjust the apparatus 10 to transmit a signal to the valve 16 which causes a suitable supply of water. This signal is corrected by the adjusting factor which the apparatus calculates on the basis of the sensors 12, 14 coupled thereto. When the apparatus is installed in a greenhouse, the opera¬ tor adjusts the apparatus to give the amount of water deemed necessary. The apparatus will then itself provide for variations occuring due to changes in the atmospheric moisture and the solar radiation. During the commission the gardener has, however, to estimate whether the adjusted basic value has been suitable and out of experience raise or lower the basic adjustment. When this period of com¬ mission is over, the apparatus can itself perform the nec- essary corrections on the basis of the measuring of atmos¬ pheric moisture and solar radiation. If new species with different irrigation requirements are planted in the growth beds, the gardener must change the basic adjustment. It may furthermore be necessary to change this basic ad- justment as a species grows or due to the seasonal changes of requirements . In a further development of the apparatus such changes of the basic adjustment may, however, be prearranged in a particular control part of the apparatus, so that it pro- vides for the seasonal changes, or so that the operator only has to encode the name of the species and the planting date or age. In an alternative embodiment - shown in Fig. 2 - an ap¬ paratus 30 according to the invention is used together with a traditional irrigation control 20. The apparatus 30 receives a signal for the moisture from a sensor 32 and forms an average value signal which in the signal processing means is converted into a control signal of a solenoid valve 36. The moisture signal from the sensor 32 is preferably converted into a digital signal processed in a microprocessor, which is adapted on its outlet to transmit a suitable number of pulses or a puls of a suit¬ able length to a relay supplying the solenoid valve 36 with current. According to the construction of the existing system such an extension could either be made as shown by means of a bypass with an additional solenoid valve 36 or by means of an additional- circuit to the solenoid valve or in its most simple embodiment by means of an additional circuit to the controlled relay. Fig. 3 illustrates a flow chart of how the method according to the invention is preferably carried out. As it is ap¬ parent from the figure, a number of calculations are per¬ formed in a microprocessor. The microprocessor receives measured data for the wet temperature and the dry tem¬ perature, respectively, converted into digital signals and is, as it is wellknown, capable of calculating the current atmospheric moisture LF. The user preadjusts a predetermined threshold value designated LFG. If the cur¬ rent atmospheric moisture is greater than or equal to the adjusted threshold value, the moisture is of such a mag- nitude that the consumption of water of the plants will not be influenced subs antially by this atmospheric mois¬ ture, and the loop consequently returns and views a new value of the atmospheric moisture, which is consequently constantly supervised. If the calculated atmospheric mois- ture LF is smaller than the adjusted threshold value LFG it means that the atmospheric moisture is so low that a further evaporation from the surface of the plant- leaves will take place, and more water must be supplied. The difference between the current atmospheric moisture and the adjusted threshold value is then preferably calculated, and this value A is modified by means of a predetermined constant K to a socalled "simulated solar radiation" and is then transmitted to an integrator which simultaneously receives information as to the solar radiation which is also integrated, and the output signal is then used for regulating the supply of water to the irrigation system. As a result a system is obtained ensuring a sufficient irrigation both in sunny periods and in periods with little sun.

Claims: Claims 1. A method of controlling a system for irrigation in a greenhouse, said system comprising one or several con¬ trolled valves for regulating the supply of water to the growth substratum or to the earth in the growth bed of the greenhouse, whereby the atmospheric moisture within the greenhouse is determined, c h a r a c t e r i s e d in that the atmospheric moisture is integrated, and that the supply of water is controlled as a function of the integrated atmospheric moisture. 2. A method as claimed in claim 1, by means of which temperature, atmospheric moisture and influx of light are determined currently and regulated according to predeter¬ mined directions . c h a r a c t e r i s e d in that a threshold value corresponding to a predetermined atmos¬ pheric moisture is adjusted, the atmospheric moisture is compared to the adjusted thres¬ hold value, the next measuring is merely awaited, if the atmospheric moisture is greater than or equal to the threshold value, if the atmospheric moisture is smaller than the threshold value, the deviation - =» the distance is calculated in percentage of- the atmospheric moisture measured up to the adjusted threshold value, the calculated deviation A, is multiplied by a constant factor and is thereby converted into a socalled "simulated solar radiation" , the simulated solar radiation is added to the real solar radiation, which is measured currently, the irrigation is regulated as a function of the sum of real and simulated solar radiation. 3. A method as claimed in claim 1, c h a r a c - t e r i s e d in that the atmospheric moisture is in- tegrated during a given period, and that an average value of the atmospheric moisture is calculated at regular inter¬ vals, and that the supply of water is controlled as a function of the latest calculated average value. 4. A method as claimed in claim 1, c h a r a c - t e r i s e d in that the solar radiation is measured within or outside the greenhouse, and that the supply of water is controlled as a function of the atmospheric mois¬ ture as well as the solar radiation. 5. A method as claimed in claim 4, c h r a c- t e r i s e d in ttiat the heat radiation from the sun in the greenhouse is measured, and that the supply of water is controlled as a function of both the atmospheric mois¬ ture and the heat radiation. 6. An apparatus for performing the method as claimed in claim 1 or 2 and comprising a sensor (12) for measuring the atmospheric moisture, c h a r a c t e r i s e d in that the sensor on its output is connected with signal processing means (10) adapted to integrate the atmospheric moisture and to transmit one or several electric signals on the output for controlling a number of valves for re¬ gulating the supply of water to an irrigation system, said signals at least being a function of the integrated atmospheric moisture. 7. An apparatus as claimed in claim 6, c h a r a c- t e r i s e d in that the apparatus is furthermore con¬ nected to a sensor (14) for measuring the solar radiation, and that the signal processing means (10) are adapted to provide for the influence of the solar radiation on the consumption of water. 8. An apparatus as claimed in claim 7, c h a r a c¬ t e r i s e d in that the signal processing means in- tegrate the solar radiation - preferably including the heat radiation - during a given period of time and on the basis hereof calculate the light factor, which is again corrected by a moisture factor calculated on the basis of an average value of the relative atmospheric moisture during the given period of time. 9. An apparatus as claimed in claim 7 or 8, c h a r a c¬ t e r i s e d in that the radiation sensor (14) in par¬ ticular measures the heat radiation of the sun.

Inventors: JENSEN NIELS THORKILD, JENSEN, NIELS, THORKILD
Applicants: THORKILD JENSEN NIELS, JENSEN, NIELS, THORKILD
Application year: 1986
Main classification: A01G9
IPC codes: A01G9