In the winter irrigation is low and in summer more water is used. "With a drip system, irrigation in summer is a maximum of 10 liters per square meter per day and in winter this is only 0.25 liters. That is a factor 40 difference, something you normally do not encounter," says Stefan Bakker, product manager at Revaho. "And yet growers want an installation that can deliver the 0.25 and 10 liter accurately. This requires advanced measurement techniques."
Varying tap compartment size
In addition to the relationship between irrigation in winter and summer, there are also companies with varying tap compartment size in the irrigation system. For example, 5 to 30 m3 / hour. During the winter period only one drip session of 90 seconds per day is provided, the irrigation water at the tap compartment of 5 m3 / hour is 125 liters and at that of 30 m3 / hour it is 750 liters. In addition to the deviations in the system, also inaccuracy in the water measurement is caused by the slowness in the system. A liter counter, which emits a pulse every 10 liters, produces at 750 liters an inaccuracy of 1.3% (10/750). At 125 liters this is 8% (= 10/125).
Trend to higher pulsing
With a water meter with a higher pulse output, for example at 1 liter (1 on 1), measuring is more accurate. At an irrigation of 30,000 liters per hour, these are 30,000 pulses, or 8 pulses per second. Bakker: "A read contact cannot handle so many pulses, which results in contact flapping. The contact begins to flap because it opens and closes so quickly that additional pulses are created. This is a limitation of the water meter. Yet growers want a high accuracy, because a deviation of 8% is too much and so it is preferable to a pulse output of 1 to 1 and no contact flapping."
In a mechanical water meter with a propeller also pollution of the blades plays a role. As a result, the wheel rotation slows, reducing the accuracy of the water meter. Wear and tear also makes the wheel turn stiffer and deviating (less accurate water measurement). For uniformity it is important to continue to measure well and to have the correct pulses.
Electronic water meter
The solution is a water meter with electronic output without read contact. These meters do not have a counter (mechanical mechanism) anymore. An ultrasonic water meter is an example of such a meter. With this meter a higher accuracy has been achieved in the horticulture sector. "Increasing the measuring accuracy is possible by taking a step in the technology. Even giving 10 pulses per liter is possible. This does not solve the slowness of the system, but rather the measuring accuracy at low frequency and low water quantity", according to Bakker.
Source: Glastuinbouw Waterproof