Defying the frost

Agricultural company Thiermann uses SIMATIC S7-1200 controllers to protect its blueberry crop against springtime cold snaps. 
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Dangers of spring

Cold spring nights pose a particular challenge to fruit growers such as Heinrich Thiermann of Kirchdorf, in the state of Lower Saxony, Germany. Overnight frost – often following the first warm days of the year – is a major threat to the farm's huge blueberry orchards. But the family business is well prepared, utilizing water to combat frost and avoid the risk of losing its crop.

The farm grows fruits and vegetables in addition to ­conventional agricultural crops; raises pigs; grows wheat and corn; and it also produces biogas and wind power. A large workforce is employed to run the farm's opera­tions – including the marketing and logistics of its products – using state-of-the-art technology that enables the company to achieve a sustainable, eco-friendly production environment.

However, not even relentless effort can guarantee the ­protection of its sensitive blueberry crop from the threat of freezing overnight temperatures. In fact, as this fruit matures, the more susceptible to the cold it becomes; and if blueberry buds freeze, no fruit will be produced and an entire crop could be wiped out – creating a major loss in revenue. In 2010, Thiermann experienced such an event in dramatic fashion: almost half of its approximately 2,000-ton blueberry crop fell victim to frost. As a result, the company now utilizes automation systems from Siemens to prevent the recurrence of such a disaster – specifically, the LOGO! logic module coupled with SIMATIC S7-1200 controllers.    


Combating ice with water

Thiermann has installed a water sprinkler system in its orchards, which effectively counters any sudden drop in temperature and thus eliminates frost damage. Several hundred sprinklers were placed at regular intervals throughout its approximately 617-acre blueberry orchard site, in order to spray the tops of the bushes with water if necessary.

"The sprinkler system is a way of preventing the sensitive blueberry fruit from freezing," explains blueberry orchard manager, Rainer Plenge. "The timing of when to activate the sprinklers depends on how far advanced the fruit is. If the buds are still closed, we wait until the temperature drops to minus 0.5°C. But as soon as they are open, we activate the pumps when the temperature reaches the freezing point."

This method of protection against frost relies on the ­physical properties of water. When water transitions from the liquid to the solid aggregate state, heat is created. As a result of water being continuously sprinkled onto the frozen bushes, the process of freezing is sustained – and the internal temperature of the iced-up bushes, buds or fruit actually increases and protects them from frost damage. "But the method only works if we sprinkle the fruit with water continuously," Plenge explains. "If sprinkling is interrupted, the fruit will freeze because its surface will lose heat due to evaporation chill. As soon as the daytime temperature rises back above freezing, we shut down the sprinklers. The ice melts, and the water seeps away into the soil."    

Without the sprinklers, we would have suffered losses totaling millions of euros.
Rainer Plenge, Blueberry Orchard Manager

State-of-the-art pump automation

In order to ensure that the sprinkler system is continually supplied with water, wells were dug along the perimeter of the orchards and fitted with pumps. In addition, a control cabinet was installed at each pumping station equipped with the necessary control components. The components installed at each station include a LOGO! 8 logic module with a 24V power supply unit, and an analog expansion module for connecting pressure and temperature sensors. There is also a SIRIUS soft starter to limit the power when switching on the pump, along with a SCALANCE M826-2 router.

Seventeen of the 34 pumping stations are connected by the router to a central header station via two-wire DSL cables, while the others use an additional SCALANCE M874 router to connect over a GSM mobile network. Featuring firewall functionality and VPN tunneling, a SCALANCE S615 security module protects the network and integrated systems against unauthorized access; and it is additionally connected to the SINEMA Remote Connect management platform. The distributed stations then can be centrally controlled and serviced in a secure, user-friendly manner via remote access. The SINEMA server provides a reliable basis for further expansion of the network and also makes it easier to configure station parameters and administer IP addresses.

In the header station's control cabinet, four SIMATIC S7-1200 controllers perform various monitoring and control tasks. If the ambient temperature falls to 0.7°C, an alert is sent to a SIMATIC PLC. A 12-inch SIMATIC HMI TP2100 Comfort color display enables personnel to switch the units on and off, and to monitor and control the pressure and temperature at each individual pumping station – even from a smartphone – using the Smart Server option.


Success thanks to SIMATIC S7-1200

This level of automation has not always been in place. When the sprinkler system was first installed in 2010, water was sprayed with the aid of mechanical pressure switches and timer relays. The pressure switches were extremely difficult to adjust, so in early 2013, the system was made electronic.

Pressure sensors dictate when a pump needs to switch to self-locking mode; and LOGO! controls the startup phase by way of a timer relay until the correct pump pressure has been built up. As soon as a sensor detects a high or low pressure in a pipeline, the logic module shuts down the electric pump. In addition to pressure, the microcontroller also monitors ­temperature by means of resistance thermometers: if the temperature reaches a predefined threshold value, it ­notifies an S7-1200 CPU in the header station, and a worker then activates the sprinkler system on the touch panel. The command is sent to the LOGO! controller at the corresponding field station, which monitors all pump-­related data and activates the pump.

The controls and electrical systems were implemented by contractor Wilhelm Schwenker Elektro with the ­assistance of Helmut Kiehling, a design engineer with ­electrical wholesaler Frommeyer + Ziegemeyer K. Beine GmbH & Co. KG.

Adjusting performance data quickly and precisely

The logic modules permit precise, extremely fast adjustment of the specified performance data. The actual values measured by the sensor are indicated on the LOGO! display, and presets can be changed using the keypad. The program also takes into account safety factors such as shutdown in instances of zero or minimal pipeline flow. Control and status information is continuously exchanged between the S7-1200 controllers and the LOGO! modules in the field. These SIMATIC controllers have been configured using the TIA Portal engineering framework, while the programs for the logic modules were developed using LOGO! Soft Comfort.

The extent to which the Thiermann family's blueberry crop is benefiting from this new technology was demonstrated once again in the spring of 2017. From early April to mid-May, there were a number of cold snaps triggering frost alerts. "On fourteen nights, temperatures fell so low that we had to sprinkle the bushes," recalls orchard manager Plenge. "On a few occasions, the crops were still covered with ice in the early afternoon. Without the sprinklers, we would have suffered losses totaling millions of euros."

Note on industrial security:
Appropriate security measures (e.g., network segmentation) must be taken to ensure secure operation of the system. Find out more about industrial security.

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