The system consists of the following elements:
- 1 SIEMENS PLC S7-314-2DP programable controller.
- 1 input node with 2 output modules with 4 analog 4-20 mA inputs each.
- 4 humidity-temperature sensors with 4-20 mA outputs.
- 1 PC with Windows 2000 equipped with a CP 5611 SIEMENS communication card running Siemens WinCC-based SCADA.
The programmable controller and remote I/O node form a PROFIBUS DP network in which the controller is configured as master and the remote I/O as a slave. Communication between the programmable controller and the computer is established via an MPI point-to-point line.
The programmable controller autonomously runs a continuous control program, and transfers and receives the data it requires from the computer. The controller also permanently monitors the operation of the computer and emits a signal to reset the computer if a malfunction is detected (block). The automatic controls programmed into the controller, and configurations settable from the SCADA system control the micro-sprinkler system by performing rotations or cycles for each of the plant growing areas and leaving rest periods between each cycle.
Rotations begin if the system is in AUTO mode and the operator has activated one of the two sub-modes of operation: by time or by limits.
BY TIME: The micro-sprinkler system automatically switches on and off according to two daily periods defined by a start and end time. Every day, until the operating mode of the system is changed, the micro-sprinkler is activated and rotates for the periods specified. The figure shows how the system always ends the current cycle, even if the sub-mode is disabled or the period ends. In contrast, the change from automatic to manual is performed immediately.
BY LIMITS: The system connects and disconnects the micro-sprinkler automatically based on given limits of temperature and humidity for the greenhouse. The operator can set:
- Maximum temperature limit
- Minimum temperature limit
- Minimum humidity limit
- Hysteresis range for temperature
- Hysteresis range for humidity
The main features of the SCADA application are:
- enables data to be visualised in real time
- enables the micro-sprinkler system to be operated manually
- enables all the automatic micro-sprinkler system parameters to be configured
- stores sensor readings in database
- enables graphics to be produced from database information.