Design Of Plant Factory Controller For Optimal Growth Of Tomatoes

Instructions are listed by mnemonic in alphabetical order. The information provided about each instruction is: its assembler syntax, its attributes (i.e., whether it takes a byte, word, or longword operand), its description in words, the effect its execution has on the condition codes, and the addressing modes it may take. The effect of an instruction on the CCR is specified by the following codes:
U The state of the bit is undefined (i.e., its value cannot be predicted)
- The bit remains unchanged by the execution of the instruction
* The bit is set or cleared according to the outcome of the instruction.

Unless an addressing mode is implicit (e.g., NOP, RESET, RTS, etc.), the legal source and destination addressing modes are specified by their assembly language syntax. The following notation is used to describe the 68000's instruction set.

Instructions for Designing the Plant Factory Controller

The objective is to design a plant factory controller so as to optimise the environmental conditions and promote the growth of tomatoes within the facility. The controller is expected to affect actuators so as to maintain the required ambient temperature and humidity. The controller make decision depending upon the end product received from the sensors install it with its locations within the facility achieve these objectives we need to achieve following smaller milestones in the sequence as mentioned

• Refer to research in agricultural production practices and determine the optimum conditions for the growing of tomatoes
• Design a system specification for the control system to provide optimum growth conditions at the farm

3) Select most effective components needed to implement this system

4) Develop required programmes for system controller

5) A comparative evaluation of the developed systems

Completion of above listed milestones will help us design a system that is capable of delivering the required output and maintain the growth parameters to the maximum efficiency level within the facility.

Procedures:

1. The first step to achieve the objectives is to study the growth pattern of tomatoes and its growth cycle. The required environmental free parameters like temperature humidity soil temperature and light conditions.
2. Study different kind of sensors and actuators, list their operating range and their working conditions. This shall help choose the best possible device options for input sensors and output actuators.

• Work through the voltage and current ratings for the sensors and microcontrollers and develop interfaces.

1. Create software program for the PLC or the microcontroller and test out the design after interfacing the required sensors in the controlled test environment
2. Optimize the design and the program to work efficiently for long working hours during different times of day and night.
3. Install the design in test facility and monitor the results for possible duration.

Flowchart:

Flowchart for the program to control the system parameters.

1. Read Temperature sensors
2. Read humidity sensors

• Compare the measurements and provide indications using Tower light. Adjust Fan speed and direction as per readings

1. If  Temp 22-28, Humidity 60%-80%: Tower Light Green; Fan off
2. If Temp < 22 or Humidity < 50% ; Tower Lights Orange: Fan on : inflow
3. If Temp > 30 or Humidity > 80% ; Tower Light Oraange: Fan on: outflow

• If Temp < 15 or Humidity < 25%; Tower Light Red; Fan on : inflow
• If Temp > 40 or Humidity > 85%; Tower Light Red; Fan on : outflow

1. Loop

Discussion:

Research about the operations of a plant and collect information about process of growth of tomatoes in a closed environment. This is followed by selection of sensors required to capture the required parameters. Once sensors are attached to the controller, their readings can be used to affect the conditions of the plant using suitable systems. This will involve use of actuators to activate mechanism installed in the facility for temperature control, humidity control and other environmental conditions as necessary to promote growth of the tomato plants.

1. Research to determine the optimum conditions for the growing of tomatoes and the use of this information to determine the specifications for the control system. Plant factory is concept to mechanize the farming process so that products can be grown in controlled environment irrespective of climate and region. This involves being able to control factors like light intensity, air temperature, air humidity, mineral nutrition, water flow etc. to an optimal level and promote growth of crops. The central control system at the facility controls the heater, fan, water pump, and nutrient solution and humidifier actuators as per feedback from sensors in real time.

A threshold needs to be set for the actuators to be fired for certain duration. The threshold decision is based on values read by sensors deployed at the plant. For a tomato plantation various studies have been conducted. The plant growth is divided into 5 stages. Time for first fruition depends upon the variety of the plant but mostly fall in the range of 70-80 days. Expected temperature for the plants also depends upon their growth stage but a usual 22-25?C range is considered conducive to growth. Next important parameter is humidity. There are three ways it is measured in terms of absolute humidity, specific humidity and relative humidity. Out of these relative humidity is most commonly used term of measurement.  The humidity range between 60-90% is considered appropriate for growth of the tomato plants in a closed environment.

1. A selection process to determine the most appropriate components for such a system. The system shall require two types of sensors to measure temperature and humidity. Some kind of actuators would be needed to activate fan and control fan direction. Another set of actuators would be required to toggle between Tower light colors.

Sensors are device that measure a physical measureable quantity and provide an equivalent value as an electrical signal directly proportional to the value being measured. The sensors ability to measure smallest change is called its resolution and ability to measure the smallest possible and largest possible temperatures is called its range. Sometimes the measurements are in form of continuous or analog signals and sometimes as digital discrete signals. The one we choose depends up on the interface being used in the design and capability of the controller.

We need two types of sensors that measure temperature and humidity. The sensors must provide this input to the microcontroller in a digital format or else the system will need to use an Analog to Digital convertor to convert the analog values into digital byte value.

1. Temperature sensors: The sensors use ability of materials to change their resistivity or capacitance in response to change in their surrounding temperature. This change causes fluctuation in current or voltage across the affected material. This change is converted into an analog signal and measured as evidence of change in temperature. The relation of change in current or voltage to temperature depends upon heat sensitive material being used. The type that suits the plant requirement is one with low resolution but wider temperature range from 0C to at least 70C. Also the sensor needs to be low cost as many would be needed across the location with capability to provide current levels high enough to travel substantial distance. Else signal may fade to an erroneous value before being captured by the controller.
2. Humidity Sensor: These measure the amount of water vapor present in air. The sensor uses a material that can respond to change in its conductivity in relation to moisture level in air. The change in current or voltage is measured as a response to change in water moisture level in the surrounding area of the sensor. Since the sensor must operate without error for long duration in testing conditions, it must be made sure that it can deal with oxidation without affecting its functionality.  So it is expected to be encased in a plastic casing exposing only the required sensor area to air for taking measurements. Again the requirement is the signal generated by the sensor must be amplified enough to travel distance up till it is received by the controller.

Procedures to Design the Plant Factory Controller

The sensors must be tested from time to time after installation to check their accuracy as long operation times in continuous harsh environments may affect their ability to measure the parameters. A reference sensor must always be kept in safe place to use as reference when calibrating the installed sensors. The model and make of the sensors used for calibration and installation must be the same.

1. Actuators: The devices are needed that can be turned on or off by the controller and can affect other device. For the plant design, relays are best suited and they can operate at high voltage and act like a switch. The relay can be connected between the power supply and the device and controlled from distance to allow or disallow flow of current to the device. The relay must be large enough to allow sufficient amounts of current to pass through them when turned on but at the same time, capable to be switched on by small amount of current. They are driven from microcontroller via an interface. Interface is required to match output current levels of the controller that is in range of few microamperes with that of the input current requirements of the relay in range of few hundred mill amperes. Interface must also take into account the distance between the controller physical location and placement of relays in the plant.

 The controller can then decide about switching the fans on or off to get the required conditions within the plant area. In case Microcontroller is used, the temperature may be provided as 8 bit value that can be interpreted by the controller and decided upon. In case a PLC is used, the sensors need to provide a single bit input like above 25 and below 25 to decide the position of fans.

• Selection of microcontroller: The controller plays an important role in the effectiveness of the whole system. The decision making is done by the controller.
  1. Any delay in responding to the inputs can affect the overall system effectiveness. This requires the controller to have speed of operation that matches the requirements of the plant.
  2. The programming of the controller should provide the ability to manipulate the sensor inputs and drive values to output ports. The instruction set and hardware should have capability for bit manipulation and arithmetic operations for calculations of sensor values.
  3. Microcontroller also needs to have sufficient number of I/O interfaces to connect with all possible sensor inputs and drive the required number of actuators. The interfacing circuit must be minimized as additional circuits increase the cost and complexity.
  4. Casing of the entire controller and device interfaces needs to be packaged in an environment resistant package. The controller should be capable of working in highly humid environment without errors.

1. System Design: The block level design of the typical plant is discussed here that can be expanded to larger area if needed. The left hand side shows all sensors and right hand side has all of actuators. Central part is the controller that processes the measurements and generates suitable outputs.

The system shall receive the inputs from sensors as analog voltage signal continuous in time. The inputs from sensors shall get converted into digital values using an A/D convertor. The digital signal is such that entire range is divided into 256 levels. The output of ADC is 1 byte in size for one sample value read from sensor. This digital value is now read by controller and matched to pre-programmed values. The decision is taken as per the program control flow. The result is then passed on as a digital 1 byte signal to the Digital to analog convertor. The convertor drives the actuators as required.

1. Controller Program: the program depends upon the actual controller model being used. A generic pseudo code for the program would be:

Initialize Port 1 as input

Initialize Port 2 as ouput

Start:

Scan Port 1 for sensor values

If temperature value with 22-28 and humidity 60-80

Call Tower_Green

Call Fan_Off

Loop_start

If temperature value < 22 or humidity < 50

Call Tower_Orange

Call Fan_Inflow

Loop_start

If temperature value > 30 or humidity > 80

Call Tower_Orange

Call Fan_Outflow

Loop_start

If temperature value < 15 or humidity < 25

Call Tower_Red

Call Fan_Inflow

Loop_start

If temperature value > 40 or humidity > 85

Call Tower_Red

Call Fan_Outflow

Loop_start

1. A comparative evaluation of the developed systems: Systems based on Microcontroller are more adaptable to change in setup if need be. The optimum temperature and humidity conditions vary based on variety of tomato and may be entirely different for a different crop type. Using microcontroller with input feature to set required temperatures and humidity levels can help in case of a new crop or new variety. Sensor calibration is also possible in case microprocessors are used. All of this flexibility is not possible in case of PLCs.

Next is hardware upgrade is easier with Microprocessor if a new sensor has to be added to the existing system or a new actuator is to be added. PLC is hardwired that makes it hard to modify or upgrade to accommodate a new input/output device. Overall microprocessor is more costly at initial stage but flexibility of the system pays off in the long run.

Conclusion

Sensors need to be chosen for wider range of measurement than for higher resolution. Temperature sensor with range of 0?C to 100?C is preferred in resolution of 1?C. Speed of communication is not a concern but operating time should be in weeks without fail. Sensors must be checked for calibration from time to time.

A microprocessor based system is preferred for implementation for the plant. The number of sensors and actuators will depend upon the area to be supervised and may need external interface to multiplex sensor inputs to the controller. Similarly de-multiplexer might be needed as an external interface to connect actuators for devices.

References

Clifford K. Ho, *. A. (2005). Overview of Sensors and Needs for Environmental Monitoring. Retrieved from https://www.ncbi.nlm.nih.gov: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3909362/

Genting Garden. (n.d.). Retrieved from https://hanwell.com/: https://hanwell.com/app/uploads/genting-gardens-case-study.pdf

Redmond Ramin Shamshiri, J. W. (2018). Review of optimum temperature, humidity, and vapour pressure deficit for microclimate evaluation and control in greenhouse cultivation of tomato: a review. Internation Agrophysics.

Tian, L. &.-h. (2014). A Study on Crop Growth Environment Control System. International Journal of Control and Automation.