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Many of the lab experiments run by the AguaClara team use Process Controller, a LabVIEW based program, to run methodically run experiments and collect data. Users can configure sensors to control the system and collect data simultaneously. Before any experiments are run, Process Controller must be programmed correctly to control the processes of the experiment. There are four types of things that need to be defined in Process Controller in order for the program to control any process. These are Set Points, States, Rules and Sensors.
Basics
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- States: States represent different control configurations. Each has different control settings and each have different rules that determine when the state ends and what state comes next. Each state has independent control settings which means that each is defined uniquely by which pumps are on or off and which valves are opened or closed. It is these states that tell Process Control what to make the system do. Not all are necessarily used in a process; states can be designed for testing pumps, to clean the system and so on. States are listed in a drop-down list and can be added or removed BUT they are place sensitive meaning each is assigned an identification number in the list of states so deleting a state will alter the number ID of the states proceeding it. When using a state you must pull it using this number. Also important to remember is that the first position is "0", not "1".
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- Rules: Rules set exit conditions for states. It tells a state when to turn on, off, or switch to a different state. Rules can have multiple conditions and can be based of sensor values, time elapsed in a state, etc. They are executed sequentially and the state will change upon reaching the first true rule ("if" statement-causes state to exit). Rules are defined using a greater-than or equal to sign so one must be careful to ensure that set points are defined properly.
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- Sensors: Process Control is setup so individual sensors and meters (such as a turbidimeter) can directly transmit their information to Process Controller. Information obtained from these is stored and can also be used to control how the program behaves. They must be properly calibrated with the Process Controller software in order to obtain meaningful units. There are conversion files for doing this.
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- Set Points: Values that process controller uses in defining States and Rules. They can be either constant or variable and can define the flow rate through a pump for example. Like states, set points are assigned a numerical identification number based upon their position in the list. Set points can be called by name, unlike states, but they are still identified internally by this number. When one is deleted the internal sequences becomes a mess so generally we do not delete set points once they are created, even if they are not being used. Set points can use pre existing methods (in the methods folder) that will need to be imported. The set points (if) required by the method will be listed under Required Set Points and these required set points will need to be selected. If the set points used do not match those required the light next to "data match" will be red, indicating an error.
Experimentation
Before running process controller for the day, you first must create a new folder to save data collected on this day. To do this, go to Datalog directory path and click the folder icon to the right. Create a new folder titled with the days' date in the format of MM.DD.YY and save by selecting Current Folder. Process Controller will save two excel files of the experiment in this folder: a datalog file and statelog file. The first column in both files is a time stamp that records time as a fraction of the day. The statelog file tracks when a state changes and what caused it to change; whether it was a rule or it was changed by an operator.
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