Harsh Kaji, Shruti Annigeri, Prof. Prafulla Patil / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 3, Issue 2, March -April 2013, pp.1329-1333 1329 | P a g e Designing PID Controller using LabVIEW for Controlling Fluid Level of Vessel Harsh Kaji, Shruti Annigeri,*Prafulla Patil Instrumentation Department, Vidyavardhini‟s College of Engineering and Technology *Professor, Instrumentation, Vidyavardhini‟s College of Engineering and Technology ABSTRACT The primary aim of our project is to replace the PID instrument with virtual PID that has equal controlling capabilities as that of instrument. This designing is possible on software called LabVIEW developed by National Instruments. We also intend to use a DAQ card for interfacing with the hardware. This DAQ card is product of the same company National Instruments. The hardware is a Multiloop Trainer Kit mounted with a tank whose level has to be controlled using a feedback control loop. The flow of project execution is: The designed PID will be generating the necessary controlling electronic signal. This signal will be acquired by DAQ card. The DAQ card transfers it to the I to P converter which will convert the electrical pulses 4-20mA into pneumatic signal 3-15psig to actuate the control valve. This conversion take place as the control valve acts on pneumatic signals only. The control valve controls the fluid flow to maintain the fluid level in tank. The tank is fitted with a capacitive level sensor and a transmitter. This assembly takes the level readings from tank and transmits it to the DAQ card. These values are called process values and are further processed into the designed PID. This way a closed loop system is formed. KEYWORDS DAQ card (Data Acquisition),LabVIEW (Laboratory Virtual Instrument Engineering workbench),PID. INTRODUCTION In the present era of Industrial Automation, ease of work is one of the major concerns. This design enables the operator to operate the process sophisticatedly with an ease. Instead of giving manual inputs to the PID, this designed PID can adjust the input parameters just by mouse clicks. Firstly what is a control system? A control system is a device, or set of devices to manage, command, direct or regulate the behavior of other device(s) or system(s). There are two common classes of control systems: logic or sequential controls, and feedback or linear controls. There is also fuzzy logic, which attempts to combine some of the design simplicity of logic with the utility of linear control. I. PID THEORY The „P‟ stands for proportional control, „I‟ for integral control and „D‟ for derivative control. This is also what is called a three term controller. The basic function of a controller is to execute an algorithm (electronic controller) based on the control engineer's input (tuning constants), the operators desired operating value (set point) and the current plant process value. In most cases, the requirement is for the controller to act so that the process value is as close to the set point as possible. In a basic process control loop, the control engineer utilizes the PID algorithms to achieve this. Proportional action: It simply amplifies the error based upon the gain. P mode generates offset. Integral action: The integral term magnifies the effect of long-term steady-state errors, applying ever-increasing effort until they reduce to zero. In the example of the furnace, working at various temperatures, if the heat being applied does not bring the furnace up to set point, for whatever reason, integral action increasingly moves the proportional band relative to the set point until the PV error is reduced to zero and the set point is achieved. In the furnace example, suppose the temperature is increasing towards a set point at which, say, 50% of the available power will be required for steady-state. At low temperatures, 100% of available power is applied. When the PV is within, say 10° of the SP the heat input begins to be reduced by the proportional controller. (Note that this implies a 20° "proportional band" (PB) from full to no power input, evenly spread around the set point value). At the set point the controller will be applying 50% power as required, but stray stored heat within the heater sub-system and in the walls of the furnace will keep the measured temperature rising beyond what is required. At 10° above SP, we reach the top of the proportional band (PB) and no power is applied, but the temperature may continue to rise even further before beginning to fall back. Eventually as the PV falls back into the PB, heat is applied again, but now the heater and the furnace walls are too cool and the temperature falls too low before its fall is arrested, so that the oscillations continue. Derivative action: The derivative part is concerned with the rate-of-change of the error with time: If the measured variable approaches the set point rapidly,