Duhok Polytechnic University College of Technical Engineering Department of Petrochemical
LEVEL CONTROL FLOW CONTROL PRESSURE CONTROL By
Siyar M. SALEEM Nabee H. MULHAM Ibrahim ABDULQADIR Dildar MUSHIR PROCESS CONTROL Practical
Group B Report No. 1
TABLE CONTENT
Experiment Experiment C1: Level Control Control ................................. .................................................. .................................. ...................2 ..2 Experiment Experiment C2: Flow Control Control .................................. ................................................... ................................. ................ 10 Experiment Experiment C3: Pressure Control Control ................................. .................................................. .............................. ............. 21 Experiment Experiment C4: Temperature Control .................................. ................................................... ...................... ..... 29
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Experiment 1: Level Control
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OBJECTIVES
To study the main components of a level control system. To study the influence of controller design on control action and disturbance response.
To study the stability of a control loop.
To study the controller optimization.
INTRODUCTION
The RT 010 liquid level control model represents a typical loop control system, as is standard and widespread in engineering. The actual loop is a cylindrical liquid level tank made of transparent plastic. A water supply tank positioned below it contains an electrically operated immersion pump. This acts as the actuator and is used to deliver water into the liquid level tank. The liquid level in the tank is measured by a pressure sensor using the height of the water column and is transmitted as an electric voltage signal. The liquid level can also be read on a scale on the tank itself. To represent the removal of water from the tank, an electric proportional valve acts as an adjustable discharge. This means that additional disturbances are possible in the system. The water pours back into the supply tank, resulting in a closed circuit that does not require an additional water supply. The model must be supplemented by a separate external controller to create a complete control loop. It communicates with the peripheral equipment (e.g. a PC) via a USB interface. The most suitable control and regulation program is the associated software RT 010- RT 060.
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DESCRIPTION
1)
EQUIPMENT LAYOUT:
1.
Liquid level tank
2.
Pump
3.
Pump Overflow
4.
Supply tank
7.
Pump switch
8.
Button for complete opening of bleeder valve (Z = 100 %)
9.
Bleeder valve signal lamp
5.
Bleeder valve, electric, proportional
6.
Pump signal lamp
10.
Master switch
11.
Pressure hose for liquid level measurement
USB plug-in connection (rear of unit). Mains connection (rear of unit).
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2)
PROCESS DIAGRAM
3)
FUNCTION
The RT 010 liquid level control model is used as a simple loop for a controller. It does not include a controller itself; all control processes must be run externally. The model communicates with external devices via a USB interface, for which it has a plug-in connection on the rear. The actuator is an electric immersion pump (2), which delivers water from a supply (4) in to the liquid level tank (1). The pump must be actuated by an external input signal, e.g. from a controller. The liquid level is recorded using the pressure of the water column in the tank. The level tank contains an ascending pipe for this purpose. An air hose (11) conveys the pressure from its upper end to a pressure sensor inside the unit. The liquid level is then provided as an electric voltage signal. The electrically operated bleeder valve (5) can be used to set the discharge from the tank by assigning the influencing variable Z. the valve operates proportionally and can be variably adjusted. Its position can only be influenced by external control (e.g. via a PC). 5
The exception is a disturbance in the system. The bleeder valve can be spontaneously switched to Z = 100% using the button (8). The overflow (3) prevents water from escaping if the discharge through the valve (5) is not sufficient. The pump signal lamp (6) and the bleeder valve signal lamp (9) indicate whether the respective elements are actuated.
NOTE: to deliver water into the filling tank, the pump must overcome the pressure of the water column up to the tank cover (~ 30cm = 30mbar). This means that water only reaches the tank with an input signal above ~ y ≥ 40%. 4)
COMMISSIONING
Using the hole in the cover, fill the supply tank (4) with water until the pump is completely submerged and all hoses and pipe ends are below the water level (~3.5ltr) Connect the model to the mains using the connecting socket on the rear. Using the USB port on the rear of the model, connect it to an external controller (e.g. PC). Switch on the model at the master switch (10). Press the button (8) to check the functioning of the bleeder valve. The model is now ready for use.
NOTE: Differing values for the liquid level maybe displayed on the PC. This is because the water level in the ascending pipe does not exactly correspond to that in the tank (e.g. due to residual water, air bubbles etc.). REMEDY:
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Switch off the pump and completely drain the liquid level tank by pressing the button (8). Carefully remove the air hose (11) on the top of the filling tank. Using the fitting, blow air into the ascending pipe to expel any residual water or air bubbles located in the pipe.
SHUTTING DOWN
To shut down, switch off the model at the master switch. If the model will not be used for a long period of time, disconnect it from the mains and drain the water. To do this, allow the water to drain out through the bleeder on the rear of the supply tank with a suitable hose. The unit is maintenance free and does not require any additional servicing. EXPERIMENTAL PROCEDURE
The loop behavior is determined by a step in the reference variable and observation of the resulting transient response
Select “Manual” operating mode.
Set disturbance Z= 10 %
Set manual regulation ratio Y= 40 %, wait for steady state, and TAKE CARE OF OVERFLOW. Perform step in manual regulation ratio,
Y= 40 %
Observe the response.
Perform step in manual regulation ratio,
Y= 100 %
Perform step in manual regulation ratio,
Y= 0 %
Observe the response.
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100 %, wait for overflow of liquid level tank.
0 %, allow liquid level to drain. 50 %, wait for overflow of liquid level tank.
Experiment 2: Flow Control
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OBJECTIVES
To study the main components of a flow control system. To study the influence of controller design on control action and disturbance response.
To study the stability of a control loop.
To study the controller optimization.
INTRODUCTION
The RT 020 flow control model represents a typical loop control system, as is standard and widespread in engineering. The actual loop is a piping system, through which water is constantly pumped in a circuit from a tank. The flow in this system can be influenced by an electric regulator valve. To do this, it is actuated by an external controller. As a disturbance, the speed of the pump can be changed. In the system, the flow is recorded using an electric flow sensor on the turbine principle. The circuit also contains a flow meter with float. The model must be supplemented by a separate external controller to create a complete control loop. It communicates with the peripheral equipment (e.g. a PC) via a USB interface. The most suitable control and regulation program is the associated software RT 010- RT 060.
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DESCRIPTION
1)
EQUIPMENT LAYOUT:
1.
Flow meter, with float
2.
Regulator valve
3.
Pump signal lamp
4.
Pump
5.
Water tank
6.
Flow meter, turbine
7.
Master switch
8.
Valve signal lamp
9.
Pump switch
USB plug-in connection (rear of unit). Mains connection (rear of unit).
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2)
PROCESS DIAGRAM
3)
FUNCTION
The RT 020 flow control model is used as a simple loop for a controller. It does not include a controller itself; all control processes must be run externally. The model communicates with external devices via a USB interface, for which it has a plug-in connection on the rear. A water tank (5) contains an immersion pump (4), which is responsible for constantly delivering water through a piping system in a circuit. An electrically operated proportional valve (2) acts as the actuator for this circuit. This valve must be actuated by an external input signal, e.g. from a controller. The flow is determined using a sensor, which works on the turbine principle. It emits a pulse signal, the frequency of which is proportional to the flow. This signal can be transmitted externally to a meter output via the USB connection and then analyzed. In addition, the piping system includes a float flow meter for verification and comparison purposes. In normal operation, the pump always runs at Y=100 %. As a disturbance, it can be throttled with the signal Z= 0…99 %. As this 11
disturbance is subtracted directly from the input signal, Z= 100 % means that the pump comes to a stop as there is no input signal remaining. The pump signal lamp (3) and the valve signal lamp (8) indicate whether the respective elements are actuated. 4)
COMMISSIONING
Using the hole in the cover, fill the water tank (5) with water until the pump is completely submerged and all hoses and pipe ends are below the water level (~3.5 ltr) Connect the model to the mains using the connecting socket on the rear. Using the USB port on the rear of the model, connect it to an external controller (e.g. PC). Switch on the model at the master switch (7). Switch on the pump (4).
SHUTTING DOWN
To shut down, switch off the model at the master switch. If the model will not be used for a long period of time, disconnect it from the mains and drain the water. To do this, allow the water to drain out through the bleeder on the rear of the water tank with a suitable hose. The unit is maintenance free and does not require any additional servicing.
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EXPERIMENTAL PROCEDURE
CONTROL ACTION OF FLOW LOOP:
The actuator on the RT 020 is an electrically operated pump. Observe which flow values X occur when varying the actuation signal Y in undisturbed operation. Y= 0…100 % Z= 0 % DISTURBANCE RESPONSE OF FLOW LOOP:
Another important feature of a loop is its response to disturbances. Observe the response of this loop to disturbance by actuating the actuator (pump) with Y= 100 % and the disturbance variable Z is varied. Y= 100 % Z= 0…100% DETERMINATION OF LOOP TYPE:
The loop behavior is determined by a step in the reference variable and observation of the resulting transient response Select “Manual” operating mode.
Set disturbance Z= 0 % Set manual regulation ratio Y= 20 %, wait until a steady state is reached. Perform step in manual regulation ratio,
Y= 20 %
Observe the response.
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80 %
Experiment 3: Pressure Control
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OBJECTIVES
To study the main components of a pressure control system. To study the influence of controller design on control action and disturbance response.
To study the stability of a control loop.
To study the controller optimization.
INTRODUCTION
The RT 030 pressure control model represents a typical loop control system, as is standard and widespread in engineering. The actual loop is a cylindrical metal pressure vessel. An externally actuated, electrically operated compressor performs the function of the actuator and is used to increase the air pressure in the vessel. The value of the relative excess pressure in the vessel is recorded by piezo-electric pressure sensor and provided as an electric voltage signal. Two valves are used to bleed the air from the vessel. One of them is a manual valve, which can be used to simulate continuous pressure tapping. An additional electric valve can also be connected as a sudden disturbance. The model must be supplemented by a separate external controller to create a complete control loop. It communicates with the peripheral equipment 9e.g. a PC) via a USB interface. The most suitable control and regulation program is the associated software RT 010- RT 060.
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DESCRIPTION
1)
EQUIPMENT LAYOUT:
1.
Compressor
2.
Compressor switch
3.
Bleeder valve
4.
Disturbance valve, electrically operated
5.
Pressure sensor
6.
Manometer
7.
Pressure vessel
8.
Compressor signal lamp
9.
Disturbance valve signal lamp
10.
Master switch
USB plug-in connection (rear of unit). Mains connection (rear of unit).
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2)
PROCESS DIAGRAM
3)
FUNCTION
The RT 030 pressure control model is used as a simple loop for a controller. It does not include a controller itself; all control processes must be run externally. The model communicates with external devices via a USB interface, for which it has a plug-in connection on the rear. A compressor (1), which is powered by a DC motor, is used as an actuator. The compressor pumps air into a pressure vessel (7). This pressure is directly indicated on a manometer (6) and is also measured using a piezo-electric sensor, which outputs a corresponding voltage signal for possible control. The bleeder valve (3) is used to set variable continuous pressure tapping. As a disturbance in the system, a second electrically operated valve can be connected. The disturbance valve can also be variably adjusted. Its switching behavior is not proportional; it has binary switching (open or closed). The disturbance valve can only be influenced by external control (e.g. via PC).
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Note: The compressor has a response threshold. This means that it only starts to move when the control signal y is at least 30% of its full final value (~ 3.5 V). The compressor cannot start up against pressure.
EXPERIMENTAL PROCEDURE
PREPARING THE LOOP:
Switch on the master switch (10) and compressor switch (2) on the RT 030 unit and start the “RT 010 – 060 Principles of Control Engineering” software. Select “Manual” operating mode and set the manual regulation ratio to y = 100 %. The compressor starts. Open the bleeder valve (3) and adjust it to give a constant pressure of ~ 1 bar. Then use the “Z” button to open the disturbance valve (4) and adjust it to give a pressure of ~ 0.8 bar.
DETERMINATION OF LOOP TYPE:
The loop behavior is determined by a step in the reference variable and observation of the resulting transient response Select “Manual” operating mode, set the manual regulation ratio to y = 40 % and wait until the pressure reaches a steady state. Carry out a step in the manual regulation ratio of : y = 40 % y = 60 % Observe the response.
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DISCUSSION
Why Control Valves used ?
Process plants consist of hundreds, or even thousands, of control loops all networked together to produce a product to be offered for sale. Each of these control loops is designed to keep some important process variable such as pressure, flow, level, temperature, etc. within a required operating range to ensure the quality of the end product. Each of these loops receives and internally creates disturbances that detrimentally affect the process variable, and interaction from other loops in the network provides disturbances that influence the process variable. To reduce the effect of these load disturbances, sensors and transmitters collect information about the process variable and its relationship to some desired set point. A controller then processes this information and decides what must be done to get the process variable back to where it should be after a load disturbance occurs. When all the measuring, comparing, and calculating are done, some type of final control element must implement the strategy selected by the controller
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Principles of Operation
The most common final control element in the process control industries is the control valve. The control valve manipulates a flowing fluid, such as gas, steam, water, or chemical compounds, to compensate for the load disturbance and keep the regulated process variable as close as possible to the desired set point. Control valves may be the most important, but sometimes the most neglected, part of a control loop. The reason is usually the instrument engineer's unfamiliarity with the many facets, terminologies, and areas of engineering disciplines such as fluid mechanics, metallurgy, noise control, and piping and vessel design that can be involved depending on the severity of service conditions. Any control loop usually consists of a sensor of the process condition, a transmitter and a controller that compares the "process variable" received from the transmitter with the "set point," i.e., the desired process condition. The controller, in turn, sends a corrective signal to the "final control element," the last part of the loop and the "muscle" of the process control system. While the sensors of the process variables are the eyes, the controller the brain, then the final control element is the hands of the control loop. This makes it the most important, alas sometimes the least understood, part of an automatic control system.
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