Experiment 3 Air Temperature Process Process Control
Process Dynamics & Control Lab
EXPERIMENT NO. 3
3.0 EXPERIMENTAL PROCEDURE
Air Temperature Process Control (AT 922) OBJECTIVES
3.1 IDENTIFICATION OF MAJOR COMPONENTS IN THE PLANT
1. To identify identify the important components components of the air temperature control control system and to
1. Walk Walk around the experimental equipment, equipment, IDENTIFY and MARK MARK the following major
mark them in the P&I Diagram.
components of the system in the P&I Diagram provided at the end the lab manual.
2. To carry out the the start-up procedures procedures systematically. systematically. 3. To determine determine the values values of parameters for a first order order plus dead time time transfer function function model of a thermal process.
AR90
Air pressure regulator at the process inlet
FS90
Flow switch (cut-off the heater power when very low air is detected)
4. To control control the air heater process using using PID controller. controller.
MV90A Manual Manual valve at the process inlet PRV90 PRV90
Pressure relief valve to prevent excessive pressure from AR90
KEYWORDS
TCY90
Thyristor (installed inside the cubicle, below the control panel)
Air temperature system, PID controller, controller, Dead time, FOPTD transfer function model
TE91
Resistance temperature detector (RTD), measures the temperature of the hot air at the exit of the heater
1.0 INTRODUCTION
TIT92
This model uses air to simulate a gas or vapor phase temperature process. The
TR91
Temperature Temperature indicating indicating transmitter for TE92 Recorder
temperature process is a multicapacity lag/dead time process with no noise. It uses a
TIC90
ON/OFF temperature controller PID temperature controller - Loop 1
thyristor to adjust the heat flow to the heater. The air flow rate is measured using a
TIC91
rotameter. rotameter. A selective control technique is employed here that automatically select only a
TIC92
PID temperature controller - Loop 2
less heat demanding output to manipulate only final control element (the thyristor/heater).
FI90
Variable area flow meter
This system requires a high gain PID controller.
VT
Process vent
HV90
Heater by-pass
2.0 EXPERIMENTAL EQUIPMENT
This equipment used in this experiment is the air temperature process control training
3.2 START-UP PROCEDURES
system, Model AT 922.
1. The following steps constitute the start-up procedure. Go through these steps before
2.1 AIR TEMPERATURE PROCESS PLANT (AT 922)
2. Switc h the "PANEL, SCADA/DDC" selecto r switch at the front of the cubicle to
starting any experiment.
The process plant consists of a forced convective annulus electric heater to heat the
"PANEL,SCADA"position. Switch ON the main power supply at the front of the
incoming process air from an external air supply system. The process air is connected to a
cubicle. All the panel instruments will lit up. (Make sure the heater is switched OFF at
air pressure regulator (AR90) and flows into the heater and then to the process vent, VT or
this point)
to another air process control training system. By varying the air flow rate at the discharge manual valve downstream downstream of the rotameter, FI90, the air flow load changes through the heater can be implemented. The purpose of the the PID control is to maintain the air temperature (TE91/TIT91) (TE91/TIT91) at the heater exit, at the operator setpoint without burning out the heater.
3. If any annunciator gets activated, press the ACKNOWLEDGE button to silence the buzzer. 4. Shut the manual valve MV90A and set air supply regulator AR90 to the pressure indicated at the air regulator (45 psig). 5. Make sure the heater heater by-pass valve HV90 and manual valve MV90B are shut. Open the vent valve VT fully to discharge air to the atmosphere.
Page 1
Experiment 3 Air Temperature Process Control
Process Dynamics & Control Lab
9.The slope of the steepest tangent gives the Response Rate (RR).
6. The followings should be verified: i) Annunciator
FAL90
is
activated
and
should
be
“ACKNOWLEDGED” (Reason - No air flow because MV90A is shut at the moment) ii) The pressure gauge PG90 reads as atmospheric pressure. If it reads more, then check and open the vent valve VT. iii)The variable area flow meters FI90 shows no air.
10. The process gain, Kp is equal to the maximum change in the air temperature (" PV) at the exit divided by the % change in the manipulated variable (" MV%). 11.The time constant,
!
is equal to the Response Rate (RR) divided by the maximum
change in the air temperature at the exit (" PV). *The air temperature process is governed by a first order plus time delay (FOPTD) transfer function.
iv) Check the temperature at recorder TR91 is not rising because the heater is still OFF.
( ) = X ( s ) Y s
FOPTD transfer function,
7. Manually open fully the inlet valve MV90A so that the air flow rate at flow meter FI90 reads about 45 Nm3/hr. (Do not alter the air pressure that was previously set at air
K .e
!! s
" s + 1
K = process gain # =
supply regulator AR90)
time delay/dead time $=
8. Check the pressure gauge PG90 should reads slightly above atmospheric pressure.
time constant
9. Now, press the “RCD” button on the recorder TR91 to start recording the temperature response.
3.4 CONTROL OF AIR HEATER SYSTEM 1. Check the vent VT is fully opened.
3.3 DETERMINATION OF PROCESS TRANSFER FUNCTION PARAMETERS
2. The process air supply and flow rate should remain as previously set in Section 3.3.
The following procedures are conducted for determining the process transfer function
3. Set a suitable setpoint, SV (i.e. range from 60°C to 120°C) at the temperature PID
parameters.
controller, TIC91, say 10°C higher than the current setpoint SV. (TIC91 is still in
1. Make sure the air flow rate at variab le area flow meter FI90 is 45 Nm3/hr. If it is not
Manual (M) mode)
read as 45 Nm 3/hr, adjust inlet valve MV90A. 2. Wait for the temperature response to be almost stable. (Red pen - TE91/TIT91 and Green pen - TE92/TIT92 are almost steady) 3. Note the average air flow rate at the variable area flow meter FI90.
4.Set “SSW” (at the “PID2” page) to “1” so that only TIC91 is used/activated. This step makes PID 2, Loop 2 disabled. 5. Access the PID values in controller TIC91/TIC92 and set the first (I) trial values. PB1 = 10%, TI1 = 100 s, TD1 = 25 s
4. With TIC91 in Manual (M) mode, adjust its MV = 30%.
6. Transfer TIC91 to Auto (A) mode and make sure the heater is ON.
5. Switch ON the heater and mark on the recorder chart paper the instant the heater is
7. Observ e patien tly the tempera ture response of both the heater surface temperature
switched ON. 6. Wait until the temperature response become steady. 7. Stop the recorder TR91 by pressing “RCD” button and take out the chart paper and
(TE90/TIC90, Green pen) and the heated air temperature (TE91/TIC91), Red pen). Wait until the temperature response is steady at its setpoint value, SV.
Experiment 3 Air Temperature Process Control
Process Dynamics & Control Lab
9.The slope of the steepest tangent gives the Response Rate (RR).
6. The followings should be verified: i) Annunciator
FAL90
is
activated
and
should
be
“ACKNOWLEDGED” (Reason - No air flow because MV90A is shut at the
10. The process gain, Kp is equal to the maximum change in the air temperature (" PV) at the exit divided by the % change in the manipulated variable (" MV%). 11.The time constant,
moment) ii) The pressure gauge PG90 reads as atmospheric pressure. If it reads more,
!
is equal to the Response Rate (RR) divided by the maximum
change in the air temperature at the exit (" PV). *The air temperature process is governed by a first order plus time delay (FOPTD)
then check and open the vent valve VT.
transfer function.
iii)The variable area flow meters FI90 shows no air. iv) Check the temperature at recorder TR91 is not rising because the heater is still OFF.
( ) = X ( s ) Y s
FOPTD transfer function,
7. Manually open fully the inlet valve MV90A so that the air flow rate at flow meter FI90 reads about 45 Nm3/hr. (Do not alter the air pressure that was previously set at air
K .e
!! s
" s + 1
K = process gain # =
supply regulator AR90)
time delay/dead time $=
8. Check the pressure gauge PG90 should reads slightly above atmospheric pressure.
time constant
9. Now, press the “RCD” button on the recorder TR91 to start recording the temperature 3.4 CONTROL OF AIR HEATER SYSTEM
response.
1. Check the vent VT is fully opened. 3.3 DETERMINATION OF PROCESS TRANSFER FUNCTION PARAMETERS
2. The process air supply and flow rate should remain as previously set in Section 3.3.
The following procedures are conducted for determining the process transfer function
3. Set a suitable setpoint, SV (i.e. range from 60°C to 120°C) at the temperature PID
parameters.
controller, TIC91, say 10°C higher than the current setpoint SV. (TIC91 is still in
1. Make sure the air flow rate at variab le area flow meter FI90 is 45 Nm3/hr. If it is not
Manual (M) mode)
read as 45 Nm 3/hr, adjust inlet valve MV90A.
4.Set “SSW” (at the “PID2” page) to “1” so that only TIC91 is used/activated. This step
2. Wait for the temperature response to be almost stable. (Red pen - TE91/TIT91 and
makes PID 2, Loop 2 disabled. 5. Access the PID values in controller TIC91/TIC92 and set the first (I) trial values.
Green pen - TE92/TIT92 are almost steady)
PB1 = 10%, TI1 = 100 s, TD1 = 25 s
3. Note the average air flow rate at the variable area flow meter FI90. 4. With TIC91 in Manual (M) mode, adjust its MV = 30%.
6. Transfer TIC91 to Auto (A) mode and make sure the heater is ON.
5. Switch ON the heater and mark on the recorder chart paper the instant the heater is
7. Observ e patien tly the tempera ture response of both the heater surface temperature
switched ON.
(TE90/TIC90, Green pen) and the heated air temperature (TE91/TIC91), Red pen).
6. Wait until the temperature response become steady.
Wait until the temperature response is steady at its setpoint value, SV.
7. Stop the recorder TR91 by pressing “RCD” button and take out the chart paper and DO NOT FORGET TO MARK THE PID VALUES AND THE SET-POINT ON THE
examine the response. 8. Draw the steepest tangent for the temperature response to intersect the baseline to calculate the deadtime (DT). ( Measure the distance (in mm) between the point of
CHART PAPER WHENEVER THE VALUES ARE CHANGED. ALSO MARK ON THE CHART THE BEGINNING OF EACH PART OF THE EXPERIMENT.
intersection and the instant when heater was switched ON) 8. Note that the heated air temperature (TE91/TIC91), Red pen) overshoots the setpoint,
The dead time is given by:
Deadtime
Dis tan ce( mm) =
Re cordchartspeed ( 500 mm hr )
!
3600 s 1hr
SV even when the heater surface temperature (TE90/TIC90, Green pen) has started decreasing.
Page 2
Experiment 3 Air Temperature Process Control
Process Dynamics & Control Lab
9. Repeat the experiment with the following disturbances(using first (I) PID trial values): i) Load disturbance Switch the controller TIC91 to Manual (M) mode. Increase the control output, MV at about 10% to 20%. Then, quickly switch the controller TIC91 to Auto (A) mode. Observe the temperature response. ii) Setpoint change Switch the controller to Manual (M) mode. Step increase the temperature setpoint, SV at controller TIC91 so that it is about the 10 - 15°C above the current setpoint, SV (do not exceed 120°C). Then, quickly switch the controller TIC91 to Auto (A) mode. Observe the temperature response. 10.Repeat Step (9) for the following PID trial values: Second (II) trial value: PB1 = 20%, TI1 = 70 s, TD1 = 1 8 s Third (III) trial value: PB1 = 10%, TI1 = 22 s, TD1 = 5 s
Figure 3.1: An example of process response for PID controller 4.0 SHUTDOWN PROCEDURES
1. Stop the recorder chart by pressing ”RCD” pressbutton at recorder FPTR91. 2. Switch TIC91 to Manual mode with MV = 0%. 3. Switch off the heater and let the air flows to cool down the heater for sometime. 4. Switch off the main power supply. 5. Shut off the process air supply at AR90. 6. Shut off the instrument air supply. 5.0 RESULTS 1. The recorder FPTR91 records the results of the experiments. Suitable portions of the recorder chart paper should be submitted as RESULTS of the experiment. 2. The report should contain: i) The P&I Diagram with all major components marked clearly. ii) Using data/results from Section 3.3, determine the parameters of the first order plus time delay and its transfer function.
Experiment 3 Air Temperature Process Control
Process Dynamics & Control Lab
9. Repeat the experiment with the following disturbances(using first (I) PID trial values): i) Load disturbance Switch the controller TIC91 to Manual (M) mode. Increase the control output, MV at about 10% to 20%. Then, quickly switch the controller TIC91 to Auto (A) mode. Observe the temperature response. ii) Setpoint change Switch the controller to Manual (M) mode. Step increase the temperature setpoint, SV at controller TIC91 so that it is about the 10 - 15°C above the current setpoint, SV (do not exceed 120°C). Then, quickly switch the controller TIC91 to Auto (A) mode. Observe the temperature response. 10.Repeat Step (9) for the following PID trial values: Second (II) trial value: PB1 = 20%, TI1 = 70 s, TD1 = 1 8 s Third (III) trial value: PB1 = 10%, TI1 = 22 s, TD1 = 5 s
Figure 3.1: An example of process response for PID controller 4.0 SHUTDOWN PROCEDURES
1. Stop the recorder chart by pressing ”RCD” pressbutton at recorder FPTR91. 2. Switch TIC91 to Manual mode with MV = 0%. 3. Switch off the heater and let the air flows to cool down the heater for sometime. 4. Switch off the main power supply. 5. Shut off the process air supply at AR90. 6. Shut off the instrument air supply. 5.0 RESULTS 1. The recorder FPTR91 records the results of the experiments. Suitable portions of the recorder chart paper should be submitted as RESULTS of the experiment. 2. The report should contain: i) The P&I Diagram with all major components marked clearly. ii) Using data/results from Section 3.3, determine the parameters of the first order plus time delay and its transfer function. iii) The PID temperature control responses for load disturbances and setpoint changes for different controller settings. iv) Discussion on the response characteristics for different controller settings. v) Temperature process is typically slow compared to others (level, flow and pressure). Discuss the statement. vi)Temperature process usually exhibits overshoot. Discuss on this matter as well.
Page 3
Experiment 3 Air Temperature Process Control
Process Dynamics & Control Lab
Experiment 3 Air Temperature Process Control
Figure 3.2: P&I Diagram for Air Temperature Process Control Plant
Page 4
Process Dynamics & Control Lab
