This notebook contains material from CBE32338; content is available on Github.

< 2.0 Model Identification | Contents | 2.2 Fitting Step Test Data to Empirical Models >

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2.1 Step Testing

In [2]:
%matplotlib inline
import matplotlib.pyplot as plt
import pandas as pd

from tclab import TCLab, clock, Historian, Plotter

2.1.1 Executing the Step Test

Verify an Initial Steady State

A step test assumes the system is initially at steady state. In the case of the Temperature Control Lab, the initial steady with no power input would be room temperature. It generally takes 10 minutes or more to reach steady state. We'll do a measurement to confirm the initial temperature.

In [3]:
lab = TCLab()
print(lab.T1, lab.T1)
lab.close()

TCLab version 0.4.9
Arduino Leonardo connected on port /dev/cu.usbmodem2101 at 115200 baud.
TCLab Firmware 1.5.1 Arduino Leonardo/Micro.
26.06 26.06
TCLab disconnected successfully.

2.1.1.1 Conduct the Experiment

In [4]:
# experimental parameters
Q1 = 50
tfinal = 800

# perform experiment
with TCLab() as lab:
    h = Historian(lab.sources)
    p = Plotter(h, tfinal)
    lab.Q1(0)
    for t in clock(tfinal):
        p.update(t)
        lab.Q1(Q1)

---------------------------------------------------------------------------
OSError                                   Traceback (most recent call last)
~/opt/anaconda3/lib/python3.7/site-packages/serial/serialposix.py in read(self, size)
    492                     break   # timeout
--> 493                 buf = os.read(self.fd, size - len(read))
    494                 # read should always return some data as select reported it was

OSError: [Errno 6] Device not configured

During handling of the above exception, another exception occurred:

SerialException                           Traceback (most recent call last)
<ipython-input-4-7eb0f8936a68> in <module>
     10     for t in clock(tfinal):
---> 11         p.update(t)
     12         lab.Q1(Q1)

~/opt/anaconda3/lib/python3.7/site-packages/tclab/historian.py in update(self, tnow)
    288     def update(self, tnow=None):
--> 289         self.historian.update(tnow)
    290 

~/opt/anaconda3/lib/python3.7/site-packages/tclab/historian.py in update(self, tnow)
    147             if valuefunction:
--> 148                 v = valuefunction()
    149                 if isinstance(v, Iterable):

~/opt/anaconda3/lib/python3.7/site-packages/tclab/tclab.py in scan(self)
    209         #self.send('SCAN')
--> 210         T1 = self.T1  # float(self.receive())
    211         T2 = self.T2  # float(self.receive())

~/opt/anaconda3/lib/python3.7/site-packages/tclab/tclab.py in T1(self)
    156         """Return a float denoting TCLab temperature T1 in degrees C."""
--> 157         return self.send_and_receive('T1', float)
    158 

~/opt/anaconda3/lib/python3.7/site-packages/tclab/tclab.py in send_and_receive(self, msg, convert)
    147         self.send(msg)
--> 148         return convert(self.receive())
    149 

~/opt/anaconda3/lib/python3.7/site-packages/tclab/tclab.py in receive(self)
    139         """Return a string message received from the TCLab firmware."""
--> 140         msg = self.sp.readline().decode('UTF-8').replace('\r\n', '')
    141         if self.debug:

~/opt/anaconda3/lib/python3.7/site-packages/serial/serialposix.py in read(self, size)
    508                 if e.errno not in (errno.EAGAIN, errno.EALREADY, errno.EWOULDBLOCK, errno.EINPROGRESS, errno.EINTR):
--> 509                     raise SerialException('read failed: {}'.format(e))
    510             except select.error as e:

SerialException: read failed: [Errno 6] Device not configured

During handling of the above exception, another exception occurred:

OSError                                   Traceback (most recent call last)
~/opt/anaconda3/lib/python3.7/site-packages/serial/serialposix.py in write(self, data)
    536             try:
--> 537                 n = os.write(self.fd, d)
    538                 if timeout.is_non_blocking:

OSError: [Errno 6] Device not configured

During handling of the above exception, another exception occurred:

SerialException                           Traceback (most recent call last)
<ipython-input-4-7eb0f8936a68> in <module>
     10     for t in clock(tfinal):
     11         p.update(t)
---> 12         lab.Q1(Q1)

~/opt/anaconda3/lib/python3.7/site-packages/tclab/tclab.py in __exit__(self, exc_type, exc_value, traceback)
     98 
     99     def __exit__(self, exc_type, exc_value, traceback):
--> 100         self.close()
    101         return
    102 

~/opt/anaconda3/lib/python3.7/site-packages/tclab/tclab.py in close(self)
    121         global _connected
    122 
--> 123         self.Q1(0)
    124         self.Q2(0)
    125         self.send_and_receive('X')

~/opt/anaconda3/lib/python3.7/site-packages/tclab/tclab.py in Q1(self, val)
    192         else:
    193             msg = 'Q1' + sep + str(clip(val))
--> 194         return self.send_and_receive(msg, float)
    195 
    196     def Q2(self, val=None):

~/opt/anaconda3/lib/python3.7/site-packages/tclab/tclab.py in send_and_receive(self, msg, convert)
    145     def send_and_receive(self, msg, convert=str):
    146         """Send a string message and return the response"""
--> 147         self.send(msg)
    148         return convert(self.receive())
    149 

~/opt/anaconda3/lib/python3.7/site-packages/tclab/tclab.py in send(self, msg)
    131     def send(self, msg):
    132         """Send a string message to the TCLab firmware."""
--> 133         self.sp.write((msg + '\r\n').encode())
    134         if self.debug:
    135             print('Sent: "' + msg + '"')

~/opt/anaconda3/lib/python3.7/site-packages/serial/serialposix.py in write(self, data)
    569                 # https://www.python.org/dev/peps/pep-0475.
    570                 if e.errno not in (errno.EAGAIN, errno.EALREADY, errno.EWOULDBLOCK, errno.EINPROGRESS, errno.EINTR):
--> 571                     raise SerialException('write failed: {}'.format(e))
    572             except select.error as e:
    573                 # this is for Python 2.x

SerialException: write failed: [Errno 6] Device not configured

2.1.1.2 Verify the Experimental Data

In [3]:
t = h.t
T1 = h.T1
T2 = h.T2
Q1 = h.Q1
Q2 = h.Q2

plt.plot(t, T1, t, T2, t, Q1, t, Q2)
plt.legend(['T1','T2','Q1','Q2'])
plt.xlabel('time / seconds')
plt.grid()

2.1.1.3 Convert to a DataFrame

In [4]:
import pandas as pd

df = pd.DataFrame([t, T1, T2, Q1]).T
df.columns = ['Time', 'T1', 'T2', 'Q1']
df = df.set_index('Time')
df.plot(grid=True)
Out[4]:
<matplotlib.axes._subplots.AxesSubplot at 0x10fc2b748>

2.1.1.4 Save DataFrame as a .csv file

In [5]:
df.to_csv('Step_Test_Data.csv')

2.1.1.5 Verify the Data File

In [2]:
%matplotlib inline

pd.read_csv('Step_Test_Data.csv').set_index('Time').plot(grid=True)
Out[2]:
<matplotlib.axes._subplots.AxesSubplot at 0x11615e208>
In [7]:
df.head()
Out[7]:
T1 T2 Q1
Time
0.0 20.9 21.54 0.0
0.0 20.9 21.54 50.0
1.0 20.9 21.54 50.0
2.0 20.9 21.54 50.0
3.0 20.9 21.54 50.0
In [8]:
df.tail()
Out[8]:
T1 T2 Q1
Time
795.00 55.38 31.53 50.0
796.00 55.38 31.53 50.0
797.00 55.38 31.53 50.0
798.01 55.38 31.53 50.0
799.00 55.38 31.53 50.0

< 2.0 Model Identification | Contents | 2.2 Fitting Step Test Data to Empirical Models >

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