Problem with the data acquisition time function provided by Arduino

Question

I’m doing a Plot temperature vs Time via Arduino in a graphical interface. The program is crashing. Problem is in the function of time:

# -*- coding: utf-8 -*-
import matplotlib
import matplotlib.pyplot as plt
from PyQt4 import QtGui, QtCore
from PyQt4.QtCore import*
from PyQt4.QtGui import* # create winodow
from pyqtgraph.Qt import QtGui, QtCore
import pyqtgraph as pg
import numpy as np
import time
import pause
import matplotlib
import sys
from PyQt4 import QtGui
import serial




temperaturaLM35 = []
time_array = []



port = 'COM31'
velocity = 9600
tempo = 1
arduino = serial.Serial(port,velocity)

cnt = 0


class Window(QtGui.QMainWindow):

    def __init__(self):

        super(Window, self).__init__()
        self.setGeometry(50, 50, 600, 300)
        self.setWindowTitle("Test Window for PyQt")
        self.setWindowIcon(QtGui.QIcon('logo_python.png'))
        QtGui.QApplication.setStyle(QtGui.QStyleFactory.create("Plastique"))

        pg.setConfigOption('background', 'w')
        pg.setConfigOption('foreground', 'k')                 

        self.plot5 = pg.PlotWidget(self)
        self.plot5.setTitle("TEMPERATURE LIVE PLOT")
        self.plot5.setXRange(0, 11, padding=0, update = True)
        self.plot5.setYRange(0, 50, padding=0, update = True)

        self.plot5.setLabel('left','Temperature',units='ºC',
                            color='#c4380d',**{'font-size':'11pt'})
        self.plot5.resize(500,200)
        self.plot5.move(30,30)
        self.plot5.showGrid(x = True, y = True, alpha = 0.7)
        self.plot5.setLabel('bottom','Time',units='s',**{'font-size':'11pt'})

        self.plot5.getAxis('left').setPen(pg.mkPen('#c4380d',widht=1.1))               
        self.plot5.setLabels(left=('Temperature', '°C')) 

        self.plot5.setLabels(bottom=('Time', 's'))
        self.plot5.enableAutoRange('xy', True)

        self.plot5.plot(temperaturaLM35, pen='b', symbol='o', symbolPen ='b', symbolSize = 5)

        self.home()      

    def home(self):
        global tempo
        self.cb = QCheckBox(" ", self)
        self.cb.move(5, 5)
        self.cb.stateChanged.connect(self.makeFig)

        self.btn1 = QPushButton("tempo",self)
        self.btn1.move(10,250)
        self.le1 = QLineEdit(self)
        self.le1.setReadOnly(True)
        self.le1.setFixedWidth(40)
        self.le1.move(120,250)
        self.btn1.clicked.connect(self.tempo1)



        self.show()


    def monitorar(self):
        if self.checkbox.isChecked():
            self.sensorTempLM35()           
            self.makeFig()
            QtCore.QCoreApplication.processEvents()
            pause.seconds(tempo)

            self.plot5.plot(time_array, temperaturaLM35, pen='b', symbol='o', symbolPen ='b', symbolSize = 5)

        else:
            event.ignore()

    def tempo1(self):
        global tempo
        tempo,ok = QInputDialog.getDouble(self, "Time","Enter the value of time (s):",tempo, 0.01, 10000, 2)

        if ok:
             self.le1.setText(str(tempo))



    def sensorTempLM35(self):
        global temperaturaLM35
        arduino.write('x')

    def makeFig(self):
        global temperaturaLM35
        global time_array

        arduinoNumber = float(arduino.readline()[:-1])
        timer = QElapsedTimer()
        timer2 = np.round(np.float(timer.elapsed())/1000, decimals=2)

        temperaturaLM35.append(arduinoNumber)
        time_array.append(tempo)



        cnt = cnt + 1

        print temperaturaLM35
        print time_array
        self.plot5.plot( temperaturaLM35, pen='b', symbol='o', symbolPen ='b', symbolSize = 5)

        if(cnt > 50):
            temperaturaLM35.pop(0)
            time_array.pop(0)
        else:
            pass

        arduino.close()

def run():        
    app = QtGui.QApplication(sys.argv)
    GUI = Window()
    sys.exit(app.exec_())

run()