eletrical engineer UTFPR Measurements and Electrical Circuits – Description
Question 1. A strain gauge is calibrated using a TiAl6V4 titanium alloy plate to obtain the Transverse Sensitivity Factor ( ). The strain gauge has a nominal resistance of 120Ω and Gage Factor = 1.94 The properties of the titanium alloy are given in Table 1, while the experiment for calibration is shown in Figure 1. In Figure 2 the stress diagrams for the strain test are shown. 4 point flexion. The normal stress, strain and moment of inertia of the section can be calculated using equations (1), (2) and (3).
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For the reading of strain gauges, the circuit shown in Figure 3 is used. The circuit is the same for both the extensometer oriented in the longitudinal direction and the extensometer oriented in the transverse direction. What differentiates the circuits is the output pin (A0 for longitudinal and A1 for transverse) and the gain of the amplifier controlled by potentiometer RV1 with a nominal value of 10 Ω.
The potentiometer of the longitudinal strain measurement circuit is positioned at a resistance value 1 = 8 Ω and the potentiometer of the transverse strain measurement is positioned at a value of 2 = 3 Ω. When a force of 1000 N is applied during the test, the reading on Arduino pin A0 is 4.7481 V and the reading on Arduino pin A1 is 4.2098 V. Obtain the Strain Gage cross sensitivity value.
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Question 2. An experiment is carried out to obtain the thermal conductivity coefficient of flexible polyurethane foam (PUR). For this, the experiment presented in Figure 4 is carried out. Two LM35 temperature sensors are positioned 20 mm apart from each other. A 6.25 W source is used to heat the system at one end and all heat is removed at the other end. Equation (4) describes the behavior of the heat flux ” (W/m²) as a function of the temperature variation dT (°C), the thermal conduction coefficient ( / ° ) and the position variation dx (m), while the heat input into the system q (W) is given by equation (5).
Figure 5 shows the circuit for measuring the temperature of the two LM35 sensors used in the experiment. The T2 sensor indicates a temperature of 27°C and the sensitivity of the LM35 sensor is 10 mV/°C. Under these conditions, the reading taken at pin A0 is 2.9355 V. Obtain the thermal conduction coefficient of the polyurethane foam.
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