Lab 9 Manual

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York University *

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2502

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Mechanical Engineering

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Jan 9, 2024

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pdf

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17

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1 | P a g e MECH 2502 Lab 9 Manual MECH 2502 - Instrumentation and Measurement Techniques Instructor: Professor Marina Freire-Gormaly Laboratory 9: Sensor applications: A strain gage-based weighing scale Fall 2023
2 | P a g e MECH 2502 Lab 9 Manual By the end of this week (lecture and laboratory) students will become familiar with: Quarter- and half-bridge Wheatstone bridges Strain gage temperature compensation Strain gage self/Ohmic heating Make sure to carefully study the “Background” section of this manual and complete the “ Pre-lecture Assignment ”.
3 | P a g e MECH 2502 Lab 9 Manual 1 Background In this laboratory you will explore a typical application of a strain gage sensor in a measurement system. You will construct a weighing scale using a strain gage as schematically shown in Figure 1.1. The measurement system will consist of a cantilever beam with two attached strain gages clamped to a table. Signal conditioning is achieved by means of a Wheatstone bridge and amplification prior to the signal being acquired by a data acquisition system. You will hang a series of masses on the free end of the beam to calibrate the output of the measurement system in terms of mass. Figure 1.1 Schematic diagram of the strain gage weighing scale As part of the activities of this lab, you will: Amplify the differential output of a Wheatstone bridge using the LM324 op-amp. Compare the sensitivity of a quarter-bridge versus a half-bridge Whetstone bridge configuration. Examine the effect of self/Ohmic heating due to a higher bridge excitation voltage. Observe temperature compensation when using a half-bridge configuration Calibrate the measurement system in terms of mass Detailed information pertaining to strain gage, operational amplifiers, and the QuansarQ8-USB DAQ is provided in the background sections of laboratory 5 and 8 manuals. Review both manuals prior to conducting this laboratory. Strain gages Cantilever beam Clamp Table Calibrated masses Wheatstone bridge Amplification Quanser Q8-USB DAQ PC/LabVIEW
4 | P a g e MECH 2502 Lab 9 Manual 1.1 Pre-lab Assignments Prior to completing this laboratory, you are required to investigate several topics and submit your findings through Moodle as the pre-lab assignment: 1. Consider a strain gage-based scale similar to Figure 1.1. Using the calibration data provided in the table below, which relates the output signal of the system versus a series on known inputs, determine the systems: a. calibration equation b. sensitivity (mV/kg) Hint: Sensitivity of a sensor is defined as the change in output of the sensor per unit change in the physical quantity being measured. For example, a sensitivity of 10 mV/kg means the system outputs a 10 mV signal for each kilogram of applied load. Mass (kg) Amplified system output (mV) 0 10 2.5 525 5 1,050 2. In a Wheatstone bridge in a quarter-bridge configuration, recall the following relationship between bridge output voltage ( V O ), bridge excitation voltage ( V Ex ), gage factor (GF), and strain ( ): 𝑉 𝑂 𝑉 𝐸𝑥 = − ?? ∙ 𝜀 4 ( 1 1 + ?? ∙ 𝜀 2 ) Assuming that the strain gage-based scale described in question 1 has a gage factor of 2.09, uses a bridge excitation voltage of 2.5 VDC, and amplification factor of 100x, determine the induced strain ( s) for each applied mass. 3. Load cells are sensors that generate an electrical signal proportional to the force/load being measured. Using online resources identify 2 different types of load cells and provide a brief explanation of how each type operates.
5 | P a g e MECH 2502 Lab 9 Manual 2 In-Lab Exercises The exercises for this laboratory are divided into two modules. In module 1, you will implement the weighing scale using a quarter-bridge Wheatstone bridge configuration. Furthermore, you will examine how slight changes in ambient temperature affects the output of the strain gage. In module 2,you will implement a half-bridge Wheatstone bridge configuration in order to compare the sensitivity of the quarter-bridge and half-bridge configurations. Furthermore, you will examine the effect of self/Ohmic heating due to a higher bridge excitation voltage. 2.1 Module 1: Quarter-Bridge Configuration The purpose of this module is to implement a weighing scale using a cantilever beam/strain gage assembly in a quarter-bridge configuration. The output of the Wheatstone bridge will be amplified using an LM324 op-amp configured as a differential amplifier. Using the supplied VI, you will calibrate the amplified output of the bridge in terms of mass. Furthermore, you will observe how slight changes in ambient temperature affects the output of the strain gage. You are required to complete the following tasks: a) construct a quarter-bridge Wheatstone bridge circuit b) construct a differential amplifier using an LM324 op-amp that amplifies the output of the bridge circuit prior to being read by the Quanser Q8-DAQ c) calibrate the output of the circuit in terms of mass using the supplied VI and a series known masses d) observe the effect of change in ambient temperature on the output of the strain gage Experimental Setup The setup for this module consists of the following components: Quanser Q8-USB DAQ Flexible ruler with two mounted 2-wire strain gages Clamp Bench-top power supply Handheld digital multi-meter Prototyping breadboard Jumper wires LM324 op-amp Rotary potentiometer, 1 k
6 | P a g e MECH 2502 Lab 9 Manual Resistors - 120 , 2 pieces - 150 , 1 piece - 800 , 2 pieces - 80 k , 2 pieces RCA to Alligator cable 100 g mass, 4 pieces Procedure Follow these steps to complete module 1: 1. Follow the instructions of the laboratory instructor on how to securely clamp the cantilever beam assembly to the laboratory bench. 2. Ensure the power supply is switched off. 3. Using the supplied components, construct the circuit shown in Figure 2.1. Refer to laboratory 8 manual to determine the LM324 pin configuration.
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