Question

Problem 5: (30") A pressure transducer outputs a voltage to a readout device that converts the signal b to pressure. The device specifications are: ack Resolution: 0.1 psi Sensitivity error: 0.1 psi Linearity error: within 0.1% of reading Drift: less than 0.1 psi/6 months (32-90 F) The transducer has a claimed accuracy of within 0.5% of reading. For a nominal pressure of 100 psi at 70°F, estimate the design-stage uncertainty in a measured pressure.

Answer 1

Calculate the uncertainty in the transducer (u_d)_transducer = squareroot u_It^2 + u_oz^2 = squareroot u_It^2 + 0^2 = u_It = 0.005 times 100 = 0.5 Psi Convert the following terms interms of pressure: Repeatability, e_1 = 0.1 Psi Linearity, e_2 = 0.1 % reading = 0.001 times 100v/1v/psi = 0.1 Psi drift, e_3 = 0.1 Psi/6 months times 6 months = 0.1 Psi For input panel meter, the uncertainty is: i_Ipm = squareroot e_1^2 + e_2^2 + e_3^2 = squareroot 0.1^2 + 0.1^2 + 0.1^2 = 0.17 Psi For o/p panel meter, the uncertainty is u_opm = 0.5 resolution = 0.05 Psi Calculate the uncertainty in the panel meter (u_d)_panel meter = squareroot u_Ipm^2 + u_opm^2 = squareroot 0.17^2 + 0.05^2 = 0.18 Psi Calculate the uncertainty in the measured pressure (u_d)_mp = squareroot (u_d)^2_transducer + (u_d)^2_panel meter = squareroot 0.5^2 + 0.18^2 = 0.53 Psi (U_d)_mp = 0.53 Psi