Question

A pressure sensor has the following specifications:

$\text{Sensitivity at the design temperature = 10 V/MPa.}$

$\text{Zero drift = 0.01 V/°C}$

$\text{Sensitivity drift = 0.01 (V/MPa)/°C}$

When the sensor is used in an ambient 20°C above the design temperature, the output from the device is 7.4 V. The true value of the pressure will be

• A. 0.71 MPa
• B. 0.68 MPa
• C. 0.5 MPa
• D. 0.61 MPa

Answer 1

The correct option is A 0.71 MPa

$\text{Sensitivity = 10 V/MPa}$

$\because \text{10 V corresponds to 1 MPa}$

$\therefore \text{7.4 V corresponds to}\frac{1}{10}\times 7.4=0.74MPa$

$\text{Errors:}$

$\text{1) Due to zero drift}$

$\text{Zero drift = 0.01 V/°C}$

$\because \text{1°C corresponds to 0.01 V}$
$\therefore \text{20° corresponds to 0.01 × 20 = 0.2 V}$

$\text{2) Due to sensitivity drift}$

$\text{Sensitivity drift = 0.01 (V/MPa)/°C}$

$\text{for 0.74 MPa and 20°C, the voltage error is}$

$\text{0.01 × 0.74 × 20 = 0.148 V}$

$\text{Total error voltage}$

$\text{= 0.2 + 0.148 = 0.348 V}$

$\therefore \text{True output voltage should be}$

$\text{7.4 - 0.348 = 7.052 V}$

$\text{Sensitivity of instrument = 10 V/MPa}$

$\therefore \text{10 V}\Rightarrow \text{1 MPa}$

$\therefore 7.052\Rightarrow \frac{1}{10}\times 7.052=0.7052MPa$

$\simeq 0.71MPa$