Piezo-resistive Pressure Sensor Measurement Explained

A piezo-resistive pressure sensor is a type of transducer that converts pressure into an electrical signal. This conversion happens due to the change in electrical resistance of the sensing element when pressure is applied. These sensors are widely used in various applications to measure pressure accurately.

Understanding Sensor Sensitivity

The sensitivity of a sensor indicates how much output signal it produces for a given change in the input physical quantity. For a piezo-resistive pressure sensor, sensitivity is often expressed in units like mV/V/kPa. This means for every unit of excitation voltage and every unit of pressure, a specific millivolt output is generated.

• The unit mV/V/kPa can be understood as: (Output in millivolts) / (Excitation Voltage in Volts) / (Pressure in kiloPascals).
• It essentially describes the output voltage per unit of pressure per unit of excitation voltage.

Given Parameters for Pressure Sensor

We are provided with the following information for the piezo-resistive pressure sensor:

• Output voltage (\(V_{out}\)): 6 mV
• Excitation voltage (\(V_{exc}\)): 5 V
• Sensitivity (S): 2 mV/V/kPa

Formula for Pressure Calculation

The relationship between the output voltage, excitation voltage, sensitivity, and the pressure measured by a piezo-resistive sensor can be expressed by the following formula:

\[ V_{out} = S \times V_{exc} \times P \]

Where:

• \(V_{out}\) is the output voltage
• \(S\) is the sensitivity of the sensor
• \(V_{exc}\) is the excitation voltage
• \(P\) is the pressure measured

To find the pressure measured (\(P\)), we can rearrange the formula:

\[ P = \frac{V_{out}}{S \times V_{exc}} \]

Step-by-Step Pressure Calculation

Now, let's substitute the given values into the formula to calculate the pressure:

1. Identify the given values:

• \(V_{out} = 6 \text{ mV}\)
• \(V_{exc} = 5 \text{ V}\)
• \(S = 2 \text{ mV/V/kPa}\)

2. Apply the formula:

\[ P = \frac{V_{out}}{S \times V_{exc}} \]

\[ P = \frac{6 \text{ mV}}{(2 \text{ mV/V/kPa}) \times (5 \text{ V})} \]

3. Perform the multiplication in the denominator:

\[ P = \frac{6 \text{ mV}}{10 \text{ mV/kPa}} \]

(Note: The 'V' from mV/V/kPa cancels with 'V' from Excitation Voltage, leaving mV/kPa)

4. Perform the division to find the pressure:

\[ P = \frac{6}{10} \text{ kPa} \]

\[ P = 0.6 \text{ kPa} \]

Final Pressure Value

Based on the calculations, the pressure measured by the piezo-resistive sensor is 0.6 kPa.