Strain Gauge Pressure Sensors

Strain Gauge Pressure Sensors are widely used for measuring pressure by converting the mechanical strain (caused by applied pressure) into an electrical signal. These sensors operate on the principle that when pressure is applied to a diaphragm, the strain gauge experiences a change in resistance, which can be measured and converted into a corresponding pressure value.

How Strain Gauge Pressure Sensors Work:

1. Strain Gauge: A strain gauge is a sensor whose resistance varies with applied force. It is bonded to a material that deforms when pressure is applied.

2. Pressure Application: The strain gauge is typically attached to a diaphragm that flexes under pressure. As the diaphragm deforms, the strain gauge stretches or compresses, causing a change in its electrical resistance.

3. Electrical Resistance Change: The change in resistance is proportional to the strain, which is directly related to the applied pressure.

4. Wheatstone Bridge Circuit: Strain gauges are usually configured in a Wheatstone bridge circuit to accurately measure small changes in resistance and produce a corresponding voltage output.

Components of a Strain Gauge Pressure Sensor:

Strain Gauges: Bonded to the diaphragm, these measure the strain due to pressure.

Diaphragm: The flexible component that deforms under pressure.

Wheatstone Bridge: A circuit used to convert the small changes in resistance into a measurable voltage.

Amplifier: Often used to boost the signal for better accuracy and readability by a microcontroller or analog-to-digital converter (ADC).

Wheatstone Bridge Circuit:

A strain gauge is typically used in a Wheatstone bridge configuration, which consists of four resistors (R1, R2, R3, R4). The strain gauge forms one or more of these resistors, and as the strain changes, the imbalance in the bridge results in a measurable output voltage.

Wheatstone Bridge Configuration:

R1               R2

       +--/\/\/\--+--/\/\/\--+

       |                        |

       Vout                    Vin

       |                        |

       +--/\/\/\--+--/\/\/\--+

       R4               R3

When no pressure is applied, the bridge is balanced, and the output voltage is zero or close to zero.

When pressure is applied, the resistance of the strain gauge changes, causing the bridge to unbalance, and a voltage output (Vout) is generated, which can be measured.

Applications:

Industrial pressure measurement: For monitoring and controlling processes like hydraulic or pneumatic systems.

Automotive industry: To monitor oil pressure, fuel pressure, or tire pressure.

Medical devices: In devices like blood pressure monitors or respiratory systems.

Aerospace and aviation: For monitoring pressure in fuel systems or environmental conditions.

Using a Strain Gauge Pressure Sensor with Arduino:

Components Required:

Strain gauge pressure sensor.

Arduino board (e.g., Uno).

Wheatstone bridge circuit (integrated in the sensor).

Instrumentation amplifier (e.g., HX711 or INA125) to amplify the small signal from the strain gauge.

Jumper wires and breadboard.

Wiring and Circuit Setup:

1. Sensor to Amplifier:

Connect the strain gauge sensor's Wheatstone bridge output to the inputs of the amplifier.

Power the amplifier using the 5V pin from the Arduino.

Connect the Vout from the amplifier to an analog input pin on the Arduino (e.g., A0).

2. Amplifier to Arduino:

The amplified signal (Vout) is connected to the analog input (A0) on the Arduino to read the voltage corresponding to the applied pressure.

Code to Read Pressure:

Here's an example Arduino code to read the pressure using an analog strain gauge pressure sensor with an amplifier:

const int sensorPin = A0;  // Analog input pin for the strain gauge pressure sensor

void setup() {

  Serial.begin(9600);  // Initialize serial communication

}

void loop() {

  int sensorValue = analogRead(sensorPin);  // Read the analog input

  float voltage = sensorValue * (5.0 / 1023.0);  // Convert analog value to voltage

  

  // Assuming a linear relationship between voltage and pressure, you can add calibration here

  float pressure = voltageToPressure(voltage);  // Custom function to convert voltage to pressure

  

  Serial.print("Pressure: ");

  Serial.print(pressure);

  Serial.println(" kPa");  // Print pressure in kilopascals (or another unit)

  

  delay(1000);  // 1-second delay between readings

}

float voltageToPressure(float voltage) {

  // Calibration equation to convert voltage to pressure

  // Example: Assume 0V = 0kPa and 5V = 100kPa (for linear sensors)

  return voltage * (100.0 / 5.0);  // Adjust based on your sensor's specifications

}

Calibration:

The relationship between voltage and pressure depends on the specific sensor. To accurately measure pressure, you may need to calibrate the sensor by applying known pressures and measuring the corresponding output voltages.

Pressure vs. Voltage Curve: Some sensors have a linear response (where output voltage increases linearly with pressure), while others may require more complex calibration equations.

Advantages of Strain Gauge Pressure Sensors:

High accuracy: Can measure small changes in pressure with precision.

Wide pressure range: Can measure a broad range of pressures from very low to very high.

Robustness: Suitable for harsh environments, as strain gauges are typically durable and resistant to mechanical wear.

Limitations:

Sensitivity to temperature: Strain gauge sensors can be affected by temperature variations, requiring temperature compensation.

Signal amplification: The output signal from a strain gauge is often very small and requires amplification for practical use.

Strain gauge pressure sensors are ideal for applications where precise and reliable pressure measurement is required, especially in industrial, automotive, and medical fields. By pairing the sensor with an amplifier and microcontroller (like an Arduino), you can accurately measure and monitor pressure in real-time.