Differential Pressure Sensor : Circuit, Interfacing, Types, Testing, Symptoms & Its Uses

Sometimes it is not significant to identify the total pressure of a liquid (or) a gas but as an alternative, simply the variation between two points within the system being observed needs to be identified. So in such conditions, a differential pressure sensor is used. This sensor provides a comparative measurement between two points before & after a valve within a pipeline. If the valve is completely open, then the pressure on the two sides must be similar. If there is a variation within the pressure, then it could be the valve isn’t open (or) there is an obstruction. This article briefly explains the differential pressure sensor, their working, and their applications.

What is a Differential Pressure Sensor?

A differential pressure sensor is a type of sensor used to measure the variation within pressure at two points & provides a relative measurement between these two points. These pressure sensors are well known for their reliability & quality. The function of the differential pressure sensor is to provide data regarding the mutual connection of two pressure ranges within gases, liquids & steam. These are utilized to decide the pressure variation securely & reliably. This sensor has numerous applications in a variety of industries including control & optimization. These can also be found in safety-critical systems, filter monitoring, and level measurement within closed containers.

These sensors are designed mainly with capacitive sensing technology. This sensor has thin diaphragms, arranged between two parallel metal plates. Whenever outside force is provided, the diaphragm will flex a little, causing a change within the capacitance and thus a change within the o/p of the sensor.

Differential Pressure Sensor Working

The differential pressure sensor works by measuring the pressure drop between two points within a pipe. At one point in the pipe, it reports the charge condition of the particle filter & checks its function whereas at another point, it controls the low-pressure exhaust gas recirculation. Generally, these sensors are packaged with two ports where pipes can be connected. After that, the pipes are coupled simply to the system wherever the measurement is to be made.

Differential Pressure Sensor Circuit

The differential pressure sensor circuit using two strain gauges is shown below. This circuit uses a matched couple of strain gauges. Whenever the differential pressure is enhanced, then one strain gauge will become compressed whereas the other strain gauge will be stretched. In the following circuit, a voltmeter will register the imbalance of the bridge circuit & it will be displayed as a pressure measurement:

By using this circuit, we can determine the following:

Recognize which port in the circuit is the “high” pressure port.

Port “B” in the circuit is the “high” pressure port.

If the R1 fixed resistor fails to open, recognize what the voltmeter registers.

If the fixed resistor ‘R1’ fails to open then the voltmeter in the circuit drives completely upscale.

Identify a fault component that drives the voltmeter completely upscale.

A fault component that drives the voltmeter completely upscale follows as;

Strain gauge1 fails, it will be shorted.
Strain gauge 2 fails then it will open.
When ‘R1’ fails, it will open.
When ‘R2’ fails, it will be shorted.

MPX7002DP Differential Pressure Sensor Interfacing with an Arduino Uno

The MPX7002DP differential pressure sensor interfacing using an Arduino Uno is shown below. This interfacing helps in designing an open-source medical device. This medical device is used by doctors as well as medical professionals to treat a variety of respiratory disorders. Here a differential pressure sensor breakout board is used which uses the MPX7002DP differential pressure sensor.

The required components to make this interfacing mainly include; an MPX7002DP differential pressure sensor and an Arduino Uno board. The connections of this interfacing follow as;

The GND of the MPX7002DP differential pressure sensor is connected to the GND pin of the Arduino Uno board.

The +5V pin of the sensor is connected to the +5V of the Arduino.

The analog pin of the sensor is connected to the A0 pin of the Arduino.

Once all the connections are made, upload the code into the Arduino board which reads the pressure sensor into the Arduino.

// MPX7002DP Test Code
// This code exercises the MPX7002DP
// Pressure sensor connected to A0
int sensorPin = A0; // select the input pin for the Pressure Sensor
int sensorValue = 0; // variable to store the Raw Data value coming from the sensor
float outputValue = 0; // variable to store converted kPa value
void setup() {
//Start serial port at 9600 bps and wait for the port to open:
Serial.begin(9600);
while (!Serial) {
; // wait for the serial port to connect. Needed for native USB port only
}
pinMode(sensorPin, INPUT); // Pressure sensor is on Analogue pin 0
}
void loop() {
// read the value from the sensor:
sensorValue = analogRead(sensorPin);
// map the Raw data to kPa
outputValue = map(sensorValue, 0, 1023, -2000, 2000);
// print the results to the serial monitor:
Serial.print(“sensor = ” );
Serial.print(sensorValue);
Serial.print(“\toutput = “);
Serial.println(outputValue);
// wait 100 milliseconds before the next loop
// for the analog-to-digital converter and
// pressure sensor to settle after the last reading:
delay(100);
}

The output of the differential pressure sensor is connected to the A0 analog pin. So the actual data will be stored like an integer value within a sensorPin variable.

The raw converted analog data is stored within an integer variable known as sensorValue.

The output data changed in kPa will be stored within a float variable known as outputData.

The serial communications in the setup function are initialized & the sensorPin variable can be stated as an input.

The sensor data in the loop function is read from the analog pin & mapped to a kPa value.

After that, the data is sent to the serial terminal, then it can be reviewed.

To allow the system to resolve, a one-hundred-millisecond delay is introduced

After that, the entire procedure repeats forever!

Differential Pressure Sensor Types

The types of differential pressure sensors that are commonly used are; resistive, piezoelectric, capacitive, MEMS & optical.

Resistive Type

A resistive differential pressure sensor uses the change within a strain gauge electrical resistance to measure pressure variations. It is bonded to the diaphragm that is uncovered to the pressure medium. The strain gauge includes a metal resistive element on a flexible backing and is connected to the diaphragm, (or) deposited with thin-film processes directly. The metal diaphragm provides high over-pressure & burst-pressure ability.

A strain gauge is deposited on a ceramic diaphragm with a thick-film deposition procedure. As compared to metal-diaphragm devices, burst-pressure and Over-pressure tolerance are normally much lower. These sensors take benefit of the change within semiconductor materials’ resistivity whenever subjected to strain because of diaphragm deflection. The magnitude of the change will be a hundred times better as compared to resistance change generated within a metal strain gauge. Thus these sensors measure smaller pressure changes than ceramic or metal sensors.

Piezoelectric Type

This type of differential pressure sensor uses the piezoelectric materials property to produce a charge over the surface whenever pressure is provided. Here, the applied force and charge magnitude is proportional to each other & the polarity expresses its path. The charge builds up & dispels quickly when pressure alters by allowing fast-changing dynamic pressure measurement.

Optical Type

This type of differential pressure sensor uses interferometry for measuring pressure-induced change within optical fiber which is uninterrupted through electromagnetic interference. It is used in noisy environments (or) near sources like radiography equipment. These can be formed with small components (or) MEMS technology which is safe medically for topical use. It measures the pressure at several points along the optical fiber.

MEMS Technology

The term MEMS in MEMS sensor stands for “Micro-Electro-Mechanical System” which has a capacitive or piezo pressure-sensing mechanism that is fabricated on silicon on micron-level resolution. The electrical output of small-magnitude MEMS can be converted to an analog (or) digital signal by Co-packaged signal-conditioning electronics. These are small surface-mount devices typically just about 2 to 3mm for each side.

Please refer to this link for Steps to the fabrication of MEMS.

How to Test Differential Pressure Sensor?

The differential pressure sensor can be tested with a multimeter by setting it to 20V & a pressure gauge. The step-by-step process of testing is discussed below.

• First, connect the multimeter GND to the negative terminal of the battery & run a fast plausibility by verifying the battery voltage. It must be 12.6 V approximately by turning ON the battery & turning OFF the engine.
• Check with the service manual of the manufacturer to recognize the signal, GND, 5V reference & back-probe the wires.
• Turn on the ignition switch without starting the engine. So the multimeter must display a voltage in the range of 4.5 to 5V mainly for the 5V reference, a stable 0V for the GND wire. For the signal wire, it ranges from 0.5 & 4.5 volts.
• Turn ON the engine through the signal wire back-probed.
• Reverse the engine & observe if there is a change within the voltage reading. If there is no change, go on to check the connecting hoses through a pressure gauge.
• Take out the hoses from the pressure sensor when the engine is still running,.
• With the help of a pressure gauge, calculate both hoses’ pressure. For adequate accuracy, utilize an exhaust back pressure gauge to measure 0 to 15 PSI.
• Again verify the signal voltage and the voltage must read a number in between the hose pressure values.
  If your voltage highly changes or the values of pressure do not equal the voltage reading, then the differential pressure sensor is defective and will require to be changed.

Symptoms

The bad symptoms of differential pressure sensors include contamination, damaged electronics from severe engine heat, and clogged and vibration injuries from prolonged experience within the engine section.

• The most commonly caused issue in this type of sensor is harm to the diaphragm. So this causes the differential pressure sensor to be distorted (or) lose the capability to flex & react to changes within the pressure.
• One more issue is harm to the port region of the sensor due to contamination lodging or debris within the tube & restricting the proper flow of liquid into the sensor.
• Whenever the differential pressure sensor ends signaling the PCM to restart, then this sensor becomes obstructed by pollutants.
• Some of the signs that specify the sensor that it is not regenerating correctly because of the sensor failing, poor fuel economy, poor engine performance, high engine temperatures, an increase in black smoke from the exhaust, maximum transmission temperatures, etc.
• Whenever the sensor fails, then exhaust gases cannot be purged completely when backpressure thrusts exhaust back into the combustion chamber causing the sensor to mix through the engine oil.
• The main symptoms of differential pressure sensor failure include; misfire/ detonation, lack of engine power, check the engine light is on, extreme fuel utilization, and the engine will start poorly.
• When troubleshooting engine sensors, it is recommended to look for any signs of visible damage first. Check all connections, starting with the sensor electrical connector, and look for any damage such as cracking or melting. Any damaged wires will need to be replaced.
• Next, inspect the hoses connected to the sensor. Again, look for any damage such as cracking or melting.
• If the hoses are damaged, they will need to be replaced and most likely rerouted so they are not damaged the same way again. If the hoses look to be in good physical condition, check for any blockage or clogs. If clogged, the hoses will need to be cleared or replaced.

Uses/Applications

The differential pressure sensor applications are discussed below.

• The differential pressure sensors are used in the medical field for deep vein thrombosis treatment.
• These are also used in infusion pumps, respirators & breathing detection equipment.
• These sensors are found in numerous locations for Flow sensing, level or depth sensing, and leak testing.
• Differential pressure sensors are frequently found in industrial environments wherever a variation within pressure can be utilized to decide the flow of liquids or gases.
• These are used in effluent treatment plants, subsea oil & gas processing, and remote heating systems that use heated water (or) steam.
• Generally, these are used for differential pressure monitoring & controlling of water, gases, and oil.
• These are also found in level measurement within closed containers, filter monitoring & safety-critical systems.
• These sensors are used in numerous applications within data centers.
• These are very helpful in measuring flow across venturi tubes, pitot tubes, orifice plates & other flow-based applications.
• The differential pressure sensor is used to monitor process flow, measure safe levels within liquid tanks, and manage control loops.
• These are used in clean rooms, HVAC & building automation, hospitals, isolation chambers, laboratories, the pharmaceutical industry, etc.
• The extremely accurate devices use these sensors for all non-aggressive & non-flammable gases.
• These can be used for monitoring filters within different applications
• Differential pressure sensors can be found in fire protector systems in their sprinkler unit.
• These are very helpful whenever the amount of a liquid within a closed vessel must also be measured.

Thus, this is an overview of a differential pressure sensor, its working, and its applications. This sensor is an essential component in different applications across various industries. This sensor can measure pressure variations with high accuracy which allows the secure and efficient process of many systems.

Measuring devices are simply exposed to a broad range of thermal, chemical, or mechanical stresses so that the measured values vary & lose precision over time. For instance, hysteresis or Zero offsets can lead to security risks & a reduction in process efficiency. So frequent calibration cannot avoid such changes, although detects them within time. Thus, it is suggested to perform a Calibration yearly once to electrical & mechanical pressure measuring devices. Here is a question for you, what is a pressure sensor?