Introduction

Overpressure (also called overload pressure), proof pressure, and burst pressure are important specifications for pressure sensors and systems. They represent different levels of pressure that a sensor or system can withstand. Let’s examine each one in detail and discuss their relationships:

Overpressure

The maximum pressure that can be applied to the sensor without causing a shift in performance or calibration.

Overpressure is the highest pressure a pressure sensor can handle without affecting its performance. It also refers to cases where the pressure goes beyond the set limits. While it’s not the best situation, pressure transducers can tolerate occasional pressures up to their overpressure rating and will return to normal afterward.

Characteristics of overpressure including:

• Temporary and reversible
• Does not cause permanent damage
• Sensor returns to normal operation when pressure is reduced
• Typically: 1.5 to 2 times the full-scale pressure range

Proof Pressure

Proof pressure is the maximum pressure that a pressure sensor can withstand without experiencing permanent damage or a significant shift in its performance characteristics. It’s typically higher than the normal operating pressure range but lower than the burst pressure.

Characteristics of proof pressure including:

• May cause temporary changes in calibration
• No permanent physical damage occurs
• Sensor may require recalibration after exposure
• Typically: 1.5 to 3 times the full scale pressure range

Burst Pressure

Burst pressure for a pressure sensor is a critical specification that defines the maximum pressure the sensor can withstand before catastrophic failure occurs.

Burst pressure for a pressure sensor is a critical specification that defines the maximum pressure the sensor can withstand before catastrophic failure occurs.

Burst pressure tests are usually destructive and performed on sample units, not on every sensor produced.

Unlike proof pressure events, there is no expectation of the sensor returning to normal operation after experiencing burst pressure.

Characteristics of burst pressure including:

• Causes permanent and irreversible damage
• Sensor is destroyed and cannot be used again
• Often determined through destructive testing
• Typically: 3 to 5 times the full-scale pressure range (or higher)

Overpressure Duration Time & Repetition

Let’s explore how overpressure and duration, repetition can affect sensor accuracy using a below example. We’ll consider a piezoresistive pressure sensor with the following specifications:

Background

Sensor Specifications:

• Measurement Range: 0-100 bar
• Rated Overpressure: 150 bar
• Initial Accuracy: ±25% Full Scale (FS)
• Output: 4-20 mA

Initial Calibration:

• 0 bar = 4.00 mA
• 50 bar = 12.00 mA
• 100 bar = 20.00 mA

3 scenarios and their performances

Let’s examine three scenarios with varying overpressure durations and repetitions:

• Scenario 1: Short Duration, Single Occurrence, Overpressure: 140 bar for 1 second, once
• Scenario 2: Extended Duration, Single Occurrence, Overpressure: 140 bar for 1 hour, once
• Scenario 3: Short Duration, Multiple Occurrences, Overpressure: 140 bar for 1 second, repeated 100 times over a week

	Output signal (mA)	Output signal (mA)	Output signal (mA)
Pressure (bar)	【1】140 bar for 1 second	【2】140 bar for 1 hour	【3】140 bar for 1s, repeated 100 times
0	4.02	4.08	4.15
50	12.01	12.05	12.10
100	20.03	20.10	20.18

Analysis: how we understand it?

Duration Effect

• Short duration (Scenario 1) caused minimal accuracy degradation.
• Extended duration (Scenario 2) led to more significant zero shift and span error.

Repetition Effect

• Multiple exposures (Scenario 3) resulted in cumulative damage, causing the most severe accuracy degradation.
• Repeated stress likely caused material fatigue in the sensing element.

Zero Shift

• Increased with both duration and repetition.
• Most pronounced in Scenario 3, indicating potential permanent deformation.

Span Error

• Generally less affected than zero shift.
• Increased with duration and repetition, but not as drastically as zero shift.

Linearity

• Minimal impact in short-duration scenarios.
• Became noticeable with repeated exposures (Scenario 3).

Overall Accuracy

• Degraded from initial ±25% FS to:
• Scenario 1: ±3% FS
• Scenario 2: ±55% FS
• Scenario 3: ±1% FS

	Zero shift	Span error	Overall accuracy
Scenario 1	0.125%/FS	0.0625% FS	±0.3% FS
Scenario 2	0.5% FS	0.125% F	±0.55% FS
Scenario 3	0.9375% FS	0.1875% FS	±1% FS

This example demonstrates that both the duration and frequency of overpressure events play crucial roles in sensor accuracy degradation. While sensors are designed to withstand some overpressure, repeated or prolonged exposure can lead to cumulative damage and significant accuracy issues.

Take an example to show the relationships

Background:

• Measurement range: 0-100 bar
• Overpressure rating: 180 bar (1.8 times full scale)
• Proof pressure rating: 250 bar (2.5 times full scale)
• Burst pressure rating: 400 bar (4 times full scale)
• Accuracy: ±5% Full Scale (FS)
• Output: 4-20 mA

Overpressure Event

1. Normal operation: At 50 bar, sensor outputs 12 mA (±0.08 mA)

2. Overpressure event: Sensor exposed to 170 bar for 1 minute

3. During overpressure: Output exceeds 20 mA and accuracy not guaranteed

4. After pressure returns to 50 bar:

• Immediate reading: 12.1 mA (slight offset)
• After 5 minutes: 12.02 mA (nearly normal)
• After 15 minutes: 12 mA (within original accuracy)

5. Subsequent performance:

• 0 bar: 4.01 mA (minimal zero shift)
• 100 bar: 20.02 mA (minimal span change)
• Linearity and hysteresis within specs

Proof Pressure Event

1. Normal operation: At 50 bar, sensor outputs 12 mA (±0.08 mA)

2. Proof pressure event: Sensor exposed to 240 bar for 10 minutes

3. During proof pressure: Output significantly exceeds 20 mA, and accuracy not guaranteed

4. After pressure returns to 50 bar:

• Immediate reading: 12.4 mA (significant offset)
• After 1 hour: 12.3 mA (still notable shift)
• After 24 hours: 12.2 mA (improved, but outside original accuracy)

5. Subsequent performance:

• 0 bar: 4.2 mA (noticeable zero shift)
• 100 bar: 20.4 mA (span change)
• Linearity slightly affected

6. Recalibration process:

• Zero adjustment: -0.2 mA
• Span adjustment: -0.4 mA
• After recalibration, sensor returns to original accuracy

Burst Pressure Event

1. Normal operation: At 50 bar, sensor outputs 12 mA (±0.08 mA)

2. Burst pressure event: Sensor exposed to 380 bar

3. During burst pressure: Output becomes erratic and unpredictable and sensing element physically ruptures

4. After pressure is removed:

• Sensor output remains at 0 mA or shows random fluctuations
• Physical inspection reveals damaged diaphragm or cracked housing

5. Subsequent attempts at operation:

• Sensor fails to respond to pressure changes
• No meaningful output can be obtained

Key differences: what we find

1. Reversibility: Overpressure effects are quickly reversible, proof pressure effects require recalibration, burst pressure causes irreversible damage.

2. Operational status: After overpressure and proof pressure, the sensor can still function (though may need recalibration). After burst pressure, the sensor is permanently non-functional.

3. Pressure magnitude: Each scenario involves progressively higher pressures, demonstrating different aspects of the sensor’s pressure endurance.

4. Recovery process: Overpressure requires no intervention, proof pressure requires recalibration, burst pressure requires complete sensor replacement.

This comprehensive example illustrates the distinct characteristics and impacts of overpressure, proof pressure, and burst pressure on a pressure sensor.

What is Overload Pressure

Overload pressure (also called overpressure) refers to a situation where the pressure applied to a sensor exceeds its specified maximum operating range.

Overload pressure can significantly impact the accuracy and reliability of pressure sensors by causing mechanical deformation, calibration shifts, hysteresis, material fatigue, and compromised signal integrity. Understanding these effects and implementing preventive measures is crucial for maintaining the performance and longevity of pressure sensors in various applications.

Effects of Overload Pressure on Accuracy

Mechanical Deformation and Damage

Overloading can cause permanent deformation of the sensor’s diaphragm or other mechanical components.

For piezoresistive and capacitive sensors, this deformation changes the mechanical properties, leading to shifts in the baseline output and reduced accuracy.

In extreme cases, the diaphragm or sensing element may fracture or rupture, rendering the sensor unusable. This is particularly critical for piezoelectric sensors that rely on the crystalline structure to generate a charge.

Calibration Shift

In another hand, overload especially more than durable overload can cause a permanent shift in the zero point of the sensor, meaning it will no longer read zero pressure accurately when no pressure is applied.

The sensitivity or span of the sensor (the relationship between input pressure and output signal) can also be altered. This means that for a given pressure range, the sensor may output incorrect values, deviating from its calibrated slope.

Hysteresis

After experiencing overload, the sensor might exhibit hysteresis, where its output for increasing and decreasing pressures does not follow the same path. This non-linear response can lead to inaccuracies, especially in dynamic applications where pressure fluctuates.

Electrical and Material Fatigue

Overloading can lead to micro-cracks in the piezoelectric material, causing a reduction in its ability to generate charge under stress. This results in lower sensitivity and accuracy.

Repeated overloading can cause fatigue in the strain gauges, leading to changes in their resistance characteristics and thus affecting the sensor’s output.

Compromised Signal Integrity

Overloading can induce electrical noise or signal interference, particularly in sensors with integrated electronics. This can degrade the signal-to-noise ratio, making it difficult to obtain precise readings.

Take an example

Let’s take an example to illustrate how overpressure can affect pressure sensor accuracy. We’ll consider a hypothetical piezoresistive pressure sensor designed for measuring pressures in the range of 0-100 psi.

Background

Sensor Specifications:
– Measurement Range: 0-100 psi
– Rated Overpressure: 150 psi
– Accuracy: ±0.5% Full Scale (FS)
– Output: 0-5V linear

Initial Calibration:

• 0 psi = 0.00V
• 50 psi = 2.50V
• 100 psi = 5.00V

Steps

Step 1: Normal Operation
Under normal operating conditions (0-100 psi), the sensor performs within its specified accuracy of ±0.5% FS, which is ±0.5 psi.

Step 2: Overpressure Event
Let’s say the sensor is accidentally exposed to 140 psi (below the rated overpressure but above the measurement range).

Step 3: Post-Overpressure Performance
After the overpressure event, we retest the sensor:

• 0 psi = 0.05V (instead of 0.00V)
• 50 psi = 2.52V (instead of 2.50V)
• 100 psi = 5.03V (instead of 5.00V)

Step 4: Analyze the Impact

1. Zero OffsetShift:
   The zero point has shifted by 0.05V, which translates to 1 psi (0.05V / 0.05V/psi).
2. Span Change:
   The span has increased slightly from 5.00V to 4.98V (5.03V – 0.05V).
3. LinearityChange:
   The midpoint (50 psi) reading is now slightly off the ideal linear response.

1. Overall Accuracy:
   – At 0 psi: Error is 1 psi (1% FS)
   – At 50 psi: Error is 0.4 psi (0.4% FS)
   – At 100 psi: Error is 0.6 psi (0.6% FS)

The sensor’s accuracy has degraded from the original ±0.5% FS to about ±1% FS due to the overpressure event.

This example demonstrates how an overpressure event, even within the sensor’s rated capabilities, can significantly affect accuracy through zero offset shifts, span changes, and linearity alterations. It underscores the importance of protecting sensors from overpressure conditions and regular calibration in demanding applications.

Duration Time| Repeat Times | Working Temperature

Overload Duration Time

As mentioned above, when a pressure sensor is subjected to pressures beyond its specified range (overload), its accuracy can be compromised, now let’s talk about the duration time.

Prolonged exposure to overload conditions can cause physical deformation or damage to the sensor element, leading to permanent shifts in calibration and reduced accuracy.

Some pressure sensors are designed to withstand temporary overloads, but the duration and magnitude of overload should be within the sensor’s specifications to prevent damage.

In another words, the longer a sensor is exposed to overload conditions, the greater the risk of mechanical failure or drift in the sensor’s output. This is because excessive force can alter the mechanical structure of the sensor, causing wear or damage that affects its long-term stability and accuracy.

Pressure sensors are typically designed with a safety margin, allowing them to withstand short-term overloads without damage. However, if overloads are frequent or sustained, it may be necessary to select a sensor with a higher pressure rating or incorporate protective mechanisms and choose the most durable cell material.

Working Temperature

Most pressure sensors have a specified temperature range in which they operate optimally. Deviations from this range can lead to errors due to changes in material properties or signal conditioning circuits.

High temperatures can cause drift in the output signal, while low temperatures might affect the sensor’s mechanical components or introduce additional noise.

Temperature changes can affect both the sensor’s materials and its electronic components. Thermal expansion can lead to mechanical stress, while temperature-sensitive electronic components can experience changes in resistance or capacitance, affecting the output signal.

In fact, many pressure sensors include temperature compensation features to minimize the impact of temperature variations on accuracy.

This can involve using materials with low thermal expansion coefficients or incorporating electronics that adjust the output based on temperature readings.

However, don’t forget the duration & repeat time!

The duration of over-temperature exposure can also significantly affect a pressure sensor’s performance and reliability, similar to how overload conditions impact the sensor.

Prolonged exposure to temperatures beyond the specified operating range can lead to material degradation. This includes changes in the sensor’s structural materials, like polymers or elastomers, which can become brittle or lose elasticity.

Metal components might also experience changes in mechanical properties, leading to compromised sensor integrity.

Repeated or sustained exposure to high temperatures can induce thermal stress. This stress can cause mechanical deformation or fatigue in the sensor’s elements, leading to permanent calibration shifts or even mechanical failure. The effects are more pronounced if the sensor undergoes rapid temperature cycling.

Take an example

Let’s explore how overpressure duration and repetition can affect sensor accuracy using a hypothetical example. We’ll consider a piezoresistive pressure sensor with the following specifications:

Background

Sensor Specifications:

• Measurement Range: 0-100 psi
• Rated Overpressure: 150 psi
• Initial Accuracy: ±0.25% Full Scale (FS)
• Output: 4-20 mA

Initial Calibration:

• 0 psi = 4.00 mA
• 50 psi = 12.00 mA
• 100 psi = 20.00 mA

Let’s examine three scenarios with varying overpressure durations and repetitions:

Scenarios

Scenario 1: Short Duration, Single Occurrence Overpressure: 140 psi for 1 second, once

Results after overpressure:

• 0 psi = 4.02 mA
• 50 psi = 12.01 mA
• 100 psi = 20.03 mA

Accuracy impact:

• Zero shift: 0.125% FS
• Span error: 0.0625% FS
• Overall accuracy: ±0.3% FS

Scenario 2: Extended Duration, Single Occurrence: Overpressure: 140 psi for 1 hour, once

Results after overpressure:

• 0 psi = 4.08 mA
• 50 psi = 12.05 mA
• 100 psi = 20.10 mA

Accuracy impact:

• Zero shift: 0.5% FS
• Span error: 0.125% FS
• Overall accuracy: ±0.55% FS

Scenario 3: Short Duration, Multiple Occurrences. Overpressure: 140 psi for 1 second, repeated 100 times over a week

Results after overpressure:

• 0 psi = 4.15 mA
• 50 psi = 12.10 mA
• 100 psi = 20.18 mA

Accuracy impact:

• Zero shift: 0.9375% FS
• Span error: 0.1875% FS
• Linearity error: 0.0625% FS
• Overall accuracy: ±1% FS

Analysis

Duration Effect:

• Short duration (Scenario 1) caused minimal accuracy degradation.
• Extended duration (Scenario 2) led to more significant zero shift and span error.

Repetition Effect:

• Multiple exposures (Scenario 3) resulted in cumulative damage, causing the most severe accuracy degradation.
• Repeated stress likely caused material fatigue in the sensing element.

Zero Shift:

• Increased with both duration and repetition.
• Most pronounced in Scenario 3, indicating potential permanent deformation.

Span Error:

• Generally less affected than zero shift.
• Increased with duration and repetition, but not as drastically as zero shift.

Linearity:

• Minimal impact in short-duration scenarios.
• Became noticeable with repeated exposures (Scenario 3).

Overall Accuracy:

• Degraded from initial ±0.25% FS to:
• Scenario 1: ±0.3% FS
• Scenario 2: ±0.55% FS
• Scenario 3: ±1% FS

How to go back to the original level after overload?

The ability of a pressure sensor to return to its original accuracy level after experiencing an overload depends on several factors, including the design of the sensor, the magnitude and duration of the overload, and whether the sensor has experienced any permanent damage.

Some pressure sensors are specifically designed to handle overload conditions without permanent deformation.

For example, if the overload is brief and within the sensor’s designed safety margin, the sensor is more likely to recover its original accuracy. Manufacturers often specify a maximum overload pressure that the sensor can tolerate for short periods.

These sensors may use materials and structures that can withstand temporary overloads, allowing them to return to their original accuracy once normal conditions resume.

On the other side:

If the overload causes permanent deformation of the sensing element or other mechanical components, the sensor may not return to its original level of accuracy. This is common if the overload exceeds the yield strength of the materials used in the sensor.

Flush Diaphragm Cell VS Monolithic Cell

Ceramic piezo-resistive pressure sensors are known for their robustness and durability, particularly in harsh environments, when it comes to ceramic piezo-resistive pressure sensor cell and module, it is a fact that the flush diaphragm cell always has better overload performance and monolithic cell.

Overload Pressure Ability Comparison Between Monolithic & Flush Diaphragm Ceramic Cell

	Pressure Range (bar)	Overload Pressure (bar)		Burst Pressure (bar)
		Monolithic Ceramic Cell	Flush Diaphragm Ceramic Cell	Monolithic Ceramic Cell	Flush Diaphragm Ceramic Cell
1	0-5	10	20	15	40
2	0-10	20	30	30	50
3	0-16	32	48	48	80
4	0-20	40	60	60	100
6	0-25	50	75	75	125
7	0-35	60	100	90	150
8	0-50	75	150	125	250
9	0-70	105	200	175	300
10	0-100	200	250	300	400
11	0-200	300	400	500	600
Above data was calculated and statistic zed between ESS501 and ESS502, for study reference only.

Why?

There are many factors can contribute to this however, here we only talk about the structure and how it leads to difference performance of overload.

Uniform Pressure Distribution

The flush diaphragm design features a flat, smooth surface that allows pressure to be evenly distributed across the entire diaphragm area. This uniform distribution minimizes stress concentrations, which are critical points where mechanical failure is more likely to occur under high pressure.

In monolithic designs, the structure often includes varying thicknesses or features such as cavities and ridges, which can lead to uneven stress distribution. These irregularities increase the likelihood of localized stress points, which can result in deformation or failure during overload conditions.

Surface Contour

The flat and continuous surface of a flush diaphragm reduces the potential for pressure to concentrate at specific points. This structural characteristic helps the diaphragm to flex uniformly under pressure, maintaining structural integrity even when pressure exceeds normal operating levels.

The varying surface profile of a monolithic sensor can create areas where pressure is not evenly distributed. Changes in contour can act as stress concentrators where the material is more likely to yield or crack under overload conditions.

Mechanical Flexibility

The structural simplicity and mechanical flexibility of the flush diaphragm allow it to accommodate pressure changes more effectively, reducing the risk of structural failure. The diaphragm can deform elastically under pressure and return to its original shape once the pressure is relieved.

On the other hand, the more complex structure of monolithic sensors can restrict their ability to flex uniformly, increasing the risk of permanent deformation during overload events.

Immediate Effects of Overload

Before Overload: The diaphragm inside the sensor flexes within its elastic limit, accurately converting pressure to an electrical signal.

• Pressure (psi): 0, 10, 20, 30, 40, 50
• Sensor Output (V): 0, 0.2, 0.4, 0.6, 0.8, 1.0

After Overload: The diaphragm is permanently deformed. Even when the pressure returns to 35 psi, the diaphragm no longer returns to its original shape.

• Pressure (psi): 0, 10, 20, 30, 40, 50
• Sensor Output (V): 0.1, 0.25, 0.45, 0.65, 0.85, 0.95

Zero Drift: Initially, the sensor reads 0 psi perfectly when no pressure is applied. After the overload, it might read 2 psi instead of 0 psi.

Span Shift: The sensor’s sensitivity changes. If it originally outputted 1 V at 50 psi, it might now output 0.9 V at the same pressure, indicating a span shift.

Accuracy Before Overload: ±0.5 psi

Accuracy After Overload: The zero drift and span shift mean that the sensor might now have an accuracy of ±2 psi or worse. This means a true pressure of 35 psi might be read as anywhere from 33 to 37 psi, a significant deviation for critical applications like tire pressure monitoring.

Preventive Measures and Design Considerations

Overload Protection Mechanisms

These are physical barriers within the sensor that prevent the diaphragm or other sensing elements from moving beyond a certain limit. This helps avoid permanent deformation.

Or one can use pressure relief valves which can be integrated into the system to release excess pressure before it reaches the sensor, thereby preventing overload.

Material Selection

Using materials with higher tensile strength for the diaphragm and other critical components can help withstand brief overloads without permanent deformation.

SS316: Offers excellent corrosion resistance, high mechanical strength, and good temperature stability, making it ideal for harsh, high-pressure environments.

SS304: Provides good corrosion resistance and mechanical strength at a more economical cost, suitable for general industrial applications.

Ceramics: Provide exceptional hardness and chemical resistance, ideal for high-temperature and highly corrosive environments but require careful handling to avoid brittle failure.

Redundant Sensing Elements

Incorporating redundant sensing elements that can take over if the primary sensor fails due to overload can maintain system reliability, some designs also include a secondary diaphragm that acts as a backup in case the primary one fails, ensuring continuous operation.

Electrical Protection

In practice, by using surge protection devices, it can shield the sensor’s electronics from high voltage spikes that might occur during an overload event.

On the other hand, by incorporating filtering capacitors, it can also help eliminate electrical noise and ensure signal integrity, even if the sensor experiences brief overloads.

What is pressure sensor offset?

Imagine you have a pressure sensor connected to a gauge that is supposed to read 0 when there is no pressure. But even when nothing is connected, the gauge shows it as +1 psi.

This is called an pressure sensor offset error. It means the sensor is not perfectly calibrated and shows a small pressure reading when there should be none.

To give some real numbers, let’s look at specifications:

Offsets can occur due to small differences in the sensor’s physical structure or electronic components. Engineers try to minimize them through calibration testing.

Let’s take an example,

Let’s say a sensor has an offset of +1 psi.

Then:

If the actual pressure is 0 psi, the sensor will read 1 psi instead of the correct 0 psi.

This is a full 1 psi error just because of the offset.

If the actual pressure is 5 psi, the sensor will read 6 psi instead of 5 psi. The error is now the 1 psi offset.

As pressure increases, the impact of a fixed offset error becomes smaller as a percentage. But the reading is still absolutely inaccurate.

For small pressure changes near zero, the offset could be a major source of inaccuracy, swamping the actual pressure variation.

The greater the offset value, the larger these errors will be. This is why industries like aerospace that require very high accuracy specify sensors with offsets smaller than +/- 0.1% of full scale.

What is the relationship between offset and sensitivity

All pressure sensors are sensitive to very small pressure changes. But they aren’t always perfect – some may have a small offset error where it reads a non-zero pressure when there is actually none.

Let’s look at two examples:

A low-cost sensor has a sensitivity of 1 PSI, meaning it can detect 1 PSI changes. Its offset is ±2 PSI.

A high-precision sensor has a greater sensitivity of 0.1 PSI. But its smaller offset is only ±0.5 PSI.

We can see here that higher sensitivity sensors, which can detect smaller pressure variations, typically have lower offset errors.

This is because making a sensor more sensitive, say by having a thinner diaphragm, also makes it more susceptible to unwanted stresses that can cause offsets.

So reducing a sensor’s offset requires design optimizations that may lower its maximum sensitivity as a trade-off.

How to reduce offset error?

Improved diaphragm flatness

Improving diaphragm flatness is very effective. If the diaphragm bows up in the middle even 1 micron, it causes offset. By polishing with precision machines accurate to 0.01 microns, offsets reduced from 1 PSI to 0.1 PSI.

The designer can follow below step to get the good flatness

Thermal stabilization

Adding a small thermistor provides temperature data to a processor. It adjusts the sensor output up/down by 0.1 PSI depending on whether it’s 20°C or 30°C, cutting thermal drift offsets in half.

All parts in a sensor expand and contract slightly with temperature changes. This thermal effect alone can cause up to 2 PSI offset errors over a 100°C range in many sensors!

To prevent this, engineers add a tiny thermistor nearby the pressure sensing element. This thermistor acts like a thermal checker.

As temperature rises, the thermistor’s electrical resistance changes in a precise and known way based on its material properties.

An on-board microchip continuously monitors the thermistor and compares its reading to the chip’s internal temperature-resistance data.

If it detects a 1°C rise, it knows the sensor housing and components will expand just enough to induce 0.1 PSI of offset error. So it automatically subtracts 0.1 PSI from readings.

This digital thermal compensation holds offset steady within +/-0.05 PSI over the full operating range. Without it, drifting offsets would ruin measurement accuracy.

By intelligently accounting for temperature, sensors can self-correct for a major source of potential errors. This ensures reliable pressure readings regardless of ambient conditions.

Reduced vacuum pressure

Earlier, sensors held 0.5 PSI vacuum using one rubber seal which caused 4 PSI offsets over time. Switching to a dual O-ring viton seal maintained vacuum for over a year, lowering offsets to a stable 0.2 PSI.

Engineers also lowered die attachment stress by changing from heavy duty epoxy to super thin cyanoacrylate glue. This reduced residual mounting strain, cutting the offset from 1 PSI down to 0.3 PSI.

Digital calibration

Traditional sensors use trim potentiometers that may adjust offset by 0-5% of the sensor’s full scale range. This is like correcting a reading by up to 5 psi on a 100 psi sensor.

Modern sensors add an on-chip microchip and convert the analog output to a digital number out of 4095 counts. Factory calibration determines the reading should be 1010 at zero pressure.

If uncalibrated, the sensor delivers 1020 counts instead. The chip calculates it needs to subtract 10 counts from its results to trim offset to the proper 1010.

It does this digitally by programming resistor settings inside to lower the bridge output by exactly 10 units. Now offset is reduced from 1020-1010 to the desired 1010, an error of only 0.2% full scale.

Traditional sensors lacked this level of digital precision. By controlling offsets down to a granularity of 0.025% rather than 5%, much cleaner zero pressure readings result even over time and temperature changes.

A few takeaway points

1. Response time refers to how quickly a sensor detects and reports pressure changes. It’s an important specification that depends on sensor design and materials.

2. Applications with rapidly fluctuating pressures like engines require very fast sub-millisecond response times. Slower processes can tolerate response times of 10-100ms.

3. Higher sensitivity generally means slower response times due to design tradeoffs. The right balance is needed for each application.

4. Offset errors occur when sensors read a non-zero pressure at zero pressure applied. This directly impacts measurement accuracy.

5. Improving factors like diaphragm flatness, thermal stabilization, calibration precision are used to minimize offset errors.

6. Digital calibration and compensation techniques allow reducing offsets to levels far below what analog designs provide.

7. Understanding response time and error specifications is critical for selecting a pressure sensor that can meet the measurement needs and tolerances of different industrial processes.

8. With optimized designs and materials, sensor engineers can enhance performance to enable highly precise real-time dynamic pressure monitoring.

What is pressure sensor response time?

All pressure sensors need some time to react when the pressure changes. This reaction time is called the response time.

Imagine you blow up a balloon and tie a knot in it after it’s inflated. You then connect the balloon to a pressure sensor. When you suddenly cut the knot with scissors, the air pressure inside the balloon will drop very fast. The sensor needs to quickly sense this pressure change.

The response time tells us how fast the sensor can do this sensing. It’s measured in milliseconds (ms), which is thousandths of a second. For example, a sensor with a 1ms response time means it takes 1ms to sense 90% of the full pressure change.

Pressure changes happen very rapidly in some applications like cars or machines. Their sensors need super quick response times, maybe just a few 100 microseconds. Other uses like weather stations see slower pressure shifts. There sensors can have response times of 10s of ms.

To get a fast response, sensor designers build them with thin, flexible materials to let pressure changes impact them rapidly. Electronics are optimized for speed too. But accuracy matters too, so a balance must be found.

How significant of response time in pressure measurement

When measuring pressure, you need to know the pressure level accurately over time. This is especially true if the pressure is changing rapidly.

Think about measuring engine pressures in a race car. The pressures inside the engine can change drastically within milliseconds as the pistons move up and down.

A sensor with a slower response time might not be able to track these fast pressure swings accurately. It might miss peaks or valleys in the pressure waveform.

Now let’s look at some actual sensor specs:

A high-performance sensor suitable for race cars may have a response time of just 250 microseconds (0.00025 seconds).

Meanwhile, a standard sensor used in a home weather station might be around 10 milliseconds (0.01 seconds).

We can calculate how far off these sensors could be using some common pressure changes:

Let’s put it in simple, the faster pressure changes, the more important a very fast response time is to get accurate real-time pressure measurements.

This is crucial for applications like engines but less critical for slower weather changes.

What is the relationship between response time and sensitivity

Sensitivity refers to how much the sensor’s output changes in response to a small pressure change. A highly sensitive sensor will produce a large output change for even a tiny amount of pressure difference.

Response time, as we discussed earlier, is how quickly a sensor responds to a pressure change by settling at its final output value. A fast response time is important to accurately track rapid pressure fluctuations.

So how are response time and sensitivity related? Sensors with higher sensitivity generally have slower response times, and vice versa.

Let me give a practical example:

A highly sensitive medical sensor may detect 0.1 psi changes in airway pressure. But due to its design focusing on sensitivity, its response time is 50 milliseconds.

Meanwhile, a sensor for measuring engine RPM has a response time of only 1 millisecond. However, its sensitivity is lower at 1 psi, since performance is optimized for speed over tiny pressure detection.

The physics of how pressure sensors work means improving one characteristic typically reduces the other. Application needs dictate the right balance between sensitivity and response time for accurate real-time pressure measurement. A faster or slower response may be preferable depending on the specific measurement demands.

Which is high response industry and which is low?

Industries like racing and aerospace that need very fast sensor response times of 1ms or less:

• Engine pressures inside a F1 car may swing 100 PSI in just 2ms during acceleration.
• Jet engine turbine pressures fluctuate up to 200 PSI every 20ms during flight.

To capture these rapid 10’s-100’s of psi/ms transients, sensors use thin foil or MEMS technology with times below 1ms.

Meanwhile, industries like weather monitoring or building automation with slower 10-100ms response sensors:

• Hurricane pressure drops 30 PSI over 30 seconds, a slow 0.1 PSI/sec decline.
• HVAC systems experience 0.5-2 PSI swings every few minutes during operation.

In these stable environments with gradual 0.01-1 PSI/sec changes, sturdier sensor designs involving thicker diaphragms or bourdon tubes are sufficient.

So fast industries need microsecond-range sensors to precisely track 10’s-100’s PSI/ms transients, while slow industries can use lower-cost 10-100ms sensors well-suited for measuring 0.01-1 PSI/sec pressure variations.

How to build high response time pressure sensor?

To sense pressure changes quickly, the sensor needs a part that can flexibly move in response to even tiny pressures. A common choice is a thin flexible silicon diaphragm. It will bend sharply under very small pressure differences.

On the back of the diaphragm a pressure sensor chip is placed with piezoresistive strain gauges. These are thin wires made of a material that changes electrical resistance when bent. As pressure bends the diaphragm, the strain gauges bend and their resistance changes.

To build a 1ms sensor, the silicon diaphragm could be only 10 microns thick – that’s 1/10 the width of a human hair! At this size it will flex very quickly when pressures shift. The wires could be even smaller at only 1 micron width.

The sensor chip circuitry is also optimized for rapid responses. It uses a Wheatstone bridge circuit to quickly turn the tiny resistance changes into an output voltage signal. Processing this with high-speed components further boosts measurement speed.

Everything is miniaturized – the whole sensor could be smaller than a grain of rice! Its small size means pressures cause instant flexing of the diaphragm and strain wires for sub-millisecond responses.

By intelligently designing the flexible elements and high-speed circuitry, engineers can create ultra-responsive pressure sensors suitable for demanding fields like race cars or jet engines.

Is high response time always better than low response time?

We can take the same example as earlier.

A race car engine needs to measure 0-200 PSI changes every 2 milliseconds.

A sensor with a 1ms response time would accurately catch 90% of each pressure swing. But a 10ms sensor would only see 20% of the change before it starts going back down. The fast sensor is better here.

Now a weather station monitoring hurricanes. Pressure drops 30 PSI over 30 seconds.

Even a slower 10ms sensor would still track 99.9% of the change since it’s gradual. A 1ms sensor offers no real benefit for this use.

To give real numbers from product specs:

• A high-end 1ms sensor costs $50 but its thin parts break easily.
• A standard 10ms sensor is only $25 and built tough for outdoor use.

If the weather station just needs general pressure readings during storms, the lower cost 10ms sensor works fine.

So obviously, for fast-changing dynamics, faster is better for precision measurements. But when changes are slow and gentle, a lower response time can be adequate while offering benefits like lower cost or greater durability. It depends on the specific application needs.

Different sensing technology and different response time

Different sensing mechanisms like piezoresistive, capacitive, optical and resonant can give responses ranging from 1ms to below 1us depending on the technology and sensor design/needs. Newer approaches like MEMS are also pushing response times lower.

• Piezoresistive: These utilize silicon strain gauges that change resistance under pressure. Very common and inexpensive. Response times range from around 1-10ms.
• Capacitive: Work by measuring capacitance changes between a diaphragm and a base plate under pressure. Generally faster than piezoresistive, with responses as low as 500us.
• Optical/Fiber Optic: Leverage how pressure alters light properties in an optical fiber. Can attain ultra-fast responses below 100us due to lack of electrical components.
• Resonant: Involve a diaphragm that vibrates at a set frequency, shifting under pressure loads. Some have response times less than 1us but are more expensive.
• Piezoelectric: Rely on generated electric voltage from pressures applied to quartz or ceramic material. Fast responses of 10-100us but cannot measure static pressures.
• Electromagnetic: Monitor pressure-induced variations in a magnetic field inducing voltage in a coil. Often have the fastest response times below 1us for dynamic measurements.

Enhancing Pressure Sensor Response Time in Practice

By optimizing both the mechanical sensor design and electronic components handling the signals, engineers can significantly boost performance to capture even the most rapid pressure transients experienced in applications like race cars, aircraft and manufacturing machinery. Faster and better measurements result.

Here are some ways engineers can enhance a pressure sensor’s response time using easy to understand examples:

• Using a thinner material for the flexible diaphragm is very effective. A common diaphragm may be 50 microns thick – about half the width of a human hair. Making it 25 microns allows much faster bending under even small pressure changes.
• Improving circuit speed is also key. Racing engineers upgraded a sensor’s microchips to operate at 200 kHz instead of 100 kHz. This doubled the sampling rate, reducing the signal processing delay from 5 milliseconds to just 2.5 ms.
• Replacing bulkier wire connections with glass fiber optic threading eliminated an extra 1 millisecond latency per sensor signal sent to the data logger. Together with circuit tweaks, response improved from 8 ms to 4 ms.
• MEMS sensor arrays are another option. Instead of one large diaphragm, 100 tiny separate sensors are combined. Each has a 1 micron thick diaphragm that flexes extremely fast. Working together, they provide a full pressure reading with an ultra-quick 1/10th millisecond response.

Wrap up

Pressure sensor response time refers to how quickly the sensor responds to changes in pressure. It’s defined as the time for the sensor output to reach 90% of its final value after a step change. Response times can range from microseconds to seconds depending on the application and sensor design.

Understanding response time is important when selecting a sensor, as applications with rapidly fluctuating pressures on fast timescales like engines or aircraft require very fast response times under 1ms. Slower industrial processes and weather monitoring can tolerate slower sensors in the 10-100ms range.

Faster response sensors using thin flexible materials can detect transients but sacrifice accuracy. Slower sensors prioritize precision over speed. Sensitivity also relates to response – higher sensitivity correlates to slower responses. Sensor designers employ techniques like optimized circuits and MEMS arrays to boost response times for demanding applications requiring real-time dynamic pressure measurement.