Common Terms Used with Pressure Sensors
If you have ever selected a pressure sensor or pressure transmitter, you must have seen many technical words in the datasheet.
Full scale, proof pressure, IP rating, wetted parts, span tolerance…
Sometimes it feels like we need another manual just to understand the first manual.
But don’t worry. Once you clearly understand these common terms, reading any pressure sensor datasheet becomes much easier and more confident.
Let us go through the most common pressure sensor terms one by one, in very simple language, with practical examples.
FS (Full Scale or Full Span)
Full Scale means the maximum pressure value that the sensor is designed to measure.
In simple words, it is the top end of the measuring range.
What it means
If a pressure sensor range is 0 to 10 bar, then
Full Scale (FS) = 10 barWhy it matters
All accuracy, error, and tolerance values are usually mentioned as a percentage of full scale.Real example
If accuracy is ±0.5% FS for a 10 bar sensor,
error = ±0.05 bar (not ±0.5% of actual reading)
So FS is always your reference point for performance.
Gauge Pressure
Gauge pressure means pressure measured relative to atmospheric pressure.
Atmospheric pressure is treated as zero in gauge measurement.
What it means
Gauge Pressure = Process Pressure – Atmospheric PressureWhere it is used
Most industrial pressure measurements are gauge type:
pumps, compressors, pipelines, hydraulic systems, etc.Real example
A pressure gauge showing 5 bar means:
5 bar above atmosphere, not total absolute pressure.
When you see “barg”, it means bar gauge.
Sealed Gauge Pressure
Sealed gauge is similar to gauge pressure, but the reference is a sealed internal air pressure, not open atmosphere.
What it means
Instead of open vent to air, the sensor is sealed with a fixed reference pressure.Why it is used
Used when atmospheric pressure variation can affect accuracy, such as in:
high-altitude locations or outdoor instrumentsReal example
Aircraft instruments and weather monitoring systems often use sealed gauge sensors.
It gives more stable readings than normal gauge sensors.
Absolute Pressure
Absolute pressure is measured relative to perfect vacuum.
Here, zero means no pressure at all.
What it means
Absolute Pressure = Gauge Pressure + Atmospheric PressureWhere it is used
Vacuum systems, reactors, altitude measurement, gas laws, and scientific applications.Real example
If a vacuum system shows –0.8 bar gauge,
absolute pressure ≈ 0.2 bar absolute
Datasheets will show unit as “bara” or “kPa abs”.
Compensated Temperature
Temperature compensation means the sensor output remains accurate even when temperature changes.
Because temperature affects sensor electronics and sensing element.
What it means
Sensor is calibrated to correct errors caused by temperature variation.Why it is important
Without compensation, pressure reading may drift when ambient temperature changes.Real example
Outdoor sensors exposed to sun and night cooling need good temperature compensation.
Better compensation = more stable pressure reading.
Operating Temperature
Operating temperature is the safe temperature range in which the sensor can work properly.
What it means
Outside this range, accuracy may drop or sensor may fail.Two types of temperature
Ambient temperature (around the sensor)
Process temperature (media temperature)Real example
If operating temperature is –20°C to +85°C,
do not install it near hot steam lines without protection.
Always check both ambient and media limits.
Proof Pressure
Proof pressure is the maximum pressure the sensor can handle without permanent damage.
But accuracy may be affected during that pressure.
What it means
Sensor will survive, but may go out of calibration.Why it is important
Protects against short pressure spikes during startup or valve closure.Real example
Range = 10 bar
Proof pressure = 20 bar
Sensor will not break at 15 bar, but recalibration may be needed.
Think of proof pressure as “survivable overload”.
Burst Pressure
Burst pressure is the pressure at which the sensor physically fails or ruptures.
This is a safety limit.
What it means
Above this, mechanical damage occurs.Why it is critical
Important for safety in high-pressure systems.Real example
Range = 10 bar
Proof = 20 bar
Burst = 50 bar
Always ensure system pressure never comes near burst pressure.
Long Term Drift
Drift means slow change in sensor output over time even when pressure is constant.
What it means
Sensor gradually loses calibration.Why it happens
Aging of electronics, mechanical stress, temperature cycles.Real example
Drift = ±0.2% per year
After one year, recalibration is recommended.
This is why calibration intervals are important in plants.
Span Tolerance
Span tolerance is the allowed error in the measuring range width.
It affects how much output changes from zero to full scale.
What it means
Difference between actual and ideal full-scale output.Why it matters
It directly affects transmitter scaling and control accuracy.Real example
If span tolerance is ±0.3% FS, control loop accuracy may suffer if ignored.
Always combine span error with zero error when checking total accuracy.
Pressure Port
Pressure port is the physical connection where process pressure enters the sensor.
What it means
Thread type and size:
G1/4, 1/2 NPT, M20x1.5, etc.Why it matters
Wrong port type can cause leakage or installation issues.Real example
Gas lines may use NPT,
hydraulic systems often use metric threads.
Always match port with piping standard.
Wetted Parts
Wetted parts are all parts of the sensor that come in direct contact with the process fluid.
What it includes
Diaphragm, pressure chamber, seals.Why it is important
Material must be compatible with process fluid to avoid corrosion.Real example
For corrosive chemicals, stainless steel or Hastelloy wetted parts are required.
Wrong material = short sensor life.
IP Ratings
IP rating tells how well the sensor is protected against dust and water.
What it means
IP65, IP67, IP68, etc.Two digits meaning
First digit = dust protection
Second digit = water protectionReal example
IP67 = dust tight + temporary water immersion protection
Outdoor installations must always check IP rating.
Accuracy
Accuracy tells how close the measured value is to the true pressure value.
Usually given as % of full scale.
What it includes
Linearity error
Hysteresis
RepeatabilityWhy it matters
High accuracy is needed in custody transfer, test benches, and control loops.Real example
Accuracy ±0.25% FS means reliable performance across entire range.
Never confuse accuracy with resolution.
Repeatability
Repeatability means the sensor gives same output for the same pressure every time.
Even if absolute value is slightly off, it should be consistent.
What it means
Pressure applied → reading → release → apply again → same readingWhy it is important
Control systems depend more on repeatability than absolute accuracy.Real example
Flow control loops prefer stable repeatable sensors for steady operation.
Good repeatability means predictable performance.
What we learn today
Understanding pressure sensor terms is not just for datasheet reading but it directly affects:
• Correct sensor selection
• Plant safety
• Measurement accuracy
• Maintenance planning
• Calibration strategy
Next time you open a pressure transmitter datasheet, don’t skip these terms.
They tell you exactly how the sensor will behave in real plant conditions.
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