What is Absolute Pressure Transmitter?
Absolute pressure transmitters are sensors that measure pressure using absolute vacuum (0 bar) as a reference. They convert the sensed physical pressure value into a standardized electrical signal, such as 4-20 mA or 0-10 V, for processing by control systems or monitoring equipment.
They are often called “industrial barometers” or “technical barometers” because they can measure true, absolute pressure unaffected by environmental fluctuations.
Featured Absolute Pressure Transmitters
We at Sino-Inst supply silicon-based and capacitive absolute pressure transmitters, and support customization of range and materials.
Benefits
Measurement Stability: Measurement values remain unchanged regardless of fluctuations in local atmospheric pressure or changes in installation altitude.
High Accuracy and Long-Term Stability: Designed for precision measurements, it boasts exceptional long-term stability.
Flexibility: Typically supports multiple range selections and output signal switching (e.g., via DIP switches), adapting to diverse industrial environments.
Rugged and Durable: Generally equipped with high protection ratings (e.g., IP65/IP68), it prevents dust and water jet intrusion, ensuring operation under harsh conditions.
How Do Absolute Pressure Sensors Work?
The working principle of an absolute pressure transmitter is similar to that of a regular gauge pressure transmitter. The main difference is that the core of an absolute pressure transmitter is a fully sealed reference chamber. This chamber is evacuated to an absolute vacuum state during the manufacturing process using a high-temperature process.
Pressure Deformation:
When external process pressure is applied to the transmitter’s diaphragm, the diaphragm undergoes a slight deformation.
Vacuum Reference:
Because the pressure inside the reference chamber is constantly zero, the sensor output is always a pure pressure value relative to a vacuum, eliminating interference from external atmospheric pressure.
Signal Conversion:
A high-precision capacitive/piezoresistive sensor on the diaphragm converts the deformation displacement into a standard signal such as 4-20mA.
Applications of Absolute Pressure Transmitters
Vacuum System Monitoring:
Such as etching equipment in semiconductor manufacturing, vacuum packaging, and various ultra-high vacuum (UHV) environments.
Meteorology and Aviation:
Used in weather stations and meteorological services to accurately record atmospheric pressure unaffected by altitude differences.
HVAC (Heating, Ventilation, and Air Conditioning):
Compensates for atmospheric pressure fluctuations caused by weather in ventilation systems, ensuring constant airflow.
Liquid Level Measurement in Sealed Containers:
Accurately calculates liquid level in sealed storage tanks that are not connected to the atmosphere using absolute pressure values.
Industrial Gas Handling:
Such as the storage and transportation of liquid hydrogen (H₂), which requires absolute pressure monitoring to prevent phase changes due to pressure variations.
Gauge vs Absolute vs Differential Pressure
Pressure measurements are mainly categorized into gauge pressure (relative pressure), absolute pressure, and differential pressure.
| Measurement Types | Reference Standard | Features |
| Gauge Pressure | Local Atmospheric Pressure | Measurement values vary with weather and altitude. If the measured pressure is equal to atmospheric pressure, the reading is 0. |
| Absolute Pressure | Absolute Vacuum (0 bar) | Independent of environmental influences, representing true physical pressure. |
| Differential Pressurete | Difference between two pressure points | Used to measure the pressure difference before and after a filter or the liquid level in a container. |
Mathematical relationship: Absolute pressure = Gauge pressure + Local atmospheric pressure
Output Signals
Absolute pressure transmitters typically provide industry-standard signals:
- Current signal: 4 – 20 mA (strong anti-interference capability, suitable for long-distance transmission).
- Voltage signal: 0 – 10 V, 1~5VDC, 0~5VDC.
- Communication protocols: Modbus RS485, HART
Absolute Pressure Transmitter Calibration
When the absolute pressure transmitter is powered on or connected to the atmosphere, the reading should be close to the local atmospheric pressure. If the reading is 0 or negative, it indicates that the absolute pressure transmitter setting is incorrect.
In systems measuring pressures above absolute zero, a negative reading from the absolute pressure transmitter is impossible. If it occurs, it can be determined that the zero point has been incorrectly reset. Calibration must be stopped immediately.
Calibration can refer to:
Zeroing Prerequisite: Zero point calibration of the absolute pressure transmitter must be performed in an absolute vacuum environment (e.g., using a vacuum pump to 0.001 bar), and cannot be zeroed in open atmosphere.
Setting Steps: This can usually be done through the online parameter setting interface, navigating to “Parameter Setting” > “Pressure/Differential Pressure” > “Process Variable” > “PV Offset”, and selecting “Set PV to 0”.
Maintenance Recommendations: Although the equipment is factory calibrated and has long-term stability, for applications requiring high precision, such as meteorological applications, periodic recalibration is recommended to eliminate environmental influences such as temperature drift.
After calibration, the absolute zero point of an absolute pressure transmitter is set. Any “zeroing” operation performed under atmospheric pressure will incorrectly set the current atmospheric pressure to zero, causing the absolute pressure transmitter to become a “gauge pressure transmitter,” resulting in completely erroneous measurement results.
Absolute Pressure Transmitters Selection Guide
When selecting an absolute pressure transmitter, the following key factors should be considered:
- Determine the measurement range:
- Maximum pressure (Pmax): The upper limit of the range should cover the highest possible pressure, with a 20%-30% safety margin to prevent damage to the sensor from impact pressure.
- The lower limit of the range should be “absolute pressure 0,” and the upper limit should be calculated as “maximum absolute pressure + safety margin” (e.g., for a vacuum system with a maximum absolute pressure of 0.1MPa, select a 0-0.15MPa absolute pressure range).
- Normal operating pressure: Should be at least 10% above the upper limit of the range to ensure measurement accuracy.
- Accuracy requirements: Select an accuracy class of 0.2 or 0.5 based on the allowable error range of the process.
- Temperature: For high-temperature environments, heat dissipation measures or models with temperature compensation should be considered.
- Corrosivity: If the medium is corrosive, special diaphragm materials such as 316L stainless steel or Hastelloy should be selected.
- Display requirements: Determine whether an integrated display screen is needed for on-site inspection.
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Vacuum Pressure Sensors | Vacuum-Negative Pressure Measurement
Sino-Inst’s absolute pressure transmitters can extend the minimum measurement range to 0-1 kPa, 2 kPa, 5 kPa, and 10 kPa without significant loss of output signal. Coupled with a special, stable, high input impedance signal processing module, they possess excellent overall measurement accuracy, meeting the needs of vacuum measurement. They are widely used in scientific research, aerospace, pharmaceuticals, leak detection, and automation equipment.
If you require a customized absolute pressure transmitter, please feel free to contact our sales engineers!