In industrial processes, selecting a pressure transmitter based only on its measuring range is not sufficient. Selecting the appropriate gauge pressure, absolute pressure, or differential pressure measurement type is critical for measurement accuracy, process control, safety, and long-term operating performance.
Siemens SITRANS pressure transmitters offer different measurement principles and configuration options for a wide range of process requirements.
The main measurement types are:
Gauge Pressure: Measures pressure relative to atmospheric pressure.
Absolute Pressure: Measures pressure relative to vacuum and is independent of changes in atmospheric pressure.
Differential Pressure: Measures the pressure difference between two different process points.
These three measurement types serve different purposes. For example, gauge pressure may be suitable for monitoring pump discharge pressure, while absolute pressure can be preferred for vacuum processes. Differential pressure is commonly used for flow, closed-tank level, filter ΔP, and other pressure-difference applications.
Siemens current SITRANS pressure transmitters, particularly models such as P320 and P420, provide advanced technical features for a wide range of industrial process applications.
Key features include:
Measuring ranges up to 10 mbar–700 bar, depending on model and measuring cell
Accuracy up to 0.065% for P320 and 0.04% for P420
4–20 mA + HART communication
PROFIBUS PA
FOUNDATION Fieldbus
PROFINET over Ethernet-APL on applicable configurations
Diagnostic functions based on NAMUR NE107
IEC 61508-based safety functions for SIL2/SIL3 applications on applicable configurations
Proof-test intervals of up to 15 years on applicable configurations
316L stainless steel, Hastelloy, Monel, tantalum, and other diaphragm material options
Different housing and protection options depending on configuration
P420 capability to store up to 1,500 measured values including process values and trend information
Note: Accuracy, measuring range, materials, communication protocol, SIL functions, protection rating, and other technical parameters depend on the selected model and complete MLFB configuration. Therefore, technical suitability should not be evaluated based solely on the product family name.
A gauge pressure transmitter measures process pressure relative to atmospheric pressure.
This measurement type is widely used in industrial applications where monitoring process pressure relative to atmospheric conditions is sufficient.
Pump discharge and suction pressure
Process pipelines
Compressor systems
Hydraulic systems
Gas pressure
Steam and utility process lines
Filter and equipment pressure
Machine and skid systems
Gauge pressure is commonly preferred when process pressure needs to be monitored relative to atmospheric pressure.
An absolute pressure transmitter measures pressure relative to vacuum.
Since atmospheric pressure can vary depending on process and environmental conditions, absolute pressure may be required in applications where the absolute pressure value is critical.
Vacuum processes
Vacuum pumps
Distillation systems
Process equipment operating under vacuum
Pressure-controlled processes
Applications where atmospheric pressure variations could affect the measurement
Selecting the correct reference point is particularly important in vacuum and low-pressure applications.
A differential pressure transmitter measures the pressure difference between two process connections.
DP transmitters are not limited to direct ΔP measurement. With the appropriate primary element and process configuration, they can also be used for flow and level measurement.
Filter ΔP monitoring
Flow measurement with orifice plates
Venturi flow measurement
Flow nozzle applications
Closed-tank level measurement
Pump performance monitoring
Heat exchanger pressure loss
Process equipment differential pressure monitoring
For DP applications, transmitter selection should consider not only differential pressure but also static pressure, process temperature, fluid properties, primary element, impulse lines, and diaphragm material.
Differential pressure transmitters are an important part of flow measurement systems when used together with an appropriate primary flow element.
For example, the pressure difference generated by primary elements such as:
Orifice plates
Venturi tubes
Flow nozzles
can be measured by a DP transmitter.
Before selecting a transmitter for a flow application, the following parameters should be evaluated together:
Primary element type
Design flow rate
Minimum and maximum flow
Generated ΔP
Line pressure
Process temperature
Fluid density
Impulse line arrangement
Square-root extraction requirements
Therefore, selecting a flow transmitter based only on a nominal transmitter range such as “10–700 bar” is not technically sufficient.
Differential pressure measurement is widely used for level measurement in closed tanks.
The transmitter measures the pressure difference between the upper and lower process connections of the tank, allowing the liquid level to be determined.
The following parameters are important in these applications:
Tank geometry
Liquid density
Minimum and maximum level
Tank internal pressure
Process temperature
Vapor-phase conditions
Wet leg / dry leg arrangement
Remote seal requirements
Diaphragm and wetted-part materials
Particularly in applications involving high temperature, corrosive fluids, or crystallization risks, a different process connection or remote seal solution may be required instead of a standard impulse-line arrangement.
One of the important application areas of differential pressure transmitters is monitoring pressure loss across process equipment.
Monitoring the pressure difference between the inlet and outlet of a filter can help track filter fouling and restriction.
An increase in ΔP can help indicate:
Filter contamination
Flow restriction
Maintenance requirements
Reduced process performance
Monitoring the pressure difference between the inlet and outlet of a heat exchanger can help evaluate:
Flow restrictions
Fouling
Pressure losses on the process side
The pressure difference between the suction and discharge sides of a pump can be used to evaluate pump operating conditions.
Therefore, DP transmitters can be considered not only as measurement devices but also as part of condition monitoring and maintenance strategies for process equipment.
Siemens SITRANS pressure transmitters can be used in a wide range of industrial processes when the appropriate model and configuration are selected.
Reactor pressure
Tank pressure
Column applications
Filter ΔP
Flow measurement
Level measurement
Steam lines
Boiler systems
Auxiliary processes
Pump and equipment pressure
Filter and heat exchanger ΔP
Pump stations
Filter systems
Tank level measurement
Pressurized lines
Process pipelines
Tanks
Columns
Differential pressure applications
Flow and level measurement
Pressurized lines
Filter ΔP
Gas and liquid processes
Pump and fan systems
When appropriately configured, Siemens SITRANS pressure transmitters can provide several operational advantages in measurement systems:
✔ Different configurations for gauge, absolute, and differential pressure applications
✔ High accuracy and long-term stability
✔ HART and industrial fieldbus communication options
✔ IEC 61508-based functional safety in applicable system architectures
✔ NAMUR NE107 diagnostic approach
✔ PROFINET over Ethernet-APL in applicable applications
✔ Storage of measured values and trend information on P420
✔ Different process connection, measuring cell, and diaphragm material options
These features allow the transmitters to be used not only for pressure measurement but also as part of process automation and maintenance strategies.
Selecting a Siemens pressure transmitter is not limited to answering the question: “Gauge, absolute, or differential?”
The following parameters should be evaluated together:
Measurement type: Gauge / Absolute / Differential
Measuring range
Overpressure conditions
Process pressure and temperature
Fluid properties
Process connection
Diaphragm / wetted-part material
Housing and electrical connection
Output signal
HART / PROFIBUS PA / FOUNDATION Fieldbus / Ethernet-APL requirements
Hazardous area and certification requirements
SIL requirements
Remote seal or special process connection requirements
Replacement/cross-reference compatibility with the existing transmitter
Especially when replacing older Siemens transmitters, comparing only the model name is not sufficient. The comparison should be based on the complete MLFB and technical configuration.
The following checks should be performed when commissioning a Siemens SITRANS pressure transmitter:
Verify the complete MLFB
Check the measurement type
Compare the measuring range with the process requirements
Verify measuring cell suitability
Confirm the process connection
Check diaphragm/wetted-part material compatibility with the process fluid
Verify the electrical connection
Confirm the communication protocol
Check H/L connections in DP applications
Verify zero/span or relevant configuration parameters
Configure damping and square-root extraction where required
Verify the loop and process signal
Check alarm and diagnostic parameters
Particularly for DP transmitters, correct H (High) and L (Low) connections are critical for ensuring the correct measurement direction and process value.
|
Problem |
Possible Cause |
Solution |
|
Incorrect pressure value |
Incorrect measurement type or range |
Check the MLFB, measurement type, and measuring range |
|
ΔP is reading in the wrong direction |
H/L connections reversed |
Check the High and Low connections |
|
No output signal |
Power supply, cable, or loop problem |
Check the power supply and electrical connections |
|
Unstable measurement |
Process fluctuation, impulse line problem, or damping setting |
Check process conditions and the impulse line system |
|
Incorrect flow value |
Primary element or square-root configuration mismatch |
Check the orifice/Venturi/nozzle and transmitter configuration |
|
Incorrect level value |
Incorrect density, zero setting, or connection arrangement |
Check process density, zero setting, and impulse line arrangement |
|
ΔP higher than expected |
Pressure loss across filter/heat exchanger or connection problem |
Check the process equipment and connections |
|
Diagnostic alarm occurs |
Sensor-, process-, or configuration-related condition |
Check device diagnostics and NAMUR NE107 status |
For Siemens pressure transmitters, the product family name alone is not sufficient.
Within the same product family, the following may vary:
Measurement type
Measuring cell
Measuring range
Process connection
Diaphragm material
Output signal
Communication protocol
Housing option
Electrical connection
Certifications
Special configurations
Therefore, the complete MLFB/order code should be checked.
Particularly when replacing older Siemens SITRANS P series transmitters, the existing device's MLFB, datasheet, nameplate information, and process conditions should be evaluated together.
Replacement of Siemens pressure transmitters is not simply a matter of matching an old model with a new model name.
When replacing legacy products such as SITRANS P DS III / P410, the following should be compared:
Existing MLFB
Measurement type
Measuring range
Measuring cell
Process connection
Diaphragm material
Output and communication
Electrical connection
Certifications
Process temperature and pressure
An older transmitter may have P320 or P420 as an appropriate successor, but this should not automatically be assumed to be a direct one-to-one replacement. Technical configuration comparison should be performed before ordering to reduce the risk of product incompatibility.
For this reason, replacement projects should follow a MLFB verification + datasheet comparison + application suitability approach.
The following information should be provided as completely as possible during the quotation or purchasing stage:
Siemens product family/model
Existing MLFB or order code
Gauge / Absolute / Differential
Measuring range
Process pressure
Process temperature
Fluid information
Process connection
Diaphragm material
Output signal
Communication protocol
Electrical connection
Hazardous area requirements
SIL requirements
Certifications
Quantity
Project / delivery country
Existing datasheet or technical specification
Providing this information helps both identify the correct product and evaluate technically suitable alternative or successor products.
For Siemens pressure transmitters, particularly legacy, special-configuration, or project-based products, identifying the correct MLFB is only one part of the procurement process. Technical configuration verification is equally important.
With an independent and brand-independent industrial sourcing approach, Yeşil Grup Enerji can provide project-based support for Siemens products in areas including:
MLFB verification
Technical configuration checks
Gauge / absolute / differential measurement type verification
Measuring cell and range verification
Process connection and diaphragm material checks
Technical datasheet and documentation review
Replacement / cross-reference research
Evaluation of legacy Siemens transmitters
Current product and successor research
Global sourcing
Alternative sourcing-channel research
Project-based RFQ management
International project supply
Yeşil Grup Enerji is not an official Siemens distributor or authorized representative.
With an independent and brand-independent industrial sourcing approach, Yeşil Grup Enerji can support Siemens SITRANS pressure transmitter requirements through MLFB verification, technical configuration checks, replacement/cross-reference research, global sourcing, and project-based RFQ processes.
This approach can be particularly useful for international sourcing, legacy product replacement, special configurations, and international project requirements where alternative sourcing channels need to be evaluated.
If you require a Siemens gauge, absolute, or differential pressure transmitter, you can request a project-based evaluation of product suitability and sourcing options by sharing the existing MLFB, product code, datasheet, or technical specification.
For replacement or re-supply of an existing Siemens transmitter, it is recommended to provide the nameplate information and existing MLFB, together with the relevant process conditions whenever possible.
Yeşil Grup Enerji provides independent sourcing support with the product evaluated not only at the brand/model level, but also according to its technical configuration and application requirements.
Gauge pressure is measured relative to atmospheric pressure. Absolute pressure is measured relative to vacuum. Differential pressure measures the pressure difference between two different process points.
When an appropriate primary element such as an orifice plate, Venturi tube, or nozzle is used, a differential pressure transmitter can be used for flow measurement.
In closed tanks, a differential pressure transmitter can be used to determine liquid level based on the pressure difference between the upper and lower tank connections.
An absolute pressure transmitter may be preferred when the absolute pressure of the process is important.
In typical applications where pump discharge pressure needs to be monitored relative to atmospheric pressure, a gauge pressure transmitter can be used.
No. Particularly for legacy products, complete MLFB, measuring cell, range, process connection, materials, output, communication, and certification should be compared.
Siemens SITRANS pressure transmitters can be used for a wide range of industrial applications, including process pressure, vacuum, differential pressure, flow, and level measurement through gauge, absolute, and differential pressure measurement types.
Selecting the correct transmitter requires more than simply checking the pressure range. Measurement type, measuring cell, range, process pressure and temperature, process connection, diaphragm/wetted-part materials, communication protocol, certification, and SIL requirements should be evaluated together.
When an existing Siemens transmitter needs to be replaced or re-supplied, complete MLFB verification and technical configuration comparison are particularly important.
Yeşil Grup Enerji is not an official Siemens distributor or authorized representative. With an independent and brand-independent industrial sourcing approach, Yeşil Grup Enerji can support Siemens SITRANS pressure transmitter requirements through MLFB verification, technical product evaluation, replacement/cross-reference research, global sourcing, and project-based RFQ processes.
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