Differential pressure transmitters are industrial measurement devices that measure the pressure difference between two different process points according to the principle ΔP = P₁ − P₂ and transmit the measured value to the process control system.
The Siemens SITRANS P320/P420 family can be used not only for differential pressure measurement but also, depending on the application, for level, volumetric flow, and mass flow measurement. Therefore, DP transmitters are important measurement solutions in chemical, petrochemical, power, process industry, water and wastewater, HVAC, machinery, and utility applications.
Differential pressure transmitters are particularly useful for applications such as flow measurement, level measurement in closed tanks, filter ΔP monitoring, heat exchanger pressure-drop monitoring, and pump ΔP monitoring.
Depending on the selected version and measuring cell, the SITRANS P320/P420 family offers measuring ranges from 10 mbar to 700 bar. Siemens specifies accuracy values of up to 0.065% for P320 and 0.04% for P420 in its current technical information. (Siemens)
✔ Differential pressure (ΔP) measurement
✔ Measuring ranges from 10 mbar to 700 bar, depending on version and measuring cell
✔ Accuracy up to 0.065% for P320 and 0.04% for P420
✔ Response time down to 105 ms
✔ Long-term stability of ≤0.125% over 5 years
✔ 4–20 mA + HART communication
✔ PROFIBUS PA and FOUNDATION Fieldbus options
✔ PROFINET over Ethernet-APL option
✔ Advanced diagnostics according to NAMUR NE107
✔ Configurations supporting SIL2/3 applications in accordance with IEC 61508
✔ Proof-test intervals of up to 15 years in suitable safety applications
✔ Remote Safety Handling for remote access to safety-related functions
✔ Stainless steel, Hastelloy, Monel, tantalum, and other configuration-dependent diaphragm options
✔ Aluminum or configuration-dependent stainless-steel housing
✔ IP66/IP68 protection options depending on configuration and connection
✔ Process value/trend recording of up to 1,500 measured values on P420
Not all of these features are available in every device configuration. The exact technical specifications should be verified using the complete MLFB/order code. (Siemens)
|
Parameter |
Siemens SITRANS P320 / P420 |
|
Measurement type |
Differential pressure; depending on application, pressure, level, and flow measurement |
|
Measuring range |
10 mbar–700 bar, depending on version and measuring cell |
|
Accuracy |
P320: up to 0.065%; P420: up to 0.04% |
|
Response time |
Down to 105 ms |
|
Long-term stability |
≤0.125% / 5 years |
|
Output / communication |
4–20 mA + HART, PROFIBUS PA, FOUNDATION Fieldbus, PROFINET/Ethernet-APL |
|
Safety |
SIL2/3 applications according to IEC 61508 |
|
Diagnostics |
NAMUR NE107 |
|
Diaphragm options |
316L stainless steel, Hastelloy, Monel, tantalum, gold-plated and other options |
|
Housing |
Aluminum or configuration-dependent stainless steel |
|
Protection |
IP66/IP68, depending on configuration and connection |
|
Remote Safety Handling |
Available on suitable P320/P420 configurations |
|
Trend recording |
Up to 1,500 measured values on P420 |
Siemens technical documentation indicates that measuring cell, turndown, and accuracy values for differential pressure and flow versions vary depending on the selected configuration. Therefore, this table represents the general technical framework of the product family. (Siemens technical documentation)
One of the most important applications of differential pressure transmitters is ΔP-based flow measurement.
Primary elements such as orifice plates, Venturi tubes, and nozzles create a controlled pressure difference in the process fluid. The transmitter measures this differential pressure, and the flow rate is calculated using the appropriate process and flow equations.
Typical applications include:
Flow measurement with orifice plates
Venturi flow measurement
Nozzle-based flow measurement
Steam flow
Gas flow
Liquid flow
Process air and gas lines
Energy and utility systems
For flow applications, selecting the transmitter alone is not sufficient. The primary element, measuring range, process pressure, temperature, fluid properties, and impulse-line system should be evaluated together.
SITRANS P320/P420 differential pressure configurations are available for flow applications. Siemens technical documentation also specifies that square-root extraction can be used for flow measurement. (Siemens technical documentation)
Differential pressure transmitters are widely used for level measurement in closed tanks.
The basic principle is:
ΔP = Pbottom − Ptop
The pressure difference between the lower and upper points of the tank is measured to determine the liquid level.
This method can be considered for applications such as:
Pressurized tanks
Process vessels
Chemical tanks
Process tanks containing steam
Boiler applications
Closed storage tanks
For level measurement, not only the transmitter measuring range but also the following should be evaluated together:
Tank geometry
Liquid density
Minimum/maximum level
Static pressure
Process temperature
Impulse-line arrangement
Diaphragm material
For high-temperature, corrosive, or special process conditions, a remote diaphragm seal / diaphragm seal solution may also be required.
Siemens positions the P320/P420 family as a multifunctional pressure transmitter family that also supports level measurement. (Siemens)
Another important application of differential pressure transmitters is measuring the pressure difference between the inlet and outlet of a filter.
The basic principle is:
ΔP = Filter inlet pressure − Filter outlet pressure
As the filter becomes contaminated or clogged, the pressure differential increases. This value can be used for maintenance and process performance monitoring.
Typical applications include:
Process filters
Gas filters
Air filters
Pump inlet filters
Compressor systems
Water treatment systems
Industrial filtration systems
In these applications, defining suitable alarm limits, selecting a transmitter range appropriate for the process conditions, and keeping the impulse lines clean are important.
The pressure difference between the inlet and outlet of a heat exchanger can be monitored to evaluate pressure loss across the process equipment.
An increase in ΔP over time can help evaluate conditions such as:
Fouling
Blockage
Changes in flow
Changes in process conditions
The pressure difference between the pump inlet and outlet can be monitored to evaluate pump performance.
This measurement can be used for:
Pump performance monitoring
Differential pressure control
Process optimization
Pre-failure condition assessment
Siemens differential pressure transmitters can be considered for the following applications:
Flow measurement: ΔP-based flow measurement using orifice plates, Venturi tubes, and nozzles
Level measurement: Hydrostatic ΔP measurement in closed tanks
Filter ΔP: Monitoring the pressure difference between filter inlet and outlet
Heat exchanger ΔP: Pressure-drop monitoring across heat exchangers
Pump ΔP: Pump performance and differential pressure monitoring
Steam systems: Steam flow and process measurement
Gas systems: Pressure and flow measurement in gas lines
Chemical and petrochemical: Critical process pressure and level measurement
Power plants: Boiler, steam, and utility applications
Water and wastewater: Filtration, pump, and closed-tank applications
Process automation: Transmission of pressure and process information to PLC/DCS systems
Siemens positions the P320/P420 family for a broad range of industrial applications, including demanding chemical and petrochemical processes and safety-critical applications. (Siemens)
Accuracy values of up to 0.065% for SITRANS P320 and 0.04% for P420 support precise process measurement when the appropriate measuring cell and operating conditions are selected.
The P320/P420 family can provide response times down to 105 ms. This can be advantageous in applications where rapid process changes need to be monitored. (Siemens)
NAMUR NE107-based diagnostics help evaluate device status and support maintenance planning.
On suitable P320/P420 configurations, Remote Safety Handling supports safety-related configuration and verification procedures from the control room.
In suitable safety applications, proof-test intervals of up to 15 years can contribute to optimized maintenance and service planning. (Siemens)
PROFINET over Ethernet-APL supports power and data communication over a two-wire infrastructure, enabling process devices to be integrated into modern digital automation architectures.
Siemens specifies communication speeds of up to 10 Mbit/s and distances of up to 1,000 meters for PROFINET over Ethernet-APL. (Siemens)
Selecting the correct Siemens DP transmitter is not limited to asking, “What pressure range is required?”
The following parameters should be evaluated together:
Measurement type: Differential pressure, flow, or level
Measuring range: Minimum and maximum ΔP
Static pressure: Total process pressure to which the transmitter will be exposed
Process temperature
Fluid properties
Diaphragm material
Process connection
Communication protocol
Ex / hazardous-area requirements
SIL requirements
Remote seal requirements
Primary element: Orifice, Venturi, or nozzle for flow applications
PLC/DCS integration
Therefore, particularly in project-based procurement, the complete MLFB should be checked together with the relevant technical datasheet
Correct commissioning of a differential pressure transmitter is important for both measurement accuracy and process safety.
First, the complete device MLFB/order code should be verified.
In particular, the following should be checked:
Measuring cell
Measuring range
Process connection
Diaphragm material
Fill fluid
Communication protocol
Electrical connection
Ex certification
Remote seal configuration
For differential pressure transmitters, the High (H) and Low (L) process connections must be installed correctly.
Reversing the connections can cause the ΔP value to be displayed in the wrong direction or result in an incorrect process value.
In flow and level applications, impulse lines should be checked to ensure that they:
Are connected correctly
Are free from blockage
Do not leak
Have suitable installation and routing
Are compatible with the process fluid
After the process conditions have been verified, the required zero adjustment and measuring-range configuration should be performed.
Where HART, PROFIBUS PA, FOUNDATION Fieldbus, or PROFINET/Ethernet-APL is used, the PLC/DCS and device configurations should be checked for compatibility.
|
Problem |
Possible Cause |
Check / Solution |
|
Incorrect ΔP value |
Measuring cell or range mismatch |
Check the MLFB and measuring range |
|
ΔP is reversed |
H/L connections reversed |
Check the High and Low connections |
|
No output |
Power supply or cable problem |
Check loop power and electrical connections |
|
Incorrect flow calculation |
Primary element or transmitter range mismatch |
Check the orifice/Venturi/nozzle and transmitter configuration |
|
Incorrect level value |
Density or zero adjustment incorrect |
Check process density and transmitter settings |
|
Unstable level value |
Impulse-line problem |
Check lines, valves, and connections |
|
Incorrect filter ΔP |
Blocked impulse line or unsuitable range |
Check the lines and measuring range |
|
Fluctuating measurement |
Process pulsation |
Check process conditions and the impulse-line system |
|
Diagnostic alarm |
Device or process problem |
Check the NAMUR NE107 status |
|
No communication |
Protocol or device configuration mismatch |
Check HART/PA/FF/Ethernet-APL settings |
For Siemens differential pressure transmitters, knowing only the P320 or P420 product family is not sufficient to determine the correct device.
Different configurations can include different:
Measuring cells
Measuring ranges
Process connections
Diaphragm materials
Fill fluids
Communication protocols
Electrical connections
Housing options
Ex certifications
Remote seal options
Therefore, during purchasing or replacement processes, the complete MLFB/order code, nameplate information, and technical datasheet should be reviewed together whenever possible.
This is particularly important when replacing older Siemens transmitters. Instead of selecting a new device based only on the old product name, the complete technical configuration of the existing device should be evaluated.
Replacement of Siemens differential pressure transmitters should not be treated simply as matching an old model number with a new model number.
A proper replacement analysis should consider:
Existing MLFB → measuring cell → range → static pressure → process connection → diaphragm → communication → Ex/SIL → mechanical configuration → new MLFB
all together.
When replacing older-generation SITRANS P DS III / P410 devices, the existing configuration may need to be technically compared with the P320/P420 family.
Such a transition may require:
Identifying the existing MLFB
Checking the product lifecycle status
Identifying the current Siemens product family
Comparing measuring cells
Checking process connections
Comparing diaphragm materials
Checking the communication protocol
Evaluating Ex/SIL requirements
Verifying the new MLFB
Therefore, replacement/cross-reference should be treated as a technical configuration comparison rather than a simple one-to-one model-name match.
Before submitting a Siemens differential pressure transmitter requirement for RFQ, preparing the following information can improve quotation accuracy:
✔ Existing or requested complete MLFB
✔ Measuring range
✔ Minimum / maximum process pressure
✔ Static pressure
✔ Process temperature
✔ Fluid type
✔ Flow / level / filter ΔP application
✔ Process connection
✔ Diaphragm material
✔ Communication protocol
✔ Ex certification
✔ SIL requirements
✔ Remote seal requirement
✔ Required quantity
✔ Delivery country and project information
Especially for older Siemens devices, a nameplate photograph and existing MLFB can significantly improve the accuracy of replacement and cross-reference analysis.
For Siemens differential pressure transmitters, finding the correct product may require more than a simple product-name search, particularly when replacing older or discontinued devices.
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 provide project-based support for Siemens differential pressure transmitter requirements in areas including:
MLFB verification
Technical configuration checks
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
In particular, for Siemens SITRANS P320/P420, older SITRANS P DS III/P410, and other Siemens pressure transmitter requirements, the appropriate model can be identified, existing device specifications can be compared, and suitable sourcing options can be researched on a project basis.
If you need a new Siemens differential pressure transmitter or require a replacement / cross-reference analysis for an existing device, you can initiate an RFQ process by providing the following information whenever available:
• Complete MLFB / order code
• Nameplate information or photograph
• Technical datasheet
• Measuring range
• Flow / level / filter ΔP application
• Process connection
• Diaphragm material
• Communication protocol
• Ex / SIL requirements
• Required quantity
• Delivery country
If the complete MLFB of the existing Siemens device is not known, the product configuration can also be investigated based on a nameplate photograph or available technical documentation.
Siemens differential pressure transmitters provide a broad range of applications for ΔP, flow, level, filter, and process pressure-difference measurement. The SITRANS P320/P420 family offers high accuracy, advanced diagnostics, multiple communication options, functions for safety-related applications, and integration capabilities for modern process automation systems. (Siemens)
However, selecting the correct transmitter is not completed simply by identifying the product family. Measuring cell, range, static pressure, process connection, diaphragm material, communication protocol, Ex/SIL requirements, and application conditions should be evaluated together.
For replacement of older Siemens transmitters, complete MLFB verification and technical cross-reference analysis 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 differential pressure transmitter requirements through technical product verification, replacement/cross-reference research, global sourcing, and project-based RFQ processes.
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