Water Pipe Pressure Sensor QBE2002-P25 QBE2 002-P25 QBE2002-P25

Siemens QBE2002-P25 | Pressure Sensor — 0–25 bar, DC 0–10V, Piezo-Resistive, Ceramics Diaphragm, HVAC

Overview

The Siemens QBE2002-P25 is a piezo-resistive pressure sensor from Siemens Building Technologies, covering 0 to 25 bar with a linear DC 0–10V output — the highest-range member of the QBE2002 series that spans from 1 to 40 bar in distinct measurement variants.

At 25 bar (362.6 psi / 2.5 MPa), this sensor serves the higher-pressure end of HVAC hydraulic circuits: primary district heating networks, high-rise building water supply risers, steam systems, and pressurised chiller circuits where the 10 or 16 bar variants would be insufficient.

The measurement principle is piezo-resistive with a ceramics diaphragm — thick-film hybrid technology where the strain-sensing resistors are screen-printed directly onto a high-purity Al₂O₃ ceramic disc and fired at high temperature.

This direct deposition method is the source of the QBE2002's long-term stability: there is no adhesive bond between the sensing element and the diaphragm that can creep, delaminate, or change properties over years of temperature cycling.

The measured pressure deflects the ceramic disc; the resistor network changes resistance in proportion; the on-board electronics condition the bridge output to the 0–10V signal.

The stainless steel 1.4404 (AISI 316L) pressure connection resists corrosion from the water, glycol, and steam media in HVAC circuits.

FPM fluoroelastomer sealing at the connection interface provides chemical resistance compatible with standard HVAC process fluids. The 1.5m pre-wired cable connects directly to the controller or field wiring without additional connector hardware.

Key Specifications

0–10V Output in HVAC Control Systems

The DC 0–10V signal is the standard analogue input format for Siemens HVAC controllers, DDC systems, and most building management system field controllers. Zero volts represents 0 bar gauge (atmospheric pressure); 10V represents 25 bar.

The scaling is linear across the range, which means the controller's software configuration simply needs the measurement range (0–25 bar) entered alongside the 0–10V signal type to display and process the pressure value correctly.

In practice, many HVAC hydraulic circuits operate well below the 25 bar ceiling — a typical chilled water system runs at 6–12 bar, using only the lower portion of the sensor's output range.

This is a common trade-off: the 25 bar range provides safety margin against occasional pressure excursions and is the same range used across many different HVAC installation types, but it sacrifices some resolution at the controller input for systems that never approach the upper range.

Where higher resolution at lower pressures is needed, the QBE2002-P10 (0–10 bar) variant delivers the same output span mapped across half the pressure range.

Successor Note: QBE2003-P25

The QBE2002-P25 has been discontinued. The QBE2003-P25 covers the same 0–25 bar range with a compatible supply voltage and 0–10V output, but uses a different housing and a DIN EN 175301-803-A plug connection rather than the QBE2002's pre-wired cable.

Installations being converted from QBE2002-P25 to QBE2003-P25 need to address the wiring termination difference; the measurement and output signal compatibility allows the controller's configuration to remain unchanged.

FAQ

Q1: Can the QBE2002-P25 measure negative pressure (vacuum)?

No. The QBE2002-P25 measures gauge pressure from 0 to 25 bar — it is a relative pressure sensor referenced to atmospheric.

The 0V output corresponds to atmospheric (zero gauge), and 10V corresponds to 25 bar gauge. It does not extend into sub-atmospheric (vacuum) measurement.

For vacuum monitoring, a sensor with a range that includes negative gauge pressures is required.

Q2: What is the maximum overpressure the QBE2002-P25 can withstand without damage?

Siemens specifies a maximum admissible overpressure for the QBE2002 series above the rated measuring range. The exact value is stated in the Siemens QBE2002-P technical data sheet.

In hydraulic and pneumatic installations, it is important to verify that system pressure transients — during valve closures, pump starts, and load changes — stay within this overpressure limit, as sustained or repeated exceedances above the maximum can cause zero offset shift or permanent sensor damage.

Q3: What supply voltage does the QBE2002-P25 require?

The QBE2002-P series is designed for use with Siemens HVAC controllers and their auxiliary supply outputs.

The exact supply voltage specification is given in the Siemens product data sheet for the QBE2002-P25. 

This should be confirmed before installation, particularly when upgrading from QBE2002 to QBE2003 variants, as the two series may have different supply specifications.

Q4: Is the QBE2002-P25 interchangeable with the QBE2003-P25?

The measurement range (0–25 bar) and output signal (0–10V) are compatible between the two, and the supply voltage is also stated to be compatible by the successor. However, the housing dimensions and electrical connection format differ — the QBE2003-P25 uses a DIN EN 175301-803-A plug rather than the pre-wired cable of the QBE2002-P25.

A 1:1 physical replacement is not guaranteed without adapter cables or rewiring the field termination. Always verify the technical data of the replacement product before installing.

Q5: What is FPM sealing, and is it suitable for glycol antifreeze mixtures in HVAC systems?

FPM (fluoroelastomer, also sold under trade names such as Viton) is a synthetic rubber with excellent resistance to water, aqueous solutions, steam, glycols, and most hydrocarbon fluids.

It is the standard seal material for HVAC pressure sensors because it is compatible with the water-glycol mixtures used in chilled water and heating circuits across a wide temperature range.

FPM is not compatible with certain ketones, low-molecular-weight esters, and specific amines — media not typically found in standard HVAC systems.