SIEMENS QBE3000/3100 differential pressure

SIEMENS QBE3000/3100 Differential Pressure Sensor: Precision Measurement and Engineering Practice for HVAC Systems

Introduction: Challenges and Solutions for Differential Pressure Measurement in HVAC Systems

In HVAC systems, differential pressure monitoring is a critical step in controlling filter clogging, pump/fan flow, liquid level, and valve pressure differentials. The core challenges faced by on-site engineers include medium corrosiveness, temperature drift, long-term stability, and compatibility of electrical interfaces. When it is necessary to replace old or discontinued differential pressure switches/transmitters, choosing a sensor that combines mechanical robustness and electronic accuracy becomes a top priority for system modification.

The Siemens QBE3000-D series and QBE3100-D series differential pressure sensors are designed specifically for this type of application. They are based on a unique ceramic lever measurement principle and are designed specifically for neutral and weakly corrosive gases and liquids. They are widely used as control sensors or measurement transmitters in building automation, industrial refrigeration stations, thermal pipelines, and clean air conditioning systems. This article will provide a complete professional reference from five dimensions: technical parameters, core materials, electrical connections, engineering installation, and troubleshooting.

Product series and model coding rules

The QBE3000/QBE3100 series are divided into two sub series based on output signals, each providing a total of 7 standard pressure ranges from low to high, covering the vast majority of HVAC application scenarios.

2.1 Differences in output signal types

Typical application scenarios of series output signal power supply voltage

QBE3000-D DC 0... 10 V AC 24 V ± 15% or DC 18-33 V with Siemens PLC or building control DDC controller (analog input 0-10V)

QBE3100-D DC 4... 20 mA DC 11-33 V long-distance signal transmission (>30 meters), strong anti-interference requirements, or compatible with 4-20mA input cards

2.2 Corresponding Table of Full Range Models

The following are the nominal pressure ranges (in bar and MPa) for each model, and all models have completed linearization and temperature compensation calibration before leaving the factory.

Model Code Order Number (Example) Pressure Range [bar] Corresponding Output Signal Range

QBE3000-D1 / QBE3100-D1 S55720-S173 / S179 0 … 1 0-10V / 4-20mA → 0-1 bar

QBE3000-D1.6 / QBE3100-D1.6 S55720-S174 / S180 0 … 1.6 0-10V / 4-20mA → 0-1.6 bar

QBE3000-D2.5 / QBE3100-D2.5 S55720-S175 / S181 0 … 2.5 0-10V / 4-20mA → 0-2.5 bar

QBE3000-D4 / QBE3100-D4 S55720-S176 / S182 0 … 4 0-10V / 4-20mA → 0-4 bar

QBE3000-D6 / QBE3100-D6 S55720-S186 / S187 0 … 6 0-10V / 4-20mA → 0-6 bar

QBE3000-D10 / QBE3100-D10 S55720-S177 / S183 0 … 10 0-10V / 4-20mA → 0-10 bar

QBE3000-D16 / QBE3100-D16 S55720-S178 / S184 0 … 16 0-10V / 4-20mA → 0-16 bar

Selection prompt: Confirm whether the system static pressure (the common pressure acting on both the high and low pressure sides) exceeds the allowable value of the sensor. For models with a nominal range ≤ 6 bar, the maximum allowable system pressure is 25 bar; Models with a range of ≥ 10 bar allow a maximum system pressure of 50 bar. The blasting pressure is 1.5 times the system pressure.

Core technology: Ceramic lever measurement system

Traditional differential pressure sensors often use metal strain gauges or capacitive diaphragms, but there are problems such as large temperature drift, long-term creep, and medium corrosion. The QBE3000/3100 series adopts Ceramic Lever Technology, with the following specific advantages:

Extremely low temperature sensitivity: The thermal expansion coefficient of ceramic materials is close to that of the sensor housing metal, coupled with the built-in temperature compensation circuit (TC zero point<± 0.04% FS/K, TC sensitivity<± 0.015% FS/K), resulting in minimal output drift in the full temperature range of -15~85 ℃.

No mechanical aging and creep: Ceramics have high elastic modulus and fatigue resistance, and even under long-term alternating pressure, there will be no plastic deformation or zero drift commonly seen in metal membranes. Long term stability meets the DIN EN 60770 standard and is better than ± 0.5% FS/year.

Excellent medium compatibility: The ceramic itself is corrosion-resistant, and combined with FPM (fluororubber) seals, it can be used for neutral and weakly corrosive liquids (such as dilute ethylene glycol solution, light oil) as well as humid gases.

Measurement principle description: The measured differential pressure acts on the ceramic sensing element, causing it to produce a small displacement (lever effect). This displacement is converted into an electrical signal by the internal ASIC, and then linearized, temperature compensated, and amplified to output a standard analog signal. The sensor has completed multi temperature point calibration before leaving the factory, and users do not need to calibrate it on site.

Detailed explanation of electrical parameters and interface matching

4.1 Power Supply and Consumption

QBE3000-D series: Supports a wide power supply range - AC 24 V (± 15%, 50/60 Hz) or DC 18... 33 V. When powered by AC 24V, the typical power consumption is less than 5 mA, which is very suitable for centralized power supply of AC 24V transformers commonly used in building automation.

QBE3100-D series: Only supports DC 11... 33 V power supply, typical power consumption<20 mA. Note: When supplying 4-20 mA circuit, its working resistance (load) needs to meet the formula:

RL≤V supply−11V 0.02  A

RL≤ 0.02AV supply−11V

For example, when the supply voltage is 24 V DC, the maximum load resistance is (24-11)/0.02=650 Ω. If the supply voltage is 18V, the maximum load is 350 Ω. When designing, it is necessary to ensure that the input impedance of the PLC/DCD card is within this range.

4.2 Output signal characteristics

0... 10 V output (QBE3000): Output short-circuit protection and reverse polarity protection. Require the input impedance of the receiving end to be greater than 10 k Ω, otherwise it will cause voltage division errors.

4-20 mA output (QBE3100): Two wire current loop, also equipped with short-circuit and reverse protection. Current output is particularly suitable for long-distance transmission (up to hundreds of meters) and harsh electromagnetic environments on site.

4.3 Dynamic Response

Response time:<5 ms (from pressure step change to output signal reaching 90% final value). This is much faster than conventional mechanical differential pressure switches (usually 100-500 ms) and is very suitable for fast pressure fluctuation monitoring or PID closed-loop control.

Load alternating frequency: Supports up to 50 Hz, which means accurate output can still be achieved with 50 pressure changes per second. The sensor can still faithfully reflect high-frequency pressure components such as compressor pulsation and pump cavitation.

Mechanical installation and process connection

5.1 Pressure interface

The sensor is equipped with G1/8 "external thread as the standard pressure interface. Two adapters are included with the product, specifically designed to connect copper pipes with an outer diameter of 6 mm (commonly used for refrigerant, water pressure, or pneumatic signal pipelines). If other specifications of pipelines (such as 1/4 "NPT or 10mm nylon pipes) need to be connected on site, the adapter should be purchased by oneself.

Please note during installation:

Two pressure interfaces are labeled as "High" (P1) and "Low" (P1) respectively, P2）。 Do not connect in reverse, otherwise the output signal will decrease in reverse as the pressure difference increases (but will not damage the sensor).

Allow unilateral overload (only P1 or P2 side pressurized) to reach twice the nominal range. For example, a sensor with a range of 1 bar can achieve a maximum pressure of 2 bar on one side without damage. But if it exceeds twice the range for a long time, it is still recommended to use a three valve group or a five valve group for protection.

Medium temperature range: -15...+85 ℃. For steam or high-temperature hot water (>85 ℃) applications, condensation bends or heat sinks need to be installed.

5.2 Shell and Protection

Shell material: Aluminum alloy (AlMgSi1), cover made of aluminum; The part in contact with the medium is made of stainless steel 1.4305 (equivalent to 304 stainless steel) and ceramic components.

Protection level: IP65 (IEC 60529). When installed correctly and the cable sealing joint (PG9) is tightened, it can resist water jet and dust intrusion. But it is not suitable to be immersed in water for a long time.

Electrical interface: Comes with a plug that complies with DIN EN 175301-803-A standard (not pre connected), containing a sealing ring and PG9 cable connector. Users need to weld or crimp internal wires themselves. The plug is designed with an anti misoperation structure and allows for 360 ° rotation to adjust the direction of the outgoing line.

5.3 Installation bracket and direction

The sensor comes with a stainless steel (1.4305) mounting bracket that can be fixed to pipes, walls, ceilings, or control cabinets. Any installation direction is acceptable - because factory calibration is performed in the standard direction with the pressure interface facing downwards, but internal temperature compensation and gravity effects have been corrected. To ensure long-term stability, it is recommended to keep the sensor as high as possible above the process pipeline to prevent condensation from flowing back into the ceramic components.

Accuracy and performance data

The following are the common measurement characteristics across the entire series, based on factory calibration (compliant with EN 60770):

Parameter Value Remarks

Comprehensive accuracy (linear+hysteresis+repeatability)<± 0.5% FS FS=full scale

Zero offset<± 0.4% FS can be ignored

Zero temperature coefficient (TC zero)<± 0.04% FS/K Zero drift caused by temperature change per Kelvin

Sensitivity temperature coefficient (TC sensitivity)<± 0.015% FS/K with minimal gain drift

Long term stability ± 0.5% FS 1-year cycle

Resolution 0.1% FS analog output without quantization step

Response time<5 ms electronic response, no mechanical hysteresis

Compatibility, Compliance, and Environmental Product Declaration

7.1 System compatibility

The output signal of QBE3000/QBE3100 is an industrial standard analog quantity, which can be connected to:

Siemens building control products (Desigo, Apogee, Synco)

Rockwell, Schneider ABB、 Analog input module for Honeywell and other PLCs

Various DDC controllers, data acquisition cards, digital instruments

No additional converters or signal isolators are required (but if there are grounding loop issues, it is recommended to use 4-20mA signals with isolation barriers).

7.2 Electromagnetic Compatibility and Safety

EMC standards: comply with EN 61326-2-3 (industrial environment immunity), EN 61000-6-2 (immunity), EN 61000-6-3 (emission).

CE marking: Complies with Directive 2004/108/EC (now updated to 2014/30/EU).

C-Tick (EMC Australia) has also been certified.

Protection level: Level III (EN 60730), which means safe ultra-low voltage power supply without grounding.

Environmental Product Declaration: Compliant with RoHS hazardous substance restrictions and provides product disposal guidelines (CE1E1922en) to support green building assessments.

Engineering Installation and Debugging Guide

8.1 Installation steps

Mechanical assembly: Fix the installation bracket on a flat surface. Tighten the G1/8 "joint with a wrench (excessive force is not recommended, recommended torque is 5-7 N · m). When connecting 6mm copper pipes, the clamp nut should be fitted first, inserted into the pipeline to the bottom, and then tightened.

Electrical connection: Open the matching DIN plug and connect according to the wiring diagram:

QBE3000 (0-10V): Terminal 1 → Power Supply+(AC/DC), Terminal 2 → GND, Terminal 3 → Signal Output Vout

QBE3100 (4-20mA): Terminal 1 → Power Supply+(DC), Terminal 2 → Signal Output/Power Supply - (Shared Circuit)

(Note: The actual label on the product cover shall prevail, and may be adjusted for different batches.)

Use PG9 connectors to secure the cable and ensure that the sealing ring is in place.

Pipeline exhaust: For liquid media, it is necessary to open the exhaust valve or slightly loosen the upper end joint to exhaust all bubbles. Bubbles can cause output signals to bounce or response to lag.

Power on inspection: Use a multimeter to measure the power supply voltage and confirm that it is within the specified range. Measure the output signal, and the theoretical value at zero pressure difference should be 0 V (or 4 mA). If there is a deviation, check if both sides of the pressure interface are open to the atmosphere (unpressurized).

8.2 Quick Check Table for On site Troubleshooting

Possible causes and solutions for the phenomenon

No output (0V or 0mA) power supply missing, wiring error, output load short circuit check terminal voltage; Check if there is a short circuit between the terminals

The output is always at full range (10V or 20mA). The high pressure side is not pressurized, and the low pressure side pressure is too high; Or confirm the direction of pressure difference due to internal damage; Disconnect the pressure and test the sensor separately

There are bubbles or pulse pressures in the output jumping or unstable medium; Electromagnetic interference pipeline exhaust; Increase damping or buffering; Use shielded cables

Zero drift is large (>0.1V) and the ambient temperature exceeds the range; The sensor is subjected to overvoltage impact to check the temperature of the medium; Factory calibration (usually not on-site zeroing)

Slow response to pressure pipe blockage; Clean the pipeline if it is too long; Shorten the pressure pipe to<10 meters

8.3 Maintenance Suggestions

Sensors do not require regular maintenance (no movable wear parts). But it is recommended to conduct an annual visual inspection to confirm that the cable joints are not corroded and the pressure interface is not leaking. If used for dusty gases, a filtering device can be installed on the low-pressure side to prevent surface deposition of ceramic components from affecting accuracy.

Selection Comparison: QBE3000 vs QBE3100 Decision Matrix

Project QBE3000 (0-10V) QBE3100 (4-20mA)

The optimal transmission distance is ≤ 30 meters ≤ 300 meters

Moderate to strong resistance to electrical noise

Wiring with controller with 3 wires (power+, GND, signal) and 2 wires (loop power supply)

Convenience of fault detection: can directly measure voltage, read and output 0mA when broken, easy to identify

Multi sensor shared power supply can be powered in parallel, but the signal lines need to be independent and the total load of the circuit needs to be calculated

Typical application control cabinet, short distance connection of PLC on-site sensors to remote transmission in the central control room