Views: 2 Author: Site Editor Publish Time: 2026-08-20 Origin: Site
How can you detect air leaks invisible to the naked eye?
How can you prevent costly equipment damage caused by cooling system blockages?
As critical components in industrial fluid control, the PF2A and PF3W digital flow switches serve not only as measuring instruments but also as core tools for enabling predictive maintenance and energy consumption management.
Quick Decision Table
| Your Requirements | Recommended Models | Key Advantages |
| Monitoring air/nitrogen and detecting leaks | PF2A Series | Rapid response with negligible pressure loss |
| Monitoring laser or mold cooling water | PF3W Series | Anti-clogging design; supports flow-interruption alarms |
| Integration with PLC for remote monitoring | Models with Analog Output/IO-Link | Real-time data transmission enabling predictive maintenance |
| High precision and long service life | Digital Flow Meters | No mechanical wear; more reliable than rotameters |
1. What is a digital flow sensor?
Simply put, these two products convert abstract flow rates into intuitive digital signals by "sensing" the flow of the fluid.
PF2A digital flow switch (Air): Designed specifically for non-corrosive gases such as compressed air and nitrogen. It serves as the "flow manager" for pneumatic systems and is widely used in automated production lines across industries including packaging, electronics, lithium battery manufacturing, and automotive production.
| Model | PF2A710 | PF2A750 | PF2A711 | PF2A721 | PF2A751 | |
| Working medium | Dry Air, Nitrogen | |||||
| Rated flow range | 1 to 10L/min | 5 to 50L/min | 10 to 100L/min | 20 to 200L/min | 50 to 500L/min | |
| Mininum set unit | 0.1L/min | 0.5L/min | 1L/min | 2L/min | 5L/min | |
| Accumulated pulse flow rate exchange value(Pluse width:50ms) | 0.1L/pulse | 0.5L/pulse | 1L/pulse | 2L/pulse | 5L/pulse | |
| Display units*1,2) | Instantaneous flow rate | L/min, CFM×10 -2 | L/min, CFM×10 -1 | |||
| Accumulated flow | L, ft³×10 -1 | |||||
| Working temperature | 0 to 50℃ | |||||
| Accuracy*3) | ±5%F.S. | |||||
| Repeatability | ±1%F.S. | ±2%F.S. | ||||
| Temperature characteristics | ±3%F.S. (15 to 35℃, 25℃ reference), ±5%F.S. (0 to 50℃, 25℃ reference) | |||||
| Current consumption | 150mA or less | 160mA or less | 170mA or less | |||
| Port size(Rc, NPT, G) | 1/8, 1/4 | 3/8 | 1/2 | |||
| Detection type | Heater type | |||||
| Operating pressure | -50kPa to 0.5MPa | -50kPa to 0.75MPa | ||||
| Proof pressure | 1.0MPa | |||||
| Accumulated flow range*4) | 0 to 999999L | |||||
| Output specifications*5) | Switch output | NPN open collector | Max. load current: 80mA; Internal voltage drop: 1V or less Max. applied voltage: 30V; 2outputs | |||
| PNP open collector | Max. load current: 80mA; Internal voltage drop: 1.5V or less; 2outputs | |||||
| Accumulated pulse output | NPN or PNP open collector (same as switch output) | |||||
| Status LED's | Lights up when output is turned ON OUT1: Green; OUT2: Red | |||||
| Response time | 1 sec. or less | |||||
| Hysteresis | Hysteresis mode: Variable (can be set from 0), Window comparator mode : 3-digit fixed | |||||
| Power supply voltage | DC12 to 24 V±10% | |||||
| Environment | Enclosure | IP65 | ||||
| Working temperature | Operating: 0 to 50℃, Stored: -25 to 85℃ (with no freezing and condensation) | |||||
| Withstand voltage | AC 1000V for 1 minute between terminals and housing | |||||
| Insulation resistance | 50MΩ or more (DC 500V measured via megohmmeter) between terminals and housing | |||||
| Noise resistance | 1000V P-P pulse width1μs lasts 1ns | |||||
For further details, please refer to the brochure: 
PF2A Series Digital Flow Switch.pdf
PF3W digital flow sensor (Liquid): Dedicated to monitoring the flow of water and coolant. It acts as the "safety guardian" for the cooling circuits of high-heat equipment, such as lasers, injection molding machines, and welding machines.
| Model | PF3W704 | PF3W720 | PF3W740 | PF3W711 | PF3W721 | |
| Working medium | Water and ethylene glycol aqueous solution (with viscosity of 3MPa·s [3 cP] or less) | |||||
| Detection type | Karman vortex | |||||
| Rated flow range | 0.5 to 4L/min | 2 to 16L/min | 5 to 40L/min | 10 to 100L/min | 50 to 250L/min | |
| Display flow range*1) | 0.35 to 5.5L/min | 1.7 to 22L/min | 3.5 to 55L/min | 7 to 140L/min | 20 to 350L/min | |
| Set flow range | 0.35 to 5.5L/min | 1.7 to 22L/min | 3.5 to 55L/min | 7 to 140L/min | 20 to 350L/min | |
| Smallest settable increment | 0.01L/min | 0.1L/min | 1L/min | 2L/min | ||
Conversion of accumulated pulse (Pulse width: 50ms) | 0.05L/pulse | 0.1L/pulse | 0.5L/pulse | 1L/pulse | 2L/pulse | |
Fluid temperature (No freezing or condensation) | 0 to 90°C | 0 to 70°C | ||||
| Display unit | Instantaneous flow: L/min, Accumulated flow: L | |||||
| Accuracy | Display value: ±3% F.S. Analog output: ±3% F.S. | |||||
| Repeatability | ±2.0% F.S.*2) | |||||
| Temperature characteristics | ±5.0% F.S. (25℃ reference) | |||||
| Operating pressure | 0 to 1MPa | |||||
| Proof pressure | 1.5MPa | |||||
| Pressure loss | 20kPa (at maximum flow rate) | |||||
Pressure loss (Without flow adjustment valve) | 45 kPa or less at the max. flow | 60 kPa or less at the max. flow | ||||
| Accumulated flow range*3) | 0 to 9,999,999,999L | 999,999,999L | ||||
| By 0.1L | By 0.5L | By 1L | ||||
| Pressure characteristics | ±1.5% F.S. (0.1 to 1.5 MPa, 0.7 MPa reference) | |||||
| Switch output | Nil | NPN open collector output | ||||
| Max. load current | 80mA | |||||
| Max. applied voltage | DC 28V | |||||
| Internal voltage drop | NPN: 1V or less, PNP: 1.5V or less (at load current of 80 mA) | |||||
| Response time*2,4) | 0.5s/1s/2s | |||||
| Output protection | Short-circuit protection | |||||
Flow rate output mode | Select from Hysteresis, Window comparator, Accumulated output, or Accumulated pulse output modes | |||||
Temperature output mode | Select from Hysteresis mode or Window comparator mode | |||||
| Analog output | Response time*5） | 0.5s/1s/2s (linked with the switch output) | ||||
| Voltage output | Output voltage: 1 to 5V Output impedance: 1 kΩ | |||||
| Current output | Output current: 4 to 20 mA Max. load impedance: 300 Ω for DC 12V, 600 Ω for DC 24V | |||||
| Hysteresis | Variable | |||||
| External input | Voltage free input: 0.4V or less (Reed or Solid state), input for 30ms or longer | |||||
| Display method | 2-screen display (Main screen: 4-digit, 7-segment, 2-color, Red/Green Sub screen: 6-digit, 11-segment, White) | |||||
| Indicator light | Output 1, Output 2: Orange | |||||
| Power supply voltage | DC12 to 24 V ±10% | |||||
| Current consumption | 50 mA or less | |||||
| Environment | Enclosure | IP65 | ||||
| Working temperature | 0 to 50℃ (with no freezing and condensation) | |||||
| Working humidity | Operation, Storage: 35 to 85% R.H. (No condensation) | |||||
| Withstand voltage*6) | AC 1000V for 1 minute between terminals and housing | |||||
| Insulation resistance | 50 MΩ or more (DC 500V measured via megohmmeter) between terminals and housing | |||||
| Standards and regulations | CE, RoHS | |||||
| Wetted parts material | PPS, FKM, SCS13, SUS304 | |||||
| Non-grease | ||||||
| Piping port size*7） | 3/8 | 3/8, 1/2 | 1/2, 3/4 | 3/4, 1 | 1 1/4, 1 1/2 | |
For further details, please refer to the brochure: PF3W Series 3-color Display Digital Flow Switch for Water.pdf
2. Working Principle and Advantages
PF2A (Thermal principle): An internal heating element detects the difference in heat carried away by the airflow.
Advantages: Extremely fast response, no mechanical parts (such as rotors), high durability, and negligible pressure loss.
PF3W (Kármán vortex principle): Liquid flowing past an internal obstruction generates vortices; the flow rate is calculated by detecting the vortex frequency.
Advantages: Tolerant of varying water quality, provides stable readings, and is suitable for long-term monitoring of circulating water.
3. Key Features and Highlights
Dual-color digital display: Real-time and cumulative flow rates are visible at a glance; supports screen rotation and multi-angle viewing.
Multiple signal outputs:
Switch output (NPN/PNP): Triggers alarms or protective shutdowns when preset flow thresholds are reached.
Analog output (4–20 mA / 1–5 V): Provides real-time feedback on flow fluctuations to the PLC for closed-loop control.
Totalization: Records total gas or water consumption, facilitating energy cost accounting by month or shift.
Peak monitoring: Automatically records maximum and minimum flow values during operation, aiding in fault diagnosis and traceability.
4. PF2A vs. PF3W Digital Flow Sensor Selection Comparison Table
| Selection Criteria | PF2A Digital Flow Switch (for Air) | PF3W Digital Flow Switch (for liquids) |
| Measured Medium | Compressed air, nitrogen (dry, non-corrosive) | Water, deionized water, ethylene glycol solution (coolant) |
| Key Application Scenarios | Pneumatic branch monitoring, air consumption tracking, air leak detection | Cooling monitoring for lasers/injection molding machines; flow-loss alarm |
| Detection Principle | Thermal type: extremely fast response | Kármán vortex: Rugged and durable construction |
| Typical Flow Range | 10, 25, 50, 100, 200, 500, 1000 L/min | 4, 16, 40, 100, 250 L/min |
| Pressure Loss | Very low (negligible impact on system pressure) | Low (optimized internal structure) |
| Connection Specifications (Rc/G/NPT) | 1/8, 1/4, 3/8, 1/2, 3/4, 1 | 3/8, 1/2, 3/4, 1, 1-1/4, 1-1/2 |
| Output Signal Options | NPN/PNP switch output, 1–5 V / 4–20 mA analog output | NPN/PNP switch output, 1–5 V/4–20 mA analog output |
| IO-Link Communication | Supported (select models) | Supported (select models) |
| Display Type | 3-color/2-stage digital display (green/red/orange) | 2-color/2-stage digital display (green/red) |
| Ingress Protection Rating | IP40 or IP65 (depending on model) | IP65 (jet-proof; suitable for humid environments) |
| Straight Pipe Run Requirements | Strict: upstream ≥10D, downstream ≥5D | Strict requirements: ≥10D upstream, ≥5D downstream |
FAQ
1. Can the PF2A digital flow sensor measure nitrogen?
Yes. The PF2A is suitable for non-corrosive gases such as compressed air and nitrogen.
2. Does the PF2A digital flow sensor support PLC connection?
Yes. It supports NPN, PNP, analog, and IO-Link communication options.
3. Why is the flow rate display unstable?
Common causes include: Turbulent airflow, Piping vibration, Insufficient straight pipe length, Sensor contamination.
4. Does the digital flow meter require calibration?
For high-precision applications, periodic calibration is recommended in accordance with your company's maintenance schedule.
5. Can the PF3W digital flow sensor be used for laser cutting machines?
Yes. The PF3W is widely used for monitoring cooling water flow in laser equipment.
6. Can the digital flow meter detect air leaks?
Yes. If abnormal flow is detected while the equipment is shut down, it usually indicates a system leak.
The PF2A and PF3W digital flow meters are widely used for flow monitoring in industrial automation systems. For equipment manufacturers, system integrators, and end-user factories, selecting the right model and ensuring proper installation not only enhances operational efficiency but also effectively reduces operating costs associated with compressed air and cooling systems.
If you are looking for digital flow meters compatible with the PF2A and PF3W series (as alternatives to SMC models), VPC Pneumatic offers a wide range of options regarding flow ranges, port sizes, and output types, providing reliable flow monitoring solutions for automation equipment and industrial fluid control systems.
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