Flow Sensors: Calorimetric Flow Meters and Flow Switches
Flow and temperature sensors with no moving parts and orientation-independent mounting: when to select which model.
First Identify What You Need
Searches for "flow sensor", "flow switch", and "flowmeter" correspond to four distinct needs. The right instrument is selected accordingly:
- Is there flow or not? (pump dry-run protection, cooling water loss): Wenglor weFlux² or UniFlow with switching output, used as a flow switch.
- Will flow velocity and temperature be monitored continuously? (cooling circuit, CIP line, heat exchanger): the 4-20 mA or IO-Link output of the same sensors; velocity is converted into volumetric flow rate using the pipe cross-section.
- Actual flow rate of a dosing pump? EFS mounted on an Iwaki EWN-Y pump.
- Analyzer sample line (mL/min)? Pyxis FS series ultrasonic flowmeters.
Flow Sensors and Flowmeters
Values are taken from the Wenglor Fluid Sensors catalog and brochure, the Iwaki EFS product page, and the Pyxis FS user manual.
| Instrument | Principle | Measuring range | Media / pressure | Output | Typical use |
|---|---|---|---|---|---|
| Wenglor weFlux² (FXFF) compact stainless steel | Calorimetric flow + temperature | 10–400 cm/s (water); liquid temperature -25…150 °C; measurement error 2% | Aqueous media; 100 bar; IP68/IP69K; 1.4404 housing | IO-Link 1.1; 2 switching outputs; 0-10 V / 4-20 mA; or 2 x 4-20 mA (flow and temperature) | CIP/SIP lines, food and pharma, cooling circuits |
| Wenglor UniFlow FFAF plastic housing, with display | Calorimetric flow + temperature | Water: 10–300 cm/s; oil: 15–100 cm/s (family value); example model: 15–200 cm/s water | Aqueous and oily media; liquid 0…100 °C (short-term 140 °C); 60 bar; IP67 | 1 or 2 switching outputs; 4-20 mA flow and temperature; relay option | Pump protection, cooling water monitoring |
| Wenglor UniFlow FFXF stainless steel housing, with display | Calorimetric flow + temperature | Family range same as UniFlow (water 10–300 cm/s) | Liquid 0…100 °C; 60 bar; IP67/IP69K; G1/2 inch CIP compatible | 1 switching output; 4-20 mA flow or temperature | Hygienic and washdown lines |
| Iwaki EFS dosing line | Electromagnetic, no moving parts | Dosing flow rate of EWN-Y pump; feedback 0–360 spm | Liquid conductivity at least 1000 mS/m | Digital value on pump display; FL.ER and F.CHK alarms | Feedback dosing, batch dosing, flow interruption alarm |
| Pyxis FS-100 / FS-200 sample line | Ultrasonic, transit-time | FS-100: 0–3000 mL/min; FS-200: 0–10000 mL/min; resolution 1 mL/min | Water; 4…49 °C; inlet pressure 0.05–0.689 MPa; ½ inch NPT; IP65 | 2 isolated 4-20 mA outputs; RS-485 Modbus RTU; 24 VDC, 2 W | Analyzer sample and feed lines, regulating valve control via PID |
The FS-101 and FS-201 versions feature PPS and GF polymer wetted parts for corrosive aqueous solutions. Contact us for details on the Pyxis FS series.
Calorimetric Flow Measurement and Velocity-to-Flow Conversion
No moving parts
Because there is no impeller, paddle, or vane, mechanical wear, jamming, and scaling issues are avoided. Wenglor specifies a response time of 1–5 s and a temperature step response time of 10 s.
Orientation-independent mounting
Thanks to the patented measuring method, the probe does not need to be aligned with the flow direction; the sensor mounts into the pipe in any orientation. Flow and temperature are measured in a single probe, allowing two readings to be taken with a single sensor at heat exchanger inlets and outlets.
From velocity to flow rate
The sensor outputs velocity in cm/s. Volumetric flow rate is found by Q = v × A (where A is the internal cross-sectional area). Example: in a pipe with a 50 mm internal diameter, 1 m/s equals approximately 7.1 m³/h. If the cross-sectional area is uncertain, the result should be evaluated as a threshold value (flow present/absent) rather than volumetric flow rate.
Limitations
weFlux² is intended for aqueous media such as water, while UniFlow covers aqueous and oily media. For water, the measuring range starts at 10 cm/s; flows below this velocity cannot be measured. For very low-flow sample lines, instruments with mL/min resolution such as the Pyxis FS series are appropriate.
Which Flow Sensor for Which Line?
Pump dry-run protection
When the line runs dry, the switching output stops the pump, protecting the mechanical seal and bearings. weFlux² or UniFlow is used as a flow switch, with the threshold velocity set from the menu.
Cooling water and heating circuits
In lines such as generator cooling, heat exchangers, and reactor jackets, flow loss alarms and inlet/outlet temperatures are monitored with a single sensor. Wenglor lists generator cooling water monitoring as an application in its catalog.
Food, beverage, and pharma: CIP/SIP
With its one-piece 1.4404 housing, FDA-compliant design, and EHEDG certification on selected connections, weFlux² verifies flow and temperature in CIP/SIP lines. Filling machine flow monitoring is also among the catalog applications.
Chemical dosing line
The pump-mounted Iwaki EFS is used to verify that the dosing flow rate is actually being pumped. For pump selection, see our pumps page.
Related pages: Wenglor weFlux² and UniFlow · Iwaki EFS · Online analyzers · Pressure gauge selection
Frequently Asked Questions About Flow Sensors
Calorimetric principle, flow switches, velocity-to-flow conversion, dosing lines, and sample lines.
How does a calorimetric flow sensor work?
An element at the tip of the probe is heated; the flowing liquid carries away the heat, and the amount of cooling is proportional to the flow velocity. Liquid temperature is also measured in the same probe. Wenglor states that its patented measuring method does not require aligning the probe with the flow direction; the sensor can be mounted into the pipe at any angle. There are no moving parts.
Are a flow sensor and a flow switch the same thing?
The same sensor can be used in two roles. A flow switch provides a switching output when the flow velocity drops below or rises above a set value (pump protection, cooling water loss alarm). A flow sensor continuously transmits the measured velocity via a 4-20 mA analog output or IO-Link. In the Wenglor weFlux² and UniFlow families, PNP/NPN switching output and analog output are available together.
How do I convert flow velocity into volumetric flow rate (L/min, m³/h)?
The sensor measures velocity (cm/s); volumetric flow rate is the product of velocity and the internal cross-sectional area of the pipe: Q = v × A. For example, in a pipe with a 50 mm internal diameter, a velocity of 100 cm/s (1 m/s) corresponds to approximately 7.1 m³/h. The UniFlow display can show flow as a percentage or in L/min. When the internal pipe diameter is known accurately, the velocity value can be reliably converted into volumetric flow rate.
What is the difference between weFlux² and UniFlow?
weFlux² is compact, displayless, and has a one-piece stainless steel (1.4404) housing: 10–400 cm/s for water, liquid temperature -25…150 °C, 100 bar, IP68/IP69K, with IO-Link 1.1 and dual analog output options. UniFlow is the series with a large 7-segment display; it offers a 10–300 cm/s range for water, 15–100 cm/s for oil, and plastic or stainless steel housing options.
Can the sensor be used in oily media and hygienic lines?
UniFlow is specified for aqueous and oily media (15–100 cm/s for oil). weFlux² is for aqueous media; it holds EHEDG certification with its FDA-compliant housing and selected process connections. CIP-compatible G1/2 inch and 50.5 mm clamp connections are available.
How do I measure the actual flow rate on a dosing pump discharge line?
Inline flow sensors are intended for water and process water. The EFS electromagnetic flow sensor, mounted directly on the discharge of an Iwaki EWN-Y dosing pump, measures the actual dosing flow rate; the pump adjusts its stroke rate accordingly (0–360 spm) and triggers a no-flow alarm. The EFS works exclusively with EWN-Y pumps and requires a liquid conductivity of at least 1000 mS/m.
What measures flow at the mL/min level in an analyzer sample line?
Pyxis FS series ultrasonic flowmeters operate on the transit-time principle: FS-100 measures 0–3000 mL/min and FS-200 measures 0–10000 mL/min, with 1 mL/min resolution, ½ inch NPT connection, and 24 VDC, 2 W power supply. It features two isolated 4-20 mA outputs (one for flow rate, one for a regulating valve) and RS-485 Modbus RTU output, along with a 1.44-inch color screen. These instruments are intended for small sample and feed lines rather than main pipelines.
Send the make and model of your current instrument to [email protected] — our engineers will propose the equivalent with the same connection and measuring range.
Planning a project? Send us your flow rate, feed water source and target water quality to [email protected] — our engineers will reply with a technical proposal.