WIKA FSD-4 Electronic Flow Switch with Display for Liquids

WIKA FSD-4 electronic flow switch with display for liquid media

The WIKA FSD-4 is an electronic flow switch with a four-digit LED display for liquid media. It works on the calorimetric principle, so there are no moving parts to wear, and it can be set up through three buttons or optionally through IO-Link 1.1. WIKA names the control of cooling lubricant systems, the monitoring of coolant circuits, the control of filter units and dry-run protection of pumps as typical uses. The measuring range is 0 … 3 m/s with a temperature measurement of -20 … +85 °C. Seven Star LLC supplies the FSD-4 in Oman and the GCC as an independent supplier in Muscat, and this page explains the output variants, process connections and set-up so that an RFQ can specify them correctly.

How the FSD-4 detects flow

A calorimetric flow sensor heats a probe slightly above the temperature of the liquid and measures how much heat the flowing medium carries away. More flow means more cooling of the heated element, and the electronics convert the temperature difference to a flow velocity. The same probe also measures the medium temperature, which is why the FSD-4 can offer a temperature output as well. There is no turbine or paddle, so deposits on moving parts are not a concern, but deposits or contamination on the probe surface affect the heat transfer, which the data sheet lists as a factor in accuracy.

The manufacturer is open about the limits of the method. Accuracy depends on flow profile, flow conditions, viscosity or thermal conductivity of the medium, and contamination or deposits on the sensor, so the quoted values are valid only under the calibration conditions (water, pipe inner diameter 26 mm, upstream 1 m and downstream 0.5 m straight pipe, process connection downwards). As a flow switch it is suited to reliable monitoring such as detecting dry running, while the flow value output should be used only as a trend indicator to monitor process changes. A teach function sets zero point and maximum flow at the actual measuring location, which adapts the switch to the pipe and medium.

Technical specifications of the FSD-4

Output variants and process connections of the FSD-4

One of three output variants is chosen at order, and the signal types are programmable at commissioning. Variant 1 gives two switching outputs, variant 2 gives one switching output and one analogue output, variant 3 gives two switching outputs and an analogue output. Switching outputs carry a maximum of 250 mA each at supply voltage minus 1 V, with hysteresis or window function and normally open or normally closed contact. Hysteresis is adjustable, with a minimum of 1.7 % of end value for flow and 1.8 K for temperature. IO-Link is optional with all variants.

Process connections are M18 x 1.5 (insertion length 52 mm), G 1/4 A (28 mm), G 1/2 A in four insertion lengths (30, 49, 79 and 119 mm), 1/4 NPT (22 mm), 1/2 NPT (38 mm) and a version for a compression fitting (140 mm), which lets the user set the immersion depth and alignment to the pipe diameter. Seals are FPM/FKM for M18, and NBR as standard or FPM/FKM or none as options for G threads. The compression fitting lowers the rated pressure to 20 bar and the vibration limit to 3 g.

Where the FSD-4 fits and related WIKA switches

The data sheet names the PSD-4 electronic pressure switch and the TSD-30 electronic temperature switch as similar products, which share the 3-button operation, display and IO-Link approach. A skid or machine can therefore use PSD-4 for pressure, FSD-4 for flow and TSD-30 for temperature with the same wiring and parameter handling. For high-pressure or industrial-process flow measurement a different flow family would be needed, because the FSD-4 is rated to 40 bar and 85 °C.

Selection and ordering checklist for the FSD-4

• Medium: water-based liquids, coolant or oil, and the pipe diameter.
• Thread and insertion length to reach into the flow, or the compression fitting for variable depth.
• Output variant 1, 2 or 3, PNP or NPN, and analogue signal type.
• IO-Link option.
• Seal material: NBR, FPM/FKM or none.
• Maximum pressure and temperature, including derating with two switching outputs.
• M12 connector with 4 or 5 pins.

Installation, commissioning and maintenance of the FSD-4

Install the probe so the sensing tip is in the flow and the marking is facing upstream, as shown in the operating instructions. Use straight pipe before and after the sensor wherever possible. At commissioning run the teach function at no flow and at maximum flow, then set the switch points. Check derating: with two switches at the highest medium temperature the maximum ambient and switching current per channel are reduced (the ambient limit at 85 °C medium is lower than 70 °C, as the derating curves show). Inspect the probe at shutdowns and clean deposits, since they affect the heat transfer.

Typical applications in Oman and the GCC

In Oman and the Gulf the FSD-4 is a fit for chilled water and cooling water loops on machines, coolant circuits on machine tools, lubrication systems, filter bypass monitoring and pump dry-run protection on skids. Hot ambient temperatures call for attention to the derating curves. For critical safety interlocks, a certified safety flow device should be specified instead.

FSD-4 output variants

Information to send with an RFQ

• FSD-4 with output variant
• Process connection and insertion length
• Medium, pipe diameter and temperature
• Seal material and IO-Link requirement
• Quantity and delivery site

Documents and quotation

The WIKA data sheet for the FSD-4 is attached on this page.

Send the connection, output variant and medium and Seven Star LLC will confirm availability and a quotation.