Thermodynamic

Technology overview: thermodynamic (calorimetric) flow sensing

Thermodynamic (also called thermal dispersion or calorimetric) flow sensors contain a tiny heated element a few degrees above the medium. As the fluid moves, it carries heat away from the sensor; the electronics measure the resulting temperature difference (or the power needed to maintain a constant ΔT) and infer flow velocity. Because there are no moving parts, the devices are robust, resistant to fouling, and create no pressure loss. They work in liquids and gases, with versions for standard and hazardous (ATEX/IECEx) areas.

Key points for buyers and specifiers

• Principle: heated probe + temperature reference → cooling effect ∝ local flow velocity.
• Media: water, oils, chemicals and air/gases, provided they’re sonically/thermally conductive.
• Advantages: non intrusive tip, no moving parts, wide turndown, simple setpoint adjustment, and options for switching or 4–20 mA outputs.
• Considerations: best performance with correct insertion depth/position, appropriate straight runs, and selection of materials (e.g., stainless steel, PTFE, Hastelloy, titanium) for the medium.

Overview of the PCT thermodynamic sensor range

• LNZ — Air Flow Sensor / Controller (gases):
  • Application: monitoring supply/extract ducts, ventilation and process air; ½″ BSP screw in.
  • Range: 0.5–30 m/s; relay or 4–20 mA versions.
  • Build: compact body, LED bargraph, options for 24 VDC or 115/230 VAC, IP67, up to 30 bar.
• SC440 — Compact Liquid Flow Controller (switch):
  • Application: water and oils; cooling water, pump run dry protection, filter monitoring. ¼″ or ½″ BSP, ½″ NPT options.
  • Detection: water 1–150 cm/s, oils 3–300 cm/s; 24 VDC, PNP switching; IP67; M12 connector; LED array. Sensors available in multiple immersion lengths; up to 100 bar.
• SN 450 — Robust Liquid Flow Controller (switch or analogue):
  • Application: rugged, compact ½″ BSP models for water/oils; ideal in corrosive/industrial environments.
  • Options: relay or 4–20 mA output; power 24 VDC or 115/230 VAC; IP67; LED bargraph; common lengths 31/48/80/120 mm; typical response 1–13 s; up to 100 bar.
• ST Series — Liquid Probe (no integrated amplifier):
  • Application: insertion probe for water/oils where you want the probe remote from the electronics (use with SKM/SKZ amplifiers); ½″ BSP, 48 mm immersion.
  • Materials: stainless steel or PTFE wetted parts for chemical compatibility. PTFE versions offer different pressure/response characteristics. IP67/IP68 variants available.
• STK Series — Short thread Liquid Probe (no integrated amplifier):
  • Application: compact, short insertion (25/31 mm) where space is tight; pair with SKM/SKZ amplifiers. ¼″ or ½″ BSP.
  • Performance: water 1–150 cm/s, oils 3–300 cm/s; typical start up 2–15 s, reaction 1–13 s; IP67/IP68, 316 SS, up to 100 bar.

Features & benefits

• LNZ — Air Flow Sensor / Controller (gases):
  • Fast to install (screw in, ½″ BSP) and simple to commission with LED bargraph and either relay threshold or 4–20 mA trending—ideal for fans, extraction and solvent vapour areas.
  • Durable design (IP67, up to 30 bar) for plant air lines and ducts.
• SC440 — Compact Liquid Flow Controller (switch):
  • All stainless, IP67 compact switch with M12 connector and multiple probe lengths—perfect for cooling water, pump run dry and filter monitoring without adding pressure drop. Up to 100 bar.
  • Universal threading (¼″/½″ BSP, ½″ NPT) and 24 VDC supply for easy PLC integration.
• SN 450 — Robust Liquid Flow Controller (switch or analogue):
  • Choice of relay or 4–20 mA gives either a simple switch or a signal you can trend for condition monitoring; AC or DC power variants simplify retrofit.
  • Rugged housing, IP67, and wide sensor length options support applications from skids to heavy industry.
• ST & STK probes (liquid, remote electronics):
  • Keep the electronics out of harsh areas—use SKM/SKZ amplifiers remotely while the stainless/PTFE probe sits in the line. Great for heat, splash or chemical exposure.
  • Short thread STK variants (25/31 mm) solve tight space installs while retaining pressure capability (up to 100 bar) and IP67/68 sealing.
• All EGE thermodynamic sensors:
  • No moving parts → minimal maintenance and reliable switching even where inline paddle/float devices struggle.
  • Broad materials and Ex rated families available across the portfolio for aggressive media or hazardous zones.

FAQs for thermodynamic flow sensors & these models