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Thermal Dispersion Flow Switch


SMC’s ALTS flow switch represents the state-of-the-art in gas and liquid flow switching and liquid level control. This device continues the SMC tradition of providing the highest quality flow instrumentation. Flow & level detection is accomplished by using a high-resolution thermal differential technique. The sensor consists of a pair of matched Resistance Temperature Detectors (RTD’s). One RTD uses a self-heated constant DC current while the other RTD is unheated and provides an accurate process temperature reference. The temperature differential created between the reference and the heated RTD pair is a function of the density and/or velocity of the media in which the sensor is in contact. The sensor and wetted parts are comprised of durable 316L stainless steel, all welded construction with no moving parts. The switch is easy to install and adjust; providing reliable, low maintenance performance in the most demanding applications.


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  • Flow switch employing thermal mass flow sensing technique for the detection liquid and gas flow
  • No moving parts and no leak paths, no o-rings or graph oil seals to wear, fail, or leak
  • Point level switch for liquid level detection
  • Wide operating temperature range -100 – 850 °F (-70 – 458 °C)
  • Flow Switch range of 0-5 feet/sec (0-1.5 mps) liquids and 0.2-500 feet/sec (0.07 – 150 mps) gases
  • Level Switch switches on level change 0.03″ (0.076 cm)
  • Fast flow switch response time of 0.5 to 10 seconds (media dependant)
  • Level switch response time of 0.1 to 1 second of wetting (media dependent)
  • CE, CENELEC and CSA approvals
  • Insertion length from ½” to 39⅜” (1.27cm to 100 cm)
Process Connections:¾” MNPT standard. ½” to larger MPNT, Sanitary and flanges optional
Process temperature:-100 – 390 °F (-70 – 200 ℃) standardMedium T: to 572 °F (300 ℃)Hight T: to 850 °F (485 ℃)
Operating pressure:to 3000 psia (207 bar)
Velocity Range:Dependant on fluid mediaLiquids: 0-5 fps (0-1.5 mps)(Adjustable flow rate)Gas: 0.2-500 fps(0.07-150 mps)(Adjustable rate)
Repeatability:± 1% of setpoint (Flow) or ⅟32” (0.8mm) Level
Material :316 SS standard.Hastelloy, Monel, Inconel
Operating Temperature – Electronics:-40 – 140 °F (-40 – 60 °C )
Housing Protection:Explosion Proof; NEMA 3,4X,7,9
Insertion Length:2.0” standard. ½” or greater optional
Flow Switch:over a range of ± 50 °F (10 °C) ; Temperature compensated over entire range
Stability:<0.5% from calibrated setpoint
Ex-protection:CSA, FM, UL, CENELEC and EECS approved
Power requirements :115 VAC, 50/60Hz or 230 VAC, 50/60Hz24VDC optional. 3.1 Watt maximum
Output:5A 250 VAC DPDT with fail safe capability

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