Dwyer Instruments Series TDFS thermal flow switch

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The Series TDFS thermal flow switch indicates whether the flow rate is above or below a user set flow rate with NO and NC NPN outputs.

Setpoint is easily field set, just tap the included magnet on the setpoint target three times at the desired flow rate and it’s done. Incorporated into the unit are two LED status indicators on opposite sides of the unit providing visual switch indication, green when the flow is above setpoint, red when the flow is below setpoint.

The TDFS uses an impulse thermal dispersion measurement technique to measure the flow rate where the probe is heated above the process temperature and then is allowed to cool down to the process temperature. Empty pipe is not a problem with the TDFS unlike some competitor units that will overheat. Thermal flow switches can offer better long-term reliability and life expectancy than mechanical flow switches.

Benefits of the TDFS over mechanical flow switches include: no paddles or vanes to break off into the flow; no jams or material stopping the paddle movement; no seals on movement assembly to wear or leak; low pressure drop, only needs to be 10% into the flow (eg, 1/8″ for 3/4″ schedule 40 pipe).