• Best Value In Solids Flow Detection
  • Superior Application Versatility
  • Excellent Sensitivity
  • Indicate Flow/No-Flow In Chutes, Feeders and Pipelines
  • On/Off Flow Detector
  • Hazardous Location Approval
  • Senses Light And Heavy Materials, Small And Large Particles
  • Non-Contact Sensor Detects Flow Through Most Non-Metallic Surfaces
  • Non-Intrusive Flush Mounting-No Probe Protruding Into Material Flow
  • SFD-2 Provides Relay Outputs and Convenient Remote Electronics
  • SFI Solids Flow Indicator Provides Variable Analog Signal
  • Sensors Include CSA Class II, Division I Approval for Hazardous Locations
Monitor's line of microwave solids flow monitors are high quality, industrial grade instruments capable of providing a signal indicating the flow/no-flow condition of solids and powders in gravity chutes, feeders and pneumatic pipelines. The Model SFD-2 Solids Flow Detector provides relay outputs that can be setup to indicate changes in the target flow stream (on/off). The Model
Unit of Measure


Operating Voltage

N/A Universal 100-240 VAC( ±10%)

Sensor Approvals

N/A Hazardous Locations (North America) (Sensor ONLY)


N/A Teflon

Power Supply

N/A Power Supply/Cond. Board in Fiberglass Enclosure with Lights


N/A None, signal from transceiver is delivered to and processed by power supply/conditioning circuit board


N/A Die Cast Aluminum, Beige Polyester Powder Coated

Enclosure Protection

N/A NEMA 4, IP66

Ambient Operating Temperature

N/A -40 to 185 ºF-40 to 85 ºC

Process Temperature

N/A 250° F (121° C) if ambient air temp, below 150° F (65° C)

Pressure Ratings

N/A 75 psi intermittent

Process Connection

N/A 1 1/4 NPT (1-1/2" w/SS Adapter)

Conduit Connection

N/A (2) 1/2 NPT

Detection Range

N/A 0 to 10 ft free air, env, and target dependent


N/A Switch selectable HI/LOW

Minimum Velocity

N/A 2.5 ft/sec762 mm/sec


N/A Green LED-power Yellow LED - loop, intensifies with disturbance detected


N/A 24.125 GHz, FCC & IC certified, energy levels less than 1 mW/cm° (OSHA limit at 10mW/cnf)


N/A CE Mark (Ordinary Locations) CSA US/C, Class II, Div. 1 & 2, Groups E, F & G

Power Requirements

N/A Provided by power supply/conditioning PCB

Power Supply / Conditioning Board

Enclosure (if supplied) 

N/A PBT/Polycarbonate

Enclosure Protection 


Ambient Operating Temperature 

N/A -40 to 158 ºF

Interconnection Distance 

N/A 2500 ft max (minimum wire size 22 AWG)


N/A Universal 100-240 VAC, ±10%, 50/60HZ

Power Consumption 

N/A 5 VA max


N/A DPDT dry contact, 5A at 250VAC, 30 VDC

External lights (if applicable) 

N/A Red-output operate Sensitivity Solid state LED clusters Yellow-material sense


N/A Single-turn adjust 0 to 100% of sensor range

Time Delay Hold-off 

N/A Single-turn adjustment, 0.25 to 15 sec.

Time Delay Hold-on 

N/A Single-turn adjustment, 0.25 to 15 sec.


N/A Switch selectable, (Flow/No-Flow)


N/A Green LED-power Red LED-output Yellow LED-sense


N/A CE Mark (Ordinary Locations) CSA US/C, ordinary locations, industrial control equipment

Principle of Operation

N/A Both the SFD-2 and SFI utilize a microwave transceiver (combination transmitter/receiver) enclosed within a watertight, dust-ignition proof powder coated aluminum housing with a screw on/off cover. A process seal (Teflon® or Ryton®) acts as a transparent window through which the microwave energy is transmitted and the reflected return signal is received. The transceiver module generates and transmits a microwave sig nal into the area where material flow is to be monitored. The reflected microwave signal shifts in accordance with the Doppler Effect phenomena. The Doppler-shifted energy is analyzed to determine the appropriate output from the unit.

The SFD-2 has a split-architecture design consisting of the transceiver and a separate power supply/conditioning circuit board. The relays are incorporated on the power supply/conditioning circuit board, which is optionally available with a fiberglassenclosureand indicating lights. With the SFD-2, the Doppler-shifted energy signal from the transceiver is car


N/A Monitor's Solids Flow Detector and Indicator can be used in a variety of applications to detect flow/no-flow conditions of powders and bulk solid materials. The selection of either SFD-2 Solids Flow Detector or the SFI Solids Flow Indicator is based upon the type of output required (relay or analog).

Typical applications include:

  • Detection of a partial or full plug in a conveying line
  • Detecting the bridging of material in a storage vessel upstream
  • Sensing inadequate or a lack of flow due to upstream equipment failure (conveyor, blower, diverter valve, feeder)
  • Verifying flow conditions
  • Turning on/off equipment or processes downstream

Use of SFI Analog Output

N/A The Model SFI Solids Flow Indicator can be used to infer the relative amount of flowing material within the target conduit (by monitoring the available analog signal). However, it should be noted that this device provides an output that should be con sidered, at best, a very rough estimate of the flow of material. The analog signal corresponds to the magnitude of the Doppler-shifted energy created by the flow of material through the microwave energy field.

Note: Monitor Technologies LLC accepts no responsibility for the accuracy of the analog output signal. This signal can be influenced by several varying factors including, but not limited to, particle size distribution, dielectric constant variation, moisture content variation, dispersion of material flow, variation in velocity of material flow, movement of auxiliary equipment, temperature variations and type of conveying system. Please consult the factory to discuss applications where the accuracy of the analog output is of importance.



  • Powder coated Nema 4 cast aluminum construction
  • Approved for Class II hazardous areas
  • Meets applicable FCC regulations
  • Screw-on/off cover
  • Teflon® process seal is standard
  • Connects to transceiver using an inexpensive, low voltage 3-wire system
  • Convenient controlfunctionsfortimedelay, sensitivity and fail-safe selection
  • Control function changes can be made without accessing the transceiver
  • Yellow and Red LEDs indicate material flow intensity and output activation
Both the SFD-2 and SFI come standard with a Teflon® process seal window through which the transmit/receive signal pass es. While this material is compatible with most applications, a Ryton® seal is available for use in applications where the seal is subjected to high pressure or abrasive materials.

The standard SFD-2 does not provide an enclosure for the power supply/conditioning circuit board. This allows the user to install the board wherever is appropriate. A NEMA 4X enclo sure is available. When selected, the power supply/conditioning circuit board is supplied installed within a fiberglass enclosure furnished with long-lasting LED indica tors flush with the enclosure face.


N/A Monitor Technologies LLC warrants each SFD-2/SFI it manufactures to be free from defects in material and workmanship under nor mal use and service within two (2) years from the date of purchase. The purchaser must give notice of any defect to Monitor within the warranty period, return the product intact and prepay transportation charges. The obligation of Monitor Technologies LLC under this warranty is limited to repair or replacement at its factory. This warranty shall not apply to any product which is repaired or altered outside of the Monitor Technologies LLC factory, or which has been subject to misuse, negligence, accident, incorrect wiring by oth ers or improper installation.

Monitor Technologies LLC reserves the right to change the design and/or specifications without prior notice.

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