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64 Series Heat Flux Transducers

Product Details

Raptor Scientific 64 Series Heat Flux Transducers offer dependable direct measurement of heat transfer rates in a variety of applications due to careful design, rugged quality construction and versatile mounting configurations. Each transducer will provide a self-generated 10-millivolt (nominal) output at the design heat flux level. Continuous readings from zero to 150% design heat flux are made with infinite resolution. The linear transducer output is directly proportional to the net heat transfer rate absorbed by the sensor.

64 Series transducers are of two basic sensor types, the Gardon type sensor, standard in the ranges from 5 to 4000 Btu/(ft²s), and the Schmidt-Boelter thermopile type sensor, standard in the 0.2 to 4 Btu/(ft²s) rangesIn both type sensors heat flux is absorbed at the sensor surface and is transferred to an integral heat sink that remains at a different temperature than the sensor surfaceThe difference in temperature between two selected points along the path of the heat flow from the sensor to the sink is a function of the heat being transferred, and a function of the net absorbed heat flux. At two such points, our transducers have thermocouples/thermopiles to form a differential thermoelectric circuit, thus providing a self-generated emf at the output leads that is directly proportional to the heat transfer rateNo power supply or thermoelectric reference junction is needed. 

Gardon gages absorb heat in a thin metallic circular foil and transfer the heat radially (parallel to the absorbing surface) to the heat sink welded around the periphery of the foil. The emf output is generated by a single differential thermocouple between the foil center temperature and foil edge temperature. 

Schmidt-Boelter gages absorb the heat at one surface and transfer the heat in a direction normal to the absorbing surface. The emf output is generated by a multi-junction thermopile responding to the difference in temperature between the surface and a plane beneath the surface.  The Schmidt-Boelter thermopile sensor is always used below 5 Btu/(ft²s).  It can be optionally specified up to 100 Btu/(ft²s). 

 64 Series transducers have met thousands of application challenges in ground and flight aerospace testing, fire testing, flammability heat flux standards, heat transfer research, materials development, and furnace development. 


  • Linear Output
  • Output Proportional To Heat Transfer Rate
  • Accurate, Rugged, Reliable
  • Convenient Mounting
  • Uncooled, Water Cooled, Gas Purged Models
  • Radiometer And Limited View Accessories
  • Measure Total Heat Flux
  • Measure Radiant Heat Flux


  • Accuracy, Ruggedness And Reliability are provided by the thoroughly proven Gardon and Schmidt-Boelter sensors.
  • Long Transducer Life And Signal Stability are enhanced by the massive body of OFHC copper.
  • Protection Against Rough Handling in mounting is provided by a stainless steel flange when specified.
  • Signal Integrity is protected by the use of welded connections, stranded lead wire with braided copper shielding and Teflon insulation firmly secured in the transducer body with strain relief to ensure resistance to rough handling and stray signals.


  • Removable Window Attachments, with the standard sapphire or optional window materials, are available to limit the basic transducer to measurement of radiation heat flux only.
  • View Restrictor Attachments are available to limit the angle of view for the basic transducer to 60°, 30°, 15°, or 7° for narrow view angle measurements.
  • Direct Reading Heat Flux Indicators Models H-201, H-203, and H-204 are available for direct digital readout in any heat flux units from any linear heat flux transducer input. An amplified analog output is provided on some. Ask for Bulletin.
  • Body Temperature Thermocouple measurement can be provided by an optional copper/constantan 24 AWG solid conductor thermocouple, with TIG welded junction and Teflon insulated duplex wire.

The basic transducer may be selected with either of four mounting configurations and with or without provisions for water cooling of the transducer body.  The listed radiometers are provided with gas purging to keep the radiation-transmitting window clean. When the purge provision is included, the window is installed internally and is not an accessory. Basic transducers can be converted to unpurged radiometers by addition of a window attachment, but the standard purged radiometers cannot be converted to basic transducers.  

Standard Mounting Configurations Illustrated Below.  There is the smooth body with flange, the threaded body with flange, the smooth body without flange, and the threaded body without flange.  All mounting flanges are 1.73″ dia. with 0.150″ dia. mounting holes equally spaced on a 1.375″ dia. bolt circle.  Water-cooling tubes (when specified) and gas purge tubes are 1/8″ dia.  SST. All tubes are 4″ long.  (Other tube diameters, lengths, and fittings are available.)  All threaded bodies have 1-12UNF-2A threads. 

Smooth body with flangeThreaded body with flangeSmooth body, no flangeThreaded body, no flange
Model No. 64-xx-16 

Basic, uncooled 

Model No. 64-xx-17 

Basic, uncooled  

Model No. 64-Xx-14 

Basic, uncooled 

Model No. 64-xx-15 

Basic, uncooled 

Model No. 64-xx-20 

Water cooled

Model No. 64-xx-21 

Water cooled 

Model No. 64-Xx-18 

Water cooled 

Model No. 64-xx-19 

Water cooled 

Model No. 64P-xx-24 

Radiometer, Gas  purged, cooled 


Model No. 64P-xx-25 

Radiometer, gas purged, cooled 


Model No. 64P-xx-22 

Radiometer, gas purged, cooled 


Model No. 64P-xx-23 

Radiometer, gas purged, cooled 


Optional Features  

Optional features include window attachments, water cooling provisions, or thermocouples for body temperature measurement.  Water-cooling should be specified if the uncooled transducer is expected to reach above 400°F.  The gas purging provision should be included on radiation transducers that are to be used in a sooty environment.  The purge is designed to pass rigid NASA performance tests with fuel-rich oxy-acetylene flames directed towards the window at close range. 

Window Attachments 

may be added for elimination of convective heat transfer, thus making the transducer a radiometer or radiation heat flux transducer.  Sapphire is the standard window material.  A broad selection of other materials is available per the list on page 4.  Standard view angles available are:  90°, 120°, and 150°.  Window attachments are removable and replaceable by the user.  When the window is used the sensitivity of the basic transducer is reduced to a nominal fraction of the original as follows:  90°, 43%; 120°, 64%; and 150°, 79%.  Thickness of the attachment varies with view angle and sensor type from1/16″ to 3/8″. 

View Restrictor Attachments for limiting the area viewed or seen by the sensor are available for making spot radiation or remote temperature measurements.  Attachments may be ordered with or without water-cooling and with or without an additional calibration with the attachment in place.  Flanged transducers attach to the back. A 1/4″-20 UNC set screw holds unflanged transducers and provides tripod mount access. 

  • Standard Ranges Available: Full scale design heat flux level: 4000, 3000, 2500, 2000, 1500, 1000, 500, 250, 200, 100, 50, 30, 25, 20, 15, 10, 5, 2, 1, 0.5, 0.2 Btu/(ft²s).  (Custom ranges available.) 
  • Output Signal: linear output, 10 millivolts nominal at full range. 
  • Maximum Allowable Operating Body Temperature:  400 °F. 
  • Overrange Capability: to 150% range for 2-1000 Btu/(ft²s) ranges. 
  • Maximum Non-Linearity: ±2% of full range. 
  • Repeatability: ±1/2% 
  • Calibration Expanded Uncertainty: ±3% for ranges to 250 Btu/(ft²s), coverage factor k=2, for approximate 95% confidence level. 
  • Sensor Absorptance (Hemispherical): Gardon gages, .92, nominal, from 0.6 to 15.0 µm.  Thermopiles, .95, nominal, from 0.6 to 15.0 µm. 
  • Spectrum Transmitted By Sapphire Window (When used): 85%nominal from 0.15 to 5.0 µm.  Other window materials are optional. 
  • Lead Wire:  24 AWG stranded copper twisted pair, Teflon insulation over each, braided copper shield, Teflon jacket overall, 36″ standard length with stripped ends. (The optional body thermocouple wire is 24 AWG Teflon/Teflon insulated duplex solid conductor.) 
  • Time Constant: (63.2% response to a step radiant heat Input)
    • 250 to 4000 Btu/(ft²s): less than 50 ms
    • 50 to 200 Btu/(ft²s): less than 100 ms
    • 2 to 30 Btu/(ft²s): less than 250 ms 
  • Sensor Type: (Standard, options available)
    • 5 to 4000 Btu/(ft²s): Gardon Gage (Except S-B for 64P-5 models)
    • 0.2 to 4 Btu/(ft²s): Schmidt-Boelter (Schmidt-Boelter sensors are also available as an option from 5 to 100 Btu/(ft²s) ranges. 
  • Nominal Impedance: (with standard leadwire)
    • Less than 10 ohms on Gardon Gages
    • Less than 250 ohms on Schmidt-Boelter Gages. 
  • Heat Capacity of Uncooled Units: Energy that can be absorbed by transducer in an adiabatic installation (defined as all surfaces perfectly thermally insulated except for 1-inch diameter sensor face) before exceeding the 400 °F maximum body temperature limitation: Model without water cooling provisions:  6.2 Btu, Models with water cooling provisions but without water: 4.2 Btu 
  • Maximum Purge Gas Pressure: 150 psi over ambient 

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