• Multiple Space Flight Qualified Options Available
• Example 24 Series Product Shown: Model 20850
• Models are configurable with standard options:
  • Heat flux ranges of 5 BTU/ft²s to 800 BTU/ft²s
  • Total heat flux transducer and radiometer with selectable window material
  • Contact us for full product selection options

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64 Series transducers are of two basic sensor types, the Gardon type sensor, standard in the ranges from 5 to 4000 Btu/(ft²⋅s), and the Schmidt-Boelter thermopile type sensor, standard in the 0.2 to 4 Btu/(ft²⋅s) ranges.  In 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 surface.  The 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 rate.  No 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/(ft²⋅s).  It can be optionally specified up to 100 Btu/(ft²⋅s). 

 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. 

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Our fine wire thermocouple probes provide a rugged mounting method for inserting ultra-fine wire thermocouple junctions for precise rapid response gas temperature measurements. These probes are designed for applications such as air compressors, internal combustion engines, and wind tunnels where vibration, shock, or bending conditions in the environment preclude use of ordinary fine wire thermocouples. 

Thermocouple wires as small as 0.0005 inch are made capable of extended life by use of a unique fine wire mounting technique. Large (.010 – .013 inch diameter) thermocouple wires are swaged with magnesium oxide insulation within a corrosion resistant metal sheath. The ends of the wires are flattened and 0.005 inch dia. holes are drilled through the flattened ends. Each fine wire is then welded to the appropriate large wire, coiled around it, passed through the drilled hole and fusion welded at the hot junction. The welds to the large wire are then encapsulated in high  temperature ceramic cement. With this construction, the fine wires can be bent or vibrated without weakening the welded connection of the fine wire at its weld to the large wire. This feature assures a longer life for the fine wire thermocouple than would a conventional welded connection. 

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The standard thermocouples described in this brochure satisfy a broad range of requirements; however, when special configurations or thermo-elements are required, 

The fast response thermocouples shown in this quick introduction are only one of the lines of thermal sensors. Heat flux transducers for the measurement of total and radiant heat flux are widely used by government agencies and many industries worldwide. We have been engaged in the design, development, construction and analysis of thermal instruments since 1970, and maintains a highly qualified professional staff and modern facilities that are available to help fill the customer’s thermal instrumentation needs. 

Thermocouple  Designs 

There are three (3) basic thermocouple designs in our fast response thermocouple line. Each has unique advantages, as outlined below. 

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Our tantalum sheathed thermocouple probes with compacted beryllium oxide (beryllia) insulation are designed for very high temperature measurements to 2,300°C. These probes are among the highest temperature capability choices for thermocouple probes. They are often used even up to the melting point of the materials — approximately 2,550°C for beryllia- for very short duration one-shot R&D measurements, simply because there are few other choices for those measurements. Of course, careful evaluation of the measurement results is in order for those cases. The tantalum sheath is tough with good ductility before use at high temperature but can become brittle after exposure to high temperature in some environments. Tantalum is subject to rapid oxidation above 285°C in an oxidizing environment but due to the very high melting point may be used to 2,482°C in a vacuum, high purity hydrogen, or high purity inert gas. 

Hot Junction Style Options 

Grounded  Style “G”
Ungrounded  Style “U”
Exposed  Style “E” 
Half-Shielded  Style “H” 

Type E, J, and T have 304 SST sheath. 
Type K and Type N have lnconel 600 sheath. 
Internal wire sizes for probe diameter of 0.010″- 0.0015; 0.020″- 0.004; 0.032″- 0.005; 0.040″-0.007; 0.063″-0.010; 0.125″-0.018; 0.188″- 0.025; 0.250″- 0.036. 

Mounting Fittings: Stainless steel compression-type mounting fittings are recommended for mounting these thermocouples. Welding’ or brazing of mounting fittings to the tantalum sheath is not recommended. Adjustable depth fittings have a lava gland (1000°C) for use to 5000 psi (200°C). Non-adjustable fittings have stainless steel ferrules for up to 10,000 psi. Pressure limits are lower if the fittings are at high temperature. Fittings in higher temperature alloys are available. 

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Our co-Axial thermocouple probes are coaxial thermocouples consisting of a small wire of one thermocouple material coated with a .0005″ thickness of a special ceramic insulation of high dielectric strength swaged securely in a tube of a second thermocouple material.  The insulation resistance between the wire and the tube is effective to more than 1500°C at steady state (over 1700°C for transient temperatures).  The thermocouple junction is formed by vacuum depositing a metallic coating of one to two microns thickness over the sensing end of the probe, forming a metallurgical bond.  A variety of mounting configurations and transition pieces for lead wire connections may be installed on the coaxial probe assembly. 

Fast Response Metal Wall Surface Temperature Measurements 

Our co-Ax surface thermocouple probes offer microsecond response times in the measurement of rapidly varying metal wall surface temperatures such as encountered inside combustion chambers, gun barrels, bearings, die casting dies, and apparatus for heat transfer studies. The through-the-wall mounting technique for the Co-Ax thermocouples lends itself to measurement of wall surface temperatures where it is important not to disturb the surface geometry, such as rocket nose cones, cannon projectiles, or wind tunnel models.  The wall temperatures measured in this way are often used to compute pulses of heat flux absorbed by the surface, such as aerospace models installed in shock tunnels.  The probes may also be used for measurement of internal wall temperatures where the location of the sensing element must be precisely known, such as in conduction heat transfer studies. 

The Co-Ax surface thermocouple is ideal for the applications described above because the thermal junction is formed within a one or two micron thickness at the end of the probe, thus allowing positioning of the junction within one or two microns.  The probe can be installed through an accurately drilled hole in the test surface such that the junction forms a continuous part of the test surface, or it can be installed in a “blind” hole in the test wall to measure internal temperature at a precisely known location. 

Fast Response Surface Heat Flux Measurements 

Surface heat flux is computed from the continuous or time sampled measurement of the true metal wall surface temperature versus time using computation methods reported by a number of authors since the 1950’s, several of which are described by Beck, Blackwell, and St. Clair in Inverse Heat Conduction, Wiley Interscience, New York, 1985.  The fast response capability, along with the subminiature probe diameters, allow the measurement of heat transfer rates at many points on a very small metal model in just a few milliseconds of test time.  This approach can make substantial cost savings in hypersonic tunnel heat transfer research programs. 

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Our Furnace Heat Flux Probe, Model GTW-xx-20221, is a water cooled probe with a diameter of one inch and length of four feet, containing a Schmidt-Boelter Heat Flux Sensor and is used for insertion into an industrial furnace for the direct measurement of heat flux.  The probe produces a self-generated millivolt signal which is directly proportional to the heat flux component under measurement.  The probe can be used for measuring total heat flux (convective plus radiated) or with a minor adjustment by the user can be used to measure only radiated flux. The heat flux probe is calibrated traceable to NIST standards and has a calibration accuracy of ±3%.  Probes up to 48” long are shipped in a foam lined carrying/storage case suitable for shipping or travel to site. 

The probe is typically placed through a furnace test or observation port in an environment of up to 1600 °C and the self-generated EMF is read directly on the H-201 Heat Flux Indicator or another millivolt readout device.  Each probe is designed to produce a linear output from 0 to nominally 10 mv over the heat flux range specified by the user. 

The probe can be used to measure total heat flux (convective plus radiated) or the calcium fluoride window attachment can be field installed for blocking convective flux when it is desired to measure only the radiated flux.  With the window installed, an inert gas is usually supplied to the purge port which supplies a radial flow across the window keeping it clean of soot.  The window can be removed, as in the mode for measuring total flux, and by supplying a purge flow will eliminate the convective flux for a radiated flux measurement.  This mode has the advantage of measuring the total and radiated flux alternately by turning the purge on and off without removing the probe from the furnace.  When used in this manner, a small tare correction factor is used with the radiant flux data. 

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