We want to talk to you about your heat flux application.  Contact us.

Phone: (540) 961-3576     Fax: (540) 953-3010      e-mail: mkt@vatell.com

Also known as: Gardon Gage, Circular Foil Gage, Calorimeter or Radiometer

specification sheet also available in PDF file

Thermogage Advantages
· Linear output, unaffected by Temperature
· Wide Range of Sensor and Housing Combinations
· Rugged

There are a wide variety of housing options to meet your application's geometric requirements, including custom designs.  Housing options include:

Transducer specifications:

Operating Principles:
The transducer is a differential thermocouple measuring the temperature difference between the center and the circumference of a thin circular foil disk.  The disk is bonded to a circular opening in a cylindrical heat sink. The standard foil is made of Constantan and the heat sink is copper. These materials produce an output which is directly proportional to the absorbed heat flux. These transducers are generically called Gardon gages or circular foil gages.

In its basic form, the Thermogage will measure both radiation and convection. To screen out convection, Vatell also offers a radiometer configuration, our 9000 series Thermogages, in which a window of IR transparent material is placed in front of the foil.

Response Time vs. Sensitivity:
The smaller the diameter of the foil, the faster the response time of the transducer, but the lower its sensitivity. Response times (0 to 95% rise time) can be as low as 20 ms for small diameter foils. If both fast response time and high sensitivity are required, an amplifier can be used, such as Vatell's  AMP-11 , which can provide a gain of up to 1000.

Transducer Coating: The factory applied base coat is high temperature black paint. It is selected for temperature stability and flat spectral absorbancy.  It has an emissivity of 0.95.  Other coating options include colloidal graphite, black velvet, and soot.

Output:
All transducers  are designed for 10mV maximum output.  Units may  be overdriven to 15mV without damage or loss of calibration.  Overdriving past 15mV will not harm the unit, but the calibration is not accurate in that range.  Overdriving beyond 20mV will damage the gage.

Calibration:
A continuous x-y calibration curve graph and NIST traceable calibration certificate are furnished with each transducer.
For further information on Vatell's strict calibration procedures please see: Vatell Calibrations

1000 Series: Water-Cooled

Sample Drawings:
1000 Series Water Cooled   PDF

Water-cooled circular foil heat flux gages are designed for applications with longer measurement times. The water removes the absorbed heat continuously.
Water-cooled units and conduction cooled units have identical specifications except that mounting conditions for the water cooled units are not critical, and exposure may be for an indefinite duration.

Housing  Sizes
minimum standard diameter of 0.312 inches
minimum standard length 1 inch

Ranges for Full Scale Output (10mV) :
Low end: 0 to 5 Watts/cm²
High end: 0 to 5000 Watts/cm²

Transducer Calibration Accuracy: ±3%

Repeatability: 1%

Sensitivity: Up to 2 mV/(W/cm²)

2000 Series: Conduction-Cooled

  

Sample Drawing:
2000 Series Conduction-Cooled   PDF

Conduction-cooled circular foil heat flux gages are designed for applications with short measurement times in which the total amount of heat absorbed by the gage will not raise its temperature beyond 200°C.

Housing  Sizes
minimum standard diameter of 0.187 inches
minimum standard length 0.5 inch

Ranges for Full Scale Output (10mV) :
Low end: 0 to 5 Watts/cm²
High end: 0 to 5000 Watts/cm²

Transducer Calibration Accuracy: ±3%

Repeatability: 1%

Sensitivity: Up to 2 mV/(W/cm²)

9000 Series: Radiometer


Pictured is a water cooled gas purged radiometer

Sample Drawing:
9000 Series Radiometers     PDF

When constructed as a radiometer, convective heat flux is blocked from reaching the sensor by a window.  This allows only radiation to be measured.

Customers commonly use a 1000 series to measure the total heat flux and then use a 9000 series to measure the radiative component.  This allows for an understanding of the convective and radiative components that make up the total heat transfer

The material used in the window will determine the radiation bandwidth that reaches the sensor.  The window is placed directly on the water-cooled copper surface to minimize its heating.

Window Material (9000 series only):
 
Window Material % Transmission Spectral Limit (microns)
Quartz 90 0.3 - 3
Sapphire 85 0.3 - 5
Zinc Selenide 70 0.6 - 17

Standard window materials listed, others available on a custom basis

Housing  Sizes
minimum standard diameter of 0.625 inches
minimum standard length 1 inch

Ranges for Full Scale Output (10mV) :
Low end: 0 to 10 Watts/cm²
High end: 0 to 1000 Watts/cm²

Transducer Calibration Accuracy: ±3%

Repeatability: 1%

Sensitivity: Up to 1 mV/(W/cm²)


Other Technical Information

Thermogage Use        MS Word     PDF
Thermogage Installation      MS-Word95(24KB)       PDF(13KB)

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