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  CB32 Convection/ Radiation Sensor 

Based on our BF sensor technology, the CB32 has 2 sensing circuits. One circuit is coated with a high emissivity black paint.  The other circuit has a highly reflective coating.   This design allows for the user to differentiate relatively between the convective and radiative components of heat flux. 

Operating Principles

.Each CB32 consists of two balanced, independent heat flux sensing circuits, one that is entirely under black surfaces and one that is entirely under reflective surfaces. A silvered polyester coating provides the reflective surfaces, and high temperature, high emissivity, black paint provides the black surfaces. The black squares on the sensor will absorb most of the incident radiation whereas the reflective areas will absorb a significantly smaller amount. Both black and reflective areas will pick up convective heat transfer almost equally.  The alternating nature of the chessboard pattern on the CB32 should provide some spatial averaging.  Because there are no perfect broadband reflectors, the reflective areas of the chessboard will always absorb some radiation, which makes disentangling the convection and radiation signals more complex.  That said, the chessboard design still offers valuable empirical data for relative convection/radiation ratios. The analysis of the chessboard sensor by Vatell Corporation is detailed below.  All calibrations are done with repeatable radiation tests using standardVatell calibration equipment that is regularly calibrated to standards traceable to the National Institute of Standards and Technology (NIST).

First a baseline calibration is completed.  To compare the two circuits on each board, the entire surface is coated with the black paint, to provide equal, reliable, and repeatable results. The average sensitivity of an individual circuit is 21.2 mV/W/cm², with a standard deviation of 1.6 mV/W/cm². The average difference between two circuits on the same boards was only 1.0 mV/W/cm².

Next a ratio of the emissivities of the two surfaces was computed. First radiation calibrations were run with the entire surface of the sensors being silver.Then the sensors were painted completely black and the calibrations were redone.The resulting sensitivity ratios averaged 6.6; that is the black surface absorbed 6.6 times as much radiation as the silver surface.Because the emissivity of the black paint has been computed to be 0.94 at an incident wavelength of 2 microns, the emissivity of the silver surface can be approximated at 0.14.

Finally, the sensitivity ratio between silver and black on the same sensor was measured to test for lateral heat transfer.In this case the sensors are painted in their chessboard configuration and the calibration is performed on both circuits of the sensor. In this case the average ratio was 4.2, indicating that there is some degree of lateral heat transfer on the sensor. Despite the lateral heat transfer however, the radiation signal from the black surface is still much higher than that from the silver surface.As such, the chessboard design should allow for good empirical measurements to be made to test the relative amounts of convection and radiation.

Specifications:

Area	3.96 cm x 8.25 cm
Black Sensing Areas	16 locations that are each 1cm x 1cm
Reflective Sensing Areas	16 locations that are each 1cm x 1cm
Black Total Sensitivity	15 mV/(W/cm²)
Reflective Total Sensitivity	4 mV/(W/cm²)
Sensor Thickness	0.25 mm
Max. Temperature	170 °C