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5.1x00a0;The application of HFTs and temperature sensors to building envelopes provide in-situ data for evaluating the thermal performance of an opaque building component under actual environmental conditions, as described in Practices and . These applications require calibration of the HFTs at levels of heat flux and temperature consistent with end-use conditions.
5.2x00a0;This practice provides calibration procedures for the determination of the heat flux transducer sensitivity, S, that relates the HFT voltage output, E, to a known input value of heat flux, q.
5.2.1x00a0;The applied heat flux, q, shall be obtained from steady-state tests conducted in accordance with either Test Method , , , or .
5.2.2x00a0;The resulting voltage output, E, of the heat flux transducer is measured directly using (auxiliary) readout instrumentation connected to the electrical output leads of the sensor.
Note 1:x00a0;A heat flux transducer (see also Terminology ) is a thin stable substrate having a low mass in which a temperature difference across the thickness of the device is measured with thermocouples connected electrically in series (that is, a thermopile). Commercial HFTs typically have a central sensing region, a surrounding guard, and an integral temperature sensor that are contained in a thin durable enclosure. Practice , Appendix X2 includes detailed descriptions of the internal constructions of two types of HFTs.
5.3x00a0;The HFT sensitivity depends on several factors including, but not limited to, size, thickness, construction, temperature, applied heat flux, and application conditions including adjacent material characteristics and environmental effects.
5.4x00a0;The subsequent conversion of the HFT voltage output to heat flux under application conditions requires (1) a standardized technique for determining the HFT sensitivity for the application of interest; and, (2) a comprehensive understanding of the factors affecting its output as described in Practice .
5.5x00a0;The installation of a HFT potentially changes the local thermal resistance of the test artifact and the resulting heat flow differs from that for the undisturbed building component.
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