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Technical Notes
#63  Potential Errors Caused By Ambient Temperature Effects63
If the ambient temperature of a temperature control installation changes significantly, there are several sources of potential inaccuracies that can be minimized by attention to installation details.
Reflective Errors: For situations in which the IRt/c itself is at the same temperature as ambient sources of radiated energy, the patented design of the IRt/c will compensate for reflected energy and maintain accuracy. See Tech Note #64 for discussion
If the ambient source of radiant energy is too hot for an uncooled IRt/c, the principal precaution to employ is to take advantage of the generally specular characteristics of reflected energy. The term specular means "mirror-like," and reflective errors can be minimized by avoiding viewing angles in which the surface can reflect a hot source.
Leakage Current Effects: the readout device generates appreciable leakage current, there is a potential inaccuracy due to small shifts in IRt/c impedance with ambient temperature. For example, if the readout device leakage current generates an offset of 100F (55C), which is calibrated out at installation, and sometime later the ambient temperature for the IRt/c is much hotter, the IRt/c impedance might be a few percent different than it was at calibration. Accordingly, the temperature offset caused by the leakage current will also shift by a few percent. If the original offset requirement is 100F (55C), then a shift of ~ 5% impedance will cause a shift in reading of ~ 5F ( ~ 3C). In general, always choose a readout device with the lowest leakage current available to avoid this potential problem. See Tech Note Nos. 14,16, 37, and 56 for further discussions of leakage current effects.
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