Explanations - Fluke 4180 Technical Manual

4180, 4181
Technical Guide

Explanations

u1: Calibration Uncertainty
u2: Stability (long term)
u3: Uniformity
u4: Noise
u5: Display Resolution
u6: Readout Resolution
u7: Ambient Temperature
u8: Noise
u9: Atmospheric Losses
u10: Angular Displacement
u11: Background
Temperature
u12: Spectral Variation
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This is the uncertainty provided by the IR calibrator manufacturer. It follows a
normal distribution.
This is the contribution from possible drift of the IR calibrator during its calibration
interval. It is obtained from historical data of the IR thermometer model. It is
expected to follow a normal distribution since it is likely affected by a combination
of factors.
This is the contribution from the uniformity of the IR calibrator. The IR thermometer
under test has a spot size determined by size of source testing. The contribution of
this energy is evaluated against the IR calibrator's uniformity specification. Since
the uniformity specification is given as a plus and minus tolerance, it is expected to
follow a rectangular distribution.
This is the contribution from noise of the IR calibrator. It is based on measured data
and follows a normal distribution.
This is the contribution from quantization error of the IR calibrator readout. It has a
rectangular distribution.
This is the contribution from quantization error of the IR thermometer readout. It
has a rectangular distribution.
This is the contribution from the possible range of ambient temperature, which
is given limits of 23 °C ±4 °C. It is based on information provided by the IR
thermometer manufacturer. Ambient temperature is expected to more often be
closer to 23 °C so a normal distribution is used.
This is the contribution from noise of the IR thermometer. It is based on
measured data and follows a normal distribution.
This is the contribution from differences in atmospheric attenuation between
calibration of the calibrator and calibration of the IR thermometer. It is based
modeling of standard atmospheric data. It is based on a number of factors, so
a normal distribution is used.
For this calibration, the angle is controlled within 5° of normal. According to the
IR calibrator manufacturer, this could cause a ±0.0005 change in emissivity.
This tolerance is converted to a temperature uncertainty for the uncertainty
budget. It is expected to follow a rectangular distribution.
This is the contribution from changes in temperature of surfaces facing the
plate. The plate reflects some of the incident background energy. Since the
laboratory walls are the main surface facing the plate, it is based on their
temperature variance. This temperature is limited by a tolerance during
calibration, so it follows a rectangular distribution.
This is the contribution from the uncertainty in the spectral response of the IR
thermometer measuring the plate. Since the plate is not a perfect gray body,
the spectral response of the emissivity of the IR calibrator's surface must be
taken into account. The contribution from the spectral response is based on
information given by the IR thermometer manufacturer. The spectral response
of the paint is based on emissivity data from the IR calibrator manufacturer.
These two data are modeled mathematically to determine the effect of the
spectral response uncertainty. This uncertainty is based on a number of
factors, so a normal distribution is used.