Landcal Blackbody Source
Type P1600B2
User Guide
Page 18
7 Calibration of Radiation Thermometers
7.1 Preparation
The furnace control setting is usually the normal working temperature of the
thermometer to be tested.
The target temperature is that indicated by the standard thermocouple in the
‘measuring’ position.
A convenient method of holding a fixed system radiation thermometer is to
mount a holder horizontally onto an optical bench assembly having vertical and
transverse vernier adjustments. Portable radiation thermometers are usually
hand held.
Position the holder on the optical bench at the required distance between target
and thermometer. Adjust the vernier screws to align the holder correctly.
To reduce unnecessary heating from furnace radiation, it is recommended that
a heat shield be placed between furnace and holder, and only removed during
periods when outputs from the thermometers are being measured. Ensure
that the shield is away from the sighting tube so that furnace conditions are not
altered when it is removed.
7.2 Thermometer Calibration
When soaked conditions have been obtained, place the thermometer in the
holder, remove the heat shield and measure the thermometer output on the
measuring apparatus. Immediately afterwards, measure the output from the
‘measuring’ thermocouple.
Refer to the relevant calibration tables to convert both outputs into temperature,
then compare the values.
7.3 Accuracy of Calibration
The source is designed to enable the accurate calibration of LAND radiation
thermometers. The accuracy that can be achieved by using the source is
dependent on:
1) The uncertainty of calibration and resolution of the measuring
thermocouple
2) The emissivity of the source
3) The resolution of the thermometer under test
The uncertainty specified on the calibration certificate issued by the calibration
laboratory will be a function of:
1) The capabilities of the calibration laboratory
2) The type of thermocouple under test
3) The temperature range covered
Typical values for uncertainty are ±1K / ±2°F up to 1100°C / 2000°F and ±2K
/ ±4°F over the range 1100°C to 1600°C / 2000 to 2900°F. A value of ±0.1K
to ±1K / ±0.2°F to ±2°F must be specified for the resolution, depending on the
type of measuring equipment used.
