Landcal Blackbody Source
Type P80P
Operating Instructions
Page 6
6.0
USING THE SOURCE
6.1
Introduction
The P80P has been designed to create an enclosure of uniform temperature, ideal for the calibration of radiation
thermometers. The cone point of the cavity is placed in the area of minimum gradients within the source. When
calibrating radiation thermometers the target size requirements of the thermometer should, whenever possible, be
fulfilled by the cone. If the thermometer views the walls of the cavity results of greater uncertainty will be achieved.
6.2
Measuring sensor (Platinum resistance thermometer) - if supplied
Provision has been made to measure the temperature of the target block using a Platinum resistance thermometer
which can be inserted from the front of the source into the cavity. When placed in the measuring position the junction
lies in the same plane as the cone point, but is approximately 40mm/1.5in below. The temperature of the source as
measured by the sensor agrees with the cone point radiance temperature to within ±0.5K (1°F).
The output from the sensor should be measured on an indicator or digital voltmeter having a resolution of 0.1°C.
This is the recommended way to obtain the true temperature of the target cavity. The temperature indication on the
controller should not be used as an accurate measurement of target cavity temperature.
6.3
Operation of the source at below ambient temperature
The LANDCAL Blackbody Source type P80P uses Peltier modules to cool the source to temperatures as low as -10°C/
15°F. However the modules are rated as only achieving a 30°C (55°F) below ambient cooling effect. This means that
the final cooling temperature achieved and the length of time it takes to achieve this temperature will be dependent
on the ambient temperature. For example if the source is operated in an area with ambient temperature of 30°C the
minimum achievable temperature will be approximately 0°C.
Condensation may occur inside the cavity when the source is used at temperatures below ambient and above 0°C. This
will in no way affect the operation or performance of the source. At temperatures below 0°C this condensation will
freeze and form a thin layer of ice. This ice formation will not affect the performance of the source. If prolonged
operation (say longer than 8 hours continuous) at temperatures below ambient are anticipated, it is recommended that
the cavity is purged with a dry inert gas such as Nitrogen to prevent entry of water vapour into the cavity.
