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User Guide
Landcal P80P
Calibration Source
6 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.
The length of time taken to reach a required temperature below ambient can
be reduced by inserting an insulated plug into the front of the cavity. This
plug should be removed at least 15 minutes before any readings are taken, to
allow the source temperature to stabilise.
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.