User Guide
Landcal Blackbody Source
Type R1200P
Page 9
6 Using the Furnace
6.1 Introduction
The furnace has been designed to create a target of uniform temperature with
a high emissivity at short wavelength for calibrating mainly silicon cell and
germanium detector radiation thermometers. The target is a conical cavity at
one end of a hollow cylinder, and the thermometer views the target along the
axis of the cylinder.
The cone plays an important part in establishing uniformity of radiation emitted
by the target, and when calibrating radiation thermometers the target size
requirements must be met by the cone. If the thermometer target size is so big that
the walls of the cylindrical block are viewed, a less accurate calibration will result.
6.2 Measuring thermocouple/indicator
A thermocouple embedded in the conical target is used to measure the
temperature. The “TARGET” digital indicator on the side of the furnace displays
the temperature measured.
Agreement between the thermocouple measurement and a reference standard
radiation thermometer should be better than ±10°C.
The errors are repeatable, and a correction curve can be obtained with a
Certificate of Calibration for the source. A UKAS (United Kingdom Accreditation
Service (National Measurement Accreditation Service) Certificate of Calibration
is available from LAND Instruments International.
6.3 Control thermocouple/controller
A second thermocouple is used to control the furnace temperature. As part of
the control strategy, this thermocouple is situated close to the furnace heating
elements. As a result the control thermocouple is actually hotter than the
measurement thermocouple.
The setpoint on the furnace controller will invariably need to be set higher than
the desired target temperature. The difference between setpoint and target
temperature can be evaluated for a given furnace by experiment, always using
the TARGET indicator as a measure of target temperature.
6.4 On-site use
The source is portable, so can be used either in the laboratory where the
radiation thermometers are brought to the source for checking, or taken on-site
where the source is used close to the thermometer installations.
Due to the lightweight construction of the source damage may occur if it is
mishandled. The source should always be treated with respect and handled
in the same way as any other scientific instrumentation. Following the
precautions below will extend the life of the source.
