Page 12 of 24
Pegasus R Iss.07 – 08/13
TUTORIAL: THE USE OF A PEGASUS 'R' CALIBRATED SOURCE TO
CALIBRATE RADIATION PYROMETERS
INTRODUCTION
The Pegasus 'R' is designed as a source for the calibration of radiation pyrometers over the range 200 C to 1200 C.
Most users of radiation pyrometers are unfamiliar with the procedures for calibration and the tutorial below is
intended to help new users. It is meant only as a guide and not as a gospel.
Setting up the Source
The Pegasus 'R' comprises a small tube furnace of diameter approximately 35mm.
Separately is a 3 part assembly plus a thermocouple which assembles into the tube furnace as diagram 970-20-02.
The thermocouple, as can be seen from diagram 970-20-01 has a right-angled bend in the ceramic sheath at its tip.
This bend is to facilitate insertion of the thermocouple tip into the cavity at the base of the black body target (970-01-
02) see diagram 970-20-02. (The internal wires of the thermocouple may be visible at the bend in the ceramic but this
is normal - the thermocouple is not broken). Once the tip of the thermocouple has been situated in the cavity of the
target, the target is assembled into the well of the Pegasus. The insulation piece 970-01-03 (as shown in diagram 970-
20-02) is then assembled into the Pegasus with the thermocouple alongside (which sits in the groove in the insulation
piece).
The thermocouple is connected to an indicator situated on the front of the Pegasus 'R' as shown on figure 1. The size
and shape of the insulation and the position of the thermocouple are all important and if the assembly is modified, the
calibration certificate may become invalid. Having assembled the Pegasus 'R' a temperature is set (see commissioning
later in this document).
3 steps are required to obtain the radiance temperature of the source:
a) Set the required temperature on the controller.
b) Take the reading on the indicator.
c) Add or subtract the correction from the calibration sheet, (correction may be considered to vary linearly between
calibration points) to obtain the radiance temperature.
For example: Say 1000 C is the controller set point. The indicated value might be 991 C. If the calibration certificate
is consulted, the radiance temperature is noted to be 10 C lower than the indicated value i.e. 981 C.
Using the Source
The simplest and least accurate method of using the source is to set its temperature, calculate its radiance
temperature as described above and point the radiation pyrometer at the source.
More usually a small optical bench is built to accurately hold the source and pyrometer enabling proper alignment to
take place.
Requirements for an Optical Bench (See Figure 19071)
An optical bench can be a very expensive piece of apparatus of precision ground components, or a very basic piece of
equipment built onto a wooden board.