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Medusa 510/511 Series Iss.11 – 07/12
MODE OF OPERATION
ITS-90 FIXED POINT CALIBRATION
The ITS-90 fixed point function of the Medusa is well suited for fast, convenient, mess free calibration of
thermometers to uncertainties as low at 0.001°C.
The special cell is placed into the Medusa calibration well.
The equipment incorporates a timer which can change temperatures to allow MELTING or FREEZING of a Cell.
Once initiated the Cell can be arranged to be on the melt plateau during the day and automatically frozen and bought
back to the melt plateau overnight.
It works this way:-
The Medusa automatically switches on some 2 to 3 hours before the working day starts and gets the cell onto its melt
plateau. The indicator tells the user on their arrival in the morning that the melt has begun and calibration can
commence.
If left unused the melt continues to 6 to 12 hours and probably during the night the timer switches the apparatus off
to re-freeze the cell, the cycle is repeated each day, giving the user the fixed point all day, every day without
attention except to occasionally clean the fan filter if it becomes clogged with dust.
The Medusa works by having a controller which is set about 1°C above the fixed point which is inside the apparatus It
has an indicator with a thermometer which is used to monitor the state of the fixed point cell. It is also fitted with a
timer to automatically switch on and off the apparatus.
Indium, Tin Lead and Zinc Fixed Points all look the same, being an ingot of pure metal placed in a graphite crucible
which, to keep dirt, moisture and air out are sealed, usually in quartz glass. To avoid the use of quartz glass the
graphite crucibles are sealed into metallic containers without contamination of the pure ingot inside the crucible.
On power up the timer is set to run at setpoint 1 for 20 hours at setpoint 2 for 4 hours.
METAL BLOCK BATH
The metal block bath function of the Medusa is well suited for fast, convenient, mess free calibration of temperature
sensors.
The Medusa metal insert is placed into the calibration well.
The thermometers under test are placed into suitable holes in metal insert, see accessory page. A calibrated
reference probe should be placed into the insert and the actual temperature can be read from the temperature
indicator.
For traceable calibration the actual value of the insert temperature should be recorded along with the values from the
sensors under test.
