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measurements, without any field calibration, for the lifetime of the instrument. The Calisto and
Calisto 2 detection cells take validated measurements for hydrogen and carbon monoxide (Calisto 2
only) every three hours. Validated measurements are continuously zeroed to guarantee long-term
stability and low-level detection accuracy. A continuous measurement of the hydrogen concentration
is also performed for both monitors, to indicate any variation in hydrogen concentration which may
occur between validated readings.
Vacuum tolerance is made possible because of the intrinsic properties of the capillary tubing used
to form the gas sample and because the oil circulating and conditioning systems inside the
Calisto/Calisto 2 can both sustain vacuum. As a result, no action is required to protect the monitor
if the transformer is put under vacuum for degassing purposes.
Precise moisture measurement is achieved using a capacitive thin-film sensor immersed directly
in circulating oil to continuously measure dissolved moisture. Moisture content can be reported in
parts per million (ppm), %RS at 25
o
C (77°F) or %RS at a specific transformer temperature using the
Expert Series Calisto Precision Oil Temperature Probe.
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