HygroCal100 User’s Manual
Michell Instruments
1
INTRODUCTION
1 INTRODUCTION
The HygroCal100 Portable Humidity Validator enables quick and convenient generation
of a known humidity condition at ambient temperatures.
The chamber allows seven relative humidity probes of various diameters to be installed
into the chamber simultaneously. The probes can be powered directly from the
HygroCal100, and monitored via the intuitive touch screen user interface.
This interface also allows the programming of a calibration profi le, so that a series of
humidity values can be generated and held automatically for a set time period. The
readings from all probes under test and the built-in reference can also be logged for
completely autonomous operation.
1.1 Operating Principle
The Validator operates on a divided fl ow mixing principle. The main calibration chamber
is supplemented by two reservoirs, one of which contains desiccant, the other contains
a saturator, which consists of a small quantity of distilled water and a diffuser.
A pump circulates air through the system, which is directed either to the desiccant or
saturator reservoir by a 2-way valve. When fl owing through the desiccant, moisture is
removed from the air; when fl owing through the saturator, moisture is added to almost
completely saturate it at the prevailing temperature.
A Michell Instruments' Hygrosmart 3 control sensor is installed inside the calibration
chamber, continually measuring the temperature and relative humidity inside. When a
target humidity level is set via the user interface, the control system uses the reading of
the HS3 control sensor to determine whether to add humid air or dry air to the chamber
in order to reach the desired level. When the reading of the HS3 is equal to that of the
target set point, the system alternates between injections of dry and wet air to maintain
a constant humidity condition in the chamber.
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