- Full Color Hi-Resolution LCD Touch Screen
- User Selectable Display Parameters
- Parameters Selectable as Numeric or Graphic
- User Selectable Units
?The system uses an active matrix 640x480-pixel full color liquid crystal
display with an integral touch panel. It has a high contrast ration and
a wide viewing angle for easy readability. Data is displayed with large,
easy to read characters. Using the on screen menus, you can configure the
display for for a variety of humidity, temperature, and pressure parameters.
The parameters can be viewed in either numeric or graphic (strip chart style)
format. System units are user selectable and may be set to any combination
of SI and non-SI units.
Digital Measurement and Control of Mirror Temperature
The reflected light from the mirror is continuously measured by a high
resolution A/D converter to detect the dew/frost layer thickness. This digital
signal is then used in the control algorithm to properly drive the peltier
element, establishing and maintaining the dew thickness at the equilibrium
point. The mirror temperature is measured by a 100-ohm platinum resistance
thermometer which is connected directly to a high accuracy, high precision
A/D converter. The resistance of the thermometer is measured by the A/D
converter and used, along with calibration coefficients, to computer mirror
For mirror temperatures above 0ºC, water vapor condenses on the mirror
as liquid water (dew). A condensation layer resulting from a mirror temperature
above 0ºC is considered a dew point.
For mirror temperatures far below 0ºC, water vapor condenses on the mirror
as solid ice (frost). A condensation layer resulting from a mirror temperature
far below 0ºC is considered a frost point.
However, for mirror temperatures between 0 and approximately -20ºC, the
state - water or ice - of condensed layer is indeterminate. In this temperature
range, it is difficult to know, without visual observation, whether the
mirror is controlling at the dew point or at the frost point. Since these
two states occur at different temperatures for gas of the same water vapor
content, it is important to determine which it is. The errors resulting
from this problem can be in excess of ± 2ºC.
To correct the situation, this system can be commanded to automatically
force all sub-zero condensation to a known state of frost. This is accomplished
by rapidly cooling the mirror to below -40ºC, then quickly returning it
to the previously predicted frostpoint temperature. It is then allowed to
stabilize while ensuring the mirror temperature remains below 0ºC. Once
forced to frost in this manner, the condensation will remain in frost for
all subsequent mirror temperatures that continue to remain below 0ºC.
Once the mirror temperature has risen above 0ºC, any further attempts
to stabilize in the indeterminate range between 0 and -20ºC cause the system
to once again cycle through forced frost formation. A forced frost cycle
may also occur at the completion of any automatic or manual mirror check.
By ensuring that sub-zero mirror temperatures are always forced to frost,
the mirror temperature can be taken as the frost point temperature. Since
the dew point vapor pressure and the frost point vapor pressure are equal,
dew point temperature can be mathematically computed.
ORIS allows for faster measurements at low frost points, generally below
about –60ºC. Typically, at these low frost point conditions, a chilled
mirror hygrometer must cool the mirror to a value well below the actual
frost point temperature in order to start the condensation process on the
mirror. But due to the low water vapor content of the gas, it can take a
very long time to establish a suitable frost layer on the mirror, then stabilize
it at the proper equilibrium temperature. This can often take in excess
of several hours. And the lower the frost point, the longer it takes.
ORIS solves this problem by momentarily injecting a small amount of water
vapor into the gas stream to assist the initial formation of frost on the
mirror, significantly reducing the amount of time required for a stable
measurement. Measurements that once took several hours or more, can now
be performed in a matter of minutes thanks to ORIS.
- 2 Configurable 12-Bit Analog Outputs
- User Selectable Parameter and Range
- Bi-directional RS-232
- Obtain Readings
- Read/Store System
- Configuration Parameters
- Verify/Edit Calibration Coefficients