ROTRONIC MBW 373 - Manual (Page 33)

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Cooling Requirements
Air Cooling
Mid and high range systems are equipped with air cooling. When air cooled, the fan speed is
controlled automatically by the computer. Air cooling is generally sufficient for measurements of
frost/dew points from approximately –40 to +95°C. Air cooling operates automatically and
requires no user input.
Water Cooling
In addition to air cooling, many mid and high range systems are also equipped with auxiliary
water cooling connections. Water cooling is useful for mid and high range systems when
working at the bottom end of the measuring range below -40°C if air cooling seems to be
insufficient. When using water cooling, maintain the temperature of the water above the room
ambient dew point to prevent condensation in the measuring head or cooling loop.
Refrigerated Precooler
Low range units, 373L and LX, are equipped with self-contained refrigeration systems for bulk
heat removal of the inner elements of the measuring head, allowing those units to reach much
lower frost point measurements
Heating Requirements
Head, Block, and Inner Tube Heat
All 373 systems are equipped with head heating. The purpose of head heating is two-fold. First,
head heating is used to maintain the head temperature at or above 20°C at all times, regardless
of the temperature of the mirror or the temperature of the pre cooler (if so equipped). This
minimum 20°C head temperature is controlled automatically, even when the heater is switched
off. This is done to prevent condensation of the room air on components of the head that are
external to the mirror and gas path. These components include the external portions of the
optical assembly, the cover screw, and the measuring head housing.
The alternate purpose of head heating is to maintain the components of the head which are
exposed to the gas path above the dew point temperature of the gas. If the head temperature
were allowed to fall below the dew point temperature of the gas, condensation could occur within
the gas path, thereby corrupting the dew point measurement at the mirror. Head heating is
maintained either at 20°C, or at the greater of 20°C and your defined head heating setpoint
when the Heater is switched on via the touch screen.
373H and 373HX high range units are equipped with an internal heated block housing the
components that come in contact with the gas sample, such as inlet and outlet fittings, pump,
flow meter, pressure sensor, and directional valves. In addition, the internal tubes that
interconnect the block and the measuring head are also heated. Maintaining these components
above the measured dew point temperature of the gas ensures that condensation does not
occur in any unwanted internal areas within the gas path. When measuring dew point
temperatures higher than room temperature, head heating should be switched on. When
heating is switched on, proper heating is maintained on the measuring head, the block, and the
internal tubing connected between the block and the measuring head. The head, block, and
inner tubes are all maintained at the Head Temperature setpoint.
When measuring frost point temperature, or dew point temperatures below approximately 20°C,
no heating is required and the heater may remain off (although the head, block, and inner tubes
will still be maintained at or above 20°C). When measuring dew point temperatures above 20°C,
or above your room temperature, heating is required. Your unit needs to be equipped with the
proper heating controls for head, block, and inner tube heat. In addition, your should enter a
suitable setpoint and enable heating control. To set the head temperature setpoint and enable
heating, see Heater Controls on page 17. Note that only 373H and 373HX systems are
equipped with block and inner tube heating controls.