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Measurement tips, Determine the measuring range, 373 (-60 … +20 °c) – ROTRONIC MBW 373 User Manual

Page 30: 373h (-40 … +70°c), 373hx (-30 … +95°c), 373l (-80 … +20°c), 373lx (-95 … +20°c)

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Measurement Tips

Since each particular 373 model is best suited for a specific dew/frost point range, it is important
to have some minimal knowledge of the expected value of the measurement in order to ensure
that the proper system is being used. In addition to proper system selection, your success will
depend on other factors as well, such as selection and connection of hoses, cooling and/or
heating requirements, flow rate, mirror cleanliness, and dew vs. frost determination. These and
other topics are discussed here in order to ensure that you achieve success with your
measurements.

Determine the Measuring Range

Each 373 has a specific range of operation. To cover the entire range of -95°C frost point to
+95°C dew point requires two or more separate instruments with some limited amount of overlap
between them. While your instrument may be slightly different, the following should give you
some guidelines as to the range of use of the various models.

373 (-60 … +20 °C)

The standard 373 is generally useful over a measuring range of -60°C frost point to +20°C dew
point. The mirror cooling capability and the materials used within the measuring head limit the
low end. The room ambient temperature limits the upper end. You should never attempt to
measure a dew point temperature that is at or above the temperature of the room. If you do,
condensation will form inside the tubing.

373H (-40 … +70°C)

The 373H is equipped with heated components that allow it to obtain a measuring range of
approximately -40 to +70°C. The heated components include a heated measuring head, heated
flow and pressure sensors, and heated internal and external tubing. Without these heated
components controlled at a high temperature, you should never attempt to measure a dew point
temperature that is at or above the temperature of the room. If you do, condensation will form
inside the tubing. For these high dew point measurements, external heated hoses are also
required. For continuous low frost point measurements, or in high ambient temperature
environments, cooling water may be supplied from an external source and connected to the
system if desired.

373HX (-30 … +95°C)

For extended high range use, the 373HX is equipped with a high temperature measuring head,
heated flow and pressure sensors, heated internal tubing, and controls for heated external
hoses. The measuring head is specifically designed for temperatures up to +95°C dew point.
For high dew point measurements, external hoses are required. Due to the high range design,
the lower end is generally limited to approximately -30°C frost point due to mirror cooling
capability and materials used in the design of the measuring head. If cooling water is used, the
system may be operable to approximately –40°C frost point.

373L (-80 … +20°C)

The 373L is designed for low range use, and is equipped with a compact internal refrigeration
system. It can measure frost point temperatures down to –80°C, and dew points up to +20°C.
The 373L can not be used for measuring dew points above room temperature.

373LX (-95 … +20°C)

The 373LX is designed for extended low range use. It is equipped with a larger internal
refrigeration system and a specially designed measuring head allowing it to measure frost point
temperatures down to -95°C. Like the 373L, it can only measure dew points up to +20°C, and
can not measure any dew points above room temperature.