ROTRONIC MBW 973 - Manual (Page 28)

24 Measurement Tips
Measurement Tips
Since each particular 973 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.
Understand the Measuring Range
The 973 has a specific dew / frost point measuring range. It also has a specific range of
temperature that it can measure. These values are also converted into the appropriate relative
humidity measurement range. The typical 973 measurement range is listed below.
973 (-50°C Frost Point … +20 °C Dew Point)
The standard 973 is generally useful over a measuring range of -50°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.
The measuring range of the dew / frost point, coupled with the measurement of temperature
allow the 973 to be useful for measurement of relative humidity from approximately 1% to 100%
RH when measured at approximately 25°C. Since relative humidity is relative to the prevailing
temperature, the RH range will change with changes in temperature.
Connecting Hoses
Your success with dew or frost point measurement may likely depend on proper selection and
connection of the hoses you use in configuration of your gas sampling system.
Types of Hoses
There are various types of hoses available for use in your gas sampling system. You should
consider the suitability for your application.
Teflon
Teflon tubing is flexible, easy to use, and is well suited for frost/dew point measurements in the
range of approximately –60 to +20 °C, and is therefore well suited for use with the 973.
Stainless Steel
Stainless steel tubing, while less convenient to use, is a good choice for all measurement
ranges.
Tygon, Nylon, Poly
Tygon, nylon, and poly tubing are not recommended for use with the 973. They are often
affected by permeation of water vapor through their shells which can adversely affect the
measurements.