The site requirement for NMR instruments
Lab. Air Supply Requirement
System 
Pressure(psig/kpa) 
Flow Rate(LPM/SCFH) 
Dew Point 
200  400 MHz 
35 
45 
40C 
500 and 600 MHz 
45 
48 
40C 
Solid State NMR 
90 
80 
40C 




Reference: Varian Installation Planning Guide
The house compressed air supply must provide a source of air that is clean, dry and free of contaminats, with a dew point 40 C minimum.
RH% caculator: http://einstein.atmos.colostate.edu/~mcnoldy/Humidity.html
Input the temperature of air supply, and relative humidity reading from the meter, the dew point could be calculated.
For example: the temperature is 22C and RH reading is 50%, then dew point is  43.20C
Definition of dew point:
The dewpoint temperature is the temperature to which the air must be cooled to reach saturation (assuming air pressure
remains the same). When the temperature cools to the dew point, fog or dew can occur, and the relative humidity becomes
100%.
The dew point is associated with relative humidity (RH%) . A highrelative humidity indicates that the dew point is closer to the current air temperature. Relative humidity of 100% indicates that the dew point is equal to the current temperature (and the air is maximally saturated with water). When the dew point stays constant and temperature increases, relative humidity will decrease.
Calculation of the dew point:
The Magnus formula relates the saturation vapour pressure and dew point. At a temperature T (in °C), the
saturation vapour pressure EW (in hPa) over liquid water, is
EW=a*e^((b*T)/(c+T)
For the range from –45°C to 60°C, Magnus parameters are given by a =6.112 hPa, b =17.62 and c =243.12 °C. By restating
equation, the dewpoint temperature Dp (in °C) can be expressed from vapour pressure E
Dp=(c*ln(RH*EW/100)/a)/(bln(RH*EW/100)/a)
Inserting the definition of relative humidity RH (in %), i.e. E=RH*EW/100, into equation (2) and using equation (1) leads
to the calculation of the dew point Dp from temperature T and relative humidity RH
The following simple program calculates the dew point Dp from the relative humidity RH and temperature T according to
equation (3). All temperatures are in Celsius.
H = (log10(RH)2)/0.4343 + (17.62*T)/(243.12+T);
Dp = 243.12*H/(17.62H); // this is the dew point in Celsius
Dewpoint Calculator:
http://www.decatur.de/javascript/dew/index.html
http://einstein.atmos.colostate.edu/~mcnoldy/Humidity.html
Example: RH=10%, T=25°C > Dew point = 8.77°C
RH=90%, T=50°C > Dew point = 47.90°C
This formula is a commonly used approximation. 