*Emissivity varies with purity.
Relative Humidity
Relative humidity is a measurement of moisture in the air compared to
the maximum amount of moisture the air can accommodate at a given
temperature. Air at higher temperatures can hold more “absolute
humidity” than air at lower temperatures, thus the same absolute
humidity in high-temperature air will have a lower relative humidity
value than it would in colder air. Relative humidity is measured in
percentage and is displayed in the bottom line of the DTH51 (Fig 3).
Ambient Temperature, Dew Point, and Wet Bulb
Ambient Temperature
, based on readings taken by the extended
sensor-set, is shown on the middle line of the DTH51 (Fig 4).
Temperature scale can be toggled between Fahrenheit and Celsius
using the “ “ push-button.
Dew Point
is a calculation of the temperature at which moisture in the
air will condense, based on the current level of relative humidity. This is
particularly valuable in determining if moisture will condense on an
object that has been moved from a colder temperature into warmer air.
Dew point is shown on the second line of the DTH51 (Fig 5).
Wet Bulb
is a calculation of the lowest temperature that an area can
be cooled using a process of evaporating water. The evaporation
process uses energy from surrounding heat in the air, thus cooling the
area. Wet bulb temperature is limited by a combination of ambient
temperature and relative humidity. Wet bulb temperature is shown on
the second line of the DTH51 (Fig 6).
To cycle between Ambient Temperature, Dew Point and Wet Bulb
temperature, extend the sensor set then press and release the “ “
push-button quickly until the desired function is displayed.
Differential Dew Point
Differential dew point is a calculation of the difference between the dew
point of ambient air and the actual surface temperature of an object.
This measurement can be particularly valuable when moving an object
from a cold environment to a warm environment or when trying to
determine if moisture will condense on equipment (potentially causing
damage) if environmental controls are turned off.
Differential dew point is shown on the top line of the
DTH51 when:
1. An infrared surface temperature has been measured (refer to the
i n f rared thermometer section of this manual).
2. The “ “ push-button has been pressed for two seconds then
released to invoke the “ “ icon on the left side of the top line of
the DTH51’s LCD display (Fig 7).
DTH51-MAN
P. 4
Surface
Emissivity
Nickel and its alloys
Nickel (pure)
0.1*
Nickel plate (oxidized)
0.4 to 0.5
Nichrome
0.7
Nichrome (oxidized)
0.95
Zinc (oxidized)
0.1*
Galvanized iron
0.3
Tin-plated steel
0.1*
Gold (polished)
0.1*
Silver (polished)
0.1*
Chromium (polished)
0.1*
(Fig 3)
Relative Humidity Measurement
Ambient Temperature Measurement
Wet Bulb Temperature Measurement
Relative Humidity Measurement
(Fig 4)
(Fig 5)
(Fig 6)
Differential Dew Point
Icon
Differential
Dew Point
Measurement
(Fig 7)
