Q.
Can the dew point probe attach to my PosiTector 6000 coating thickness
gage?
A.
No. Although the PosiTector Dew Point Meter shares many of the
same features as the PosiTector 6000 and has a similar appearance, probes
are not interchangeable. The dew point probe will not work on a PosiTector
6000, and a coating thickness probe will not work on a PosiTector Dew
Point Meter.
Q. Are there different models of PosiTector Dew Point Meter to
choose from?
A.
No. There is only one.
However
there are two available accessories; PosiSoft software and an HP IR
printer.
Q. Why not spend less money on a sling psychrometer, surface thermometer,
and weather tables?
A.
The PosiTector Dew Point Meter is:
Faster
while these devices take several minutes each to stabilize per measurement,
the PosiTector Dew Point Meter displays all 5 values (a Dataset) in
mere seconds.
Ta Air Temperature
Ts Surface Temperature
RH Relative Humidity
Td Dew Point Temperature
∆ - the difference between surface and dew point temperatures
Simpler no need for
counting revolutions per second in a timed interval using de-ionized
water
using a slide-rule calculator
waiting minutes for a surface thermometer to stabilize
reading analog scales
looking up values in a cross reference table
Easier one handed design with large LCD
More accurate tighter tolerances on all values. Certificate of Calibration
with traceability to NIST included.
Versatile unlike a sling psychrometer, the PosiTector Dew Point Meter
works well in cold environments. And the handy memory and auto-logging
functions make record keeping easy.
Q.
Why choose the PosiTector Dew Point Meter over other digital offerings?
A.
Smart design
White
sensor housing reduces the effects of direct sunlight and sliding
cover protects sensors when instrument is not in use.
Attachable clip & removable probe allow for one hand operation.
Ideal for accessing hard-to-reach areas.
For both indoor and outdoor use. Several other instruments warn against
outdoor use.
Rubber grip for comfortable handling with or without gloves.
A new level of confidence
·
Fast response precision sensors provide accurate, repeatable readings
with high reliability and long term stability.
·
Certificate of Calibration included
·
Audio & visual alarm to indicate when climatic conditions are unsuitable
for painting
Q.
Can the PosiTector Dew Point Meter record and calculate data on its
own?
A.
Yes, the PosiTector Dew Point Meter can be operated unattended
by automatically selecting time intervals in the Data Logger Mode. All
values are constantly updated and with a press of one button, can be
held for closer analysis, and stored in memory. This feature is important
for recording and evaluating climatic trends.
Q.
Why is it important to calculate the dew point temperature?
A.
The dew point temperature is a function of air temperature and
the relative humidity. It is the temperature to which a volume of air
must be cooled in order to reach saturation.
It
is important to calculate the dew point temperature in order to know
when conditions are suitable for applying paint.
Q.
Why is it important to calculate the difference between the surface
and dew point temperatures?
A.
According to ISO 8502-4 standards, the surface temperature should
be at least 3°C (5°F) above the dewpoint. By knowing the surface
and dew point temperature, it can be established whether or not conditions
will be suitable for painting.
Q.
Why are Relative Humidity values from the PosiTector DPM sometimes
different than those obtained from a Psychrometer?
A.
When using a psychrometer, Relative Humidity must be calculated
from the observed wet and dry bulb temperatures of a psychrometer and
there are many opportunities for interpolation errors. Slight differences
in these values as obtained from temperature scales and humidity look-up
tables can cause considerably different results.
Here
is an example: Lets assume that thermometers read in 1 degree increments,
but that you could interpolate to a ½ degree. Given a typical
+1º accuracy, if the dry bulb temperature was 75ºF and the
wet bulb temperature was 73ºF, possible recorded values could be
as follows:
Dry
Wet Relative humidity
74.5ºF 73.5ºF 95.4%
75.0ºF 73.0ºF 90.9%
75.5ºF 72.5ºF 86.6%
Although
both thermometer values are within tolerance, the resultant humidity
formula calculation differs by 8.8 percentage points! If a look-up table
is used instead of a formula calculation, the difference might be even
greater. This error budget is greatest in the wet/dry bulb calculations
at very low and very high relative humidities.
Q.
Can Saturated Salt Solutions be used as calibration references for
the PosiTector Dew Point Meter?
A.
A saturated salt solution is made with a slushy mixture of distilled
water and a chemically pure salt. The saturated salt solution is enclosed
in a sealed chamber. The atmosphere above the solution in the chamber
will yield a known humidity for a given temperature. Although saturated
salts provide a simple way to generate a known humidity environment
extreme care must be taken to ensure that the ratio of salt to water
is correct, that the solution and the air above the solution in the
chamber be iso-thermal (the same temperature), that the chamber be sealed,
and that sufficient time is given for equilibrium to be attained in
the chamber. If all precautions are followed this method of calibration
can provide a known humidity of +/-2%. If this method of calibration
is used with the PosiTector Dew Point Meter, the accuracy stated above
should be taken into consideration along with the published accuracy
of the meter.
