
To enhance repeatability of successive measurements allow the meaterial to rest between mea-
surements. One general guideline is recording the electrificaon period required for a steady state
measurement and then add one minute to the measurement me to calculate the minimum rest
period between measurements. For example, if 1 minute is used to obtain a steady state measure-
ment – plus 1 minute – the rest me between measurements of the same sample is 2 minutes. On
the other hand, if a steady state measurement is obtained in 15 seconds, the total minimum me
between measurements is 1 minute 15 seconds. Typically, materials will be precondioned at de-
fined temperature and relave humidity for 48 hours or more, and measured in the same environ-
ment using defined procedures to reduce the effect of ambient variables.
E. Calculang Volume Resisvity (ohm-cm)
Resistance is a measurement, whereas Volume Resisivity is a calculaon based on (1) a resistance
measurement, (2) fixture dimensions and, (3) material thickness. To convert resistance measure-
ments in ohms obtained with the PRF-930 to volume resisvity (ρ) in ohm-cm, we use the follow-
ing equaon to convert the resistance measurement to resisvity.
Where,
R = Resistance obtained from the material measurement in ohms
A= Area of the fixture’s center plate in cm2
d = Distance in cm between the measurement and power plates.
The relaonship of area Adivided by distance dis oen re-
ferred to as a correcon factor in cm (CF), which is mulplied
by the measured resistance to obtain resisvity. (See Sample
Calculaons, below)
Exact fixture dimensions can be obtained during fixture clean-
ing using the measurement procedures described below. When
the fixture is disassembled, and aer it is cleaned, measure the
concentric center plate with a micrometer as shown in Figure 8,
at right.
The center plate area Ais calculated using the equaon:
Where is approximately 3.1416 and ris the radius of the cen-
ter plate, which is one-half the plate diameter. The distance d
between plates is measured with a micrometer (Figure 9) aer
the fixture is reassembled. The measurement is made at the
center point of the measurement plates, midway between the
acrylic frame vercal supports.
Figure 8: Measuring Diameter of Measure-
ment Center Plate
Figure 9: Measuring the Distance dbe-
tween Plates
10 Rev. A / January 2010
PRF-930 Advanced Powder Fixture