Prostat PRF-930 User manual

User Manual
PRF-930
POWDER RESISTANCE FIXTURE


  Page
I. Introducon & Descripon 4
II. Fixture Component Descripons 4
III. Resistance Measurement Procedure 6
IV. Disassembly & Cleaning 11
VWarranty 15
General Specicaons 16

Copyright © 2011 by Prostat® Corporaon. All rights reserved. Printed in the United States of America. No part of this
manual may be used or reproduced in any manner whatsoever without wrien permission. For informaon contact
Prostat Corporaon, 1072 Tower Lane, Bensenville, IL 60106 USA
Prostat is the registered trademark of Prostat® Corporaon

 
The PRF-930 Powder Resistance Fixture measures the
bulk resistance of powder and granulated materials.
Test material is placed in the cavity between the mea-
surement plates. Once a measurement has been made
in ohms, a xture calculaon, or correcon factor, con-
verts the resistance measurement to volume resisvity
in ohm-cm. The PRF-930 provides the most accurate
measurements when used with a precision wide range
resistance instrument, such as the Prostat PRS-801
Resistance System, or equivalent laboratory system.
For guarded plate measurements use an instrument
ground reference.
The PRF-930 Powder Fixture meets requirements of “Technical Recommendaons of Naonal Instute
of Occupaonal Safety and Health JNIOSH-TR-No. 42 (2007) Recommendaons for Requirements for
Avoiding Electrostac Hazards in Industry 2007”
 
A. Acrylic Frame
An electrically insulave acrylic frame provides structural support and precise posioning of the
two measurement plates.
MATERIAL TEST CAVITY
POWER PLATE
(Test Voltage)
MEASUREMENT PLATE
(Current Sensing)
ACRYLIC FRAME


5
Rev. A / January 2010
PRF-930 Advanced Powder Fixture

Once assembled in the acrylic frame, the two plates form a cavity that becomes the material test
area. Powder substances are loaded into the xture completely lling the test cavity. A test volt-
age is applied to the power plate and current through the material is sensed on the measure-ment
plate.
B. Measurement Plate
The PRF-930 concentric measurement plate assembly
consists of a center plate with a diameter of approxi-
mately 2.4 cm (0.945 inch), having a surface area of 4.5
cm2 (0.7 in2). The center plate is separated from the
measurement guard plate by a virgin Teon™ insert
(Figure 3).
When installed in the acrylic xture the center plate is
posioned directly against the test material. The center
plate connects to the resistance instrument using the
Black receptacle on the plate’s outer surface (Figure 4).
The measurement guard plate connects to the instru-
ment’s ground reference using the Green receptacle on
the outer measurement plate assembly.
C. Power Plate
Power is applied to the material under test by the
xture’s power plate. Connecon to the power plate is
made using the Red connector (Figure 5). Test voltage
is applied to material under test by contact with the
power plate’s inner surface.






Power Plate
Outer Surface
Power Plate
Inner Surface
Power Connecon
6Rev. A / January 2010
PRF-930 Advanced Powder Fixture

 
The resistance measurement and resisvity calculaon procedure includes the following Steps:
• Filling the xture cavity with material for tesng
• Connecng the xture to a resistance instrument for measurement
• Making a material  measurement in 
• Consider variables eecng resistance measurements
• Calculang Volume Resisvity of the test material in ohm-cm
A. Filling the Fixture Cavity
Before using the xture be sure it is clean and properly assembled. (See “Disassembly & Cleaning”,
below.) The volume of the xture is approximately 15 cm3. Depending on material characteriscs
approximately 1.0 tablespoon will be required to completely ll the xture cavity. Place the mate-
rial in the PRF-930 and compress it lightly.
Material compression should be limited to the degree that represents the material’s use, transport
or storage condions. This is subjecve and best determined by personnel most experienced with
the material process and applicaons. In any event, do not compress the material to an extreme
degree beyond that which the material experiences under ordinary condions.

Follow material manufacturer or supplier’s safety precauons, procedures and han-
dling recommendaons when tesng any material.
1. Level the material at the top surface of the xture. (Figure 6)

7
Rev. A / January 2010
PRF-930 Advanced Powder Fixture

2. Be sure the wipe excess material from the top of the acrylic frame
B. Fixture Connecons
Three connecons to a precision, wide range resistance system (Figure 7) are required for accurate
measurements:
1. Connect the instrument’s test voltage (power) lead, usually from the Posive (+) terminal to
the Red connecon mounted on the xture’s power plate.
2. Connect the instrument’s current sensing lead, usually the Negave (-) terminal, to the Black
center plate recepcal.

Negave (-)
Terminal
Instrument Ground
Reference
Posive (+)
Terminal
3. Connect the instrument’s ground reference to the Green guard plate recepcal
C. Making the Resistance Measurement
The PRF-930 complies with the fundamental requirements of measuring bulk resistance of pow-
dered and granulated materials. Actual procedures and specied condions may vary between
test methods cited by standards bodies in dierent countries. The PRF-930 was designed in accor-
dance with the Recommended Pracce for Protecon against Hazard arising out of Stac Electric-
ity in General Industrie, published by The Naonal Instute of Industrial Safety, Japan, Technical
Recommendaon No. RIIS-TR-87-1. Other naonal commiees may be examining similar methods
for these measurements.
Center Plate
Connecon
Guard Plate
Connecon
Power Plate
Connecon
8Rev. A / January 2010
PRF-930 Advanced Powder Fixture

For illustrave purposes, the following procedure is based on resistance measurement protocol
developed by the Electrostac Discharge Associaon (ESDA) Standards Commiee, which is based
in Rome, New York, USA. Use other recommended measurement protocol when suitable and avail-
able.
1. Connect material lled xture to resistance measurement system as discussed above.
2. Energize the instrument in accordance with manufacturer’s instrucons.
3. Select Test Voltage of 10 volts
4. Start the instrument’s TEST sequence where test voltage is applied to the xture.
5. If indicated resistance is less than 1.0x106 ohms, record the measurement aer a steady state
value has been reached
6. If indicated resistance at 10 volts is greater than 1.0x106 ohms, stop the test
7. Reset the test voltage to 100 volts
8. Start the TEST sequence and apply 100 volts to the xture for the instrument’s electricaon
period, or unl a steady state value has been reached.

Or use the test voltage and electricaon period required by the applicable standard
test method or procedure
9. Record the measurement in ohms
D. Variables Eecng Resistance Measurements
Several factors will eect resistance measurements, including:
• Temperature
• Humidity
• Material Compression
• Material Moisture Content
• Test Voltage
• Instrumentaon Electricaon Period
• Material Composion
• Other factors depending on condions and material characteriscs
Repeatability between measurements, and reproducibility between laboratories are eected by all
of these variables. One must understand the eect of resistance measurement variables to avoid
confusion and misunderstandings between dierent test results.
Increased ambient humidity or material moisture will reduce the resistance measurement, that is:
cause the material to appear more conducve. Lower humdiy, reduces material moisture con-
tent, which increases indicated material resistance. High test voltage may (1) “boil” o moisture,
or (2) change the material’s electrical characteriscs. Idenfy and record all the apparent variables
in your measurement situaon to provide validity, repeatability and reproducibility to your mea-
surements.
9
Rev. A / January 2010
PRF-930 Advanced Powder Fixture

To enhance repeatability of successive measurements allow the meaterial to rest between mea-
surements. One general guideline is recording the electricaon 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 precondioned at de-
ned temperature and relave humidity for 48 hours or more, and measured in the same environ-
ment using dened procedures to reduce the eect of ambient variables.
E. Calculang Volume Resisvity (ohm-cm)
Resistance is a measurement, whereas Volume Resisivity is a calculaon based on (1) a resistance
measurement, (2) xture dimensions and, (3) material thickness. To convert resistance measure-
ments in ohms obtained with the PRF-930 to volume resisvity () in ohm-cm, we use the follow-
ing equaon to convert the resistance measurement to resisvity.
Where,
R = Resistance obtained from the material measurement in ohms
A = Area of the xture’s center plate in cm2
d = Distance in cm between the measurement and power plates.
The relaonship of  A divided by  d is oen re-
ferred to as a  in cm (CF), which is mulplied
by the measured resistance to obtain resisvity. (See 
, below)
Exact xture dimensions can be obtained during xture clean-
ing using the measurement procedures described below. When
the xture is disassembled, and aer it is cleaned, measure the
concentric center plate with a micrometer as shown in Figure 8,
at right.
The center plate area A is calculated using the equaon:
Where p is approximately 3.1416 and r is 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) aer
the xture is reassembled. The measurement is made at the
center point of the measurement plates, midway between the
acrylic frame vercal supports.


dbe

10 Rev. A / January 2010
PRF-930 Advanced Powder Fixture