Fluke RUSKA 2417 User manual

PN 3966494
November 2010
© 2010 Fluke Corporation. All rights reserved. Printed in USA. Specifications are subject to change without notice.
All product names are trademarks of their respective companies.
RUSKA 2413, 2417 &
2416
Differential Pressure Null Indicator
Users Manual

LIMITED WARRANTY AND LIMITATION OF LIABILITY
Each Fluke product is warranted to be free from defects in material and workmanship under normal use and
service. The warranty period is one year and begins on the date of shipment. Parts, product repairs, and
services are warranted for 90 days. This warranty extends only to the original buyer or end-user customer of
a Fluke authorized reseller, and does not apply to fuses, disposable batteries, or to any product which, in
Fluke's opinion, has been misused, altered, neglected, contaminated, or damaged by accident or abnormal
conditions of operation or handling. Fluke warrants that software will operate substantially in accordance
with its functional specifications for 90 days and that it has been properly recorded on non-defective media.
Fluke does not warrant that software will be error free or operate without interruption.
Fluke authorized resellers shall extend this warranty on new and unused products to end-user customers
only but have no authority to extend a greater or different warranty on behalf of Fluke. Warranty support is
available only if product is purchased through a Fluke authorized sales outlet or Buyer has paid the
applicable international price. Fluke reserves the right to invoice Buyer for importation costs of
repair/replacement parts when product purchased in one country is submitted for repair in another country.
Fluke's warranty obligation is limited, at Fluke's option, to refund of the purchase price, free of charge repair,
or replacement of a defective product which is returned to a Fluke authorized service center within the
warranty period.
To obtain warranty service, contact your nearest Fluke authorized service center to obtain return
authorization information, then send the product to that service center, with a description of the difficulty,
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Fluke Corporation
P.O. Box 9090
Everett, WA 98206-9090
U.S.A.
Fluke Europe B.V.
P.O. Box 1186
5602 BD Eindhoven
The Netherlands
11/99
To register your product online, visit register.fluke.com

i
Table of Contents
Chapter Title Page
1 Description and Specifications.......................................................... 1-1
Introduction........................................................................................................ 1-1
How to Contact Fluke ........................................................................................ 1-1
Safety Information ............................................................................................. 1-1
Symbols Used in this Manual ............................................................................ 1-1
General Description ........................................................................................... 1-2
Specifications..................................................................................................... 1-2
2 Applications......................................................................................... 2-1
Introduction........................................................................................................ 2-1
Gas-to-Gas..................................................................................................... 2-1
Liquid-to-Gas ................................................................................................ 2-1
Liquid-to-Liquid ............................................................................................ 2-1
3 Preparation for Use ............................................................................. 3-1
Preparation for Use ............................................................................................ 3-1
Bleeding Lower Chamber in a Liquid-To-Liquid System................................. 3-2
4 Operation ............................................................................................. 4-1
Operating Instructions........................................................................................ 4-1
5 Performance Observations ................................................................ 5-1
Actual Sensitivity versus Apparent Sensitivity.................................................. 5-1
Calibration ......................................................................................................... 5-1
Detecting Leaks ................................................................................................. 5-2
6 Maintenance......................................................................................... 6-1
Servicing the Instrument .................................................................................... 6-1
Diaphragm ......................................................................................................... 6-1
RUSKA 2413 Differential Pressure Null Indicator —Replacement of
Differential Transformer.................................................................................... 6-2
Failure Diagnoses .......................................................................................... 6-2

RUSKA 2413, 2417 & 2416
Users Manual
ii
RUSKA 2413 — Replacement of Transformer................................................. 6-2
RUSKA 2417 Transducer — Replacement of Differential Transformer ...... 6-3
Failure Diagnoses .......................................................................................... 6-4
7 Parts List .............................................................................................. 7-1
RUSKA 2413 Differential Pressure Null Indicator — Parts List ...................... 7-1
RUSKA 2417 Differential Pressure Transducer — Parts List........................... 7-5
RUSKA 2417-706 Differential Pressure Cell 40,000 PSI — Parts List ............ 7-5
8 General Information ............................................................................ 8-1
Introduction........................................................................................................ 8-1
9 Functional Circuit Description ........................................................... 9-1
Introduction........................................................................................................ 9-1
0Test Procedure .................................................................................... 1
Introduction........................................................................................................ 1
Setup Procedure ................................................................................................. 1
Appendices
A Explanation of Test Report.......................................................................... A-1

iii
List of Tables
Table Title Page
1-1. Symbols.................................................................................................................. 1-2
6-1. Failure Diagnosis ................................................................................................... 6-2
6-2. Resistance Measurements for the Windings .......................................................... 6-4
7-1. RUSKA 2413 Differential Pressure Cell - Parts List ............................................. 7-4
7-2. RUSKA 2417 Differential Pressure Cell - Parts List ............................................. 7-5

RUSKA 2413, 2417 & 2416
Users Manual
iv

v
List of Figures
Figure Title Page
7-1. RUSKA 2413-711 Differential Pressure Null Indicator - Side View .................... 7-2
7-2. RUSKA 2413-711 Differential Pressure Null Indicator - Top View ..................... 7-3

RUSKA 2413, 2417 & 2416
Users Manual
vi

1-1
Chapter 1
Description and Specifications
Introduction
This manual covers the operation and maintenance of the RUSKA 2413, RUSKA 2416
and RUSKA 2417.
How to Contact Fluke
To order accessories, receive operating assistance, or get the location of the nearest Fluke
distributor or Service Center, call:
•Technical Support USA: 1-800-99-FLUKE (1-800-993-5853)
•Calibration/Repair USA: 1-888-99-FLUKE (1-888-993-5853)
•Canada: 1-800-36-FLUKE (1-800-363-5853)
•Europe: [phone]
•China: [phone]
•Japan: [phone]
•Singapore: [phone]
•Anywhere in the world: [phone]
Or, visit Fluke's website at www.fluke.com.
To register your product, visit http://register.fluke.com.
To view, print, or download the latest manual supplement, visit
http://us.fluke.com/usen/support/manuals.
Safety Information
WWarning
The control box/null indicator must be set for the proper line
voltage prior to connection to a power source.
Symbols Used in this Manual
In this manual, a Warning identifies conditions and actions that pose a hazard to the
user. A Caution identifies conditions and actions that may damage the Differential
Pressure Null Indicator.
Symbols used on the Differential Pressure Null Indicator and in this manual are explained in
Table 1-1.

RUSKA 2413, 2417 & 2416
Users Manual
1-2
Table 1-1. Symbols
Symbol Description
BAC (Alternating Current)
JEarth Ground
WImportant Information: refer to manual
~Do not dispose of this product as unsorted
municipal waste. Go to Fluke’s website for
recycling information.
General Description
The Differential Pressure Null Detector, composed of a Differential Pressure Transducer
(RUSKA 2413 or RUSKA 2417) and Electronic Null Indicator (RUSKA 2416), is
designed to sense small pressure differences in both low and high pressure systems.
The transducer consists of two pressure chambers, separated by a thin diaphragm. A
difference in pressure in the two chambers causes a deflection of the diaphragm and a
resultant signal to the electronic circuit. The signal is obtained as the output of a
differential transformer whose movable core is attached to the diaphragm. The signal is
not a linear function of the difference in pressure; therefore, use of the instrument for
accurate evaluation of pressure differences is limited to small deflections of the
diaphragm. The principle use of the instrument is intended as a null sensor/indicator with
which the pressure of one medium may be precisely adjusted to that of another. Some of
the advantages of the instrument are its high sensitivity, high working pressure
(15,000 psi for RUSKA 2413 Series cells and 40,000 psi for RUSKA 2417 Series), and
its ability to withstand the full working pressure across the diaphragm without injury
(15,000 psi maximum over-range pressure both series).
Specifications
Inaccuracy Inaccuracy is defined as the error in the null indication. It is
expressed as the ratio of ΔP actually existing when the meter
indicates a null, to the total cell pressure, in parts per million,
or as constant ΔP — whichever is greater.
PPM ΔP PSI
Error with calibration
corrections
5 0.01
Error without calibration
corrections
20 0.1
Sensitivity The sensitivity is continuously variable from 2* 10-4 psi ΔP
per meter division to 0.01 psi ΔP per meter division. The
maximum value may exceed 2 *10-4 psi/div. because of
variations in diaphragm characteristics and circuit parameters.
Operating Pressure 15,000 psi liquid or gas for RUSKA 2413 Series cells; 40,000
psi for RUSKA 2417 Series cells (See pressure media for
limitations).
Static Test Pressure 22,000 psi for five minutes with nitrogen. The ungasketed

Description and Specifications
Specifications 1
1-3
metal seals act as relief valves when pressures exceed 22,000
psi. The bolts yield to the increased lead and permit the
excess pressure to escape. All attempts at destructive testing
of these units have failed. 50,000 psi for RUSKA 2417 Series
cells.
Over-Range Pressure 15,000 psi ΔP either side of diaphragm for both RUSKA
2413 and RUSKA 2417.
Construction Material Basic material of the transducer is one of the 400 Series
Stainless Steels.
Pressure Media Lower Chamber of pressure cell — Dry air, nitrogen,
mercury, or any fluid inert to 400- or 300-Series Stainless
Steels.
Upper Chamber — Dry air, nitrogen, or any fluid inert to
400- or 300-Series Steels, low-carbon iron, brass, copper,
PVC, cadmium-plated steel or soft solder. Electrolytes may
not be used in the upper chamber.
It is not recommended to use fluids in either cavity
containing free hydrogen. The use of such fluids is
hazardous because of possible hydrogen embrittlement of
the cell body. (Consult the manufacturer for cells of special
materials.)
Temperature Range 40º F to 160º F
Construction Details and Parameters:*
Note
Replacing diaphragm or transformer voids calibration.
Change in Null with Working
Pressure
See Specifications
The stress from the applied pressure produces a
displacement of the core within the transformer even though
the pressure across the diaphragm may be zero. The
displacement results in a shift of the apparent null with the
true null and is approximately a linear function of the
pressure. A calibration curve is supplied with each
instrument to indicate the magnitude of the null shift.
Change in Null
with Over-Range Pressure
<0.05 psi
The null change with over-range pressure arises from
dimensional variations within the cell body. The value
shown represents the maximum expected change when the
cell is over-ranges from alternate sides of the diaphragm. In
practice, a procedure is used that permits intentional over-
ranging, from only one side. After several such applications
of over-range pressure from the same side, null indication
becomes stable. If the cell is accidentally over-ranged from
the *opposite side, there is no harm except for a temporary
loss of the original null setting. The cell must be over-ranged
from the original side to reestablish the true null.

RUSKA 2413, 2417 & 2416
Users Manual
1-4
Approximate Range of ΔP: +/-2 psi
Volumes of Cavities: Upper — 29.5 cc
Lower — 0.6 cc
Effective Diameter
of Diaphragm:
1.9 inches
Thickness of Diaphragm: 0.001 inch
Types of Fittings: For RUSKA 2413 Series, RUSKA 60 degree cone with
3/8 24 straight thread male cone on fitting, female cone in
body of cell. Adapters are provided to go to DH500
(equivalent to AE F250C, HIP HF4). For RUSKA 2417
Series, DH500 (equivalent to AE F250C, HIP HF4).
*Values shown under this heading are nominal at time of this publication and are not to be
considered as binding specifications. They are subject to change with improvements in design
and technology.

2-1
Chapter 2
Applications
Introduction
The RUSKA 2416 may be employed as a null detector/indicator in the following manner:
Gas-to-Gas
The instrument may be used with dry air, nitrogen, carbon dioxide, some hydrocarbons,
and the noble gases, but not with gases containing free hydrogen or oxygen. Although
oxygen will not directly attack the materials of the lower cavity, there is the danger that
an accidentally perforated diaphragm will permit the oxygen to enter the upper cavity.
The organic materials in the upper cavity propose a hazard in the presence of compressed
oxygen. In all instances where a gas is used, no liquid vapors should be permitted to enter
the diaphragm cavity, as the surface tension effects of condensed vapors will surely spoil
the performance of the diaphragm.
Liquid-to-Gas
The instrument is used to separate a liquid pressure medium from a gas. When used with
a dead-weight gage, the transducer affords a means of calibrating elastic sensors with
inert gases. The sensors, such as transducers and bourdon-tube gages may then be used in
systems containing oxygen.
Liquid-to-Liquid
The Differential Pressure Transducer may be employed as a null detector between two
liquid systems. For instance, when calibrating elastic sensors prepared for oxygen
service, it is sometimes more convenient to use a liquid pressure medium than to use a
gas. The liquid medium, of course, must be chemically inactive in the presence of oxygen
in all concentrations. Mixtures of the volatile fluorocarbon solvents are frequently used
for this purpose. The system containing the fluorocarbon may be balanced against the oil
dead-weight gage system to pressures as high as 40,000 psi. Such systems are somewhat
more economical than equivalent liquid-to-gas systems, since the pressurizing apparatus
is less expensive.
With the possible exception of use with the highly volatile fluorocarbons, it is not
recommended that a cell be purchased for alternate use in liquid-to-liquid and
liquid-to-gas service. In order for the cell to perform properly, the diaphragm cavity must
be either completely filled with liquid, or it must be completely dry. A trace of liquid in
the otherwise dry cavity will upset the performance as quickly as will an air bubble in the
liquid cavity. In each instance, the surface tension effects are greater than the ΔP error
signal being observed.

RUSKA 2413, 2417 & 2416
Users Manual
2-2
Whenever a liquid is used in either side of the transducer, an open tube manometer must
be connected in such a way that the pressure across the diaphragm may be adjusted to
zero and that the meter may also be adjusted to indicate zero. In a liquid-to-liquid system,
two manometers must be used — one in each of the liquid systems. Manometers suitable
for this purpose are available.
A special application of the differential pressure null indicator is one in which the unit is
used when cross-floating two dead-weight gages. A by-pass valve arrangement is
provided for the purpose of directly connecting the two gags while making preliminary
balancing adjustments. When the two gages are at pressure and approximately balanced,
the valve is opened and the electrical zero adjusted. The valve is then closed and the
balancing operation continued, while observing the residual pressure difference on the
meter. As the pressures become more nearly equal, the valve is opened to verify the
correct zero adjustment and then closed and opened alternately until no difference in
meter readings is observed when the valve is either open or closed. The resolution of the
entire system is quickly determined by placing a small weight on one gage and observing
the effect on the meter. When using the transducer for this purpose, calibration of the null
shift with working pressure is unnecessary.

3-1
Chapter 3
Preparation for Use
Preparation for Use
Normally, when a transducer is shipped from the factory, it has been calibrated with
nitrogen and is dry in both cavities. Before installation, a quick performance tests may be
made by first connecting the box to the cell, with power on, adjusting the sensitivity to
maximum and the meter to zero. By pressing against the end of the open fittings with the
finger, the meter will be seen to deflect. The effect will be less when pressing on the
upper fitting, since the upper cavity has a volume some fifty times greater than the lower
cavity. At maximum sensitivity, it should be relatively easy to deflect the meter from zero
to full scale when pressing on the lower fitting.
Because of the small volume, it is of some advantage to connect the lower cavity to the
gas portion in a liquid-to-gas system. When so connected, less work will be done in
raising the gas pressure.
All fluids should be filtered before their introduction into the pressure system. A small,
hard particle, such as metal chip, in the diaphragm cavity will perforate the diaphragm
when the cell is over-ranged. Every effort should be made to keep contaminating particles
out of the transducer. In charging the upper cavity with a liquid, it is important to displace
most of the air with the liquid. There are many traps in the cavity which may retain small
air bubbles. If these bubbles remain in contact with the diaphragm or stem which carries
the transformer core, the performance will be erratic. The fact that the air bubbles
dissolve in the liquid when the pressure is increased may be used to an advantage. With
the vent plug removed, the liquid is pumped into the upper chamber until it appears at the
vent port. The plug is replaced and the pumping continued until the pressure in the liquid
system reaches 150 bar (2175 psi). At this pressure, the entrapped bubbles dissolve in the
liquid, forming a concentrated solution in the vicinity of the trap. Some time should be
allowed for the solution to diffuse so that, when the pressure is released, the bubbles will
not reappear in the same trap. The bubbles must reappear at some new point where they
may rise to the top of the chamber and be expelled through the vent port. The presence of
a bubble in the top of the cell cavity does not affect the measurement significantly, but it
does affect the response. It is therefore convenient to work the air out of the cavity as
much as is practical.
The cavity may also be charged by first evacuating and then admitting the liquid to the
evacuated chamber. Usually, some small bubbles still remain because of the difficulty in
reducing the internal pressure sufficiently through the small-bore tubing.
The presence of remaining air in the cavity may be measured if the liquid pressure
generator is a screw-type displacement pump and the system contains a Bourdon-tube
reference gage. It is first necessary to measure the air that exists in the portion of the
liquid system other than the transducer. To make this measurement, it is necessary to
isolate the liquid system from the cell and the dead-weight gage (if one is used). If there

RUSKA 2413, 2417 & 2416
Users Manual
3-2
is no valve on the line to the cell, the line must be temporarily disconnected and stopped
off. The valve to the liquid supply reservoir is opened and the plunger advanced
somewhat to remove the backlash in the pump spindle nut. With the reservoir valve
closed, the screw crank is slowly rotated until the Bourdon gage pointer is observed to
move a perceptible amount. The quantity of motion of the screw is noted. The motion of
the crank should be small — something like one-quarter turn or less. After reattaching the
differential transducer to the system and pressurizing the opposite cavity to several
hundred psi, the experiment with the screw pump is repeated. The difference in rotation
of the screw crank in the two experiments represents the quantity of air remaining in the
cell. In these experiments, the gage pointer must not be resting against a pin at zero
pressure. It is obvious that pressurizing the opposite cavity will prevent the flexible
diaphragm from spoiling the experiment. It is not difficult to keep the free air in the
differential pressure transducer below 0.05 cc.
Bleeding Lower Chamber in a Liquid-To-Liquid System
When charging the small cavity beneath the diaphragm, a bias pressure is placed in the
upper cavity to force the diaphragm against the lower cavity surface. After the plug
beneath the cell is loosened, some liquid is forced into the lower fitting until the liquid
appears around the plug threads. This method is adequate in most instances. A small
bubble is trapped in the vertical section of the input port to the lower cavity; but after
pressurizing the liquid for a period and repeating the process, the bubble is mostly
displaced or dissolved. For more thorough displacement of the air, the cell should be
inverted.

4-1
Chapter 4
Operation
Operating Instructions
In comparing the pressure of one system to that of another, it must first be established
that the comparator or indicating device is adjusted correctly. The adjustment must assure
the operator that all hydraulic and pneumatic heads have been accounted.
With the transducer connected between two systems and prepared for operation, the
power is turned on and the circuit allowed to warm up for ten minutes. A sequence of
operations must be adopted in which one of the systems is always at a higher pressure
than the other during the period of change from one pressure to another. If there is a
choice, it is of some advantage, in a liquid-to-gas system, to maintain the higher pressure
in the liquid system during the period of change. This procedure is not difficult to execute
for both increasing and decreasing changes in pressures. If it is intended to raise both
system pressures from one level to a higher one, the liquid pressure is raised first to a
value somewhat below the final one. The diaphragm of the differential pressure cell is
driven to the lower cavity surface where it supports the excess liquid pressure. The
operator is then free to concentrate on raising the gas pressure to, but not in excess of, the
liquid pressure. As the final pressure is approached, it is usually possible to raise both
systems simultaneously, while keeping them sufficiently balanced for the meter pointer to
remain on scale.
Before starting a measurement on a liquid-to-gas system, the differential pressure
transducer is intentionally over-ranged in the direction proposed by the adopted
procedure; i.e.; from the liquid side. The pressure is allowed to remain for a minute or so
and then released. In some manner, the liquid system must be opened to atmosphere at a
point level with the diaphragm. An open-tube manometer valve opened and the gas
system also opened to atmosphere, the liquid is adjusted to stand in the tube at the height
of the diaphragm. Under these conditions, the pressure across the diaphragm is zero. The
electrical circuit, with sensitivity set at maximum or whatever value has been chosen,
may then be adjusted for the meter to indicate zero ΔP. As the manometer valve is closed,
the pumping action of the stem causes the liquid to rise slightly in the tube and the meter
pointer to deflect. The deflection is a normal one which results from the disturbance of
the liquid in the tube.
Before the measurement is begun, the sensitivity is reduced by placing the shunt switch
in the ON position. The shunt switch reduces the gain of the circuit by a factor of
approximately 1000. First the liquid pressure and then the gas pressure is raised in the
manner described above. As the gas pressure becomes approximately equal to that of the
liquid, it will be observed that the two pressures will rise simultaneously as the increase
in gas pressure is continued. At this time, the diaphragm is being forced away from the
lower cavity surface by the gas. The displacement of the diaphragm increases the
pressure in the liquid system. Although the two pressures are approximately equal, a

RUSKA 2413, 2417 & 2416
Users Manual
4-2
signal will not appear on the meter until the gas pressure is within 2 psi of the liquid,
since this figure is the limiting value of the indicated differential pressure. Some liquid
must be withdrawn from the differential pressure cell, allowing the diaphragm to move
toward the center of the cavity whereupon the meter signal will approach the zero. If a
dead weight gage is connected in the system, the pressure in the liquid may build up high
enough to float the weights. With a slight excess of gas pressure, the diaphragm will then
move freely across the cavity; the weights will be seen to rise rapidly. After the
sensitivity is increased, by placing the shunt switch in the OFF position, the two pressures
may be brought to a satisfactory balance.
The increase in pressure of the two fluids is accompanied by an increase in temperature.
As the fluids give up their excess heat to the apparatus, each suffers a reduction in
energy. While the piston gage is floating, however, it acts as a regulator and holds the
pressure of the liquid approximately constant. The shrinkage of the liquid from its loss in
heat is reflected as an increase in the normal sink rate of the piston. The gas, being
confined to a single-ended system, suffers a loss in pressure as it gives up its excess heat.
The net effect is an unstable condition in which the indicator will signal a continuous
reduction in the gas pressure as through the system were leaking. For rather large changes
in the pressure level, the balance indication will approach a high state of excitement for
the first minute or so. Complete stabilization will require a period of up to one hour but,
for calibration purposes, manual control of the gas will be possible after only a few
minutes.
In reducing the pressure, the procedure is reversed. The gas pressure is first reduced and
then followed by the liquid pressure.
At the conclusion of the measurement, some time must be allowed for the transducer to
recover before the zero-pressure conditions are verified. Particularly, if the last reduction
in pressure is of one or more thousand psi, the recovery period may be as much as
5 to 10 minutes. A considerable quantity of heat is exchanged in the reduction process.
The procedure for operating a liquid-to-liquid system is much the same as described
above, except that a second manometer is required in the second liquid portion of the
system. When adjusting the differential pressure unit at the beginning of the test, both
manometers must be opened to atmosphere and each liquid adjusted to the height of the
diaphragm. It must be remembered that the density of the one liquid is often different
from that of the other; the total head correction must consider the two densities with their
interface at the diaphragm.

5-1
Chapter 5
Performance Observations
Actual Sensitivity versus Apparent Sensitivity
Although the differential pressure indicator is regarded as a null-indicating instrument,
the degree to which a true null may be achieved depends upon the readability of the error
signal displayed on the meter. In order to obtain a readable error signal, the diaphragm
must move. The sensitivity of the instrument is expressed as the change in pressure
divided by the corresponding change in meter reading — the change in meter reading
being a function of the motion or displacement of the diaphragm. The sensitivity must be
determined in such a way that the tension in the diaphragm, resulting from the applied
pressure, is the only restoring force which re-establishes equilibrium
When one side of the diaphragm is opened to atmosphere and a small increment of
pressure is applied to the other side, the diaphragm will move under the influence of the
applied pressure. The motion will continue until the forces tending to move the
diaphragm are equally opposed by the forces of tension in the diaphragm tending to resist
the motion. The sensitivity is then equal to ΔP divided by the change in meter reading.
When one side of the diaphragm is connected to a single-ended system containing a gas
under pressure, the circumstances are different. The forces of an applied pressure
increment tend to move the diaphragm as before, but the forces resisting the motion are
greater than before. As the diaphragm moves, the volume of the single-ended system is
reduced and its pressure increased. The ΔP that was applied to the diaphragm is
automatically diminished and the instrument sensitivity appears to be less than before.
An example of the extreme case is one in which the single-ended system is completely
filled with a non-compressible liquid. As the pressure is increased on the opposite side of
the diaphragm, the liquid will not permit the diaphragm to move. In this instance, the
sensitivity will appear to be very poor, but the actual sensitivity is no different than when
measured under ideal conditions.
Calibration
The calibration procedure consists of determining the pressure coefficient of the
transducer, the maximum sensitivity, and the zero shift that accompanies alternate
over-ranging pressures on the diaphragm.
The pressure coefficient is usually small — on an average, being less than 10-5/psi.
When the transducer is used in a bi-fluid system, for the calibration of elastic
pressure-measuring devices, the error of the transducer can often be disregarded. When
used in an apparatus for basic PVT studies, the coefficient is significant and its
expression is of more value if reported in units of diaphragm displacement per unit of
pressure level rather than as a change in pressure differential per unit of pressure level.
For very small samples, the displacement of the diaphragm can result in an intolerable

RUSKA 2413, 2417 & 2416
Users Manual
5-2
change in the sample volume, and the error will not be corrected by an adjustment of the
pressure in the amount indicated by a pressure correction curve. A calibrating procedure
in which the diaphragm presumably can be restored to its isostatic position by a physical
adjustment of the electrical sensing-indicating circuit has been adopted. The procedure
involves simultaneous pressurization of both sections of the transducer from a common
source and measuring the correction required to maintain a null indication throughout a
range of pressures.
The correction is applied as a change in the ten-turn zero adjusting potentiometer, the
shaft of which is equipped with a turn-counting graduated dial. In practice, the dial knob
is set near one end of its range and the transformer of the pressure cell adjusted to
indicate an approximate null when the diaphragm is exposed to atmospheric pressure on
each side. At each pressure level of operation, the dial is changed by an amount obtained
from the calibration curve. The curve is plotted as the change in dial units as a function of
operating pressure. Usually, it is necessary to decrease the dial registration as the pressure
is increased.
The advantage of maintaining a more uniform volume of the sample by accepting the
method of calibration just described outweighs the convenience of correcting the data by
a computer adjustment of the errors in pressure resulting from the strain in the transducer.
Manual adjustment of the potentiometer becomes a part of each measurement and must
not be overlooked.
Detecting Leaks
The differential pressure unit may be used to indicate a change in pressure of one system
with respect to that of another. The change may result from a leak or from a change in
temperature. When the instrument is used for detecting leaks in a system, sufficient time
must be allowed to eliminate temperature effects. Also, a leak in a liquid system will
have a different rate indication than a leak of the same magnitude in a gas system. Some
caution must be exercised when interpreting the results of this type of test.