Emerson 3098 User Manual
Technical Manual
30985020_US, Rev. B
October 2007
Micro Motion® 3098
3098 Gas Specific Gravity Meter
Contents 3098 Technical Manual
Copyright © 2007
Micro Motion, Inc.
All Rights Reserved
Micro Motion pursues a policy of continuous development and product improvement. The specification in this document
may therefore be changed without notice.
To the best of our knowledge, the information contained in this document is accurate and Micro Motion cannot be held
responsible for any errors, omissions or other misinformation contained herein. No part of this document may be
photocopied or reproduced without prior written consent of Micro Motion.
Cont-2
3098 Technical Manual Contents
IMPORTANT NOTICE
HANDLE THE 3098 WITH GREAT CARE
DO NOT drop the meter.
DO NOT use gases incompatible with MATERIALS OF CONSTRUCTION.
DO NOT operate the meter above its RATED PRESSURE.
DO NOT expose the meter to excessive vibration (>0.5g continuous).
ENSURE all ELECTRICAL SAFETY requirements are applied.
ENSURE good VENTILATION around the meter/cabinet to prevent gas build up in the unlikely
ENSURE meter is not TRANSPORTED when it contains hazardous substances. This includes
A Returns Form (see Appendix C) MUST be completed and returned together with
event of a leak.
fluids that may have leaked into, and are still contained, within the case.
the 3098 to the address given on the form.
Cont-3
Contents 3098 Technical Manual
Cont-4
3098 Technical Manual Contents
Contents
Chapter 1 Introduction
1.1 Specific gravity measurement ............................................................................................. 1-2
1.2 Functional description .........................................................................................................1-3
1.2.1 Meter sensing element .......................................................................................... 1-4
1.2.2 Installation............................................................................................................. 1-4
1.3 Definition of terms ............................................................................................................... 1-5
1.3.1 Specific gravity (G)................................................................................................ 1-5
1.3.2 Standard (base or normal) density (ρ
1.3.3 Relative density (ρ
1.4 Physical properties of gas compounds................................................................................ 1-7
1.5 Applications......................................................................................................................... 1-8
1.5.1 Supplementary gas supply .................................................................................... 1-8
1.5.2 Wobbe index measurement .................................................................................. 1-8
1.5.3 Consumer gas costing .......................................................................................... 1-8
Chapter 2 Installation procedure
2.1 Installation procedure .......................................................................................................... 2-1
2.2 Contents.............................................................................................................................. 2-1
2.3 Installing the 3098 enclosure...............................................................................................2-1
2.3.1 Important precautions ........................................................................................... 2-1
2.3.2 Connections .......................................................................................................... 2-2
2.4 Electrical connections and safety barriers / galvanic isolators............................................. 2-2
2.5 Reference chamber pressure determination ....................................................................... 2-2
2.6 Set-up procedure – purge cycling and calibration ............................................................... 2-4
2.7 Outline dimension drawings ................................................................................................2-7
)............................................................................................... 1-5
r
).................................................................. 1-5
s
Chapter 3 Electrical connections
3.1 Introduction .........................................................................................................................3-1
3.2 EMC cabling and earthing ................................................................................................... 3-2
3.3 Certificate conditions for hazardous areas ..........................................................................3-3
3.4 Use with Signal Converters and Flow Computers ............................................................... 3-4
3.5 System connections (7950/7951/7955) ............................................................................... 3-5
3.5.1 7950 2-wire configuration ...................................................................................... 3-5
3.5.2 7950 3-wire configuration ...................................................................................... 3-6
3.5.3 7951 2-wire configuration ...................................................................................... 3-7
3.5.4 7951 3-wire configuration ...................................................................................... 3-8
3.5.5 7955 2-wire configuration ...................................................................................... 3-9
3.5.6 7955 3-wire configuration .................................................................................... 3-10
3.6 System connections (customer’s own equipment) ............................................................ 3-11
3.6.1 Non-hazardous areas.......................................................................................... 3-11
3.6.2 Hazardous areas ................................................................................................. 3-11
3.6.3 Customer’s equipment, 2-wire configuration ....................................................... 3-12
3.6.4 Customer’s equipment, 3-wire configuration ....................................................... 3-13
3.7 Post-installation checks..................................................................................................... 3-14
Cont-5
Contents 3098 Technical Manual
Chapter 4 Accuracy considerations
4.1 Accuracy considerations...................................................................................................... 4-1
4.2 Calibration (for non-natural gas applications) ......................................................................4-4
4.2.1 Operation at low reference pressure levels ...........................................................4-4
Chapter 5 Maintenance and faultfinding
5.1 Introduction..........................................................................................................................5-1
5.1.1 Calibration check ................................................................................................... 5-1
5.1.2 Faultfinding............................................................................................................5-1
5.2 Maintenance ........................................................................................................................5-4
5.2.1 Main meter (3098) removal ...................................................................................5-4
5.2.2 Density meter removal...........................................................................................5-6
5.2.3 Reference chamber diaphragm removal ...............................................................5-7
5.2.4 Re-assembly procedure ........................................................................................5-8
5.2.5 3098 filter change procedure.................................................................................5-8
5.2.6 Further servicing of the density meter ...................................................................5-9
5.2.7 Leak testing the 3098 ..........................................................................................5-10
5.2.8 Post maintenance tests .......................................................................................5-10
5.2.9 Worked example of calibration certificate ............................................................ 5-10
Chapter 6 Specification
6.1 3098 specification................................................................................................................6-1
6.1.1 Performance..........................................................................................................6-1
6.1.2 Electrical................................................................................................................6-1
6.1.3 Mechanical ............................................................................................................6-1
6.1.4 Safety ....................................................................................................................6-2
Appendix A Performance optimisation
A.1 Introduction......................................................................................................................... A-1
A.1.1 The density sensor ............................................................................................... A-1
A.1.2 The non-ideal behaviour of gases ........................................................................ A-1
A.1.3 Selection of reference chamber pressure ............................................................. A-1
A.1.4 Selection of calibration gases............................................................................... A-2
A.2 Recommended calibration methods ................................................................................... A-2
A.2.1 General calibration method .................................................................................. A-2
A.2.2 Specific calibration method................................................................................... A-2
Appendix B Principles of operation
B.1 Theory – specific gravity measurement .............................................................................. B-1
Appendix C Returns forms
Cont-6
3098 Technical Manual Introduction
Chapter 1
Introduction
This chapter
This chapter contains an outline of how the 3098 works, defines some of the terms commonly used in the manual, and
also gives some practical applications for the 3098.
IMPORTANT NOTICE
The 3098 is normally installed in an IP rated enclosure prior to leaving the factory. In some instances however, the
3098 may be supplied without the enclosure, in which case the environmental and thermal performance of the meter
cannot be guaranteed. Warnings are given throughout this manual when the performance of the meter may be
affected by this.
Meters supplied complete have product labels attached to the outside of the enclosure, and none on the main
cylindrical body of the 3098. If the 3098 itself is labelled, this indicates that the product was supplied without the
enclosure.
For technical details, please refer to the system installer.
IMPORTANT NOTICE
The pressure relief valve has been factory set for the unit to conform to the Pressure Equipment Directive.
UNDER NO CIRCUMSTANCES SHOULD THIS SETTING BE CHANGED.
For further information, contact the factory using the details on the back page.
1-1
Introduction 3098 Technical Manual
1.1 Specific Gravity Measurement
Most major gas flow metering systems require the metered quantity to be presented in Heat or standard volume units. To
achieve this requirement, it is often necessary to make continuous and accurate measurements of specific gravity.
Specific gravity can be evaluated by relating the molecular weight of the gas (or gas mixture) to that of the molecular
weight of air, or by evaluating the relative density of the gas (or gas mixture) and compensating the result for the Boyle’s
Law deviation on both the gas (or gas mixture) and the air.
The 3098 Specific Gravity Meter adopts a combination of these two methods, where, by measuring the density of the gas
under controlled conditions, the value of density obtained is directly related to the molecular weight of the gas, and thus to
its specific gravity.
Figure 1-1: View of the 3098 Specific Gravity Meter
installed in a typical enclosure
1-2
3098 Technical Manual Introduction
1.2 Functional Description
INSULATING
COVER
CONTROL
PRESSURE
INDICATOR
CHAMBER FILLING
VALVE, E
REFERENCE
CHAMBER
PRESSURE
CONTROL VALVE
OUTPUT
ORIFICE
TO SIGNAL
CONVERTER
TO VENT
Gas
Line
VENT AND INPUT
FOR CALIBRATION
GASES
ISOLATION
VALVE, D
VALVE A
VALVE B
VALVE F
(PURGING VALVE)
PRESSURE
REGULATOR
INPUT
ORIFICE
FILTER
PRESSURE
RELIEF VALVE
DENSITY
METER
3098
DIAPHRAGM
VALVE C
OUTLET
Figure 1-2: Schematic diagram of a typical 3098 Specific Gravity Measuring System
The 3098 Specific Gravity Meter consists of a vibrating cylinder gas density meter surrounded by a gas reference
chamber, which helps to achieve good thermal equilibrium. The gas reference chamber has a fixed volume that is initially
pressurised with the actual line gas. It is then sealed by closing the reference chamber filling valve, thus retaining a fixed
measure and quantity of gas, now known as the reference gas.
Note: Once the chamber has been filled, do not open this valve again.
The sample gas enters the instrument at the enclosure side and passes through a filter, followed by a pressure-reducing
orifice. The sample gas is then fed through input pipework so that it enters the gas density meter at the equilibrium
temperature of the unit. The gas then flows down to a pressure control valve chamber.
The pressure of the reference gas acts on the separator diaphragm and forces the line gas pressure to rise until the
pressures on both sides are equal, thus the gas pressures within the gas density meter and the reference chamber are
equal.
As the ambient temperature changes, the pressure of the fixed volume of reference gas will change as defined by the Gas
Laws. This change in pressure will affect the sample gas pressure within the gas density meter such that the temperature
and pressure changes are self-compensating.
If the sample gas pressure rises above that of the reference chamber pressure, the pressure control valve opens to vent
the excess gas via an outlet orifice in the enclosure side, so that the sample gas pressure is reduced to equal the
reference gas pressure. For gas to flow it is necessary that the supply pressure is greater than the reference pressure,
which in turn must be greater than the vent pressure. (Typically the line pressure must be between 15 and 25% above that
of the reference chamber pressure)
[The principles of operation that describe this operation are given in Appendix B]
A pressure gauge is fitted in order to monitor the pressure within the gas density meter. This is desirable when charging
the reference chamber and also for general maintenance.
Electrical connections to the 3098 are taken through the cable gland in the enclosure side and then into the density
meter’s electronics housing.
1-3
Introduction 3098 Technical Manual
When the enclosure is sealed, the complete instrument is insulated so that rapid changes in ambient temperature will not
upset the temperature equilibrium of the unit and produce thermal shock errors.
Note that the 3098 may have been supplied without an enclosure - see Important Notice on page 1-1.
1.2.1 Meter Sensing Element
The gas density meter consists of a thin metal cylinder which is activated so that it vibrates in a hoop mode at its natural
frequency. The gas is passed over the inner and outer surfaces of the cylinder and is thus in contact with the vibrating
walls. The mass of gas which vibrates with the cylinder depends upon the gas density and, since increasing the vibrating
mass decreases the natural frequency of vibration, the gas density for any particular frequency of vibration can be
determined.
A solid state amplifier, magnetically coupled to the sensing element, maintains the conditions of vibration and also
provides the output signal.
1.2.2 Installation
The 3098 has been designed to be installed wall mounted, a typical installation set-up being given in figure 1-3 below.
ISOLATION
VALVE
GAS
LINE
GAS FOR
CALIBRATION
HAZARDOUS AREA SAFE AREA
VENT TO
ATMOSPHERE
PRESSURE
REGULATOR
VALVE A
VALVE B
VALVE F
IN OUT
ELECTRICAL
CABLE
VALVE C
Figure 1-3: Typical 3098 Specific Gravity Measuring System
SAFETY
BARRIERS
SIGNAL
CONVERTER
1-4
3098 Technical Manual Introduction
G
ρ
ρ
G
ρ
ρ
1.3 Definition of Terms
1.3.1 Specific Gravity (G)
This is the ratio of the molecular weight of a gas (or gas mixture) to that of the molecular weight of dry air; the molecular
weight of dry air is normally assumed to be 28.96469 (see Table 1).
M
i.e
=
G
M
A
where
and
1.3.2 Standard (Base or Normal) Density (
This is the absolute density of a gas at STANDARD (BASE or NORMAL) conditions of temperature and pressure and is
commonly used for STANDARD VOLUME flow determination from MASS flow measurement.
i.e
where P = Absolute pressure (bars)
1.3.3 Relative Density (
This is the ratio of the weight of a volume of gas (or gas mixture) to the weight of an equal volume of dry air (see Table 1),
where the weights of both gas (or gas mixture) and air are taken under identical conditions of temperature and pressure.
NOTE: Except for the effects of Boyle’s Law deviation upon both the gas (or gas mixture) and the air, G and
synonymous.
M
= Molecular weight of gas (or gas mixture)
G
M
= Molecular weight of dry air
A
ρ
T = Absolute temperature (degrees Kelvin)
M = Molecular weight
Z = Supercompressibility factor
R = Gas constant (taken as 0.0831434)
=
s
r)
PM
ZRT
s)
ρ
r are
M
i.e
=
where
=
=
ρ
= Density of the gas or gas mixture
G
= Density of air
A
Z
= Supercompressibility factor of the gas or gas mixture
G
Z
= Supercompressibility factor of air
A
M
GG
ρ
ρ
r
G
A
Z
Z
AA
Z
G
Z
A
1-5
Introduction 3098 Technical Manual
ρ
The relative density of mixed hydrocarbon gases at 1 bar (14.735 lb/in2) absolute and 15.56°C (60°F) by empirical
equation is:
= 0.995899G + 0.010096G
r
2
1-6
3098 Technical Manual Introduction
1.4 Physical Properties of Gas Compounds
Compound Formula Molecular Weight Specific Gravity
Hydrogen H2 2.01594 .069600
Helium He 4.00260 .138189
Water Vapour H2O 18.01534 .621976
Nitrogen N2 28.01340 .967157
Carbon Monoxide CO 28.01055 .967058
Oxygen O2 31.99880 1.104752
Argon Ar 39.94800 1.379197
Carbon Dioxide CO2 44.00995 1.519435
Air (3) - 28.96469 1.000000
Hydrogen Sulphide H2S 34.07994 1.176603
Methane CH4 16.04303 .553882
Ethane C2H6 30.07012 1.038165
Propane C3H8 44.09721 1.522447
i-Butane C4H10 58.12430 2.006730
n-Butane C4H10 58.12430 2.006730
i-Pentane C5H12 72.15139 2.491012
n-Pentane C5H12 72.15139 2.491012
Hexane C6H14 86.17848 2.975294
Heptane C7H16 100.20557 3.459577
Octane C8H18 114.23266 3.943859
Table 1
NOTES:
1. Based upon 1961 atomic weights, referred to Carbon-12 Isotope (12 AMU), recommended by the International
Commission of Atomic Weights and the International Union of Pure and Applied Chemistry.
2. Perfect gas specific gravity represents the ratio of molecular weight of compounds to the molecular weight of air.
3. Molecular weight of air based upon components of atmospheric air given in Handbook of Chemistry & Physics, 53rd
Edition (1972 - 1973). Value of 28.96469 differs from figure 28.966 provided by NBS Circular 564 due to minute
differences in component content and changes in atomic weights of the elements given in 1961 (NBS value based
upon 1959 atomic weights).
1-7
Introduction 3098 Technical Manual
M
1.5 Applications
The following are typical applications where specific gravity measurement is an essential parameter.
1.5.1 Supplementary Gas Supply
This system is used to top up normal supplies during peak periods. Specific gravity monitoring of a propane/air mixture for
example, enables accurate control to be exercised over the ratio of the mixture, therefore ensuring that the correct burning
characteristic/calorific value is maintained.
1.5.2 Wobbe Index Measurement
The burning characteristic of a gas must be well established for efficient combustion and to ensure that no flame lift or
flame light-back occurs on a particular burner. Three criteria are used to establish this characteristic; calorific value,
specific gravity and flame speed. The calorific value and specific gravity are often combined to form the Wobbe Number
i.e:
Wobbe Number = C V
√G
where CV = Calorific value
G = Specific gravity
1.5.3 Consumer Gas Costing
This major application has already been described in the introduction, MASS to BASE VOLUME unit conversion, and may
be further illustrated by the following equations:
Base Unit Volume = Mass Flow
Base Density
i.e Vs = M
ρ
G
s
ρ
AA
Z
Z
G
=
1-8
3098 Technical Manual Installation Procedure
Chapter 2
Installation Procedure
2.1 Installation Procedure
The procedure for installing the 3098 involves the following steps:
Check all components are present (Section 2.2)
Position and fix the 3098 enclosure (Section 2.3)
Connect the gas supply line (Section 2.3.2)
Make electrical connections (Section 2.4 and Chapter 3)
Select a reference pressure (Section 2.5)
Purge cycle and calibrate the 3098 (Section 2.6)
2.2 Contents
The following items should be enclosed with this 3098 unit:
3098 Specific Gravity Meter.
Labelled enclosure.
Enclosure mounting feet.
Enclosure mounting feet instructions.
This technical manual (30985020).
Safety Instructions (3095008/SI and 30988002/SI).
Accessories kit.
Temperature coefficient Calibration Certificate.
Check that all the above items are present; if not then contact your supplier immediately. (Note that the 3098 may have
been supplied without an enclosure.)
2.3 Installing the 3098 enclosure
The following installation instructions apply only to meters supplied with an enclosure (see Important Notice on page 1-1).
In all other cases, please refer to the system installer.
2.3.1 Important Precautions
Take care to observe the precautions listed at the front of this manual (page Cont-3).
The 3098 SG meter is contained inside an IP rated enclosure (which provides thermal insulation) and a mounting system
(consisting of a bracket and feet) to fix the unit in place. Whilst this structure is designed to minimise damage due to
shocks, the box and unit must not be dropped. Dropping of the 3098 either inside or outside its enclosure will damage
the meter.
Contained inside the enclosure are four box feet which, when attached to a vertical wall will hold the housing. A set of
instructions on how to attach these feet is included inside the box. Enclosure dimensions are in Section 2.7.
2-1
Installation Procedure 3098 Technical Manual
2.3.2 Connections
There are four connections that need to be made to the 3098: three gas pipeline connections and one electrical
connection through an IP rated cable gland. The gas pipeline connections take the form of ¼” Swagelok bulkhead fittings,
and are used for the gas input, gas output and pressure relief lines.
Each connection is labelled.
Caution: Connecting the gas input line to the wrong bulkhead fitting might result in damage.
A 7812 gas density meter is used as the measuring instrument in the 3098 and needs to be connected inside the
enclosure. All wiring should be connected through the cable gland to maintain the enclosure’s overall protection to dust
and water ingress.
At all stages during calibration and operation, the 3098 is designed to function with the enclosure sealed. This allows the
unit to operate in the condition of thermal equilibrium, which is essential for accurate measurement.
2.4 Electrical Connections and Safety Barriers / Galvanic Isolators
When the 3098 is mounted in a hazardous area, the electrical connections to the meter must conform to stringent
conditions. For electrical connections between the meter and its associated flow computer/signal converter, reference
must be made to safety instruction booklet 30985018/SI.
Electrical cable connection to the 3098 is made to the terminal block inside the resonator electronics housing (i.e. inside
the enclosure). Poor connection to the terminals will prevent correct operation but will not damage the unit - provided that
safety barriers or galvanic isolators are included in the circuit for hazardous areas or the maximum power supply does not
exceed the 33V maximum limit (as described in chapter 3).
The power supplied to the meter terminals should be in the range of 15.5 to 33Vd.c with the average current drawn by the
unit being <20mA. If the current consumption exceeds this value, the polarity of the connections should be checked.
A full description of how to connect the 3098 to a signal converter/flow computer is given in Chapter 3.
2.5 Reference Chamber Pressure Determination
Once the 3098 has been placed in its fixture and all relevant pipework and electrical connections made, the reference
chamber pressure needs to be determined.
The gas type and reference chamber pressure define the ‘controlled condition’ at which the unit allows gas to flow and
establishes a direct relationship between density and the specific gravity of the sample gas.
The choice of reference chamber gas pressure is dependent upon 3 factors:
1. The span of specific gravity to be measured.
2. The expected change in sample gas supercompressibility, Z.
3. The accuracy required.
2-2
3098 Technical Manual Installation Procedure
The graph below gives an indication of the typical errors associated with using different reference chamber pressures for
natural gas with a reasonably constant specific gravity (in the range of 0.55-0.8). This is typical for natural gas metering
market, where the gas is available at a line pressure of 7 Bar abs.
As can be seen, below 7 Bar abs, the total error begins to increase; using a higher reference pressure will not improve
accuracy, but may encourage gas leakage. Therefore, for the conditions specified, 7 Bar is the recommended pressure.
Typical Total Error/ °C vs Referenc e Chamber Pressure
For NATURAL GAS APPLICATIONS ONLY.
0.035
0.035
0.025
0.015
0.005
0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5 8 8.5 9 9.5 10
-0.005
-0.015
Typ % of FS Specific Gravity /°C
-0.025
-0.035
Reference Chamber Pressure (Bar A)
0.025
0.015
0.005
-0.005
-0.015
-0.025
-0.035
Typ % of FS Specific Gravity /°C
This graph should only be used for natural gas applications, and.gives typical errors seen on the 3098 if it is not used at
the recommended reference chamber pressure.
If the span of specific gravity or change in supercompressibility, Z, is large, and the gas is not a methane/nitrogen mix,
then the best reference chamber pressure can still be determined. The calculation for doing this is explained in Chapter 4,
‘Accuracy Considerations’.
Once the desired reference pressure has been found, the 3098 can now be purge cycled and then calibrated.
2-3
Installation Procedure 3098 Technical Manual
2.6 Set-up procedure - Purge Cycling and Calibration
IMPORTANT NOTICE
The pressure relief valve has been factory set for the unit to conform to the Pressure Equipment Directive.
UNDER NO CIRCUMSTANCES SHOULD THIS SETTING BE CHANGED.
For further information, contact the factory using the details on the back page.
INSULATING
COVER
CONTROL
PRESSURE
INDICATOR
CHAMBER FILLING
VALVE, E
REFERENCE
CHAMBER
PRESSURE
CONTROL VALVE
OUTPUT
ORIFICE
Gas
Line
VENT AND INPUT
FOR CALIBRATION
GASES
ISOLATION
VALVE, D
VALVE A
VALVE B
VALVE F
(PURGING VALVE)
PRESSURE
REGULATOR
INPUT
ORIFICE
FILTER
PRESSURE
RELIEF VALVE
DENSITY
METER
3098
DIAPHRAGM
VALVE C
OUTLET
Figure 2-1: Schematic diagram of a typical 3098 Specific Gravity Measuring System
TO SIGNAL
CONVERTER
TO VENT
The procedure for purging and calibrating the 3098 is given below:
1. Ensure isolation valve (D) is closed.
2. Ensure valve (A) is closed.
3. Ensure valve (B) is closed.
4. Ensure valve (F) is closed.
5. Open valve (C).
6. Open chamber filling valve (E).
7. Set the pressure regulator to the required value - i.e. the actual working pressure of the system.
8. Open isolation valve (D).
9. Open valve (A) and allow gas to flow for 3 minutes.
2-4
3098 Technical Manual Installation Procedure
Purge Cycling
10. Close valve (C).
11. When Control Pressure Indicator is at the desired value, shut valve (A) and open valve (F). Allow the gas to vent to
atmospheric pressure.
12. Close valve (F) and open valve (A).
13. When Control Pressure Indicator is at the desired value, shut valve (A) and open valve (F). Allow the gas to vent to
atmospheric pressure.
Actions 12 and 13 define the purging cycle required for setting up the reference chamber gas in the 3098.
The number of times that this procedure should be repeated depends upon the gas regulator pressure used and is defined by:
ª
=cyclespurgeofNumber
«
¬
14. Once the required number of cycles has been performed, close valve (F) and open valve (A).
15. When the desired gas pressure inside the chamber has been reached (as shown by the Control Pressure Indicator)
shut the chamber valve.
7 x 3
pressureregulatormax
º
»
¼
DO NOT open the chamber valve again.
The gas now inside the 3098 chamber is the line reference gas.
3098 Calibration using two known gases
16. Close valve (A).
17. Connect the first calibration gas bottle to the pipework and set the pressure to be typically 25% above that inside the
reference chamber.
18. Open valve (B).
19. Ensure valve (C) is open and allow gas to flow until the time period as measured by the signal converter/flow
computer is stable to ±1ns or better (the typical stability will be better than this). [For the required electrical
connections see Chapter 3]
20. Note this time period (τ
21. Shut valve (B).
22. Replace the first calibration gas bottle with the second calibration gas bottle.
23. Set pressure to typically 25% above that inside the reference chamber and open valve B.
24. Allow gas to flow until the time period shown by the meter is stable to ±1ns or better.
25. Note this time period (τ
26. Apply these noted numbers into equations (1) and (2) below:
) together with the certified SG from the bottle of gas (SG1).
1
) and the certified SG from the bottle of gas (SG2).
2
ª
K
=
«
2
2
() ()
1
¬
−=
Alternatives to this are to use the calibration certificate shown in table 4 (found in Chapter 4), or to use the Excel
program ‘Calcert.xls’ that is supplied on the attached floppy disk.
28. Shut valve (B) and disconnect the second calibration gas bottle from pipework.
29. Open the isolation valve (D).
30. Open valve (A).
SGSG
−
ττ
−
KSGK
º
21
»
2
2
¼
2
()
τ
1210
(1)
(2)
2-5
Installation Procedure 3098 Technical Manual
IMPORTANT NOTE
If the application is running with a reference pressure less than 45.5 psi (3 BarA), the maximum flow rate that can be used
for correct operation is 50cm
The unit should now give a live reading of the measured gas SG. If the unit does not output a sensible reading, certain
checks can be made. These checks are summarised in Chapter 5, ‘Maintenance & Fault finding’.
If optimum SG accuracy is required, the optimisation method described in Appendix A - which compensates for errors due
to gas velocity of sound, compressibility and temperature coefficient - should be used.
For optimum accuracy, the time period (τ) must be resolved to ±0.1ns. This can be achieved using 7950/7951/7955 signal
converters and flow computers set to a cycle time of 10s.
3
/s. A full explanation of this effect is given in Accuracy Considerations, Chapter 4.
2-6
3098 Technical Manual Installation Procedure
2.7 Outline dimensional drawings
The drawings below show a 3098 without an enclosure. For dimensions of small and large enclosures, see the following
two pages.
”
4
2.
1
m)
m
4
1
(3
4.4” (112mm)
)
”
4
.
6
8
2
(
”
5
.
0
1
2-7
Installation Procedure 3098 Technical Manual
Small Enclosure Dimensions
Large Enclosure Dimensions
2-8
3098 Technical Manual Electrical Connections
Chapter 3
Electrical Connections
This chapter
This chapter contains details and wiring diagrams for connecting the 3098 to 7950/51/55 Signal Converters and Flow
Computers, and more generally to other equipment in both hazardous and non-hazardous situations.
3.1 Introduction
The electrical connections to the 3098 are made to the 7812 gas density meter held inside the enclosure. When installed
in hazardous areas, connections between the meter and the power supply/readout equipment must be completed through
ZENER SAFETY BARRIERS [or galvanic isolators]. The electrical cable enters the enclosure (if supplied - see Important
Notice on page 1-1) through a cable gland assembly and then passes into the amplifier housing.
The meter terminal layout is shown in Figure 3-1.
The amplifier housing has two chambers. The one nearest the cable gland axis contains the terminals for connection to
the meter/signal processing instrument. The other chamber contains the maintaining amplifier unit. The amplifier board is
encapsulated in a circular plastic container, with the complete module secured by a keyway and a centrally positioned
clamping screw. Behind the amplifier there is an interconnect terminal board which links the sensor to the maintaining
amplifier, and the amplifier to the user connect board (see Figure 3-2).
SIG A
SIG B
123
Figure 3-1: Main Terminal Board Connections
4567
9110 11 12
PRT
8
3-1
Electrical Connections 3098 Technical Manual
INTERCONNECT PCB
78121503
PICK UP
COIL
DRIVE
COIL
BN
O
R
B
SPOOLBODY
78121201
2
3
4
5
BN
13 20
R
14 19
O
16 18
Y
15 17
12 4 3
TERMINAL PCB
78121502
BN PL1
R PL2
O PL5
Y PL6
22
21
23
- B+ -
SIG BSIG A
R PL3
G PL4
O PL7
I/P +
I/P -
O/P +
O/P -
V +
V -
FREQ. OUT
AMPLIFIER PC B
78121501
Figure 3-2: Interconnection diagram
3.2 EMC Cabling and Earthing
To meet the EC Directive for EMC (Electromagnetic Compatibility), it is recommended that the meter be connected using
a suitable instrumentation cable and earthed through the meter body and pipework. The instrumentation cable should
have an individual screen, foil or braid over each twisted pair and an overall screen to cover all cores. Where permissible,
the screen should be connected to earth at both ends. Note that for intrinsic safety, termination of the screen to earth in
the hazardous area is NOT generally permitted.
Typical cables that are suitable are those that meet BS5308 Multi-pair Instrumentation Types 1 and 2, such as Belden
types 9500, 9873, 9874, 9773, 9774 etc.
3-2
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