Emerson Process Management MMI-20014120 User Manual
Installation and Configuration Manual
P/N MMI-20014120, Rev. AB
August 2012
Micro Motion® 3098 Gas
Specific Gravity Meter
©2012, Micro Motion, Inc. All rights reserved. Micro Motion is a registered trade name of Micro Motion, Inc., Boulder, Colorado.
The Micro Motion and Emerson logos are trademarks and service marks of Emerson Electric Co. All other trademarks are property
of their respective owners.
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.
Contents
Chapter 1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1 Safety guidelines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 Specific gravity measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.3 Functional description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.3.1 Meter sensing element. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.3.2 Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.4 Definition of terms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.4.1 Specific gravity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.4.2 Standard (base or normal) density . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.4.3 Relative density . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.5 Physical properties of gas compounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
1.6 Applications. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
1.6.1 Supplementary gas supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
1.6.2 Wobbe index measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
1.6.3 Consumer gas costing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Chapter 2 Installation Procedure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.1 Installation procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.2 Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.3 Installing the 3098 enclosure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.3.1 Important precautions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.3.2 Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.3.3 Coalescing filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.4 Electrical connections and safety barriers / galvanic isolators . . . . . . . . . . . . . . . . . 10
2.5 Reference chamber pressure determination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.6 Set-up procedure – purge cycling and calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
2.7 Outline dimensional drawings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Chapter 3 Electrical Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
3.2 EMC cabling and earthing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
3.3 Certificate conditions for hazardous areas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
3.4 Use with signal converters and flow computers . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
3.5 System connections (7950/7951) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
3.5.1 7950 2-wire configuration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
3.5.2 7950 3-wire configuration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
3.5.3 7951 2-wire configuration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
3.5.4 7951 3-wire configuration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
3.6 System connections (customer’s own equipment) . . . . . . . . . . . . . . . . . . . . . . . . . . 27
3.6.1 Non-hazardous areas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
3.6.2 Hazardous areas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
3.6.3 Customer's equipment, 2-wire configuration . . . . . . . . . . . . . . . . . . . . . . 27
3.6.4 Customer's equipment, 3-wire configuration . . . . . . . . . . . . . . . . . . . . . . 28
3.7 Post-installation checks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Installation and Configuration Manual i
Contents
Chapter 4 Accuracy Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
4.1 Accuracy considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
4.1.1 Example 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
4.1.2 Example 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
4.1.3 Calculating parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
4.2 Calibration (for non-natural gas applications) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
4.3 Operation at low reference pressure levels. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
4.4 Calibration certificate example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Chapter 5 Maintenance and Fault Finding . . . . . . . . . . . . . . . . . . . . . . . . . . 35
5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
5.2 Calibration check . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
5.3 Fault finding. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
5.3.1 Instrument over-reads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
5.3.2 Instrument under-reads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
5.4 Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
5.4.1 Main meter (3098 specific gravity meter) removal (Figure 5-1) . . . . . . . . 38
5.4.2 Density meter removal (Figure 5-2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
5.4.3 Reference chamber diaphragm removal (Figure 5-3) . . . . . . . . . . . . . . . 40
5.4.4 Re-assembly procedure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
5.4.5 3098 specific gravity meter filter change procedure . . . . . . . . . . . . . . . . 41
5.4.6 Further servicing of the density meter (Figure 5-5) . . . . . . . . . . . . . . . . . 42
5.4.7 Leak testing the 3098 specific gravity meter . . . . . . . . . . . . . . . . . . . . . . 43
5.4.8 Post-maintenance tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
5.4.9 Worked example of calibration certificate . . . . . . . . . . . . . . . . . . . . . . . . 43
Chapter 6 Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
6.1 3098 specific gravity meter specifications. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
6.1.1 Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
6.1.2 Electrical . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
6.1.3 Mechanical . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
6.1.4 Safety. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
Appendix A Performance Optimization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
A.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
A.1.1 Density sensor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
A.1.2 The non-ideal behaviour of gases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
A.1.3 Selection of reference chamber pressure . . . . . . . . . . . . . . . . . . . . . . . . 48
A.1.4 Selection of calibration gases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
A.2 Recommended calibration methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
A.2.1 General calibration method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
A.2.2 Specific calibration method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
Appendix B Principles of Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
B.1 Theory of specific gravity measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
Appendix C Return Policy. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
C.1 General guidelines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
ii Micro Motion 3098 Gas Specific Gravity Meter
Contents
C.2 New and unused equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
C.3 Used equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
Appendix D Certified System Drawings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
D.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
Installation and Configuration Manual iii
Contents
iv Micro Motion 3098 Gas Specific Gravity Meter
Chapter 1
Introduction
This chapter contains an outline of how the 3098 specific gravity meter works, defines some of the
terms commonly used in the manual, and also gives some practical applications for the 3098.
The 3098 specific gravity meter is normally installed in an IP rated enclosure prior to leaving the factory. In
some instances however, the 3098 specific gravity meter may be supplied without an 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.
For technical details, please refer to the system installer.
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 of this manual.
Installation Procedure Accuracy ConsiderationsElectrical ConnectionsIntroduction
1.1 Safety guidelines
Handle the 3098 specific gravity meter 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 (> 0.5 g continuous).
• Ensure all electrical safety requirements are applied.
• Ensure good ventilation around the meter / cabinet to prevent gas build up in the unlikely event
of a leak.
• Ensure meter is not transported when it contains hazardous substances. This includes fluids
that may have leaked into, and are still contained, within the case.
• Ensure that a Balston coalescing filter is fitted into the gas supply line to the 3098 meter.
Either a type 85 or a 91S6 (as supplied) MUST be fitted to comply with ATEX/IECEx
approval requirements.
• To return a meter, refer to Appendix C for more information on the Micro Motion return
policy.
Safety messages are provided throughout this manual to protect personnel and equipment. Read each
safety message carefully before proceeding to the next step.
Installation and Configuration Manual 1
Introduction
1.2 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
2 Micro Motion 3098 Gas Specific Gravity Meter
Introduction
Gas
line
3098
Pressure
regulator
Insulating cover
Control pressure indicator
Chamber filling valve E
Reference chamber
Output orifice
To signal converter
To v e n t
Outlet
Val ve C
Val ve B
Valve F (purging valve)
Vent and input for
calibration gases
Isolation
valve D
Val ve A
Input
orifice
Filter
Pressure relief valve
Diaphragm
Coalescing filter
1.3 Functional description
Figure 1-2 Schematic diagram of a typical 3098 specific gravity measuring system
Installation Procedure Accuracy ConsiderationsElectrical ConnectionsIntroduction
Installation and Configuration Manual 3
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 pressurized 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 the reference chamber filling 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.
Introduction
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).
Note: 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 specific gravity meter are taken through the cable gland in the
enclosure side and then into the density meter’s electronics housing.
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: The 3098 specific gravity meter may have been supplied without an enclosure – see Safety
guidelines on page 1.
1.3.1 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.
1.3.2 Installation
The 3098 specific gravity meter has been designed to be installed mounted to a wall (wall mounted), a
typical installation set-up being given in Figure 1-3 below.
4 Micro Motion 3098 Gas Specific Gravity Meter
Introduction
SAFE AREA
HAZARDOUS AREA
Pressure
regulator
Isolation
valve
Val ve A
Val ve B
Gas for
calibration
Val ve F
Safety
barrier
Vent to
atmosphere
Signal
converter
Valve C
Electrical cable
In
Out
for example
where M
G
= molecular weight of gas (or gas mixture)
and M
A
= molecular weight of dry air
G
M
G
M
A
--------=
Figure 1-3 Typical 3098 specific gravity measuring system
Installation Procedure Accuracy ConsiderationsElectrical ConnectionsIntroduction
1.4 Definition of terms
1.4.1 Specific gravity
Specific gravity (G) 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 1-1).
Installation and Configuration Manual 5
Introduction
for example
where p = absolute pressure (bars)
T = absolute temperature (degrees Kelvin)
M = molecular weight
Z = supercompressibility factor
R = gas constant (taken as 0.0831434)
ρ
s
pM
ZRT
------------=
for example
where ρ
G
= density of the gas or gas mixture
ρ
A
= density of air
Z
G
= supercompressibility factor of the gas or gas mixture
Z
A
= supercompressiblity factor of air
G
M
G
M
A
--------=
ρGZ
G
ρAZ
A
---------------=
ρ
r
Z
G
Z
A
-------
⋅=
ρr0.995899G 0.010096G
2
+=
1.4.2 Standard (base or normal) density
Standard (base or normal) density (
ρ
) is the absolute density of a gas at standard (base or normal)
s
conditions of temperature and pressure and is commonly used for standard volumne flow
determination from mass flow measurement.
1.4.3 Relative density
Relative density (
equal volume of dry air (see Table 1-1), where the weights of both gas
ρ
) is the ratio of the weight of a volume of gas (or gas mixture) to the weight of an
r
(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
ρ
r are synonymous.
The relative density of mixed hydrocarbon gases at 1 bar (14.50377 lb/in
(60°F) by empirical equation is:
6 Micro Motion 3098 Gas Specific Gravity Meter
2
) absolute and 15.56°C
Introduction
1.5 Physical properties of gas compounds
Table 1-1 Physical properties of gas compounds
Compound Formula Molecular Weight
Hydrogen H
2
2.01594 0.069600
(1)
Specific Gravity
(2)
Helium He 4.00260 0.138189
Water Vapour H
Nitrogen N
O 18.01534 0.621976
2
2
28.01340 0.967157
Carbon Monoxide CO 28.01055 0.967058
Oxygen O
2
31.99880 1.104752
Argon Ar 39.94800 1.379197
(3)
Air
Hydrogen Sulphide H
Methane CH
Ethane C
Propane C
i-Butane C4H
n-Butane C4H
i-Pentane C
n-Pentane C5H
Hexane C6H
Heptane C
Octane C8H
– 28.96469 1.000000
S 34.07994 1.176603
2
4
2H6
3H8
10
10
5H12
12
14
7H16
18
16.04303 0.553882
30.07012 1.038165
44.09721 1.5522447
58.12430 2.006730
58.12430 2.006730
72.15139 2.491012
72.15139 2.491012
86.17848 2.975294
100.20557 3.459577
114.23266 3.943859
(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).
Installation Procedure Accuracy ConsiderationsElectrical ConnectionsIntroduction
1.6 Applications
The following are typical applications where specific gravity measurement is an essential parameter.
1.6.1 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.
Installation and Configuration Manual 7
Introduction
Wobbe number
where CV = calorific value
G = specific gravity
CV
G
--------=
Base unit volume
for example
Mass flow
Base density
----------------------------------------=
Vs
M
ρ
s
-----=
M
G
P
AZA
Z
G
--------------
--------------------=
1.6.2 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:
1.6.3 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:
8 Micro Motion 3098 Gas Specific Gravity Meter
Chapter 2
Installation Procedure
2.1 Installation procedure
The procedure for installing the 3098 involves the following steps:
1. Check all components are present (Section 2.2).
2. Position and fix the 3098 enclosure (Section 2.3).
3. Connect the gas supply line (Section 2.3.2).
4. Fit the supplied coalescing filter into the gas supply line in accordance with manufacturer’s
instructions (Section 2.3.3) .
5. Make electrical connections (Section 2.4 and Chapter 3).
6. Select a reference pressure (Section 2.5).
7. Purge cycle and calibrate the 3098 (Section 2.6).
Installation Procedure Accuracy ConsiderationsElectrical ConnectionsIntroduction
2.2 Contents
The following items should be enclosed with the 3098 unit:
• 3098 specific gravity meter
• Labeled enclosure
• Enclosure mounting feet
• Enclosure mounting feet instructions
• 3098 Installation and Configuration manual (MMI-20014120)
• Safety instructions (CE-marked units only)
• Accessories kit
• Temperature Coefficient Calibration certificate
Note: Check that all the above items are present. If not, then contact your supplier immediately. (Be
aware 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 Safety
guidelines on page 1). In all other cases, please refer to the system installer.
2.3.1 Important precautions
Take care to observe the precautions listed in Safety guidelines on page 1.
Installation and Configuration Manual 9
Installation Procedure
The 3098 specific gravity 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. While this
structure is designed to minimize damage due to shocks, the box and unit must not be dropped.
Dropping the 3098 specific gravity meter 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.
2.3.2 Connections
There are four connections that need to be made to the 3098 specific gravity meter: 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.
Connecting the gas input line to the wrong bulkhead fitting might result in damage.
A gas density meter is used as the measuring instrument in the 3098 specific gravity meter 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 specific gravity meter 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.
2.3.3 Coalescing filter
Ensure that the coalescing filter (as supplied) is fitted into the gas supply line to the 3098 meter. This
MUST be done in order to comply with the ATEX/IECEx approval requirements.
2.4 Electrical connections and safety barriers / galvanic isolators
When the 3098 specific gravity meter 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, for ATEX/IECEx installations see the ATEX/IECEx Safety
Instructions booklet (available at www.micromotion.com) and for CSA installations see Appendix D.
Electrical cable connection to the 3098 specific gravity meter is made to the terminal block inside the
resonator electronics housing (for example, 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 33 V maximum limit (as described in Chapter 3).
The power supplied to the meter terminals should be in the range of 15.5 to 33 Vdc with the average
current drawn by the unit being < 20 mA. If the current consumption exceeds this value, the polarity
of the connections should be checked.
A full description of how to connect the 3098 specific gravity meter to a signal converter/flow
computer is given in Chapter 3.
10 Micro Motion 3098 Gas Specific Gravity Meter
Installation Procedure
Typical Total Error/°C vs Reference Chamber Pressure
For NATURAL GAS APPLICATIONS ONLY.
-0.035
-0.025
-0.015
-0.005
0.005
0.015
0.025
0.035
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
Reference Chamber Pressure (Bar A)
Typ % of FS Specific Gravity /°C
-0.035
-0.025
-0.015
-0.005
0.005
0.015
0.025
0.035
Typ % of FS Specific Gravity /°C
2.5 Reference chamber pressure determination
Once the 3098 specific gravity meter 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 three factors:
• The span of specific gravity to be measured
• The expected change in sample gas supercompressibility, Z
• The accuracy required
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.
Installation Procedure Accuracy ConsiderationsElectrical ConnectionsIntroduction
Figure 2-1 Typical total error/°C versus reference chamber pressure
This graph should only be used for natural gas applications, and.gives typical errors seen on the 3098
specific gravity meter 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.
Once the desired reference pressure has been found, the 3098 specific gravity meter can now be purge
cycled and then calibrated.
Installation and Configuration Manual 11
Installation Procedure
Gas
line
3098
Pressure
regulator
Insulating cover
Control pressure indicator
Chamber filling valve E
Reference chamber
Output orifice
To signal converter
To v e n t
Outlet
Val ve C
Val ve B
Valve F (purging valve)
Vent and input for
calibration gases
Isolation
valve D
Val ve A
Input
orifice
Filter
Pressure relief valve
Diaphragm
Coalescing filter
2.6 Set-up procedure – purge cycling and calibration
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.
Figure 2-2 Schematic diagram of a typical 3098 specific gravity measuring system
12 Micro Motion 3098 Gas Specific Gravity Meter
The procedure for purging and calibrating the 3098 specific gravity meter is given below (see
Figure 2-2 for reference):
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 – for example, the actual working pressure of
the system.
8. Open isolation valve D.
9. Open valve A and allow gas to flow for 3 minutes.
Installation Procedure
⎥
⎦
⎤
⎢
⎣
⎡
pressure regulatormax
7 x 3
= cycles purge of Number
() ()
()
(2)
(1)
2
1210
2
2
2
1
21
2
τ
ττ
KSGK
SGSG
K
−=
⎥
⎦
⎤
⎢
⎣
⎡
−
−
=
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.
Steps 12 and 13 define the purging cycle required for setting up the reference chamber gas in
the 3098 specific gravity meter. The number of times that this procedure should be repeated
depends upon the gas regulator pressure used and is defined by:
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.
DO NOT open the chamber valve again. The gas now inside the 3098 chamber is the line reference
gas.
3098 specific gravity meter 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 ±1 ns or better (the typical stability will be better than
this). [For the required electrical connections see Chapter 3]
20. Note this time period (τ
) together with the certified SG from the bottle of gas (SG1).
1
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 ±1 ns or better.
25. Note this time period (τ
) and the certified SG from the bottle of gas (SG2).
2
26. Apply these noted numbers into equations (1) and (2) below:
Installation Procedure Accuracy ConsiderationsElectrical ConnectionsIntroduction
You can enter this information directly into the Calibration Certificate example in Section 4.4.
For an online version of this certificate, download the Calibration Certificate Excel file at
www.micromotion.com (located on the 3098 products page) or access the calcert.xls file on
Installation and Configuration Manual 13
the floppy disk shipped with the product.
Installation Procedure
27. Shut valve B and disconnect the second calibration gas bottle from pipework.
28. Open the isolation valve D.
29. Open valve A.
If the application is running with a reference pressure less than 45.5 psi (3 Bar A), the maximum
flow rate that can be used for correct operation is 50 cc/s. A full explanation of this effect is given
in Chapter 4.
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 summarized in Chapter 5.
If optimum SG accuracy is required, the optimization 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 ±0.1 ns. This can be achieved
using 7950/7951 signal converters and flow computers set to a cycle time of 10 s.
2.7 Outline dimensional drawings
Figure 2-3 shows a 3098 specific gravity meter without an enclosure. For dimensions of small and
large enclosures, see Figure 2-4 and Figure 2-5.
14 Micro Motion 3098 Gas Specific Gravity Meter
Installation Procedure
Dimensions in inches (mm)
∅12.4 (314)
∅8 (203.2)
4.4 (112)
17.4 (442)
11.3 (286.4)
Figure 2-3 3098 specific gravity meter without an enclosure
Installation Procedure Accuracy ConsiderationsElectrical ConnectionsIntroduction
Installation and Configuration Manual 15
Installation Procedure
20.3 (516)
19.7 (500)
12 (300)
1.2
(30)
1
/3 (8.5)
20.3 (516)
17.1 (423)
17.1 (423)
19.7 (500)
Dimensions in inches (mm)
Figure 2-4 3098 specific gravity meter with a small enclosure
16 Micro Motion 3098 Gas Specific Gravity Meter
Installation Procedure
24.3 (616)
23.6 (600)
12 (300)
1.2
(30)
1
/3 (8.5)
32.1 (816)
20.6 (523)
28.5 (723)
31.5 (800)
Dimensions in inches (mm)
Figure 2-5 3098 specific gravity meter with a large enclosure
Installation Procedure Accuracy ConsiderationsElectrical ConnectionsIntroduction
Installation and Configuration Manual 17
Installation Procedure
18 Micro Motion 3098 Gas Specific Gravity Meter
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