ISO2715 - Vol - Measurement by Turbine MTR - Aug81
ISO2715 - Vol - Measurement by Turbine MTR - Aug81
ISO2715 - Vol - Measurement by Turbine MTR - Aug81
Descriptors : petroleum products, hydrocarbons, liquids, volumetric measurement, measuring instruments, electrical installation, equipment
specification.
I R
1 0
I E International Organization for Standardization
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Foreword
IS0 (the International Organization for Standardization) is a worldwide federation of
national standards institutes (IS0 member bodies). The work of developing Inter-
national Standards is carried out through I S 0 technical committees. Every member
body interested in a subject for which a technical committee has been set up has the
right to be represented on that committee. International organizations, governmental
and non-governmental, in liaison with ISO, also take part in the work.
Printed in Switzerland
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Contents
Page
Introduction .................................................................................... 1
References ...................................................................................... 1
Installation ...................................................................................... 3
4.1 General.................................................................................... 3
5.1 General.................................................................................... 6
6.1 General.................................................................................... 7
1.2 Field of application c) All construction materials in contact with the hydrocar-
bon liquid shall neither affect nor be affected by the liquid.
The field of application is any division of the petroleum industry
in which measurement is required. The content of this Interna- d) There shall be provisions for proving the meter for the
tional Standard is general. It can be applied to the metering of entire range of normal operating conditions.
~~~
3.2 Selection of turbine meter and ancillary difficulties arising from climate, system layout and electrical in-
equipment compatibilities. These include :
3.2.1 Consideration shall be given to, and the manufacturer a) Climate. Ascertain the need for electrical safety,
consulted regarding, the following when selecting a meter and weatherproofing, corrosion- or fungus-proofing devices.
its ancillary equipment : Evaluate the high and low temperature and humidity ex-
tremes, and protect accordingly.
a) space for the meter installation and, where applicable,
the proving facility; b) System layout. Provide easy access for maintenance
and obtain recommended spare parts for items, such as
b) class and type of end connections installed on meter; electronic digital read-outs and electromechanical registers,
that have a predictable failure rate. Alternative or back-up
c) the properties of the liquid on which the meter will be devices and stand-by power supplies are suggested where
required to operate, including viscosity, density ranges, continuous service is essential.
vapour pressure, corrosiveness and lubricating properties;
c) Electrical incompatibilities. All read-out devices shall be
dl the nature and quantity of abrasive and corrosive con- compatible with the turbine meter and the transmission
taminants that may be carried in the liquid stream, including system to which they are connected. In those instances
the size and distribution of solid matter; where a read-out device is a link in a data transmission
system, special care shall be taken to ensure that it has an
e) operating rates of flow, maximum and minimum, and output compatible with the data transmission system.
whether flow will be continuous, intermittent or fluctuating;
3.3.2 Read-out devices are available which perform a number
f) range of operating pressures and pressure losses across of different functions. They shall be selected to ensure read-out
the meter when run at the maximum expected flow rate; in the desired form. The limits of each individual read-out
device shall be noted so that it may perform optimally as part of
g) temperature range within which the meter will be re- the turbine meter system. Read-out devices may be either
quired to operate, and applicability of automatic analog or digital.
temperature compensation;
h) maintenance methods and cost; and spare parts re- 3.3.3 Optimum discrimination is obtained with a digital read-
quired; out device which counts the individual pulses produced by the
turbine meter to plus or minus one count, for a given interval.
j) type, method and frequency of proving; The basic pulse counter does not necessarily display flow or
volumetric units until after logic functions are performed with
k) the meter characteristics including linearity, maximum the appropriate factors to convert the accumulated pulses into
allowable pressure loss, and frequency and voltage output units of volume or flow rate.
ísee annex A, figure 2);
A variety of electronic digital read-out devices is available for
m) types of read-out devices or indicating systems to be use with turbine meters. The following outline indicates the
employed and signal preamplification ísee annex A, types and classes in general use and includes devices for special
figure 3); application.
n) compatibility of ancillary meter read-out equipment and 3.3.4 Pulse counters which indicate every pulse received from
flow rate indication; and the method of meter registration the turbine meter usually incorporate one or more illuminated
adjustment, if applicable; display units. Counters shall be compatible with meter output
voltage and frequency. These counters may be classified ‘as
p) power supply requirements for continuous or intermit- follows :
tent meter read-out;
a) Proving counters, in which a specialgating circuit in the
q) electrical code requirements; counter is triggered by switches in the proving system to
start and stop the counter. This type of proving counter
r) security of electrical transmission system. may be supplemented when the meter pulse rate is low by
multiple electronic timers utilized to provide acceptable
3.2.2 Automatic temperature compensators, if installed, shall discrimination in the proving results.
be chosen to respond to the temperature of the measured liquid
within the required measurement tolerances under all ambient b) Digital flow rate indicators, in which a gating circuit in
conditions. the counter starts and stops the counter over a preselected
time interval. A fixed preselected time base provides uncor-
rected flow rate indication; a variable preselected time inter-
3.3 Selection of read-out devices val can provide corrected digital flow rate indication, since
meter, temperature and pressure correction factors may be
3.3.1 Special consideration shall be given to the selection of incorporated in the time base in order to provide a corrected
read-out devices for a turbine meter system to prevent possible read-out.
3.3.5 Computing counters are those in which the read-out is 4.2.5 Proper design and construction of the straightening
in terms of the number of pulses or multiples of pulses received element is important to ensure that swirl will not be generated,
by the counter. The read-out display of these counters may be thus negating the function of the flow conditioner. It is recom-
by means which require that the incoming pulses be divided. mended therefore that :
These counters may be classified as follows :
a) the cross-section shall be as nearly uniform and sym-
a) Fixed ratio computing counters, in which the incoming metrical as possible;
pulses are normally divided by 10, 100, 1 O00 etc., so that
the display is 1/10, 1/100, 1/1 OOO, etc., of the total pulses b) the design and construction shall be sufficiently rugged
received. Some of these units are designed to divide by a to resist distortion or movement at high flow rates;
fixed number other than a multiple of 10.
c) the general internal construction shall be clean and free
b) Variable ratio computing counters, in which the incom- of welding protrusions and other obstructions.
ing pulses are divided (or multiplied and then divided) by a
variable divide circuit. The divide circuits are selected
manually by means of external knobs or patch boards based 4.2.6 In addition to the use of flow straightening sections,
on turbine meter pulses per unit volume under specific there shall be ample distance between the meter run and any
operating conditions. The selection is made on pulses per pumps, elbows, valves or other fittings which may induce swirl
volume or the reciprocal of pulses per volume depending on or a non-uniform velocity profile. Flanges and gaskets shall be
the counter design. Indicate is in practical units for the internally aligned, and gaskets shall not protrude into the liquid
specific operating condition. Such counters may incor- stream. Meter flanges shall be dowelled or match marked to en-
porate the meter temperature and pressure corrections into sure proper alignment of the Straightening sections and the
the variable ratio and read out the net volume corrected to meter after assembly.
the reference base. For each batch, if four or five digit
reading discrimination is required, at least 10 O00 pulses
4.2.7 Valves
must be registered.
4.2.1 Turbine meter performance is affected by liquid swirl 4.2.7.3 Generally, all valves, and especially spring-loaded or
and non-uniform velocity profiles induced by upstream and self-closing valves, shall be of such design that they will not
downstream piping configurations, valves, pumps, joint open to admit air when subjected to hydraulic shock or to
misalignment, profruding gaskets, welding projections or other vacuum conditions.
obstructions. To overcome swirl and non-uniform velocity pro-
files, flow conditioning sections shall be installed.
4.2.7.4 For intermittent flow control, valves should be of the
fast-acting, shock-free type to minimize the adverse effects of
4.2.2 Flow conditioning is an accepted practice. It is ac- starting and stopping liquid movement.
complished by the use of sufficient lengths of straight pipe or
by a combination of straight pipe and straightening elements,
inserted in the meter run upstream and downstream of the 4.3 Piping installation
turbine meter.
4.3.1 The schematic diagram (see annex A, figure 4) provides
4.2.3 When only straight pipe is employed, the liquid shear, a working basis for the design of a turbine meter assembly with
or internal friction between the liquid and the pipe wall, shall be its related equipment. Certain items may or may not be required
sufficient to accomplish the required flow conditioning. for a particular installation; others may be added if necessary.
4.2.4 When a straightening element is employed, it usually 4.3.2 Turbine meters are normally installed in a horizontal
consists of a cluster of tubes, vanes or equivalent devices in- position. The manufacturer shall be consulted if space limita-
serted longitudinally in a section of straight pipe (see annex A, tions dictate a different attitude.
figure 5). Such straightening elements effectively assist in flow
conditioning. Straightening elements may also consist of a
series of perforated plates or wire mesh screens, but these 4.3.3 Where the flow range is too great for any one meter or
forms normally cause a larger pressure drop than do tubes or for its proving, the installation of a bank of meters in parallel
vanes. may be used. Care should be taken so that each meter in a bank
shall not operate outside its minimum and maximum flow rate. value of the back pressure may be reduced in accordance with
Means should be provided to balance flow through each meter. the recommendations of the meter manufacturer and as
mutually agreed between the interested parties.
4.3.4 Meters shall be installed in such a manner that they will
NOTE - The back pressure recommended above is a typical value.
not be subjected to undue stress or strain. Provision shall be Some manufacturers recommend substantially higher values of back
made to minimize meter distortion caused by piping expansion pressure with their equipment.
and contraction.
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4 International Organization for Standardization
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4.4 Electrical installation1) quency for flow rate indication. Signal strength may be of
relatively low power level, thus installation conditions shall be
suitable for low power level signals. The recommendations
4.4.1 A turbine meter system has a minimum of three com-
described herein are not applicable to all turbine meters but
ponents : the meter (pulse producer), the transmission line
relate to low power level signal systems.
(pulse carrier) and the read-out device (pulse counter and
display). It is essential that these three components be com-
patible and that each meet the recommended specifications of
the turbine meter manufacturer. 4.4.9 Pulse characteristics which influence proper system
operation are :
4.4.2 Electrical noise may be the most troublesome element in a) Amplitude. Any read-out device connected t o a pulse
turbine meter systems employing low-level signal outputs. producer (meter) shall have the sensitivity needed t o
Even in high-level output systems it is necessary to eliminate operate with the pulse amplitudes generated over the rated
noise and/or spurious electrical signals. Noise signals are flow range;
superimposed on meter signals from three distinct sources -
electromagnetic induction, electrostatic or capacitive coupling b) Frequency. The read-out device shall be able t o cope
and electrical conduction. with the maximum output frequency of the pulse producer
(meter) at its highest expected flow rate;
4.4.3 Great care shall be exercised in effectively isolating the
system from external electrical influences. To minimize un- c) Width. The duration, after shaping, of every pulse
wanted noise, earthing (grounding) shall be independent and generated by the pulse producer (meter), shall be long
shielding of meter and prover detector transmission cables enough to be detected and counted by the read-out device;
(where used) is essential. See also I S 0 6551.
d i Shape. A sine wave output shall not be used t o operate
a read-out device requiring a square wave input without
4.4.4 For estimating the maximum transmission line length
preamplification and shaping.
for any given turbine meter system, I S 0 6551 shall be con-
sulted.
4.4.10 Great care shall be exercised in the electrical transmis-
4.4.5 Most turbine meters have the capability of producing an sion installation so that the signal amplitude from the turbine
electrical output which may be used to operate a wide variety of meter can be maintained at the highest level while reducing the
read-out devices. More than one pick-up may be required ac- magnitude of noise, whenever possible. Optimum signal level is
cording to mandatory national regulations or design criteria. maintained by :
4.4.6 Every turbine meter system must meet two general re- a) limiting the length of transmission line from the meter
quirements to operate properly. The read-out device shall be to the read-out devices:
sufficiently sensitive to respond to every pulse produced by the
turbine meter throughout its operating range. The signal-to- b ) ensuring the correct impedance;
noise ratio shall be sufficiently high to prevent spurious elec-
trical signals from influencing the read-out device. c) using the best available and technically compatible
signal transmission cable as recommended by the equip-
ment manufacturer;
4.4.7 The output signal of a turbine meter may be considered
to be a train of electrical pulses, with each pulse representing a
d) introducing a signal preamplifier into the transmission
discrete volume of liquid passing through the meter. Examples system at the turbine meter, if transmission distance or
of two approaches which have been taken to produce electrical manufacturer’s requirements so dictate;
pulses follow. The first directly translates the mechanical
motion of the rotor into electrical energy through magnetic in- e) ensuring that supply voltages to preamplifiers and con-
duction. The second requires that external electrical power be stant amplitude pulse generating systems are of proper
supplied to a proximity or photosensing device, which may be magnitude and do not exceed the maximum noise level or
externally shaft driven, but which does not actually generate ripple requirements as specified by the equipment manufac-
electrical energy by the rotational movement of the metering turer:
element.
f ) ensuring that all pick-up coils are securely mounted and
In the first method, both pulse frequency and amplitude are properly located;
generally proportional to flow rate. In the second method, only
pulse frequency is proportional to flow rate since output
g) periodically inspecting and cleaning all terminals, con-
voltage is virtually of constant amplitude. nectors, connector pins and wiring junctions;
4.4.8 Most electronic read-out devices condition a wave form h i replacing components which, through deterioration,
for the counting of each pulse or measure the meter output fre- give a weakened signal.
1 ) Additional information, regarding electrical installation will appear in a future International Standard on ancillary equipment for meters.
1) The details of calculating meter factors and bills of lading when using meter readings to which meter factors have to be applied, as well as the cor-
rection factors required to adjust any volume at a given temperature t and a given pressure p , to standard conditions, will be covered by future Inter-
national Standards.
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6 International Organization for Standardization
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2715-81 4851903 IS0 2715-1981 (E)
higher flow rate ranges (see annex A, figure 2, and applica- used, but potential error increases-asthe magnitude of the dif-
tions A and BI. If a reliable plot of meter factor versus flow rate ference between the proving and operating conditions in-
has been developed it is safe to select the meter factor value creases. For highest accuracy, the meter should be proved in
from that curve, although if a proving system is permanently in- the range of operating conditions.
stalled it is still preferableto reprove the meter and to apply the
value so computed. If changes in flow rate exceed the lower or
5.3.5 Correction to a base or reference temperature
upper limit of the acceptable linearity (see annex A, figure 2)
then the meter should be proved at the operating rate.
Considerable meter error may be introduced into the measure-
ment of a hydrocarbon liquid, unless the volume metered is
5.3.2 Variations in viscosity reduced to a standard condition of base or reference
temperature and base or reference pressure. It is recommended
For an individual turbine meter, it may be possible to develop a that appropriate corrections be made to minimize this error
single empirical equation or plot of meter factor as a function of whenever the measurement circumstance warrants such ad-
viscosity, However this cannot be done for turbine meters as a justment. 1)
class.
Since turbine meters are viscosity sensitive, and since viscosity 6 Operation and maintenance of metering
changes with the temperature of hydrocarbon liquids, par- systems
ticularly those liquids of higher relative density, the response of
a turbine meter to a change in temperature cannot be assigned
solely to thermal variations of the liquid. 6.1 General
On the other hand, for liquids of lower relative density such as This clause covers recommended operating and maintenance
gasoline whose viscosity remains essentially unchanged with practices for turbine meter installations. All operating data per-
changes in temperature, meter factor valves likewise remain vir- taining to measurement, including the meter factor control
tually unchanged. A mathematicallybased adjustment to meter charts, should be accessible to interested parties.
factors for hydrocarbons as a class, or for turbine meters in
more viscous hydrocarbons and all crude oils, is not recorn: 6.2 Conditions affecting operation
mended. Mathematical corrections shall be applied only to in-
dividual meters when they are being operated within the range
of conditions for which they have been proved. It is advisable 6.2.1 The accuracy of measurement by a turbine meter
to prove the meter under conditions which closely approximate depends on the conditions of the meter, the proving system,
those in operation. the frequency of meter proving and the variations, if any, be-
tween operating and proving conditions. All equipment shall be
selected, operated and maintained in such a manner as to
5.3.3 Variations in temperature achieve the desired accuracy which may be established by
policy, mutual consent of the parties or, in certain countries,
In addition to the effects of change in viscosity (see 5.3.2) the appropriate regulations.
caused by changes in temperature of the liquid, significant
variations in temperature can also affect meter performance by
causing changes in the physical dimensions of the meter and in 6.2.2 Turbine meters shall be operated within the specified
the apparent volume measured by the meter because of ther- flow range and the operating conditions which produce the
mal expansion or contraction of the liquid. The extent of liquid desired accuracy (see annex BI. They shall be operated with
expansion or contraction may be calculated using approved the necessary ancillary equipment. It must also be recognized
tables or formulae. Accepted corrections may be applied for that turbine meters should not be used to make deliveries less
changes in physical dimensions of the meter, but other possible than a minimal quantity below which random errors may defeat
effects such as changes in the mechanical tolerance and blade required accuracy.
angle, could depend on the individual meter, and may not be
capable of correction for turbine meters as a class. For highest 6.2.3 If a turbine meter is used to measure reversible flow,
accuracy the meter should be proved in the range of operating meter factors shall be obtained for each direction of flow.
conditions. Usually protective devices must be located on both sides of the
meter.
5.3.4 Variations in pressure
6.2.4 Definite procedures both for operating metering
A variation in the pressure of the liquid being metered from that systems and for calculating measured quantities shall be fur-
which existed at the time of proving will result in a change in nished to meter station personnel. These should include :
the relative volume of the liquid due to its compressibility. A
change in the physical dimensions of the meter, arising from a) standard procedure for meter proving;
expansion or contraction of its housing under pressure will also
occur. Accepted correction tables for both effects may be b) operation of stand-by or spare meters;
c) minimum and maximum meter flow rates and other often inadvisable to establish a definite schedule of meter
operating conditions such as pressure and temperature; maintenance for all installations. It is best to determine when t o
repair or inspect a meter by keeping a control chart for each
d) instructions for applying pressure and temperature cor- meter on each product or grade of crude oil. Slight changes in
rection factors; meter factor will naturally occur in normal operation, but if the
value of such a change in meter factor exceeds three times the
e) procedure for recording and reporting corrected meter standard deviation í f 301, as recorded on the control chart,
volumes and other observed data; the cause of the change shall be sought. The use of 30 limits as
acceptable normal variation in meter factor value strikes a
f) procedure for estimating the volume passed in the event balance between looking for trouble that does not exist and not
of meter failure or mismeasurement: looking for trouble that does exist. (See I S 0 4124.)
g) instructions in the use of control charts and the action 6.3.3 Totalizer components and temperature and pressure
to be taken when the meter factor exceeds the established
instruments and/or transmitter should be periodically checked.
acceptable limits;
j) instructions covering reporting the breakage of any seals 6.4.1 A meter factor control chart is any suitable adaptation,
if fitted; to liquid metering problems, of the widely used statistical con-
trol chart method as explained and discussed in I S 0 4124.
k) instructions in the use of all forms and tables necessary
to record the data to support proving reports and meter 6.4.2 Meter factor control charts are essentially plots of suc-
tickets; cessive meter factor values along the abscissa at the ap-
propriate or-nate value and -between limiting abscissa
m) instructions for routine maintenance; representing X I la,X f 20, X + 30, where O is the stan-
dard deviation of the meter factor obtained from a set of prov-
n) instructions for taking samples; ing runs and x is the mean value of all these values. Such a
chart should be maintained for each product, or grade of crude
p) details of the general policy for frequency of meter oil over a range of rates, for each meter.
proving and re-proving when changes of flow rate or other
variables affect meter accuracy;
6.4.3 Meter factor control charts can be used as a warning
q) procedures for operations not included in the fore- signal for measurement trouble by showing when and to what
going, but which may be important for an individual installa- extent conditions have deviated from accepted norms. The
tion. charts can be used to detect trouble, but not the nature of the
trouble. When measurement trouble is encountered, a
systematic checking of the measurement system is recom-
6.2.5 A statistical analysis of meter proving results, and the mended. The following components of the measurement
use of control charts (see I S 0 4124)will aid judgement in deter- system should be considered, although not necessarily in the
mining : listed order :
a) the optimum time lapse between provings; a) all valves affecting meter proving;
b) the need for maintenance; b) strainers, filters, air and water separators;
c) the constancy and quantitative value of mean meter c) pulse counters, coil preamplifiers, signal transmission
factor. system, power supply, and all read-out devices;
6.3 M e t e r maintenance d) moving parts and bearing surfaces of the turbine meter;
6.3.2 Because of the many different sizes of meter, services, See annex B for three decision charts designed to aid in
liquids measured, flow rates and pressures it is difficult and diagnosing malfunction in turbine metering systems.
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8 International Organization for Standardization
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Annex A
This annex provides illustrative descriptions of turbine meter performance characteristics, accessory read-out instrumentation
possibilities, recommendedflow straightener assembly, meter accuracy curve, and names of turbine meter parts (see figures 1 to 6).
In addition to the pictorial information presented, these illustrations provide a recommendationfor standardized terminology and data
presentation. The intention of such a standardization is to simplify communication between designers, operators and manufacturers.
Flow Flow
I l
Location Density
Date viscosity
Manufacturer Temperature
Model - Size Pressure
Serial No. Operator
Liquid Report No.
r l
I
E
-
C
Manufacturer's maximum
Flow rate
capacity rating
1 1
NOTE - The meter characteristic curves shown are to be considered as illustrative only and shall not be construed as representing the likely
performance o f any given model or size of turbine meter.
I
I
------1
- r-l
Digital
logging and
mechanical control
Combinator systems
indicator
or PIA
I i
!a
converter.
I Register
-t counter
I I
L r-L-7
I I
Shielded cable
to each instrument,
grounded a t instrument
end only
-recorder controller‘ ‘D printer
I--- Register
‘amplifier
1 I I I
1
-.l----
1
I
I
t
lDigital
To vent
.1-I
I . Meter run Back-pressure and/or
---I flow rate valve or
valves for positive
shutaff
$'
{-
I
Upstream flow
conditioner
Downstream Pressure gauc
flow
conditioner @ / \\ Control vaive
Strainer 1
Flow Non-return valve
/* 1
-c-
A irlvapo ur
- / I
/
Straiahtenins
8
Meter
element
separator
Thermometer u o n n e c t i o n s to proving system
Optional if applicable
NOTE - All sections of line which may be blocked between valves shall have provisions for pressure relief.
n
Pulses per
unit volume Manufacturer's stated I
maximum flow rate \
I
l
I
\-.y*
Back pressure
too low
Curve represents
-1 flow
cavitation
Back pressure
adequate
/i I
I
Legend for upstream of the meter : Flow rate or volume per unit of time
Annex B
This annex is included as an aid in diagnosing malfunctions in turbine metering systems. However, it is not intended to replace a
detailed and systematic checking of the measurement system.
Observe totalizer
1
i s totalizer power
off or fuse
defective ?
v ,
i:)
Does power supply yes Is signal output Are there cold Replace
give proper output a t turbine meter solder joints or threshold
voltages ? shorted wires ? unit
I
or
Resolder
wires
replace
Substitute new coil.
i s signal present now ?
V *
Are circuit boards yes
w loose in their base 7
no for leakage
or leakage through the
meter ?
+ Check
- With oscilloscope are
noise signais present ?
< no meter vanes and
bearings
no
Y es
V
Are totalizer and pre- Is shielded cable I s coil grounded to coil
- amp. power supplies 3 grounded a t one
yes > case or shield to
regulated ? point only ? conduit ?
no
no
ves 4
Increase signallnoise no I s totalizer in vicinity
ratio. Does unit now < of heavy magnetic
count properly ? field ?
V
no
yes Is internal wiring
bare or shorted ? c- v
Is test switch bad ?
With oscillator a t
totalizer, does unit
count properly ?
Lay temporary line
meter to totalizer yes no
v
Recheck shield
and cable
V
Substitute or add a
no ~ parallel totalizer. I s Yes
trouble corrected 7
Replace
Is shielding cable totalizer
no
grounded only a t
totalizer 7
-
Disconnect cable. Check for Check continuity of coil. Check proximity to
no
+ short circuit between shield
and conduit or conductors.
> Is coil shorted to coil
case 7
> heavy current carrying
wires
-
Check continuity of shield
no
no G
.
Using oscilloscope, i s
noise present 7
I
yes
preamp., i f
necessary
yes r
if faulty
i f not faulty Introduce signal from Does totalizer
9 audio oscillator of > count evenly
same frequency as meter and correctly 7
Figure 9 - Case where totalizer drops count (counts slowly, intermittently or irregularly)