The following information has been transcribed from E&V
Publication 242 dated January 1951 which describes the range of
instruments and equipment manufactured at the time.
THE FOUR SERIES OF MEGGER INSULATION TESTER
Megger Insulation Testers are self-contained testing instruments,
always ready for immediate use. They consist of a hand driven generator
to produce the testing voltage, and a direct reading ohmmeter which
measures the value of the insulation resistance. These components are
mounted together in·a portable case and are constructed of materials
capable of withstanding tropical conditions. There are four patterns of
instrument, the characteristics and uses of each being briefly
described below. Some instruments, moreover, have certificates of
intrinsic safety, while the Series 1 instruments can also be supplied
with three voltage ranges, and a special Series I instrument in a
somewhat larger case is available for a testing pressure of 5.000 volts
and a range of 100,000 megohms.
SERIES 1
For testing high tension equipment, transformers, insulators,
generators. mains and apparatus having a high degree of insulation and
considerable electrostatic capacity. Testing pressures up to 2,500
volts. Ranges up to 50.000 megohms. A special 5000 volt tester is also
available.
SERIES 2
For testing power circuits. motors, etc. and apparatus operating on 500
volts, and for mains having moderate electrostatic capacity. It may
also be supplied with a second scale for testing continuity of lead
sheathing. Testing pressures up to 1.000 volts. Ranges up to 2,000
megohms.
SERIES 3
Known also as the Wee-Megger Tester for testing in house wiring, small
motors
and apparatus operating at pressures up to 250 volts. Only obtainable
with a variable pressure generator. Weight 3 lbs. Testing pressures up
to 500 volts, ranges up to 50 megohms.
SERIES 4
An intermediate instrument with the voltage and megohm ranges of the
Series 3 tester, but having a constant pressure generator. It may be
fitted with a divide by100 switch or a continuity range, refinements
hitherto only available in the Series 2 instrument. Weight 6 lbs.
The safety and reliability of electrical installations and apparatus
depends chiefly on the condition of the insulation which should
therefore be tested at regular intervals. These tests should be carried
out during manufacture, before acceptance, after installation, and
periodically while in service.
Megger Insulation Testers have received world wide recognition as the
standard appliance for making these tests. They are made exclusively by
the Evershed organisation under their registered trade mark " MEGGER,"
and are in general use throughout the civilised world.
BRIDGE MEGGER TESTERS
The Bridge-Megger Testing Set is a combination of a Megger Insulation
Tester and a complete Wheatstone Bridge. Covering a wide range of
resistance, it is an ideal instrument for the maintenance engineer
enabling the resistance of motor windings, contactor operating coils
etc., to be accurately measured, periodical insulation tests made and
faults in telephone cable located using the Varley Loop method.
The Bridge-Megger Testing Sets, Series 1 and 2 are self contained
testing instruments. Each comprises a hand driven generator of the
constant pressure type to produce the testing voltage, a change-over
switch to change from insulation to Wheatstone bridge tests. a moving
coil ohmmeter which measures directly the value of the insulation
resistance and which acts as the galvanometer for the bridge tests. A
ratio switch and a direct reading adjustable resistance complete the
bridge. This resistance is switch operated, its total value being shown
on four dials as a row of figures.
SERIES 1 TESTING SET
The Series 1 Testing Set consists or two units, the adjustable
resistance being contained in a separate case from the instrument to
which it is connected by two short leads. Both cases are constructed of
hard wood and have leather carrying handles. On the side of the
instrument there are two terminals. marked" Line" and .. Earth." which
are used for insulation tests. and at the end of the case are two pairs
of terminals marked" R ., and .. X" for connection to the resistance
box and the resistance under test when making bridge tests. All
instruments are internally guarded against surface leakage and those
scaled to I ,000 megohms and over have a guard terminal for eliminating
the effects of surface leakage on the apparatus under test. High
sensitivity instruments are provided with levelling screws. All
Bridge-Megger Testing Sets. Series I, are suitable for carrying out
Varley loop tests. Testing voltages up to 1,000 volts. Range covered ·0
I ohm. up to 2,000 megohms. Weight including resistance box 28 lbs.
SERIES 2 TESTING SET
The Series 2 Testing Set is contained in a single case of aluminium
alloy. the lid and base being,of moulded plastic material. A leather
carrying strap attached to the case is adjustable in length and can be
arranged either short-for carrying the instrument by hand, or long for
slinging from the shoulder. The normal instrument has only two
terminals marked .. Line" and .. Earth," and these are used for both
insulation and bridge tests. Instruments incorporating Varley Test
facilities have a third terminal marked" Varley Earth." Testing
voltages up to 1,000 volts. Range covered ·0 I ohm. up to 200 megohms.
Size 11x81x7 ins. Weight 12¾ lbs.
OHMMETERS
Evershed Ohmmeters are instruments intended for the rapid measurement
of electrical resistance. They are direct reading true ohmmeters in
that their accuracy is unaffected by variation in the supply voltage,
the movements being similar to those fitted in Megger Insulation
Testers. Instruments are available for the measurement of either
insulation or conductor resistances and are widely used for testing
components during manufacture.
MEGGER CIRCUIT TESTERS
Portable direct reading true ohmmeters operated from self contained 4½
volt dry batteries. No adjustment necessary for battery voltage.
Suitable for measuring the resistance of motor windings and other
conductor resistances, and for testing the bonding of conduit. Four
instruments available with ranges up to 30. 300, 50,000 and 200,000
ohms, respectively. Weight:2 lbs,
WORKSHOP OHMMETERS
Direct reading true ohmmeters operated from an external source of
supply. Employed by manufacturers of telephone and telegraph apparatus,
condensers, wireless sets, electric lamps, etc., for the rapid
measurement of the insulation and conductor resistances of electrical
components during manufacture, Instruments available for wall mounting
or bench use, and covering a wide range of resistance.
DUCTER OHMMETER
A portable direct reading true ohmmeter for the measurement of low
resistances from a few ohms down to I microhm. Each instrument has four
or five different ranges and is suitable for the testing of switch
contacts, rail bonds, windings of series motors, etc, The ohmmeter
operates from an external alkaline battery supplied with the set.
EVERSHED BOND TESTER
This is a low range true ohmmeter for testing the bonding of aeroplane
structures, metallic sheathing. etc. it has a single range of 0-0·1
ohm. and operates from a self contained alkaline cell. It is housed in
a hardwood case supported by straps. Weight 91 lbs.
SAFETY OHMMETER
This instrument is designed for testing detonator and shot firing
circuits. and the testing current cannot exceed 12 milliamperes. Though
similar in appearance to the Series 3 Megger Insulation Tester. it
comprises a low voltage generator and a true ohmmeter. and is certified
a~ intrinsically safe. Range 0-100 ohms.
EARTH TESTERS
These direct reading instruments enable the resistance to earth of
earth electrodes to be quickly and easily determined, With these
instruments it becomes an easy matter to ascertain whether at all times
the resistance of these electrodes is sufficiently low to permit the
correct operation of protective gear and to minimise the dangers due to
lightning.
There are three patterns of instrument, each consisting of a direct
reading ohmmeter and a hand generator of a special type so designed
that under most practical conditions the effects or electrolytic back
emf and of stray currents in the soil may be neglected.
The Series 1 instrument, has an evenly divided scale and can have up to
four ranges, while the Series 2 and Series 4 testers have logarithmic
scales and up to two ranges only. In general appearance these
instruments resemble the equivalent series of Megger Insulation
Testers.
MEGGER EARTHOMETER TESTERS
These instruments measure the resistance of the complete earthing
circuit which includes the resistance of the electrodes at both the
sub-station and the consumers premises, These instruments are similar
to the Series 2 and Series 4 earth testers. but each contains a neon
warning lamp and a special switch to protect the instrument as
Earthometer tests are carried out with the circuit alive. These
instruments may also be used as earth testers.
The resistivity method of prospecting has been found extremely useful
for elucidating geological conditions. This method, which reduces very
considerably the cost of a survey, is used extensively in prospecting
for mineral deposits, in the search for shallow water supplies, and in
the determination of depth to bed rock for dam foundations and the
like.
These tests can be carried out very simply by the Geophysical
Megger Earth Tester, and within its limitation by the Low
Resistance Megger Earth Tester which is similar in appearance to
the Series 1 Earth Tester, but has a lower range. Both instruments have
hand driven generators to provide the testing current, and they give
directly, without calculation, the value R in the resistivity p = 2πaR.
The Geophysical Megger Earth Tester has ranges of 0-0.3, 0-1, 0-3, 0-10
and 0-30 ohms, while those of the Low Resistance Megger Earth Tester
are 0- 1, 0- I 0, 0- 100 and 0- 1,000 ohms.
AC LEAKAGE INDICATOR
It is normal practice to connect the neutral point of an A.C. system to
earth. and a leakage ammeter is often included in this circuit. This
instrument, which may be of the indicating or of the chart recording
type, is, however, liable to damage by the passage of excessive earth
current. The Evershed Self-protecting AC Leakage Indicator and Recorder
although calibrated only to 10 amperes, are not liable to damage from
an excessive earth current of several thousand amperes, and they
require no protective relays.
MEGGER CAPACITY METER
The Megger Capacity meter is direct reading instrument for the
measurement of the electrostatic capacity of power condensers,
underground cables, and condensers for radio and other purposes. A
portable type having a self-contained hand generator, and a workshop
type for operating from A.C. mains are available. Both types can be
fitted with range switches. The self-contained portable instrument,
which is similar in appearance to the Series 1 Megger Insulation Tester
shown in Figure 1, is so constructed that the accuracy of the readings
is not impaired even if the insulation of the apparatus under test is
as low as 10.000 ohms. Lowest range available 0-3·003 microfarad.
Highest range available 0-10 microfarads.
DlONIC WATER PURITY METER OR ELECTRIC SALINOMETER
This instrument measures continuously the purity of water flowing out
of surface condensers, distilling plant, etc. The usual generating
station cubicle includes a chart recorder and an alarm indicator.
Instruments are also available for recording steam purity or boiler
concentration and marine applications.
PORTABLE DIONIC WATER TESTER
This is a direct reading instrument for measuring the electrical
conductivity of a sample of water. It provides a rapid and accurate
means of carrying out routine tests for determining the amount of
dissolved inorganic impurity. and may be used by unskilled operators.
EVERSHED ELECTRICAL TACHOMETER
This consists of a transmitter, driven by the machinery. the speed of
which is to be indicated. and connected by 2-core cable to one or more
Indicators or to ~l chart recorder, Its reliability has resulted in it
being used extensively on board ship,in paper mills and in cement works.
EVERSHED RUDDER INDICATOR
This apparatus has been used in the Royal Navy since 1893 and is also
supplied to foreign navies and for use in ships of the British and
foreign mercantile marine. This instrument, fitted on over 600 ships
operates directly from the ships mains.
PORTABLE AND SWITCHBOARD INSTRUMENTS
Various patterns of portable and switchboard instruments are
Manufactured. All have spring mounted jewels and are particularly
robust. Each instrument is calibrated throughout its entire range and
conforms to the appropriate British Standard Specification for 1st
grade or substandard instruments.
RECORDERS FOR ANY PURPOSE
Evershed recorders are available for many purposes, and to record such
quantities as amperes. volts. watts. frequency. power factor etc. Often
the electrical quantity measured represents some mechanical quantity,
e,g, speed or water level. while for some purposes a mechanical
movement may be fitted in the instrument.
Time interval or operation recorders are also available, these
instruments automatically plotting on a time basis the stopping and
starting of machines, the opening or closing of switches or any
movement of which it is desired to have a true record.
MULTIPLE RECORDERS
Instruments can be supplied with one, two or three movements mounted in
one case. Different combinations of movement can be provided. for
instance, a triplex instrument may record simultaneously on one chart
11" wide the voltage of a three phase supply (Figure 38) or other
quantities such as kilowatts. kilovolts and frequency, Operation
recorders may have 20 pens recording simultaneously, or merely one pen
on a drum chart.
FIXED OR PORTABLE INSTRUMENTS
Instruments for continuous service can be supplied for flush mounting
on a switchboard or for fixing on walls, It is. however, often
convenient to have recorders which can be used for checking the
operation of certain plant during a short period and then removed to
obtain similar records elsewhere. For this purpose Evershed portable
recorders in hard wood cases arc eminently suitable.
CHARTS
The usual pattern of recorder is of the roll or continuous chart type.
Charts are supplied in 65 ft. lengths, sufficient for one month's use
at a speed of I" per hour. They have straight time lines. a valuable
feature which facilitates the comparison of two or three quantities
recorded on one or more charts. Recorders with daily disc charts are
also available for those who prefer a fresh chart every day.
CHART SPEED AND TYPES OF CLOCK
Recorders of the roll chart type are normally supplied with either
spring driven or electrically driven clocks. The spring driven clocks
are of two types, the low speed clock with escapement control, and the
high speed clock with fly governor control. The electrical clocks are
driven by small synchronous motors of the self-starting type. A special
self-winding clock can also be supplied. This has a spring drive and
escapement control but is automatically re-wound at regular intervals
by means of a small motor. The arrangement is such that there is always
a reserve of 24 hours on the spring as a precaution against supply
failure. The clock is suitable for an alternating current supply and
for chart speeds up to 12 inches per hour only.
Recorders of the roll chart type can have a wide range of chart speeds.
The range is determined partly by the type of clock, but for each type
of clock a number of speeds can be obtained merely by changing external
gear wheels. Speeds from ½" per hour to 12" per minute can be obtained
on standard pattern recorders.
FlOWMETERS
The new Evershed “Rollflow” Meter is a transmitting type of flowmeter
for indicating or recording liquid or gas flow at a distance.
PROCESS CONTROLLERS
These instruments, which are electronically operated, provide
proportional, integral and derivative forms of control. In Figure 40
can be seen a 3-term controller in flameproof case. The instruments may
be used to control pneumatically operated valves fitted with the
Evershed Valve Positioners, the electro-pneumatic system of control
employed eliminating signal lag and removing limitations on
transmission distances.
TANK GAUGES
The Evershed Tank Contents Gauge is a diaphragm type, which records at
a distance the contents of tanks containing food stuffs, syrups and
other viscous liquids.
The Evershed Precise Tank Gauge operates on the null-point displacer
system and has an accuracy of 0.1inch irrespective of the range. The
transmitter is waterproof and flameproof, and the indicators have
double concentric dials marked in feet and inches.
POSITION CONTROLLERS
These are used for the control of engine throttles, large butterfly
valves, tuning condensers etc. Each consists of a hand operated
transmitter connected by three pilot wires to a slave unit which
operates the mechanism under control.
REMOTE INDICATORS
Evershed transmitters are available for repeating at a distance the
following measurements :-electrical quantities such as amperes, volts,
watts, steam water and gas pressure and flow, water level in
reservoirs, gasholder stock, degree of opening of valves, sluice gates
etc. Other work undertaken includes the summation of two or more
measured quantities such as electrical power gas or water flow, the
information being transmitted to a central point.
The Evershed Electronic Repeater System is fully automatic and
unaffected by variation in supply voltage or line resistance. and the
number of receivers can be varied at any time without the necessity of
re-calibration.
NOFLOTE PUMP CONTROL
This apparatus provides high and low level alarms and automatically
controls drainage and other pumps. without the use of float gear. An
installation consists of two or more adjustable electrodes, and a relay
connected to the motor starter.