AVO AVOMETER 8 Manual de Instruções - Página 11

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OPERATION

Using the 30kV Probe Multiplier

30kV de

Multiplier is available for use in series with the

meter set to its 1 OOOV de range,

readings

being made

direct

the 0-100 scale and multiplied by 300. It is most

important

ensure that the

meter is kept in

the

earthy end

the

circuit

and the

multiplier connected

either

the

positive or negative terminal whichever is at

high

potential.

This

method

connection to get forward pointer indica-

tion with the meter

earthy is recommended as

not

think it desirable to use the moving

coil

reverse button

when measuring

high voltage.

A special lead is

provided

with the

multiplier

for connection

to the high potential point.

HEAVY

AC CURRENT

MEASUREMENT

Currents between

OA and 600A may be measured by

use of the AVO Multi-range Current Transformer ( Pt.

No.

45869).

Full

operating

instructions

for its use

are

packed

with the

optional

accessory.

HEAVY DC CUR RENT MEASUREMENT

D.C.

currents between

OA and

600A may be measured

use

of the appropriate

AVO

DC Shunt

accessory.

When used

with

the

AVOMETER

8 Mk

the

shunts

produce a voltage

drop of

OOmV when

pas.

s ing

current

at their

maximum

rating.

The

Shunt

should

connected by means of

its two

main

terminals

in series with

the

circuit

be measured. The

meter set

its

50!1-A

(1 OOmV) de position should

then be

connected to the

two small studs on the shunt end

blocks.

The

AVOMETER

when so set, consumes only 5011-A

at full

scale deflection,

a value which is

negligible

in comparison

with the

full

scale current of the shunt.

The

millivolt

drop

across the

shunt

is directly

proportional

any

current

which may flow through it

and since

the

deflection

on the

meter is

directly proportional

to the

millivolt

drop across

the terminals, the instrument indicates correctly over

its

entire scale length.

NON-SINE WAVEFORMS

In as much as rectifier moving

coil

instruments give readings

on 'ac' proportional to

the

mean

and

not the r.m.s. value

the waveform with which they

are

presented,

they

depend

for their accuracy, not

only

upon their

initial

calibration,

but also upon

the

maintenance

of a

sinusoidal

waveform.

Since the form factor (r.m.s. value divided by mean value)

of a sine wave is 1.11, this has been taken into account in

calibrating

the

meter,

which

does,

therefore,

indicate

r.m.s.

values

on the assumption that the normal

sine wave

will

encountered. Generally

speaking, considerable waveform

distortion

can occur without appreciably affecting

the form

factor

and resulting accuracy of measurement, but

the

user

should

recognise

the possibility

of some error

when

using

distorted

waveforms, squarish waveshapes

producing

high

readings

and peaky

ones,

low

readings.