Marconi Instruments TF 2502 - Calibration Accuracy At.l.f

Marconi Instruments TF 2502

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general

configuration

and

spacing

of

the

transmission

line,

and

no

provision

is

made

for

adjustment.

The

validity

of

subsequent

calibration

steps

is

dependent

on

verifi-

cation

of good v.

s.

w.

r.

over

the

full

frequency

range.

During

manufacture

a

sweep

frequency

method

is

used

to

achieve

this,

but

another

method

can

be

used

if

tests

are

made

at

a

sufficient

number

of

frequencies.

Connect

the

v.

s.

w.

r.

measuring

device

to

the

socket

on

the

terminating

load·

and

check

the

v.

s.

w.

r.

at

a

selection

of

frequencies

up

to

1 GHz.

The

v.

s.

w.

r.

should

be

better

than

1.

05

over

the whole

frequency

range.

With

the

INSERT PROBE

control

fully

counter-clockwise,

connect

the

v.

s.

w.

r.

measuring

device

to

the

power

meter

input

socket

and

check

the

v.

s.

w.

r.

of

the

combined

terminating

load

and

in-line

detector

at

a

selection

of

~requencies

up

to

1 GHz.

The

v.

s.

w.

r.

should

be

better

than

1.1

over

the

whole

frequency

range.

5.4

CALIBRATION

ACCURACY

AT.L.F.

(Apparatus

required:

items

d

and

e)

The

power-reading

accuracy

is

best

checked

at

a low

frequency

-

usually

the

frequency

of

the

local

power

supply -

and

then

compared

with

that

·of a

standardized

mean-reading

power

meter

near

the

upper

limit

of

the

frequency

range.

1)

Connect

the

dynamometer

wattmeter

between

the

a.

c.

supply

and

the

power

meter

under

test.

The

current

and

voltage

coil

connections

should

be

arranged

for

minimum

error

due

to

internal

losses,

and

allowance

should

be

made

for

the

error

if

it

is

appreciable.

Owing

to

the

frequency

response

limitations

of

dynamometer

wattmeters

the

a.

c.

supply

must

have

low

distortion

(less

than

1

%)

.

2)

Set

the

Range

switch

to

10

Wand

set

the

power

input

until

the

dynamometer

indicates

the

input

figure

given

on

the

label

at

the

rear

of

the

instrument.

3)

Check

that

the

TF

2502

reading

is

8 W ±0.

5%,

if

not

adjust

RV1

until

it

is

correct.

4)

Reduce

the

applied

power

to

zero

and

allow

sufficient

time

for

the

thermocouple

to

cool.

5)

Set

the

Range

switch

to

3 W and

set

the

power

input

until

the

dynamometer

indicates

the

input

figure

given on the

label

at

the

rear

of

the

instrument.

6)

Check

that

the

TF

2502

reading

is

2. 5 W ±0. 5%,

if

not

adjust

RV2

until

it

is

correct.

16

2502

(1)