Racal Instruments 9916 User Manual

Racal Instruments 9916

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AGC

and

Attenuator

4.15

The

signal

at

04

emitter

is

passed

via

03

to

the

peak

to

peak

detector

C13,

05,

D4

and

C11.

As

the

input

signal

amplitude

increases

the

potential

across

C11

increases.

This

level

is

applied

via

the

emitter

follower

tolC31a,

which

controls

the

current

in

D2

and

D3.

An

increase

in

input

signal

increases

the

current

in

the

diodes,

reducing

their

dynamic

impedance.

The

diodes,

in

co':!iunction

with

R10, form a

potential

divider

across

the

output

of

02,

and

a

reduction

in

diode

dynamic

impedance

reduces

the

signal

passed

to

IC30.

Low Level

Inhibit

4.16

The

output

of

the

AGC

detector

is

fed

to

the

Schmitt

trigger

IC31b.

If

the

input

signal

ampl

itude

is

too

small for

stable

counting

\C3

'I

b/7

is

at

a

lower

potential

than

IC31b/6.

The

resulting

output

at

IC31b/l0,

applied

to

IC21q113,

gives

a

voltage

level

at

IC21q115

high

enough

to

inhibit

the

output

of

IC21b.

Signal

Selection

System

4.17

The

selection

of

the

lA'

Channel,

IB'

Channel

or

LF

multiplier

signal

to

be

passed

to

the

counter

input

IC4/22

is

made

by

the

Channel

Select

switch

1Sl

and

gates

I

C18a

and

b

and

I

C9a

and

b.

4.18

With

the

'A'

Channel

seiected

IC9b/5

is

set

to

'1'

via

IC10a.

Provided

IC9b/4

is

also

at

'1'

(see

paragraph

4.10)

'A'

Channel

signals

will

pass to

IC4/22.

IC8b

is

inhibited

by a

'0'

at

pin

12,

and

IC9a

is

inhibited

by

a

'0'

at

pins 1

and

2 from

IC10b.

At

the

same

time

the

-5

volt

supply

is

connected

to

the

'A'

Channel

and

disconnected

from

the

'B'

Channel

by

the

Channel

Select

switch.

The

+5

volt

supply

is

connected

to

the

'A'

Channel

by

013,

turned

on by

the

Channel

Select

switch

via

1C10a

and

IC13c,

and

disconnected

from

the

'B'

Channel

by

Q6,

turned

off

via

IC13d.

4.19

With

the

lB'

Channel

selected

le8b

is

enabled

by

'l's

at

pin

12 (from R79),

pin

9 (from

R81)

and

pin

10.

'B'

Channel

signals

From

Q5

will

pass

to

1C4/22.

IC9b

IS

inhibi'ted

by

a

'0

1

at

pin

5 from

IC10a,

and

IC9a

is

inhibited

by a

'0'

at

pins

1

and

2 from

IC10b.

The

-5

volt

supply

is

now

connected

to

the

'B'

Channel

instead

of

the

'A'

Channel,

and

Q6

and

013

connect

the

+5

volt

supply

to

the

'B'

Channel

and

not

to

the

I A'

Channel.

The

'1'

from R79,

inverted

by

ICl Oaf puts

IC14a

into

the

cleared

state,

cutting

off

the

+24V

supply

to IC26 (see

paragraph

4.59).

4.20

With

LF

selected

IC9a

is

enabled

by a

'11!

on

pins

1

and

2 from

IC10b.

IC8b

is

inhibited

by a

'0'

at

pin

10

and

IC9b is

inhibited

by a

'Q'

at

pin

5

fromlC10a.

The

power

suppl ies

remain

connected

to

the

',B

1

Channel.

4-3

9916

Vol.

2

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Racal Instruments 9916 Specifications

General

Brand	Racal Instruments
Model	9916
Category	Measuring Instruments
Language	English