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3.

5.

3

External

Trigger

Select

"Ext

Trig",

and

A

and/or

B

on

the

output

in

use.

Each

time

the

selected

slope

of

the

input

waveform

crosses

the

threshold

level

a

pulse

cycle

will

be

initiated.

3.5.4

External

Width

Select

"Ext

Trig",

and

"Square-wave"

on

the

output.

When

positive

slope

and

a

normal

positive

output

are

selected,

the

output

will

be

high

when

the

input

signal

is

above

the

thres

hold

level.

When

the

input

signal

is

a

pulse

the

output

will

have

essentially

the

same

width.

3.

5.

5

External

Gate

In

this

mode

the

"PERIOD"

oscillator

is

the

signal

source

of

the

instrument

but

it

is

able

to

oscillate

only

whilst

the

sutput

signal

is

above

the

threshold

level

(with

positive

slope

selected).

The

"PERIOD"

signal

starts

synchronously

with

the

input

signal,

but

delayed

by

a

fraction

of

a

cycle.

^

_

3.

5.

6

Countdown

Sync.

On

"External

Gate"

and

when

the

input

frequency

is

higher

than

the

PERIOD

frequency.

The

'PERIOD'

oscillator

can

be

synchronised

by

the

input

signal

up

to

a

frequency

ratio

of

100

:

1.

3.5.7

Slope

This

is

used

to

select

which

slope

of

the

input

waveform

triggers

the

unit

(initiating

pre-

pulse;

delay

A

and

on

parallel

delay,

delay

B),

or

which

part

of

the

waveform

is

used

for

the

external

width,

or

gating

signal.

On

positive

slope,

this

is

the

part

above

the

threshold

level.

3.5.8

Level

Control

Can

be

used

to

vary

the

level

on

the

input

waveform

at

which

triggering

will

occur.

It

can

also

be

used

to

vary

the

threshold

level

to

allow

triggering

from

signals

which

are

offset,

from

earth

potential.

3.

5.

9

Triggered

Light

Each

time

the

input

signal

crosses

the

threshold

level

the

lamp

flashes.

At

frequencies

above

a

few

cycles

per

second

the

lamp

appears

to

be

on

continuously.

It

is

useful

in

setting

the

trigger

level,

and

at

low

rates

to

give

a

clear

indication

of

the

instant

of

triggering.

3.

5.10

Single

Cycle

Select

"Single

Cycle",

and

A

and

/or

B

on

the

output

in

use.

Press

the

red

button

to

start

a

cycle.

3.

5.11

Manual

Step

or

Level

Select

"Single

Cycle"

and

"Square-wave"

on

the

output.

Pressing

the

red

button

produces

a

fast

step,

and

a

d.

c.

level

whilst

the

button

is

held

in.

3.

5.12

Manual

Burst

Select

this

function

by

part-pressing

one

of

the

four

black

buttons

which

is

out,

so

that

they

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7