BRUEL & KJAER 1623 - Page 9

BRUEL & KJAER 1623

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Filter

Bandwidth

6% 12%

23

%

(?(?

(y

G

M

Filter

Input

Amplitude

(oot~o!l'l

Overload

!-

Detector

0 Manual

D

E

Manual

Tuning/

Auto

-Cut-

r---

out

f >

200Hz

200Hz

~

LP

Noise

Fi

lter

6

{

Noise

4~

f Filter

Schmitt

Trigger

Preset/

Digitally

Tuned

Analogue

Filter

Filter

Output

J"\

~Frequency

~

(out

of

range)

Tuning

Range

.__

_________

~

Change Recorder

Logic

Control

/

Range

Changing

-

r--------<--1

Synchron-

.-------+---i

isation

-----o

Pulse

a:

Log f

(for

2306)

and 2309

Memory

~-----iTFimej

.,._

_____

,Frequency

requency Display

Logic

~

Battery Charger

-

!---(included)

12 V,

-

400mA

Preset

e---------1

~Preset

Power

Track

~Track

-

Supply

0

1--

External Power Suppl

y

Logic

-

T

6Vto15VDC(4W)

J

I

t

Denomina

Numerator

tor

1

1

2 MHz

Tuning

Oscillator

1

1

-to-

Counter

1

to

gg

Reference

1

99

Oscillator

Divider

Divider

760851

Fig.3.

Simplified

block

diagram

of

Tracking

Filter

Type

1623

alysis

of

machinery

containing

gear

wheels

and

shafts

rotating

at

differ-

ent

speeds a

relatively

simple

mat-

ter.

The

multiplication

ratio

is se-

lected and

clearly

indicated

by

two

pairs

of

tens

and

units

knobs on

the

front

panel.

Noise

Filter

A special

low-pass

filter

is

built

into

the

tracking

input

circuitry

in

or-

der

to

attenuate

high

frequency

rip-

ple

which

could

cause

false

trigger-

ing

at

low

frequencies

. If

the

noise

filter

is

switched

in,

it

automatically

becomes

inoperative

for

tuning

sig-

nal

frequencies

above

200Hz

.

This

filter

is

particularly

applicable

for

fil-

tering

out

the

1 kHz

synchronization

signal

when

the

1

623

is used

in

conjunction

with

the

Frequency

Re-

sponse

Test

Unit

Type

441

6 and

the

Test

Records

OR

2009

and

OR

2010

.

Principle of Operation

Reference

is

made

to

the

simpli-

fied

block

diagram

shown

in Fig. 3 .

The

tuning

signal

is

converted

by

the

Schmitt

trigger

.

into

a

uniform

pulse

form

with

a period

time

equal

to

the

period

of

the

original

input

waveform

.

This

period

time

is

mea-

sured

by

counting

the

number

of

pe-

riods

of

oscillation

of

a 2

MHz

oscil-

lator

between

each

trigger

pulse,

and

this

number

is

then

shifted

into

the

memory

. The

tracking

frequency

multiplier

function

is achieved

by

di-

viding

the

pulse

rate

and/

or

by

di-

viding

the

oscillator

rate (in

effect

multiplying

the

pulse

rate) by

the

fi-

gure

selected

on

the

denominator

and

numerator

knobs,

respectively

.

From

the

memory,

logic

circuits

digitally

control

the

tuning

of

the

main

filter

according

to

the

calcu-

lated

period

time

. The

filter

range

is

one

decade

of

frequency,

but

range

changing

is

automatic

until

the

fre-

quency

limits

are reached,

after

which

the

out-of-range

"frequency"

lamp

lights.

The

filter

is

tuned

over

each

decade

with

a

hyperbolic

sweep

consisting

of

175

discrete

steps

. The

step

width

varies be-

tween

0,8%

and

2%

of

the

tuned

frequency

as

shown

in

Fig.4.

Due

to

the

stepwise

method

of

tuning

the

filter,

the

1623

is

not

suitable

for

use

where

phase

accurate sig-

nals

are

required.

The

memory

also

controls

the

fre-

quency

display

logic

where

the

cal-

culated

period

time

is converted

to

frequency

for

the

digital

display

. So

that

the

specified

filter

gain

accu-

racy is

not

significantly

altered, it is

recommended

that

the

frequency

tuning

is

not

swept

faster

than

indi-

cated

in

Fig .5 .

This

chart

is based

on

the

filter

settling

time

. The

exam-

ple

shows

a

sweep

from

1 0

Hz

to

50

Hz

with

the

1

2%

bandwidth

fil-

ter

which

requires

a

minimum

sweep

time

of

5

s-

1 s = 4 s.

With

a

logarithmic

sweep,

the

sweep

rate

(determined

by

the

lowest

fre-

quency,

10Hz)

will

be 5 decades

per

minute.

The

sweep

rate

could

be

progressively

increased

with

in-

creasing

frequency

to

25

decades-

/

min

at

50

Hz

.

Recorder

Synchronization

Synchronization

signals

are pro-

vided

for

controlling

one of

the

axes

of

a

recorder

in accordance

with

the

tuned

frequency,

so

that

vibration

le-

vel

versus

frequency

or

r.

p.m

. plots

can be

made

.

Two

forms

of

synchro-

nization

signal

are provided: A

pulse

2,01,------

------

-~

1 ,

6+------::..-------,..--

--

----.,.,c...--1

'*-

0,8

c

0

:~

c

~

Cl

/

/

/

0,2.-""-

___

_...._

___

_.__

____

-::'

2 4 8 20

l------1

decade

of

frequency

•I

760850

Fig.4.

The

filter

is

tuned

through

each de-

cade

of

frequency

in

steps.

The

step

width

and

therefore

the

filter

defini-

tion

varies

between

0,8%

and

2%

of

the

tuned

frequency

as

shown

.

The

definition

of

the

frequency

display

va-

ries

between

0,2%

and 2%, as

traced

by

the

broken

line

3

Related product manuals

BRUEL & KJAER 1621