Rockwell-automation MHB44IND Pulse Input and Analogue Output Module Manuale Utente Scaricare il pdf (Pagina 9)

MHB44IND

October

200

5

–

Issue

2

9

Triguard

SC300E MHB44IND Pulse Input and Analogue Output Module

THEORY OF OPERATION

The

module

has

four

isolated

1Hz

to

35kHz

pulse

-

input

frequency

measuring

channels,

and

four

0

-

22mA

current

output

channels

using

a common

24V

supply

via

termination

card

TPH44A

IC.

The

circuits

are

triplicated

except

for

the

final

combining

of

the

analogue

output

stages

into

a single

voted

output.

Common functions

Power

supplies

and

monitoring

The

5V

and

12V

dual

-

redundant

supplies

from

the

backplane

are

diode

-

OR’ed

to

the

thre

e

channels

plus

an

auxiliary

section.

The

analogue

output

section

is

isolated

by

dc/dc

converters

providing

+5V

and

±15V.

All

the

supplies

and

fuses

are

monitored

by

the

CI.

An

On/Off

Line

Request

switch

on

the

front

panel

enables

a request

to

be

sent

to

the

MPPs

that

the

module

be

taken

off

-

line

for

maintenance

purposes

or

returned

on

-

line.

Mode

settings

The

module

contains

a hardware

identity

circuit

that

enables

system

identification

of

the

module,

and

seven

configuration

jumper

links

(JP1to

JP4

and

LK1

to

LK3).

The

jumper

links

JP1,

JP2,

JP3

and

JP4

must

be

set

to

the

Off

position.

The

operation

of

and

settings

links

LK1

to

LK3

is

described

below:

Link

1 allows

the

module

to

be

set

up

for

321

or

320

mode

operation

which

sets

the

threshold

that

determines

how

much

of

the

circuit

can

be

degraded

while

still

preserving

overall

operation.

320

mode

means

that

the

system

will

continue

to

function

with

two

out

of

three

serviceable

circuits.

If

the

number

falls

to

one

out

of

three

the

last

read

data

is

maintained.

In

321

mode

the

system

will

continue

to

function

with

one

out

of

three

serviceable

circuits.

If

that

fails

the

last

read

data

is

maintained

and

the

module

is

taken

off

-

line.

Link

2 (HLV/GTZ)

determines

whether,

in

the

event

of

a failure

due

to

321/32

0 action,

the

last

read

values

are

held

(HLV)

or

are

set

to

zero

(GTZ).

Link

3 is

always

set

to

HW.

Latent

fault

detection

(LFD)

on

outputs

The

voted

analogue

voltage

outputs

from

each

channel

are

compared

in

turn

with

the

D

-

to

-

A

outputs.

The

LFD

scheme

employed

is

to

change

each

channel’s

output

in

turn

by

0.4V

for

1ms,

first

negatively

then

positively,

leaving

the

other

channels

unchanged.

At

each

change,

the

discrepancy

between

every

channel

and

the

common

output

is

tested

by

a window

comparator.

If

a

difference

is

detected

on

the

deviated

channel

and

the

other

two

are

'same'

then

no

latent

fault

is

detected

and

the

Health

LED

is

illuminated.

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