Seca 780 User manual

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Service

Manual

for

seca

780,

782

Variants:

7802317004

7802321004

7822321004

7822321604

Description:

Service

Manual

Number:

17-05-01-271-

b

Valid

as

of:

01.10.00

Valid

until:

Electronic

column

scale

Bearing

determined

lever

system,

double

ending

tuning

fork

Sensor,

DETF-module

with

basic

display.

Content:

Operation

17-10-06-244

e

Function

diagram

30-34-00-629

a

Electronics

30-34-00-617

Electronics

30-34-00-618

Description

of

faults

30-34-00-588

a

Replacement

30-34-00-656

a

Calibration

30-34-00-603

spare

parts

mod.

780/782

30-34-00-651

b

Manual

number:

17-05-01-271-

b

Service

Manual

Functional

description

Functional

description

DETF

basic

scale

Introduction

The

DETF

basic

scale

is

a

mechanical

basic

module

for

various

seca

scales.

It

is

used

for

the

electronic

determination

of

the

weight

of

adults.

For

the

electronic

measurement

of

the

mechanical

quantitiy

“force”

a

double-ended

tuning

fork

sensor

(DETF)

is

used.

The

above

principle

of

operation

has

been

realized

on

the

one

hand

with

a

knife-edged

load

lever

system

to

meet

higher

accuracy

requirements

and

on

the

other

hand

with

a

more

cost

effective

bearing-determined

load

lever

system

to

meet

slightly

lower

requirements.

Weighing

When

a

load

is

placed

on

the

scale,

the

force

due

to

gravity

is

transferred

from

the

platform

(1)

to

the

load

lever

system.

The

long

load

lever

(2)

transmits

the

force

via

the

bending

element

(5)

on

to

the

hook

(6).

The

force

is

reduced

in

accordance

with

the

transmission

ratio

of

the

load

lever.

The

force

applied

to

the

short

load

lever

(3)

is

added

to

the

force

on

the

long

load

lever

via

the

centre

suspension

(4).

A

bending

load

acts

on

the

bending

element

that

increases

the

tensile

force

acting

on

the

pretensioned

tuning-fork

sensor

(7).

This

increases

its

resonant

frequency

in

a

non-linear

way,

which

is

measured

by

the

connected

electronics

(8)

and

converted

into

a

weight

using

the

stored

characteristic

curve.

The

weight

is

output

on

the

digital

display

(9).

together,

but

also

exert

an

initial

load

which

is

necessary

to

reduce

the

hysteresis.

In

the

bearing-determined

load

lever

system

two

springs

exert

a

force

which

corresponds

to

a

preload

of

approx.

15

kg.

In

the

knifed-edged

load

lever

system

4

springs

exert

a

force

which

corresponds

to

a

preload

of

approx.

11

kg.

The

platform

is

prevented

from

being

lifted

by

an

additional

locking

device

onto

which

the

long

load

lever

hits

if

the

platform

starts

to

rise

(not

for

flat

scales).

Vibration-sensitive

switch

(optional)

Any

force

exerted

on

the

platform

acts

via

load

lever

system,

hook

and

overload

protection

device

on

the

vibration-sensitive

swich

(13)

which

is

fitted

between

overload

protection

device

and

platform.

The

load

causes

the

vibration-sensitive

switch

to

generate

an

electrical

pulse

which

starts

the

connected

electronics.

Overload

protection

device

The

force

acting

on

the

hook

is

transferred

to

the

overload

protection

device

(10).

This

device

is

pressed

against

the

platform

by

a

pretensioned

spring.

If

the

load

on

the

scale

exceeds

a

permitted

value,

the

spring

yields

and

the

load

lever

system

is

lowered.

Platform

locking

device

The

platform

retaining

springs

(11)

do

not

only

hold

platform,

frame

(12)

and

load

lever

system

18.08.99

Har.

30-34-00-629A

Function

diagram

30-34-00-629

DETF

basic

scale

Blatt

3

Brief

description

of

the

DETF

module

Introduction

The

DETF

module

belongs

to

the

family

ofseca

electronic

modules

and

is

used

to

determine

weight

by

means

of

a

tuning-fork

sensor

system.

The

weight

obtained

is

displayed

on

a

separate

display

module.

To

allow

the

module

to

be

adapted

to

different

scales,

an

EEPROM

is

integrated

with

which

it

can

be

configured.

A

connection

to

the

SeSAM

bus

(Seca's

Serial

Autoconfiguring

Multicontroller

bus)

is

provided

via

which

the

scale

can

be

calibrated

and

additional

modules

can

be

connected.

The

following

block

diagram

shows

the

most

important

function

blocks

of

the

force

sensor

and

the

DETF

module:

Weight

measurement

A

tuning-fork

sensor

screwed

to

a

bending

element

is

used

as

the

weight

sensor.

If

the

scale

is

loaded,

the

bending

element

exerts

a

tensile

force

on

the

tuning-fork

sensor,

thus

increasing

its

resonant

frequency.

By

means

of

the

bandpass

filter

the

sensor

is

set

vibrating

at

this

frequency

which

is

then

measured

by

the

microcontroller.

Using

the

value

obtained

and

the

individual

calibration

data

stored

in

the

EEPROM

the

controller

calculates

the

weight.

The

first

value

obtained

after

switch-on

is

used

as

the

zeropoint.

If

the

values

obtained

later

on

do

not

deviate

strongly

from

this

value,

the

zeropoint

is

corrected

in

order

to

compensate

for

possible

drifts.

When

the

sensor

is

connected,

care

must

be

taken

that

the

wires

are

not

twisted

to

prevent

crosstalk

from

the

output

to

the

input.

Temperature

measurement

As

the

value

measured

by

the

tuning-fork

sensor

is

affected

by

temperature,

the

temperature

is

measured

regularly

and

compensated

for

accordingly.

Power

supply

Power

supply

is

provided

by

four

AA

size

batteries

and

/

or

a

seca

mains

transformer

/

desktop

mains

unit.

From

the

power

supply

the

voltage

is

passed

via

a

reverse

voltage

protection

diode

to

an

in-phase

regulator

which

provides

a

stabilized

3V

supply

voltage.

30-34-00-617

1

06.09.1999

EE/Jensen

In

order

to

avoid

measuring

errors

due

to

almost

flat

batteries,

their

voltage

is

measured

at

regular

intervals.

If

the

voltage

drops

below

a

certain

limit,

the

user

is

alerted

by

the

battery

symbol

in

the

LCD.

If

the

next

threshold

is

undershot,

„bAtt"

is

displayed

and

weighing

is

no

longer

possible.

In

order

to

extend

the

on-time

when

the

scale

is

mains

operated,

the

microcontroller

receives

a

signal

when

a

mains

transformer

is

connected.

It

is

possible

to

use

rechargeable

batteries,

but

the

batteries

will

not

be

charged

in

the

scale.

EEPROM

The

DETF

module

accommodates

an

EEPROM

on

which

all

parameters

are

stored

that

can

be

used

to

influence

the

program

sequence,

for

example

various

limit

values

or

the

coefficients

for

determining

the

weight

and

for

temperature

compensation.

Furthermore,

the

scale

can

store

values

to

be

retrieved

when

the

scale

is

switched

on

the

next

time,

e.g.

the

modules

last

connected.

Serial

bus

To

allow

the

scale

to

be

calibrated

and

additional

modules,

such

as

displays,

to

be

connected,

the

DETF

module

is

equipped

with

an

interface

to

the

SeSAM

bus.

On

this

bus

the

stabilized

and

non-stablized

supply

voltages

are

available.

Via

a

data

and

a

clock

pulse

line

all

relevant

data

is

transmitted

to

other

modules.

A

special

start

line

is

provided

via

which

the

scale

can

be

switched

on

or

other

modules

can

signal

thatthey

wantto

send

data.

Fault

handling

If

faults

occur,

the

SeSAM

bus

initiates

a

fault

message

with

the

relevant

fault

code.

Furthermore,

each

fault

message

includes

the

number

of

the

module

type

on

which

the

fault

has

occurred

and

a

code

which

indicates

how

long

the

message

is

to

stay

on

display

and

which

displays

are

to

be

suppressed.

The

fault

messages

are

transferred

to

the

SeSAM

bus

and

can

be

output

by

the

display

module

(module

type

for

the

DETF

module

=

1).

The

following

fault

messages

are

implemented:

10

20

bit

counter

overflow

11

Counts

outside

the

permissible

range

12

Switch-on

zeropoint

outside

the

permissible

range

13

Zero

follow-up

outside

the

permissible

range

14

Fault

in

the

kg

value

calculation

15

Recalibration

fault

20

Battery

voltage

too

low

21

Fault

in

battery

voltage

measurement

22

Fault

in

temperature

measurement

23

Temperature

range

exceeded

(

<

0°C

or

>

50°C)

30

General

bus

fault

32

Command

buffer

full

33

More

than

8

slaves

detected

40

EEPROM

fault

41

Incorrect

EEPROM

access

50

Other

fault

Instead

of

fault

message

20

„bAtt"

is

displayed

and

„temP"

instead

of

fault

message

23.

Time

base

30-34-00-617

2

06.09.1999

EE/Jensen

From

the

quartz's

4.19MHz

a

time

base

is

derived

which

controls

all

timed

processes

in

the

scale.

These

are,

for

instance,

various

timeouts

and

the

on-time.

After

expiry

of

the

on-time,

the

supply

voltage

for

the

bandpass

filter,

for

voltage

measurement

and

for

the

EEPROM

is

switched

off.

All

ports

are

setto

zero-signal

level

and

the

quartz

is

stopped.

Recalibration

In

order

to

compensate

for

linear

measuring

errors

of

the

scale,

which

can,

for

instance,

occur

as

a

result

of

the

different

forces

of

gravity

at

different

geographical

points,

the

module

has

a

recalibration

function.

Recalibration

is

performed

via

the

SeSAM

bus

by

means

of

a

display

module.

Technical

data

Supply

voltage:

Supply

current:

Quiescent

current:

Operating

temperature:

Storage

temperature:

Dimensions:

2.7V-

15V

typ.

0.9mA

typ.

2pA

approx.

0°C

to

50°C

-10°C

to

60°C

56mm

x

38mm

x

20mm

30-34-00-617

3

06.09.1999

EE/Jensen

Zeichnungslegende

Sensor

Bandpass

filter

Temperature

measurement

Voltage

measurement

EEPROM

Voltage

control

Battery/mains

connection

Quartz

SeSAM

bus

Power

on

reset

30-34-00-617

4

06.09.1999

EE/Jensen

Brief

description

of

the

display

module

Introduction

The

display

modules

belong

to

the

family

of

seca

electronic

modules

and

are

used

to

display

a

weight

measured

with

a

suitable

module

and

transferred

via

the

SeSAM

bus

(Seca's

Serial

Autoconfiguring

Multicontroller

bus).

Furthermore,

the

display

modules

accommodate

the

operating

elements

and

can

process

the

weight

(hold,

tare,

etc.).

The

following

block

diagram

shows

the

most

important

function

blocks

of

the

display

modules:

Display

The

weight

displayed

on

the

LCD

is

updated

approximately

every

0.8s.

A

maximum

of

five

digits

as

well

as

a

few

special

characters

can

be

displayed,

which

can

appear

as

shown

below:

TO

DOO

O*

TUUQQB;

◄

A

HOLD

TARE

NET

StS

►

Explanation

of

the

special

characters:

•

The

battery

symbol

is

used

to

alert

of

the

fact

that

the

battery

is

going

flat.

•

The

plug

symbol

indicates

that

the

scale

is

operated

on

a

mains

transformer.

•

The

warning

triangle

signals

that

the

weight

displayed

on

the

scale

is

not

verifiable.

•

Hold

indicates

that

the

weight

display

has

frozen.

•

Tare

or

Net

show

that

a

weight

on

the

scale

has

been

tared

out.

•

The

left

and

right

arrows

point

to

additional

explanations

next

to

the

display.

•

The

weightunits

on

the

rightshow

in

which

unit

the

measured

weight

is

displayed.

Power

supply

Power

supply

is

provided

via

the

SeSAM

bus.

Operation

30-34-00-618

1

06.09.1999

EE/Jensen

With

the

exception

of

a

start

button

that

might

be

available,

the

connected

buttons

can

be

configured

as

required

for

the

particular

model.

These

buttons

can

be

pressed

just

lightly

or

longer

(longer

than

1.5s).

If

you

press

another

button

when

switching

on

the

scale,

the

scale

will

switch

to

the

verification

counter

and

recalibration

mode.

SeSAM

bus

The

SeSAM

bus

connects

the

display

modules

to

the

other

modules.

On

this

bus

the

stabilized

and

non-stablized

supply

voltages

are

available.

Via

a

data

and

a

clock

pulse

line

all

relevant

data

is

exchanged.

A

special

start

line

is

provided

via

which

the

scale

can

be

switched

on

or

the

module

can

signal

that

it

wants

to

send

data.

Identification

code

If

several

display

modules

are

connected,

an

unmistakable

ID

code

must

be

assigned

to

them

using

soldering

jumpers

to

ensure

thatthe

different

modules

are

correctly

addressed

via

the

bus.

Backlighting

(optional)

Some

display

modules

are

equipped

with

a

power

supply

for

LCD

backlighting.

It

can

either

be

lit

when

the

scale

is

switched

on

oronly

when

the

scale

is

loaded.

Signal

transmitter

(optional)

Some

display

modules

are

equipped

with

a

signal

transmitter.

A

piezo

diaphragm

is

used

which

is

controlled

with

a

4

kHz

square-wave

signal.

Fault

handling

If

faults

occur,

the

SeSAM

bus

initiates

a

fault

message

with

the

relevant

fault

code.

Furthermore,

each

fault

message

includes

the

number

of

the

module

type

on

which

the

fault

has

occurred

and

a

code

which

indicates

how

long

the

message

is

to

stay

on

display

and

which

displays

are

to

be

suppressed.

The

display

module

displays

its

own

fault

messges

on

its

LCD.

Module

type

(for

the

display

module

=

3)

and

fault

number

are

output.

In

addition,

the

fault

messages

that

other

modules

have

transferred

to

the

SeSAM

bus

are

displayed.

The

following

fault

messages

are

implemented:

14

Fault

in

the

kg

value

calculation

15

Recalibration

fault

30

General

bus

fault

32

Command

buffer

full

33

More

than

8

slaves

detected

50

Other

fault

51

Menu

fault

Time

base

From

the

quartz's

4.19MHz

a

time

base

is

derived

which

controls

all

timed

processes

in

the

scale.

These

are,

for

instance,

various

timeouts.

Recalibration

In

order

to

compensate

for

linear

measuring

errors

of

the

scale,

which

can,

for

instance,

occur

as

a

result

of

the

different

forces

of

gravity

at

different

geographical

points,

the

module

has

a

recalibration

30-34-00-618

2

06.09.1999

EE/Jensen