Omega engineering Cl521 User manual

i

fcCL521

Temperature

Calibrator/Thermometer

OMEGA

warrants

this

unit

to

be

free

of

defects

in

materials

and

workmanship

and

to

give

satisfactory

service

for

a

period

of

25

months

from

date

of

purchase.

OMEGA

Warranty

adds

an

additional

one

(1)

month

grace

period

to

the

normal

two

(2)

year

product

warranty

to

cover

handling

and

shipping

time.

This

ensures

that

our

customers

receive

maximum

coverage

on

each

product.

If

the

unit

should

malfunction,

it

must

be

returned

tathe

factory

for

evaluation.

Our

Customer

Service

Department

will

issue

an

Authorized

Return

(AR)

number

immediately

upon

phone

or

written

request.

Upon

examination

by

OMEGA,

if

the

unit

is

found

to

be

defective

it

will

be

repaired

or

replaced

at

no

charge.

However,

this

WARRANTY

is

VOID

if

the

unit

shows

evidence

of

having

been

tampered

with

or

shows

evidence

of

being

damaged

as

a

result

of

excessive

corrosion;

or

current,

heat,

moisture

or

vibration;

improper

specification;

misapplication;

misuse

or

other

operating

conditions

outside

of

OMEGA's

control.

Components

which

wear

or

which

are

damaged

by

misuse

are

not

warranted.

These

include

contact

points,

fuses,

and

triacs.

There

are

no

warranties

except

as

stated

herein.

There

are

no

other

warranties,

expressed

or

implied,

including

but

not

limited

to

the

implied

warranties

of

merchantability

and

of

fitness

for

a

particular

purpose.

OMEGA

ENGINEERING,

INC.

is

not

responsible

for

any

damages

or

losses

caused

to

other

equipment,

whether

direct,

indirect,

incidental,

special

or

consequential,

^ich

the

purchaser

may

experience

as

a

result

of

the

installation

or

use

of

the

product.

The

buyer's

sole

remedy

for

any

breach

of

this

agreement

by

OMEGA

ENGINEERING,

INC.

or

any

breach

of

any

Warranty

by

OMEGA

ENGINEERING,

INC.

shall

not

exceed

the

purchase

price

paid

by

the

purchaser

to

OMEGA

ENGINEERING,

INC.

for

the

unit

or

units

or

equipment

directly

affected

by

such

breach.

Every

precaution

for

accuracy

has

been

taken

in

the

preparation

of

this

manual,

however,

OMEGA

ENGINEERING,

INC.

neither

assumes

responsibility

for

any

omissions

or

errors

that

may

appear

nor

assumes

liability

for

any

damages

that

result

from

the

use

of

the

products

in

accordance

with

the

information

contained

in

the

manual.

Direct

all

warranty

and

repair

requests/inquiries

to

the

OMEGA

ENGINEERING

Customer

Service

Department:

call

Toll

Free

1-800-622-2378,

FAX

203-359-7811;

International:

203-359-1660,

FAX:

203-359-7807.

BEFORE

RETURNING

ANY

PRODUCTfS)

TO

OMEGA,

YOU

MUST

OBTAIN

AN

AUTHORIZED

RETURN

(AR)

NUMBER

FROM

OUR

CUSTOMER

SERVICE

DEPARTMENT

(IN

ORDER

TO

AVOID

PROCESSING

DELAYS).

The

assigned

AR

number

should

then

be

marked

on

the

outside

of

the

return

package

and

on

any

correspondence.

FOR

WARRANTY

RETURNS,

please

have

the

following

information

available

BEFORE

contacting

OMEGA:

1.

P.O.

number

under

which

the

product

was

PURCHASED,

2.

Model

and

serial

number

of

the

product

under

warranty,

and

3.

Repair

instructions

and/or

specific

problems

you

are

having

with

the

product.

FOR

NON-WARRANTY

REPAIRS

OR

CALIBRATION,

consult

OMEGA

for

current

repair/calibration

charges.

Have

the

following

information

available

BEFORE

contacting

OMEGA:

1.

Your

P.O.

number

to

cover

the

COST

of

the

repair/calibration,

2.

Model

and

serial

number

of

product,

3.

Repair

instructions

and/or

specific

problems

you

are

having

with

the

product.

OMEGA'S

policy

is

to

make

running

changes,

not

model

changes,

whenever

an

improvement

is

possible.

That

way

our

customers

get

the

latest

in

technology

and

engineering.

OMEGA

is

a

registered

trademark

of

OMEGA

ENGINEERING,

INC.

©

Copyright

1991

OMEGA

ENGINEERING,

INC.

All

rights

reserved

including

illustrations.

Nothing

in

this

manual

may

be

reproduced

in

any

manner,

either

wholly

or

in

part

for

any

purpose

whatsoever

without

written

permission

from

OMEGA

ENGINEERING,

INC.

Printed

in

Finland

TABLE

OF

CONTENTS

CL521

TEMPERATURE

CALIBRATOR/THERMOMETER

SECTION

PAGE

SECTION

1

INTRODUCTION.1

1.1

General

Description.;.1

1.2

Features.

1

1.3

Available

Models.

1

SECTION

2

INSTALLATION.

2

2.1

Unpacking.

2

2.2

Removing

the

Carrying

Case.2

2.3

Charging

the

Battery.3

2.4

Wiring

Connections.

3

SECTIONS

GENERAL

OPERATION.4

3.1

Front

Panel

Functions.

4

3.2

Initial

Start-up.

6

SECTION

4

THERMOCOUPLE

AND

MILLIVOLT

MEASUREMENTS.6

4.1

Theory

of

Operation.6

4.2

Reference

Junction.7

4.3

Thermocouple

Measurements.8

4.3.1

Connections

and

Reference

Junction

Mode

Selection.

8

4.3.2

Measuring

Temperature.11

4.3.3

Checking

or

Changing

Reference

Junction

Temperature.12

4.4

Measuring

Thermocouple

Resistance.13

4.5

Measuring

Millivolts.14

SECTION

5

PtIOO

AND

RESISTANCE

MEASUREMENTS.14

5.1

General

Information.14

5.2

Connecting

a

Resistance

Probe

to

the

CL521.15

5.3

PtiOO

Temperature

Measurement.17

5.4

Resistance

Measurement.19

SECTION

6

ADDITIONAL

MEASUREMENT

FUNCTIONS.20

6.1

Using

Other

Measurement

Functions.20

6.2

Monitoring

Rate

of

Change.20

6.3

Indications

of

Deviation.20

6.4

Checking

Minimum

and

Maximum

Readings.21

6.5

Returning

to

Normal

Measurement

Mode.21

TABLE

OF

CONTENTS

(Continued)

SECTION

PAGE

SECTION

7

THERMOCOUPLE

SIMULATION

AND

MILLIVOLT

CALIBRATION.21

7.1

Principle

of

Thermocouple

Simulation

.

.21

7.2

Thermocouple

Simulation.21

7.2.1

Connection

and

Selection

of

Compensation

Modes.21

7.2.2

Simulation.24

7.2.3

Effect

of

Loading.26

7.3

Millivolt

Calibration.27

SECTION

8

RS-232C

AND

ANALOG

OUTPUT

OPTION.28

8.1

General

Description.28

8.2

Installing

the

RS-232C

Digital

Interface

Option.28

8.2.1

Data

Format

and

Baud

Rate.29

8.2.2

Connection

Cables.29

8.2.3

Output

Message

Format

and

Timing..31

8.2.4

End

Characters

of

the

Output

Message.32

8.2.5

Remote

Control

by

Computer.32

8.3

Analog

Output.35

8.3.1

Analog

Output

Specifications.36

SECTION

9

SERVICE

AND

CALIBRATION.36

SECTION

10

SPECIFICATIONS.38

ii

SECTION

1

INTRODUCTION

1.1

GENERAL

DESCRIPTION

The

OMEGA

CL521

is

a

precision,

high-accuracy

calibrator

for

use

on

the

bench

or

in

the

field.

Featuring

exceptionally

high

accuracy,

the

CL521

can

measure

any

of

ten

thermocouple

types,

platinum

RTDs,

millivolts,

or

ohms.

The

CL521

is

also

an

instrument

calibrator,

allowing

users

to

calibrate

or

check

the

above

sensor

type

instrumentation.

The

CL521

is

designed

for

ease

of

use,

with

a

large,

easy-to-read

LCD

display

with

0.41"

(10.4

mm)

digits.

A

touch-sensitive

keypad

makes

function

selection

and

value

entry

fast

and

easy,

while

a

toggle

switch

simplifies

selection

between

measurement

and

calibration

functions.

The

CL521

can

store

up

to

six

values

for

quick

selection

of

common

calibration

temperatures,

as

well

as

store

six

measurement

readings.

Other

features

include

rate

of

change

calculation,

min

and

max

storage,

and

differential

measurement

from

a

stored

value.

The

CL521D

has

all

the

features

of

the

CL521

with

the

addition

of

RS-232C

two-way

communications

and

an

analog

output.

The

RS-232C

communications

can

be

used

for

remote

computer

control

of

the

unit,

as

well

as

for

transmitting

data

to

a

computer,

printer

or

datalogger.

The

analog

output

is

a

1

mV

per

degree

signal,

with

10x

amplification

when

using

the

differential

function

of

the

CL521D.

Each

unit

is

supplied

complete

with

carrying

case,

connector

leads,

type

K

thermocouple

extension

cable

with

male

connector,

calibration

certificate,

TAS-U-5

connector,

and

AC

power

adapter.

1.2

FEATURES

•

Calibrate

and

Measure

J,

K,

T,

E,

R,

S,

B

and

N

Thermocouples

•

Measure

100

ohm

Ft

RTDs

•

Math

Functions

Calculate

Rate

of

Change

and

Difference

•

Min/Max

Storage

•

Store

up

to

Six

Simulations

for

Quick

Recall

•

Enter

Calibration

Values

Directly

from

Keypad

or

Through

Up/Down

Increment

Keys

•

Available

with

Optional

RS-232C

and

Analog

Output

1.3

AVAILABLE

MODELS

MODEL

NUMBER

DESCRIPTION

CL521

CL521D

CL521-RS232C

CL521-MA

Temperature

calibrator/indicator

Calibrator

with

RS-232C

and

analog

output

RS-232

interface

board

(includes

software)

Milliamp

board

with

24

Vdc

supply

1

SECTION

2

INSTALLATION

2.1

UNPACKING

Remove

the

packing

list

and

verify

that

all

equipment

has

been

received.

If

there

are

any

questions

about

the

shipment,

please

call

the

OMEGA

Customer

Service

Department

at

1

-800-622-2378.

Upon

receipt

of

shipment,

inspect

the

container

and

equipment

for

any

signs

of

damage.

Take

particular

note

of

any

evidence

of

rough

handling

in

transit.

Immediately

report

any

damage

to

the

shipping

agent.

NOTE

The

carrier

will

not

honor

any

claims

unless

all

shipping

material

is

saved

for

their

examination.

After

examining

and

removing

contents,

save

packing

material

and

carton

in

the

event

reshipment

is

necessary.

All

units

are

supplied

with

carrying

case,

connector

leads,

type

K

thermocouple

extension

cable

with

male

connector,

calibration

certificate,

TAS-U-5

connector,

and

AC

power

adapter.

2.2

REMOVING

THE

CARRYING

CASE

In

laboratories

and

maintenance

shops,

the

CL521

is

easiest

to

use

without

its

carrying

case.

In

order

to

remove

the

carrying

case,

be

sure

the

AC

adaptor

is

not

connected,

then

open

both

carrying

case

flaps

and

the

strap

around

the

instrument.

Lift

the

rear

of

the

instrument

about

an

inch,

lift

the

front

of

the

instrument,

and

pull

it

out

of

the

case.

The

unit's

carrying

handle

may

then

be

turned

downwards

in

front

to

act

as

a

stand

for

easier

viewing.

The

unit

is

installed

into

its

case

in

the

reverse

order.

In

the

field,

the

carrying

case

is

most

convenient.

When

carried

around

the

neck,

the

unit

can

easily

be

used

merely

by

opening

the

flap

in

front

of

the

panel

and

turning

it

over

to

the

back

of

the

case.

Figure

2-1.

Removing

the

Carrying

Case

2

2.3

CHARGING

THE

BATTERY

The

power

used

by

the

unit

comes

from

the

internal

battery,

which

also

keeps

certain

program

parameters

in

memory

even

when

the

unit

is

switched

off.

The

unit

comes

with

Its

battery

partialiy

charged

and

it

is

therefore

advisable

to

charge

the

battery

before

use.

batteries

in

the

instrument

begin

to

run

down,

the

message

BATTLO

appears

periodically

on

the

display.

If

the

battery

voltage

goes

too

low

the

instrument

switches

itself

off

to

prevent

destructive

discharge

of

the

batteries

and

loss

of

data

stored

in

the

memory

registers.

When

BATTLO

appears

on

the

display,

the

battery

should

be

recharged

as

soon

as

connector

at

the

rear

of

the

unit.

Connect

the

charger

to

the

120

VAC,

making

sure

that

the

line

voltage

is

correct.

Charge

the

battery

for

approximately

12

hours;

20

hours

if

used

during

charging.

2.4

WIRING

CONNECTIONS

The

CL521

connection

terminals

are

found

on

top

of

the

unit.

Connections

are

easily

[3?,

®''®

‘^®Pt

0^

the

way

of

the

display

and

keypad.

When

using

the

carrying

case,

the

flap

in

front

of

the

connection

panel

may

be

shut

during

use.

This

reduces

changes

in

reference

temperature

of

thermocouple

temperature

measurements,

thus

ensuring

measurement

accuracy

in

environments

where

ambient

temperature

may

vary

greatly.

The

terminal

panel

contains

two

separate

types

of

connections.

79-

®®®<^

f®’’

thermocouple

and

millivolt

measurement

and

measurement/calibration

switch

is

in

the

MtAbUKtMENT

position,

this

connection

measures

inputs.

The

CALIBRATION

^

calibration

output

signal.

The

resistance

of

a

circuit

connected

to

the

I

c

and

mV

connection

may

also

be

measured

by

using

the

TCii

measurement

function.

The

Ohm

and

PtIOO

connection

is

used

to

measure

the

resistance

of

PtIOO

or

other

resistive

probes.

Both

three

and

four-wire

connections

are

possible.

Used

in

four

wire

connections

3

SECTION

3

GENERAL

OPERATION

3.1

FRONT

PANEL

FUNCTIONS

The

functions

of

the

CL521

have

been

chosen

for

their

usefulness

in

temperature

measurement

and

calibration.

The

functions

are

easily

selected

from

the

keypad

on

the

front

panel.

CL521

functions

are

listed

below

and

shown

in

Figure

3-1.

For

more

complete

instructions,

refer

to

Sections

4

to

7.

THERMOCOUPLE

MEASUREMENTS:

-

Temperature

measurement

in

either

°C

or

°F

using

ten

different

thermocouple

types

Reference

junction

modes:

-

External

reference

junction,

if

the

temperature

value

is

not

0°C,

must

be

entered

into

the

memory.

-

Reference

temperature

is

measured

using

a

Pt100

oc

=

0.00385

resistance

probe

-

Reference

temperature

is

measured

using

an

internal

sensor

-

Millivolt

measurement

-10

to

110

mV

-

Thermocouple

resistance

measurement

RESISTANCE

MEASUREMENT:

-

Temperature

measurement

in

°C

or

°F

using

a

Pt100

<=c

=

0.00385

resistance

probe

-

Ohm

measurement

0

to

400

ohms

ADDITIONAL

MEASUREMENT

FUNCTIONS:

-

Rate

of

change

measurement

-

Measurement

of

deviation

from

a

preset

value

-

Storage

of

minimum

and

maximum

values

CALIBRATION

FUNCTIONS:

-

Thermocouple

simulation

in

"C

or

°F

-

Millivolt

calibration

-10

to

110

mV

Entry

of

calibration

values:

-

From

keypad

-

From

memory

-

Smooth

increase

or

decrease

-

Fine

adjust

using

INC

and

DEC

switches

-

Automatic

stepping

through

five

preset

calibration

values

4

5

Figure

3-1,

Front

Panel

Functions

3.2

INITIAL

START-UP

The

CL521

is

switched

on

and

off

by

pressing

the

ON

and

OFF

keys,

respectively.

After

the

instrument

is

switched

on,

it

performs

various

routines

and

self-tests.

A

message

flashes

on

the

display

indicating

the

version

of

the

CL521.

After

this,

the

unit

begins

operation

in

the

most

recently

used

mode

of

operation.

SECTION

4

THERMOCOUPLE

AND

MILLIVOLT

MEASUREMENTS

4.1

THEORY

OF

OPERATION

A

thermocouple

is

a

temperature

probe

composed

of

two

wires

of

different

materials

connected

together.

There

is

a

specific

thermopotential

between

the

wires

which

varies

non-linearly

as

a

function

of

temperature.

If

two

wires

of

different

materials

A

and

B

are

connected

in

a

loop

as

shown,

the

thermoelectric

effect

causes

a

flow

of

current

through

the

loop,

corresponding

to

the

temperatures

T1

and

T2

at

the

junction

points.

<

B

Figure

4-1.

Basic

Thermocouple

Circuit

If

the

circuit

is

broken,

its

thermopotential

can

be

measured.

Assuming

the

voltmeter

does

not

create

a

load

in

the

circuit,

the

potential

is

determined

solely

by

temperatures

T1

and

T2

(the

thermopotentials

of

the

copper

wires

and

the

thermocouple

conductors

cancel

each

other

as

long

as

both

connections

are

at

the

same

temperature).

Figure

4-2.

Thermocoupie

Circuit

with

Meter

Normally

T1

is

measured

while

the

reference

junction

temperature

is

kept

at

a

constant

temperature

T2,

or

is

somehow

compensated

for

during

evaluation

of

the

measured

value.

Frequently,

the

circuit

is

broken

at

the

reference

junction.

Thus

the

reference

junction

is

moved

to

the

point

where

the

connection

is

made

from

the

thermocouple

conductors

to

the

copper

wires.

6

T1

Figure

4-3.

Thermocouple

with

Reference

Junction

and

Voltmeter

4.2

REFERENCE

JUNCTION

TEMPERATURE

The

reference

junction

temperature

is

easiest

to

compensate

for

by

measuring

the

temperature

of

closely

situated

reference

junctions

using,

for

example,

a

resistance

temperature

probe.

Figure

4-4.

Reference

Junction

Compensation

Using

a

Pt100

Probe

The

temperature

of

the

reference

junctions

can

also

be

kept

constant

by

cooling

or

heating

them

with

the

aid

of

a

thermostat.

When

cooling,

0°C

is

most

convenient.

When

heating,

a

temperature

is

selected

which

is

somewhat

hotter

than

room

temperature,

for

example,

50°C.

Figure

4-5.

Reference

Junction

Compensation

Using

a

Temperature

Controller

L.

J

7

The

reference

junction

can

also

be

placed

into

a

"compensation

circuit."

A

temperature

sensor

measures

the

reference

junction

temperature,

and

feeds

a

correction

potential

into

the

measurement

circuit

as

the

reference

junction

temperature

varies.

Thus

the

temperature

of

the

reference

junction

appears

constant

to

the

measurement

circuit.

The

compensation

temperature

is

normally

0°C.

Reference

Junction

Temperature

Sensor

1

A

_l»_

-

4

-

\

—.

Compensation

circuit

Cu

Q

'<

.

'

_

1

Cu

f

Thermocouple

bj

To

Instrument

Figure

4-6.

Electronic

Reference

Junction

Compensation

Circuit

4.3

THERMOCOUPLE

MEASUREMENTS

4.3.1

Connections

and

Reference

Junction

Mode

Selection

Connect

the

thermocouple

wires

if

it

has

not

been

done

already.

Use

the

polarity

marked

on

the

terminal

panel.

Carefully

consider

whether

you

shall

use

copper

leads

or

thermocouple

extension

cables.

The

extension

cable

must

conform

to

the

thermocouple

both

by

type

and

polarity.

If

the

external

reference

junction

temperature

is

to

be

measured,

also

connect

a

PtIOO

probe.

The

CL521

incorporates

three

different

reference

junction

modes:

A)

Internal

reference

junction

compensation,

CJ

MODE

=

INT

B)

External

reference

junction

compensation

using

a

PtIOO

probe,

CJ

MODE

=

PROBE

C)

Manual

reference

junction

compensation,

CJ

MODE

=

MAN

A)

INTERNAL

REFERENCE

JUNCTION

COMPENSATION,

CJ

MODE

=

INT

The

thermocouple

is

connected

directly,

or

through

thermocouple

extension

cables

to

the

CL521

thermocouple

terminal

posts.

This

is

the

most

common

method

of

compensation

for

reference

junction

temperature,

but

you

must

use

the

correct

type

of

thermocouple

extension

cables.

8

Thermocouple

extension

cables

Figure

4-7.

Measurements

Using

Thermocoupie

Extension

Cabies

In

the

field,

the

ambient

temperature

may

change

suddenly.

Under

such

conditions,

accurate

reference

junction

compensation

can

be

ensured

by

closing

the

flap

on

top

of

the

terminal

panel

during

use.

The

instrument

is

shipped

complete

with

a

connecting

cable

for

a

type

K

thermocouple.

Connect

the

miniature

connector

on

the

cable

to

the

terminals

according

to

the

polarity

shown.

V.

Figure

4-8.

CL521

Terminal

Panel

9

B)

REFERENCE

JUNCTION

COMPENSATION

USING

A

Pt100

PROBE

CJ

MODE

=PROBE

In

this

mode,

the

reference

junction

T2

is

outside

the

CL521

at

a

location

where

a

PttOO

probe

is

also

installed.

The

thermocouple

is

connected

to

the

CL521

with

copper

wires

and

the

PtIOO

probe

is

connected

to

the

PtIOO

terminals.

I-'

Figure

4-9.

Reference

Junction

Compensation

Using

a

PtIOO

Probe

C)

MANUAL

REFERENCE

JUNCTION

COMPENSATION,

CJ

MODE

=

MAN

Reference

junction

temperature

compensation

is

automatically

set

to

0°C,

using

the

external

reference

junction.

The

thermoelectric

potential

is

connected

to

the

CL521

using

copper

leads.

Figure

4-10.

Manual

Reference

Junction

Compensation

10

4.3.2

Measuring

Temperature

Once

connections

are

completed,

measurements

can

be

performed.

If

the

CL521

was

most

recently

used

for

the

same

type

of

measurements,

it

is

ready

to

use

once

the

power

is

switched

on.

Otherwise:

Check

that

the

MEASUREMENT/CALIBRATION

switch

is

in

the

MEASUREMENT

position.

Choose

thermocouple

measurement

by

pressing

the

TC

&

mV

key.

If

the

display

is

showing

millivolts

(an

arrow

at

the

right

edge

of

the

display

is

pointing

to

mV),

change

it

to

temperature

display

by

pressing

the

TC/mV

key

once.

An

arrow

at

the

upper

edge

of

the

display

will

now

indicate

the

most

recently

used

thermocouple

type.

Select,

if

needed,

the

required

type

by

pressing

the

TC

TYPE

key

repeatedly.

Select

the

required

reference

junction

compensation

mode

by

pressing

the

CJ

MODE

key

repeatedly

until

the

arrow

at

the

left

edge

of

the

display

is

pointing

to

the

required

mode.

The

CL521

will

now

measure

potential

from

a

thermocouple

and

convert

it

according

to

the

NIST

Conversion

Tables

to

a

temperature

reading.

The

temperature

units

(°C

or

°F)

will

be

the

ones

most

recently

used.

To

change

the

temperature

units,

press

the

°C/°F

key

once.

A

specific

temperature

measurement

range

has

been

defined

for

each

type

of

thermocouple.

If

the

measured

temperature

is

outside

this

range,

the

display

flashes

the

corresponding

minimum

or

maximum

temperature.

If

the

reference

junction

temperature

goes

below

-10°C

or

above

+70^C,

the

unit

displays

"CJ

LO"

or

"CJ

HI",

respectively.

11

4.3.3

Checking

and

Setting

Reference

Junction

Temperature

The

temperature

in

the

reference

junction

compensation

circuit

or

the

compensation

temperature

of

an

externai

compensation

circuit

may

be

set

to

a

temperature

other

than

0°C.

The

externai

reference

junction

temperature

may

aiso

be

measured

by

methods

other

than

a

Pt100

probe,

in

aii

these

cases,

manuai

compensation

for

reference

junction

temperature

must

be

used,

and

that

temperature

vaiue

stored

into

memory

Register

9.

The

vaiue

in

Register

9

indicates

the

temperature

of

the

reference

junction

in

°C,

regardless

of

the

selected

temperature

units.

Register

9

is

automatically

set

to

zero

whenever

the

manual

reference

junction

compensation

mode

is

selected.

To

check

the

reference

junction

temperature,

or

to

change

it,

proceed

as

follows:

NOTE:

Make

sure

the

MAN

reference

junction

compensation

mode

is

selected.

Switch

the

MEASUREMENT/CALIBRATION

switch

to

the

CALIBRATION

position.

Recall

Register

9

(the

reference

junction

temperature)

to

the

display

by

entering:

RCL

9

The

display

will

show,

for

example,

"CJ

0.00

C".

To

set

the

reference

junction

compensation

temperature

to

50°C,

for

example,

enter:

5

0

STO

9

After

checking

and/or

setting

the

reference

junction

temperature,

return

the

MEASUREMENT/CALIBRATION

switch

back

to

the

MEASUREMENT

position.

Setting

reference

junction

temperature

Checking

reference

junction

temperature

Figure

4-12.

Checking

and

Setting

Reference

Junction

Temperature

12

The

reference

junction

temperature

in

Register

9

can

also

be

checked

while

using

the

internal

reference

junction

compensation

(INT),

or

whiie

measuring

the

reference

junction

temperature

with

a

PtIOO

probe

(PROBE).

4.4

MEASURING

THERMOCOUPLE

RESISTANCE

The

CL521

can

be

used

to

measure

the

resistance

of

a

thermocouple

circuit

during

thermocouple

temperature

measurements.

The

measurement

will

yield

a

correct

resistance

regardless

of

the

prevailing

thermoelectric

potential.

Display

the

circuit

resistance

by

pressing

the

TC£2

key

while

in

TC

&

mV

mode.

Return

to

the

normal

measurement

mode

by

pressing

the

TC

&

mV

key.

Figure

4-13.

Measuring

Thermocoupie

Resistance

with

the

CL521

The

resistance

measurement

range

is

0

to

400

ohms.

Exceeding

this

range

causes

the

display

to

blink

the

maximum

allowed

resistance.

If

the

measurement

circuit

is

broken,

the

display

will

indicate

"OPEN".

Thermocouple

resistance

measurements

can

be

used:

-

to

determine

the

condition

of

the

measurement

connections

and

to

help

locate

short

circuits.

-

to

help

in

adjusting

the

measurement

circuit

resistance

when

meter

movement

indication

devices

are

used

to

measure

thermoelectric

potential.

-

to

predict

the

expected

lifespan

of

a

thermocouple

by

monitoring

the

change

in

its

resistance

as

a

function

of

time,

and

comparing

the

measured

values

to

data

collected

from

-

for

various

checks

when

accuracy

requirements

do

not

warrant

the

use

of

three

or

four

wire

connections,

for

example

to

determine

the

wire

order

when

connecting

a

three

or

four

wire

probe.

13

4.5

MEASURING

MILLIVOLTS

If

the

instrument

was

most

recently

used

for

mV

measurement,

it

will

be

ready

to

use

once

the

power

is

turned

on.

If

it

was

not

recently

used

for

mV

measurement:

Check

that

the

MEASUREMENT/CALIBRATION

switch

is

in

the

MEASUREMENT

position.

Select

the

mV

input

by

pressing

the

TC&mV

key.

Check

that

the

measured

value

is

shown

in

millivolts

(

an

arrow

at

the

right

edge

of

the

display

will

point

to

mV).

If

mV

is

not

being

shown,

press

the

TC/mV

key

once.

The

CL521

will

now

measure

millivolts.

Reference

junction

compensation

is

automatically

disconnected

(the

CJ

MODE

arrow

indicates

MAN

and

Register

9

is

set

to

0°C).

If

the

potential

being

measured

goes

below

-10

mV

or

above

110

mV,

the

display

will

blink

the

minimum

or

maximum

measurement

values

to

indicate

range

underflow

or

overflow.

SECTION

5

Pt100

RESISTANCE

MEASUREMENTS

5.1

GENERAL

INFORMATION

Resistance

probes

are

often

used

for

temperature

measurement.

Currently

the

most

cornmon

probe

type

is

the

Pti

00

resistance

probe.

It

is

constructed

from

platinum

wire

having

a

resistance

of

100

ohms

at

OX.

The

resistance

increases

with

temperature,

because

metal

wires

have

a

positive

thermal

coefficient

of

resistance.

14

In

measuring

the

resistance

of

a

probe,

the

effect

of

lead

wire

resistances

between

probe

and

measuring

device

must

be

compensated

for.

Normally,

the

change

of

the

lead

resistance

as

its

temperature

changes

must

also

be

considered.

Accurate

measurements

require

that

the

connecting

cable

have

at

least

three,

and

preferably

four,

conductors.

5.2

CONNECTING

A

RESISTANCE

PROBE

Ideally,

the

best

method

of

eliminating

the

effect

of

lead

resistance

is

to

use

four

conductors

when

measuring

the

temperature

with

the

probe.

Two

conductors

are

required

to

carry

the

measurement

current

through

the

resistance,

while

the

other

two

are

used

to

measure

the

voltage

across

the

probe.

Constant

current

Figure

5-1.

Basic

PtIOO

Measuring

Circuit

The

CL521

uses

this

method

in

resistance

measurements.

By

measuring

potentials

both

with

and

without

current

flow,

the

unit

can

also

eliminate

possible

thermoelectric

potentials

caused

by

conductor

connections.

Figure

5-2.

Connecting

a

4-Wire

Resistance

Probe

to

the

CL521

15

In

three-wire

connections,

one

wire

is

connected

to

one

end

of

the

resistance

probe,

and

two

wires

are

connected

to

the

other

end.

Probe

resistance

can

be

measured

using

many

different

methods,

but

ail

of

these

require

that

at

least

two

of

the

conductors

in

the

cable

are

identical.

Some

methods

even

require

that

conductor

resistances

be

"tuned"

to

specific

constant

values.

The

voltage

across

the

probe

can

also

be

measured

with

three

wires.

The

voltage

drop

in

the

current

circuit

is

measured

and

cable

effects

are

compensated

for

on

the

assumption

that

the

voltage

drop

in

the

feed

conductor

is

identical

to

that

in

the

return

conductor.

ip{

Constant

current

IR

R

=

E-2

X

E|r

Figure

5-3.

Pt100

Measuring

Circuit

If

the

probe

is

connected

to

the

CL521

using

three

conductors,

the

instrument

automatically

detects

the

lack

of

the

fourth

conductor

and

begins

to

operate

in

the

three

wire

mode.

The

fourth

conductor

should,

however,

be

used

whenever

possible.

Figure

5-4.

Connecting

a

3-Wire

Resistance

Probe

to

the

CL521

16

Omega Engineering CL521 User manual

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