H3a Calibration Pressure Measurement

The equipment describedin this manual is manufactured and distributed by

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TBCQUIPMENT LIM1"l"HU Suppliers of technologicallaboratory equipment designedfor teaching.

BONSALL STREET,LONG EATON, NO1TJNGHAM,NG1O UN,

Tel: (0115)9722611 : Fax: (0115)9731520

ENGLAND.

@ TecQuipment Limited

No part of this publication may be reproduced or transmitted in any form or by any means, electronic or

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mechanical, including photocopy, recording or any information storage and retrieval system without the express permission of TecQuipment Limited. Exception to this restriction is given to bona fide customers in educational or training establishments in the normal pursuit of their teaching duties. Whilst all due care has been taken to ensure that the contents of this manual are accurate and up to date, errors or omissions may occur from time to time. If any errors are discovered in this manual please inform TecQuipment Ltd. so the problem may be rectified.

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1.

INTRODUCTI(»I

The

pressure

extent

gauge

fitted

in engineering

The .echania8 tube

is of a type known as the Bourdon gauge. which is used to a very great

practice.

a

thin

wall

or oval cross-section

held at one end where the pressure

sealed.

dial of the instrUDent

of the gauge may be seen through the transparent

having

rigidly

to the tester

When pressure

is admitted,

is bent to a circular

is admitted

in fig

1).

arc enco.pass1ng about 270 degrees.

It

to the tube and is free

the tube tends to straighten,

(illustrated

to 8Ove at the other

A is

end, which is

and the moV88ent at the free end operates a

_chanica I system which 8Oves a pointer round the graduated scale, the 8Ov_nt of the pointer being proportional to the pressure applied. The sensitivity of the gauge depends on the material and d18ensions of the Bourdon tube; gauges with a very wide selection When it

is

pressures

deaired

by

a

satisfactorily

to

dead

with

check

weight

water

of pressure

the

accuracy

tester

instead

of

using

Installation

oil

to

the

be

tapping

the

insert

piston

cylinder.

~.3

rro.

Fill

use,

both

.-ount

piston

and

The piston with

cylinder,

the

Care

unit.

cylinder

A small into

Allow

After

the

the

unit.

Routine

transmit

the

the

usual

pre8sure.

procedure

is

The present

to

load

experiment,

it

with

known

however,

works

Pressure GaugeCaliDrator.

Procedure

piston

used.

to

gauge,

receipt of the apparatus, all components should be checked against the accompanyins CONTENtS any items appear to be missing a careful check should be 88de aaongst all packing 88terials.

Installation Remove

a Bourdon

and Preparation

l8mediately upon PACKINGLIST. If

~

of

available.

oil.

Fig 1.

1~

ranges are com8ercially

&1r

to

delivered

and

left

allowing

in

air

remove

the

and

li8htly air

system

excess

oiled

trapped

will

water

in

not to

and should the

&ffect

escape

be

transparent the

wiped

only

tube

by

experi.ent.

through

the

top

when the tilting

and

Top up with hole

in

the

unit

water side

is

gently

of

and the

settle.

Maintenance

the

of

is

water,

-

cylinder

and piston

should be dried

with a lint

free cloth.

The piston

should be lightly

smeared w1tb 011. Th1a 1s 8O8t 18pOrtant If

the

unit

is

left

wet, and stored

allowed

to stand for 3 to 4 hours before twisting to polish

penetrating

the piaton

chalk and 011 to re8Ove diacolouration.

oil

condition,

To release

Do not attempt

the piston

in this

body.

rod with

~orrosion

should be introduced the pisto~

e8ery cloth,

free

will into

fr08

cause the piston both inlet

to stick

and outlet

parts,

finaly

in the

and the unit

the body.

or any har3h abrasive.

U3e only a mixture

of powdered

-2The

body and

piston

are lapped to obtain

a fine

sliding

fit

and are,

therefore,

not interchangable

with other

units.

2.':

EXPERIMENTAL PROCEDURE

Ensure

the

cylinder

is vertical.

Masses are added in approxi8Btely

On no account should 8Ore than the supplied onto

the

platrorm.

8a8ses be loaded.

The pressure gauge reading

eiwnt increments

up to a ..ximum or 5.2 kg.

Always load the masses gradually,

should be recorded at each incre8ent

do not drop them

or loading.

piston sticking, rotate the piston gently as each mass is added. Reverse the above procedure, the masses are removed. The croaa-sectional area and the mass or the piston should be noted.

To prevent

taking

the

readings

as

maaa) applied

to

RESULTS AND CALCULATIONS

The the

actual piston

hydro8tatic 18 siven

pressure

(p) in the 8ystem due to a 88S8 of " kg (includ1ns

the piston

bYI-

P : H x 9.81 x 1rrJ

IN/."

A

where A is the piston

area in ."

The observed and derived

results

are tabulated

in the for8 of table

1.

Increasing Pressure Mass A~ed to Piston kg

Total Mass on P ,ton

(H ) kg

Actual Presure

(P) kNJ1rr2

Table 1 Results Fr08 table be plotted.

Gauge Reading

kN/ml

for Increasing

1 graphs of the gause pressure against

actual

Gauge Error

Gauge Reldil¥J

Gauge Error

kN/m2

kN/lTil

kN/m2

and ~~reasing

pressure,

DecreasingPressure

Pressure

and gauge error

against

actual

pressure

should

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4.

. DISCUSSION CF RESULTS.

Two different

kinds of error

of hysteresis, when it range, will

friction

i8 decreaa1ns. which

be

i8

found

acceptably

Typically,

acceptably that

88811

for

read1ns are co..erc1ally

1

88Y normally

th1s

yield

the sauge te8ted

88811. error

Secondly, increases

aany engineer1ns

QUE.'3TIONSFOR FURTHER DISCUSSION

1..

What suggestions

2.

No correction

to

and

of

piston,

should.

What alterations

here will a

have an error

Firstly,

there is the possibility

when the pressure

in the ranae of 1 KN/.'

of around 2.5% of the full

gauges with an error

] ~

'1 !

1

[

than

or the entire

incorrectly.

scale readins.

It This is

of only 0.51 of the full-

have you tor improving

scale

the apparatus?

the

preuw-e

correction

to

the

gauge.

for the difference If

be made, and if

the centre ao,

how big

dimensions of the piston

in elevation

of the piston

of the gauge were 200 would

it

higher

of the dead weight than the base of the

be?

of the dead weight tester

would you sU&Sest if

desiredto calibrate a gaugehavinga full scale readingof 3500kN/.a using the -

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is increasing

due to the scale be1ns marked off

8aXiaum

purposes although

type.

gauge readings

there is error

has been made to the results

tester

smaller

obtainable.

5.

3.

be expected in a gauge of this

and backlash which will

weights.

it

were