Deadweight tester

Deadweight tester

A dead weight tester apparatus uses known traceable weights to apply pressure to a fluid for checking the accuracy of readings from a pressure gauge. A dead weight tester (DWT) is a calibration standard method that uses a piston cylinder on which a load is placed to make an equilibrium with an applied pressure underneath the piston. Deadweight testers are so called primary standards which means that the pressure measured by a deadweight tester is defined through other quantities: length, mass and time. Typically deadweight testers are used in calibration laboratories to calibrate pressure transfer standards like electronic pressure measuring devices.

example deadweight tester

Contents

Formula

piston cylinder

The formula on which the design of a DWT is based basically is expressed as follows :

p = F / A [Pa]

where :

p  : reference pressure [Pa]
F  : force applied on piston [N]
A  : effective area PCU [m2]

To be able to do accurate measurements, this formula has to be refined.

Absolute pressure with vacuum reference

p=

m.gl.

æ
è

1-

ra

rm

ö
ø

+P.d.t


A(20,0).(1+(ap+ac).(t-20)).(1+pnom.lp)
-(rN2-ra).gl.h+pvac

gauge pressure

pe=

m.gl.

æ
è

1-

ra

rm

ö
ø

+P.d.t


A(20,0).(1+(ap+ac).(t-20)).(1+pnom.lp)
-(rN2-ra).gl.h

nomenclature

p absolute pressure at reference level [Pa]
pe gauge pressure at reference level [Pa]
m total true mass load [kg]
gl local acceleration due to gravity [N/kg]
ra ambient air density [kg/m3]
rm average density mass load [kg/m3]
P.d.t surface tension effect [N]
rN2 density of pressure medium [kg/m3]
h reference level offset DWT .. DUT [m]
pvac vacuum residual pressure [Pa]
A20,0 PCU effective area at p=0 and 20oC [m2]
ap linear thermal expansion coefficient piston [oC-1]
ac linear thermal expansion coefficient cylinder [oC-1]
t temperature of PCU [oC]
lp elastic deformation coefficient PCU [Pa-1]
pnom nominal line pressure [Pa]
pe gauge pressure applied to PCU [Pa]
p absolute pressure applied to PCU [Pa]

piston cylinder design

In general there are three different kind of DWT's divided by the medium which is measured and the lubricant which is used for its measuring element :

  1. gas operated gas lubricated PCU's
  2. gas operated oil lubricated PCU's
  3. oil operated oil lubricated PCU's 

All three systems have their own specific operational demands. Some points of attention :

gas - gas

Make sure that the PCU is clean. This is a very important issue as the PCU's operation is sensitive to contamination. Also when connecting a DUT, make sure that the DUT does not introduce contamination in the measuring system.

gas - oil

Lubricant of the PCU 'leaks' in the gas-circuit of the DWT. For this reason there is a small reservoir incorporated in the system. Before commencing a calibration it is a good practice to purge this reservoir. If the reservoir is full, oil will be introduced in critical tubing and will cause an uncontrollable oil-head.

oil - oil

When connecting an oil filled DUT on an oil DWT make sure that the DUT oil will not contaminate the DWT oil. If in doubt. Incorporate a small volume between DUT and DWT and manipulate pressure in such a matter that th oil flow is directed to the DUT.

See also

External links


Wikimedia Foundation. 2010.

Игры ⚽ Поможем решить контрольную работу

Look at other dictionaries:

  • Pressure measurement — The construction of a bourdon tube gauge, construction elements are made of brass Many techniques have been developed for the measurement of pressure and vacuum. Instruments used to measure pressure are called pressure gauges or vacuum gauges. A… …   Wikipedia

  • грузовой испытатель — (пресс для испытания манометров) [http://slovarionline.ru/anglo russkiy slovar neftegazovoy promyishlennosti/] Тематики нефтегазовая промышленность EN deadweight tester …   Справочник технического переводчика

  • испытатель пласта, управляемый весом бурильной колонны — — [http://slovarionline.ru/anglo russkiy slovar neftegazovoy promyishlennosti/] Тематики нефтегазовая промышленность EN deadweight tester …   Справочник технического переводчика

  • Space Electronics — LLC is a company based in Connecticut that specializes in mass properties measurement instruments.HistoryDick Boynton founded Space Electronics in 1959 while attending graduate courses at Yale University. The company existed in Dick s basement… …   Wikipedia

  • опробователь пластов, управляемый массой бурильной колонны — — [http://slovarionline.ru/anglo russkiy slovar neftegazovoy promyishlennosti/] Тематики нефтегазовая промышленность EN deadweight formation tester …   Справочник технического переводчика

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”