A summary of Man and Absolute by Rudolph ViskerFull description
gfdgfsdFull description
A basic understanding of strain gauge
Sumber : http://physicsrox.com/2013/10/23/physics-spm-notes/ Nota ringkas Fizik yang sesuai digunakan di saat2 akhir persediaan SPM 2013. Berupaya menjadi sumber rujukan semasa calon m…Full description
Descripción completa
This report is about th
strain gauge lectureFull description
the best
igcse physics pressure
mpx4100
Difference between gauge and absolute pressure Definition: The absolute pressure pabs is the pressure compared with the zero pressure of empty space (i.e. a vacuum).
The gauge (relative) pressure p rel is the pressure compared with atmospheric pressure p amb (surrounding air pressure).
Problem: The atmospheric pressure (in hPa) changes continually, according to the altitude or weather. According to the application, the pressure will need to be measured either as gauge (relative) pressure or as absolute pressure.
Example for absolute pressure: Measuring air pressure
The atmospheric air pressure is an absolute measurement. This is used, for example, in weather forecasting or altitude measurement.
Example for gauge (relative) pressure: Filling level measurement
.
The gauge pressure transmitter measures the hydrostatic pressure (prel) of the liuid and converts it into an electrical signal. !f the density of the liuid is "nown, then this signal provides a direct indication of the filling level h.
Applications include# $ells, la"es and ponds, swimming baths, reservoirs and tan"s, heating systems.
Example: Using a vacuum pump to evacuate a vessel Aim: to switc off te pump at a residual pressure of ! mbar abs
The aim is to switch off the pump at a residual pressure of % mbar abs. The diagram shows how this can be achieved through absolute or relative (gauge) pressure. The switching point will only remain constant if absolute pressure measurement is used.
Fi ne weat her = a ir p ress ur e a bout 960 m ba r
State of the system
Ba d w eath er = a ir p ressur e a bo ut 940 m ba r
Absolute
elati!e
Absolute
elati!e
measurement
measurement
measurement
measurement
(correct)
(incorrect)
(correct)
(incorrect)
"essel contains air (atmospheric)
960 mbarabs
0 mbarrel
940 mbarabs
0 mbarrel
$9## mbar rel
# mbarabs
$9%# mbarrel
"essel is empty ( r es i d u a l p r es s u r e)
# m ba rabs
Absolute pressure Absolute pressure is referred to the vacuum of free space (zero pressure). !n practice absolute piezoresistive pressure sensors measure the pressure relative to a high vacuum reference sealed behind its sensing diaphragm. The vacuum has to be negligible compared to the pressure to be measured. &ensortechnics' absolute pressure sensors offer ranges from bar or even ** mbar as well as barometric pressure ranges.
&a'e pressure +age pressure is measured relative to the ambient atmospheric pressure. The average atmospheric pressure at sea level is *.-% mbar. hanges of the atmospheric pressure due to weather conditions or altitude directly influence the output of a gage pressure sensor. A gage pressure higher than ambient pressure is referred to as positive pressure. !f the measured pressure is below atmospheric pressure it is called negative or vacuum gage pressure. !n general a vacuum is a volume of space that is essentially empty of matter. According to its uality vacuum is divided into different ranges such as e.g. low, high and ultra high vacuum. +age pressure sensors only offer one pressure port. The ambient air pressure is directed through a vent hole or a vent tube to the bac" side of the sensing element and thus compensated.
