Preamble 
UM-22100H-U User manual ATEQ D520 Page 7/122 
3. THE DIFFERENT MEASUREMENT PRINCIPLES 
There exists two measurement principles, they are: direct measurement and the indirect 
measurement (also known as with recovery or under bell). 
The instrument can work in depressurisation (optional) both in direct and indirect 
measurement.  
3.1. DIRECT MEASUREMENT 
 
Test part 
Air pressure 
supply
 
Absolute 
pressure 
sensor
 
Calibrated flow tube
Regulator
 
Atmosphere
Differential 
pressure sensor
 
Flow
Dp
 
As shown in the diagram above the test pressure is applied directly to the test part input 
after having flowed through the calibrated flow tube. 
Once the test part is filled, the ATEQ D520 measures the drop in pressure at the 
extremities of the calibrated flow tube with a differential sensor.