Filter
Top Products
TELEDYNE API
M703E Calibrator Operator’s Manual Theory of Operation
9. THEORY OF OPERATION
9.1. PNEUMATIC OPERATION
9.1.1. GAS FLOW CONTROL
Gas flow rates are set by various flow control assemblies located in the gas stream(s).
9.1.1.1. Flow Control Assemblies
O
3
FLOW
SENSOR
O
3
Generator Assembly
O
3
GENERATOR
Flow Control
(100 cm
3
/min)
Flow Control
(5.0 lpm)
Flow Control
(1.0 to 2.0 LPM)
CHARCOAL
SCRUBBER
Figure 9-1: Location of Gas Flow Control Assemblies
9.1.1.2. Photometer Critical Flow Orifice
Critical flow orifices are a remarkably simple way to regulate stable gas flow rates. They operate without moving
parts by taking advantage of the laws of fluid dynamics. By restricting the flow of gas though the orifice, a
pressure differential is created. This pressure differential combined with the action of the calibrator’s pump
draws the gas through the orifice.
As the pressure on the downstream side of the orifice (the pump side) continues to drop, the speed that the gas
flows though the orifice continues to rise. Once the ratio of upstream pressure to downstream pressure is
greater than 2:1, the velocity of the gas through the orifice reaches the speed of sound. As long as that ratio
05744 Rev B 135