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Teledyne MODEL T703 Manual Do Utilizador

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Teledyne API T703 Calibrator Operation Manual 
Theory of Operation 
 
151 
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 
PHOTOMETER
 PRESSURE SENSOR
O
3
GEN / PHOTOMETER 
PRESSURE / FLOW SENSOR PCA
O
3
GAS INPUT 
PRESSURE SENSOR
O
3
FLO
W 
SE
NSO
R
O
3
Genera
tor A
ssembly
O
3
GEN
E
RA
TO
R
Fl
o
w
 Co
nt
ro
l 
(100
 cm
3
/min
)
REF/MEAS
Valve
On Back Panel
Chassis
GAS OUTPUT MANIFOLD
PHOTOMETER 
OUTLET
TO ANALYZER
VENT
TO ANALYZER
DRY AIR 
IN
ZERO AIR 
IN
PHOTOMETER 
INLET
EXHAUST
PHOTOMETER 
ZERO OUT
PHOTOMETER 
ZERO IN
PHOTOMETER BENCH
PUMP
Flow Control 
(800 cm
3
/min)
INTERNAL
VENT
Flo
w
 C
ont
ro
l 
(5.0 l
p
m)
Pressure 
Regulator
Filter
PUMP
Flo
w
 Co
nt
rol 
(1.0 to
 2.0  L
P
M)
blk
CHA
R
COA
L
 
SCRUB
B
ER
blk
blu
blu
orn
orn
orn
orn
red
red
pur
pur
grn
grn
yel
yel
FLOW 
CONTROL 
ASSEMBLIES
 
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 
07223B DCN6378