Principles Of Operation; Basic Principles Of Dynamic Dilution Calibration - Teledyne T750 User Manual

PRINCIPLES OF OPERATION

This section provides information about the scientific principles based on which this
instrument operates.
B P
9.1.
ASIC RINCIPLES OF
The portable calibrator generates calibration gas mixtures by mixing bottled source gases
of known concentrations with a diluent gas (zero air). Using several Mass Flow Controllers
(MFCs) the T750 calibrator creates exact ratios of diluent and source gas by controlling
the relative rates of flow of the various gases, under conditions where the temperature and
pressure of the gases being mixed is known (and therefore the density of the gases).
The CPU calculates both the required source gas and diluent gas flow rates and controls
the corresponding mass flow controllers by the following equation.
WHERE:
Totalflow is determined as:
WHERE:
For instruments with multiple source gas MFCs, Totalflow isdetermied as:
TOTALFLOW = GAS
This dilution process is dynamic. The T750's CPU not only keeps track of the temperature
and pressure of the various gases, but also receives data on actual flow rates of the various
MFCs in real time so the flow rate control can be constantly adjusted to maintain a stable
output concentration.
083730750B DCN8606
D D
YNAMIC ILUTION
= ×
C C
f i
= final concentration of diluted gas
C
f
= source gas concentration
C
i
= source gas flow rate
GAS
flow
Totalflow = the total gas flow through the calibrator
TOTALFLOW = GAS
= source gas flow rate
GAS
flow
Diluent = zero air flow rate
flow
+ GAS
flow MFC1 flow MFC2
C
ALIBRATION
GAS
flow
Totalflow
+
Diluent
flow flow
+ GAS
flow MFCn
Equation 9-1
+ Diluent
flow rate
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