The Measurement Principle - wtw OxiTop Control OC 110 Operating Manual

Overview
8
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1 Measuring head OxiTop
1.2

The measurement principle

The respirometric measurement is a pressure measurement. If oxygen is
consumed in a closed vessel at a constant temperature, a negative pressure
develops. If a gas is released, an overpressure develops. The OxiTop
measuring head measures and stores this pressure for the whole duration of a
measurement once started.
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The OxiTop OC 110 controller collects the pressure values from the
measuring heads and processes them.
The formula shown below is the basis for all calculations for the BOD using the
values from the OxiTop
BOD
M(O ) Molecular weight (32000 mg/mol)
2
R Gas constant (83.144 lmbar/molK)
T Reference temperature (273.15 K)
0
T Measuring temperature
m
V Bottle volume (nominal volume in ml)
t
V Sample volume in ml
l
a Bunsen absorption coefficient (0.03103)
p(O
) Difference of the D. O. partial pressure (mbar)
2
The interpretation of the pressure differences in the temporal course depends
on the measured material and its preparation and on the sample manipulation
(e. g. intermediate aerations) during the measuring period.
1
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-C or OxiTop
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measuring head.
 


M O V V
  

2 t l


R T V
l
m
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OxiTop Control OC 110
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-C/B

T  
 
  
m
p O
2
T 
0
ba31116e05
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07/2014