MASS-STREAM
TM
Instruction Manual D-6200
9.17.112A – Date of issue: 2017-03
Page 11 off 12
2 CTA MEASUREMENT PRINCIPLE
The direct through-flow measurement with CTA (Constant Temperature Anemometry) is
also named inline measurement. The working principle is based on King’s law of the ratio
between the heater energy and the heat degradation by means of gas flow or liquid flows
published in 1914.
Two elements, a heater and a temperature probe, are positioned in the gas flow. CTA is
aiming to keep the difference in temperature
∆
T between both sensor pins at a constant
level. The flow rate and the heater energy required to maintain this constant
∆
T are
proportional and thus indicate the mass flow of the gas. The relation between the heater
energy and the mass flow is described by the following formula:
P = P
0
+ C ·
Φ
m
n
P … Heater power
P
0
… Heater power offset at zero flow
C … Constant (device-dependent)
Φ
m
… Mass flow
n … dimensionless figure (type 0,5)
