Kobold MAS Series, Instruction Manual

Page: 4 / 54

MAS Instruction Manual
Page 3
1.2
Principle of
Operation
Figure 1-3
Two Flow Paths
Figure 1-4
Measuring Sensor Flow
*U.S. Patent No. 4,487,062.
The MAS Flowmeter is a transducer requiring a 12-15 VDC (24
VDC optional) external power source. A 0-5 VDC or optional 4-20
mA output singal linearly proportional to gas mass flow rate is
provided for recording, data-logging, or control. A 9-Pin “D” sub-
connector is provided for power input and signal output. The MAS
is available in several basic configurations with either
1 /
4
inch NPT
(female) or 1 /
4
to 1 /
2
inch O.D. tube compression inlet/outlet fittings,
with or without the digital display, or the optional power supply.
Gas enters the MAS flow body and divides into two flow paths.
Most of the flow goes through the laminar flow bypass. This creates
a pressure drop that forces a small fraction of the flow through the
sensor tube.
TWO COILS
SENSOR
TUBE
LAMINAR FLOW BYPASS
m
2
P
1
P
2
•
m
•
m
1
•
The patented* straight sensor tube is mounted parallel to the
bypass flow path. Since both paths are perfectly laminar, the ratio
of the total flow (
˙
m
) to the sensed flow (
˙
m
1
) is constant. Two
resistance temperature detector (RTD) coils around the sensor
tube direct a constant amount of heat into the gas stream.
RTD COILS
R
1
, T
1
R
2
, T
2
m
·
1
H
0
CONSTANT HEAT, H
FIRST LAW OF THERMODYNAMICS
(HEAT IN = HEAT OUT)
H = m
·
1
C
p
(T
2
– T
1
) + H
0
m
· = H–H
0
C
p
∆
T