LMM-H03
Mass Air FLow Sensor
Product Description
LMM-H03 is a thermodynamic sensing element for the bidirectional
measurement of mass air flow in a well defined channel. It is dedicated for
applications with high reliability requirements such as medical or industrial
gas flow applications. Mounted directly within the flowing media the LMM-
H03 is sensitive against the heat transfer on a micrometer scale. This heat
transfer is detected by a micro-machined silicon device which is mounted on
ceramic substrate defining the geometry of the sensing element.
Hot Film Anemometer Component
Highly reliable and long term stable
Fast reaction time
Manufactured
Bi-directional airflow measurement
The functional principle of the LMM-H03 is a hot film anemometer, which is
the thin film version of the hot wire anemometer. A thin film heating element
(heater) is heated to a defined temperature difference with respect to the air.
At zero flow there is heat dissipation due to the thermal conductivity of the air.
With applied flow the heat dissipation increases steadily with the flow rate.
The sensing element can be operated at Constant Power and Constant
Voltage mode. However, it is recommended to operate LMM-H03 in the
described Constant Temperature Difference (CTD) mode. In the CTD mode
the electronics detects any change of the thermal equilibrium very quickly
and compensates it by adjusting the power settings through the heaters. This
allows a very reliable mass flow measurement with a very short time constant
which is in the order of milliseconds.,
Can be adapted to various flow
Can be used for almost all kind of
gases and volatile substances
channel geometries
according ISO TS16949
Features
Highly reliable and long term stable
Fast reaction time
Can be adapted to various flow channel geometries
Can be used for almost all kind of gases and volatile substances
Applications
Engine Control
Industrial gas flow measurement
Leak detection in pressurized air systems
Spirometer
SENSOR SOLUTIONS
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09/2016
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LMM-H03
Mass Air Flow sensor
Absolute Maximum Ratings
Parameter
Storage Temperature
Storage Temperature
Maximum Current
Symbol
T
Store
T
Store
I
max
Condition
after bonding, with protected bond bads
before bonding, unprotected bond bads
at now flow, +25 °C ambient
Min
-40
+10
–
Typ
+25
+25
–
Max
+125
+40
20
Unit
°C
°C
mA
Operation Conditions
Parameter
Operation Temperature
Heater Overtemperature
Symbol
T
Store
Condition
after bonding, with protected bond bads
Min
-40
Typ
+25
100
Max
+125
120
Unit
°C
K
T
Heater
T
Heater
= T
Heater
- T
air
Sensing Properties
Parameter
Resistance
Ambient Temperature Sensor 1
Resistance Heater 1
Resistance Heater 2
Resistance
Ambient Temperature Sensor 2
Temperature Coefficient
R
ATS
and R
Heater
TCR Match
Symbol
R
ATS1
R
Heater1
R
Heater2
R
ATS2
Condition
Pad 1+2, T
Amb
= +25 °C
Pad 3+4, T
Amb
= +25 °C
Pad 5+6, T
Amb
= +25 °C
Pad 7+8, T
Amb
= +25 °C
measurement at T
1
= 0 °C and
T
2
= +100 °C
Min
1300
40.0
40.0
1300
5500
–
Typ
1700
45.0
45.0
1700
6000
–
Max
2100
50.0
50.0
2100
6500
100
Unit
ppm/K
ppm/K
measurement at T
1
= 0 °C and
T
2
= +100 °C
SENSOR SOLUTIONS
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09/2016
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LMM-H03
Mass Air Flow sensor
Mechanical Dimensions
Mechanical dimensions and connections of LMM-H03
The sensor membrane has a thickness of about ~2 µm. Therefore it should not be exposed to any mechanical stress. One has to take
care of a filter unit around the measurement device. High speed particles coming direct to the surface of the membrane can result in
damages or shortage of the life time. The ventilation holes shall be kept open to release air pressure built up due to heating.
Parameter
Length
Width
Height Ceramics
Height Ceramics + Metall
Heigth max. Overall
Bond Pad Width
Bond Pad Length
Symbol
L
W
H
ceramics
H
Flow
H
Total
W
Pad
L
Pad
Condition
+25 °C
+25 °C
+25 °C
+25 °C
+25 °C
+25 °C
+25 °C
Min
22.8
9.95
0.48
0.9
–
–
–
Typ
23.0
10.15
0.63
1.1
–
0.5
1.5
Max
23.2
10.35
0.78
1.2
1.8
–
–
Unit
mm
mm
mm
mm
mm
mm
mm
Specification further
Parameter
Package Type
Pad Material
Specification
Hybride Ceramics
AgPt
bondable with 150 µm Al-wire, also solderable
SENSOR SOLUTIONS
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LMM-H03
Mass Air Flow sensor
Application Example
One application of the LMM-H03 is to measure the amount of air coming into an engine. The actual mass air flow sensor module consists
of a flow channel and a measurement channel, the so called Venturi channel. The measurement channel with the LMM-H03 should be
placed in the center of the flow channel because at this place the flow is almost laminar and the flow velocity reaches its maximum. The
cross sections of both channels can be adjusted to the amount of air which is supposed to be measured. For reproducible measurement
results it is strictly required to avoid any turbulence at the surface of the sensing element.
Flow channel of application example of a mass air flow sensor
Above is shown an example of a measurement electronics using a Wheatstone-bridge.
The resistors RAx and RBx need to be trimmed to operate the heater at a defined over-temperature
NOTE: This drawing shows only the basic functionality. This is not a ready to use circuit diagram!
SENSOR SOLUTIONS
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09/2016
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LMM-H03
Mass Air Flow sensor
As an example the graphs below show the heater power as a function of flow velocity. The configuration used the following parameters:
Flow Channel Ø:
55-70 mm
Measurement Channel:
o
o
o
Height:
Width:
Length:
1-2 mm
10-15 mm
>20×Height (bidirectional)
200
150
Heater Power [mW]
100
50
0
0
10
20
30
Flow Velocity [m/s]
40
50
60
Example of a Power-Flow-Response of the LMM-H03
With a given electronics and measurement channel the measurement range can be easily adjusted by modifying the size of the flow
channel. For higher or lower flow ranges the flow channel needs to be made larger or smaller, respectively.
SENSOR SOLUTIONS
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