Flow Sensor
Please be sure to read before handling the product. Please refer to "safety instructions", "common safety instructions for products listed in this manual", "common safety instructions for flow controller" from page 24 through 35.
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21
Technical data
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FUS20 series measuring principle
The FUS20 series incorporates a platinum sensor chip (3 mm x 3.5 mm) machined with silicon micromachining. The sensor is thermally
insulated from the silicon substrate. The heating capacity is extremely low, enabling high sensitivity with a high speed response.
At the sensor, two temperature sensors are arranged with a heater in between. Platinum, which has a resistance that changes based on
temperature, is used for the temperature sensor. When the heater is turned on and heated, the temperature distribution is symmetrical about
the center of the heater if there is no flow. When flow is received, the symmetrical property of temperature distribution is lost, and temperature
upstream of the heater drops, and that downstream rises. This difference of temperature becomes the difference of the resistance level of
the temperature sensor and changes by flow rate. If flow is reversed, the temperature difference (resistance value difference) is reversed. A
bidirectional flow is thus detected. This is suitable for detecting relatively small flows.
〈
No flow
〉
Temperature distribution: symmetrical
R1
R1
R2
R2
Temperature
Resistance
Rh
Heater
R2
R1
Temp. sensor
②
FLOW
Temp. sensor
①
〈
With flow
〉
Rh
R2
R1
V out
V out
5V
Voltage
2.5V
Collapse of symmetrical temp. distributon
R1
R2
Temperature
Resistance
R1
R2
V out
V out
5V
Voltage
2.5V