6. Functional Description
The FS2012 digital flow sensor accurately measures the mass flow rate of a liquid or gaseous medium across the sensor using the calorimetric
principle.
The MEMS flow sensor comprises a resistive heater and two clusters of thermocouples (thermopiles), each positioned symmetrically upstream
and downstream of the heater. The thermopile output changes according to the rate of flow, and it is proportional to the amount of heat sensed
from the heater.
7. I
2
C
Sensor Interface
The FS2012 operates as a slave device via the digital I
2
C compatible communication protocol bus with support for 100kHz and 400kHz bit rates.
To accommodate multiple devices, the protocol uses two bi-directional open-drain lines: a Serial Data Line (SDA) and a Serial Clock Line (SCL).
Pull-up resistors to VDD are required. Several slave devices can share the bus, and multiple master devices on the same bus are supported. If
two or more masters attempt to initiate a data transfer simultaneously, an arbitration scheme is employed with a single master always winning
the arbitration. Note that it is not necessary to specify one device as the master in a system; any device that transmits a START bit and a slave
address becomes the master for the duration of that transfer.
7.1 Sensor Slave Address
The FS2012 default I
2
C address is 07
HEX.
The device will respond only to this address.
7.2 Data Read
The FS2012 is programmed to continuously output data to the I
2
C bus.
Number of bytes to read out: 2
First returned byte: MSB
Second returned byte: LSB
8. Calculating Flow Sensor Output
The entire output of the FS2012 is 2 bytes. The flow rate for gas and liquid parts is calculated as follows:
Output Data
Number of bytes to read out: 2
First returned byte: MSB
Second returned byte: LSB
Gas Part Configurations (-NG ending for part code number)
Conversion to SLPM
Flow in SLPM = [(MSB << 8) + LSB] / 1000
Liquid Part Configurations (-LQ ending for part code number)
Conversion to SCCM
Flow in SCCM = [(MSB << 8) + LSB] / 10
