The document describes the features and characteristics of the Flow Sens FS5L / FS5LA thermal mass flow sensor, which is suitable for various applications in liquids. The sensor consists of two temperature-dependent platinum resistors, one used as a heater and the other for measuring the reference temperature. A bridge circuit is used to measure the differing resistance values of the two elements, resulting in different (self) heating. The (self) heating is dependent on the applied voltage, mass flow, and the medium in which the sensor is located. Higher voltage increases self heating, while a higher flow rate increases cooling. By maintaining constant self heating with a suitable controller, the voltage increases with higher flow rates and becomes a measure of the mass flow. Due to its low thermal mass, this sensor has fast heating and cooling response times. The measurement principle of the sensor can be used for
The FS5L/FS5LA sensor uses two platinum‑resistors on a single chip: a low‑ohm heater and a high‑ohm reference. A bridge circuit converts the temperature‑dependent resistance difference into a voltage that varies with mass flow, allowing flow measurement over a wide range. Its low thermal mass provides rapid heating and cooling, resulting in a response time under 100 ms.
The sensor is supplied in a compact ceramic housing (Al₂O₃) and can be mounted in custom applications, including plastic housings as small as 6 mm. Electrical connection is provided via a 3‑pin NiPt lead with PTFE insulation, and optional JST connectors are available. Typical operating conditions cover -30 °C to +100 °C and flow rates from 0 to 10 m/s.
| Accuracy | < 3% (dependent on electronics and calibration) |
|---|---|
| Warm‑up time | < 1 min (depending on mounting) |
| Temperature range | -30 °C … +100 °C (up to 150 °C) |
| Electrical connection | 3 pins, NiPt leads 0.2 mm, insulated with PTFE tube |
| Typical bridge supply voltage | 4 – 10 V |
| Substrate material | Al₂O₃ ceramic |
It operates from –30 °C to +100 °C (up to 150 °C).
It uses a 3‑pin NiPt lead with 0.2 mm contacts insulated by a PTFE tube.