Thermal mass flow meter including heating element and temperature sensors formed on separate chips and secured to the outer periphery of the pipe
A heater chip ( 4 ) as a heat generation element is secured to the surface on the periphery of piping ( 2 ). Further, a temperature sensor chip couple ( 6 ) is placed on the surface on the periphery of the piping ( 2 ), along the direction of flow of fluid flowing in the piping ( 2 ). One ( 6 a ) of the sensor chips in the couple is placed on the upstream side of the heater chip ( 4 ) and the other ( 6 b ) is placed on the downstream side of the heater chip ( 4 ). The heater chip ( 4 ) and the temperature sensor chips ( 6 a, 6 b ) are formed in a chip type. The temperature sensor chips ( 6 a, 6 b ) as the pair are placed at positions spaced by the same distance from the heater chip ( 4 ).
1. A thermal mass flow meter comprising:
a heat generating element of a chip type for heating a fluid inside piping, the heat generating element being secured onto a surface of a periphery of the piping through which the fluid is flowing;
paired temperature sensors of a chip type formed as members separated from the heat generating element, the paired temperature sensors being secured to positions on the upstream side and the downstream side of the heat generating element on the surface of the piping, with an equal distance apart therefrom, along the flowing direction of the fluid inside the piping; and
an operation unit for finding the flow rate of the fluid flowing through the piping from the temperature difference of the paired temperature sensors;
wherein the heat generating element of a chip type consists of a chip diode or a chip resistor.
2. The thermal mass flow meter according to claim 1 , wherein
the paired temperature sensors include two pairs or more being placed at positions having different distances from the heat generating element, and
the operation unit finds the flow rate by using temperature measuring signals from any of the pairs of the temperature sensors in response to the scale of the flow rate.
3. The thermal mass flow meter according to claim 2 , wherein
the operation unit finds the flow rate by using the pair of the temperature sensors in which the temperature sensor on the downstream side is located on the downstream side from the apex position of the temperature distribution of the fluid flowing through the piping and is located closest to the apex position, among the paired temperature sensors.
4. The thermal mass flow meter according to claim 1 , wherein
the heat generating element and temperature sensors are secured to the piping through a bonding process with a thermal conductive adhesive.
5. The thermal mass flow meter according to claim 1 , wherein
the piping is embedded in a groove on a substrate so that a part of the surface of the periphery of the piping is exposed, and
the heat generating element and temperature sensors are secured to the exposed surface.
6. The thermal mass flow meter according to claim 5 , wherein
the substrate is a printed circuit board on which conductor traces are formed, and
the heat generating element and the temperature sensors are electrically connected to the conductor traces.
7. The thermal mass flow meter according to claim 1 , wherein
the heat generating element and temperature sensors are supported on a substrate and secured thereto, and
the piping is anchored on the heat generating element and temperature sensors.
8. The thermal mass flow meter according to claim 7 , wherein
the substrate is a printed circuit board on which conductor traces are formed, and
the heat generating element and the temperature sensors are electrically connected to the conductor traces.
9. The thermal mass flow meter according to claim 1 , wherein
the piping is piping through which a mobile phase is allowed to flow in high-pressure liquid chromatograph.