Flow sensor

• US 5,406,841 A
• Filed: 03/17/1993
• Issued: 04/18/1995
• Est. Priority Date: 03/17/1992
• Status: Expired due to Term

• Current Assignee: Ricoh Seiki Co. Ltd. (Ricoh Company Limited)
• Original Assignee: Ricoh Seiki Co. Ltd. (Ricoh Company Limited)
• Inventors: Kimura, Mitsuteru
• Primary Examiner(s): Goldstein, Herbert
• Application Number:
  US08/033,783
• Time in Patent Office: 762 Days
• Field of Search: 73/204.16, 73/204.18, 73/204.25, 73/204.26
• US Class Current: 73/204.26
• CPC Class Codes: G01F 1/6845 Micromachined devices

Abstract

A flow sensor is disclosed, which has a thin film heater which is formed atop a cavity formed in the substrate, and the thin film heater is formed on its upstream and downstream sides with slits for separating it and temperature sensors from the substrate. The slits have such a small width that a laminar flow of gas can be maintained. In the case where the film heater has a positive resistance temperature coefficient, the thin film heater is disposed such that current flows in a direction of the gas stream, in case when the film heater has a negative temperature coefficient, the thin film heater is disposed such that current flows in a direction perpendicular to the gas stream.

Claims

1. A flow sensor comprising temperature sensor means for detecting temperatures of upstream and downstream sides of a thin film heater exposed to a gas stream to detect the velocity of the gas from the temperature difference between the upstream and downstream temperatures of said thin film heater measured by said temperature sensor means, said thin film heater being formed atop a cavity formed in a substrate, said thin film heater having slits formed on the upstream and downstream sides to separate said thin film heater and said substrate from each other, said slits having a small width in comparison to the width of the thin film heater such as to be able to maintain a laminar state of the gas stream and said temperature sensor means being located between the upstream and downstream sides.

2. The flow sensor according to claim 1, wherein said slits thermally and electrically separate said thin film heater and said substrate from each other.

3. The flow sensor according to claim 1, wherein said slits have a width less than one tenth of the film heater width between slits.

4. The flow sensor according to claim 1, wherein said temperature sensor means is a p-n junction diode.

5. The flow sensor according to claim 1, wherein said temperature sensor means is a semiconductor thermistor.

6. A flow sensor having a thin film heater and an upstream temperature sensor and downstream temperature sensor disposed on said heater, for detecting the flow velocity of a gas stream from a temperature difference between an upstream side and a downstream side temperature of the thin film heater exposed to the gas stream by measuring said upstream side temperature with the upstream temperature sensor and said downstream side temperature with the downstream temperature sensor, wherein the improvement comprises said thin film heater having a positive resistance temperature coefficient and electrodes for providing electrical current through said heater, and said thin film heater being disposed such that said electrical current flows therethrough in a direction parallel to the gas stream.

8. The flow sensor according to one of claims 6 or 7, wherein said improvement further comprises a further temperature sensor disposed between the upstream and downstream temperature sensors for measuring the temperature of a central portion of said thin film heater, the electrical current flowing through said thin film heater being such that the temperature of said central portion is substantially constant.

7. A flow sensor having a thin film heater and upstream temperature sensor and downstream temperature sensor disposed on said heater, for detecting the flow velocity of a gas stream from a temperature difference between an upstream side and a downstream side temperature of the thin film heater exposed to the gas stream by measuring said upstream side temperature with the upstream temperature sensor and said downstream side temperature with the downstream temperature sensor, wherein the improvement comprises said thin film heater having a negative resistance temperature coefficient and electrodes for providing electrical current through said heater, and said thin film heater being disposed such that current flows therethrough in a direction parallel to the gas stream.