Direct-heated gas-flow measuring apparatus

Claim 2

A direct-heated type gas-flow measuring apparatus comprising: a flow passage for the gas flow to be measured; a film resistor, disposed in said flow passage parallel with the gas flow, for generating heat within said flow passage; a shield, disposed upstream of said film resistor in the coaxial plane of said film resistor, for reducing the accumulation of deposits on said film resistor, said shield including a heating element for burning off dirt, said shield having substantially the same thickness as that of said film resistor, said shield being sized and positioned so as to satisfy the condition: l.sub.1 /t≦50 where "l 1 " is the distance between said shield and said film resistor, and "t" is the thickness of said shield and said film resistor; means for heating said heating element of said shield; and feedback control means, connected to said film resistor, for providing power to and controlling the heat generated by said film resistor and generating a control signal indicative of the temperature of said film resistor; measuring means for providing, in response to said control signal, an indication of the rate of the gas flow.

Claim 3

An apparatus as set forth in claim 1, further comprising a temperature-dependent resistor disposed in said flow passage, said temperature-dependent resistor being not substantially affected by the heat generated from said film resistor, said feedback control means further comprising means for controlling the heat generated by said film resistor so as to maintain a constant difference in temperature between said film resistor and said temperature -dependent resistor.

Claim 4

An apparatus set forth in claim 1, wherein said heating element is rounded in cross-section.

Claim 5

An apparatus as set forth in claim 1, wherein said heating element is of a streamlined shape in cross-section in that the portion on the upstream side is rounded and the portion on the downstream side is tapered.

Claim 6

An apparatus as set forth in claim 1, wherein said heating element comprises a carrier and a thermistor film formed on the surface of said carrier.

Claim 7

An apparatus as set forth in claim 1, wherein said heating means heats said heating element for a predetermined time period every time the resistance value of said heating element becomes lower than a predetermined value.

Claim 8

An apparatus as set forth in claim 1, further comprising a switch, said heating means heating said heating element for a predetermined time period every time said switch is turned off.

Claim 9

A direct-heated type gas-flow measuring apparatus comprising: a flow passage for the gas flow to be measured; a film resistor, disposed in said flow passage parallel with the gas flow, for generating heat within said flow passage; a first shield, disposed upstream of said film resistor in the coaxial plane of said film resistor, for reducing the accumulation of deposits on said film resistor, said first shield including a heating element for burning off dirt said shield having substantially the same thickness as that of said film resistor, said first shield being sized and positioned so as to satisfy the condition: l.sub.1 /t≦50 where "l 1 " is the distance between said shield and said film resistor, and "t" is the thickness of said shield and said film resistor; means for heating said heating element of said shield; and feedback control means, connected to said film resistor, for providing power to and controlling the heat generated by said film resistor and generating a control signal indicative of the temperature of said film resistor; measuring means for providing, in response to said control signal, an indication of the rate of the gas flow; and a second shield, disposed downstream of said film resistor near thereto and in the coaxial plane of said film resistor, for reducing the accumlation deposites on said film resistor, said second shield comprising a second heating element for burning off dirt.

Claim 10

A direct-heated type gas-flow measuring apparatus comprising: a flow passage for the gas flow to be measured; a film resistor, disposed in said flow passage parallel with the gas flow, for generating heat within said flow passage; a first shield, disposed upstream of said film resistor in the coaxial plane of said film resistor, for reducing the accumulation of deposits on said film resistor, said first shield including a heating element for burning off dirt said shield having substantially the same thickness as that of said film resistor, said first shield being sized and positioned so as to satisfy the condition: l.sub.1 /t≦50 where "l 1 " is the distance between said shield and said film resistor, and "t" is the thickness of said shield and said film resistor; means for heating said heating element of said shield; and feedback control means, connected to said film resistor, for providing power to and controlling the heat generated by said film resistor and generating a control signal indicative of the temperature of said film resistor; measuring means for providing, in response to said control signal, an indication of the rate of the gas flow; and a second shield, disposed downstream of said film resistor near thereto and in the coaxial plane of said film resistor, for reducing the accumlation deposites on said film resistor, said second shield comprising a second heating element for burning off dirt.

Claim 11

An apparatus as set forth in claim 8, wherein said shield has substantially the same thickness as said film resistor.

Claim 12

An apparatus as set forth in claim 9, wherein l.sub.2 /t≦50 wherein l 2 is a distance between said second shield and said film resistor.

Claim 13

An apparatus as set forth in claim 8, wherein said second heating element is rounded in cross-section.

Claim 14

An apparatus as set forth in claim 8, wherein said second heating element is of a streamlined shape in cross-section in that the portion on the upstream side is tapered and the portion on the downstream side is rounded.

Claim 15

An apparatus as set forth in claim 8, wherein said second heating element comprises a carrier and a thermistor film formed on the surface of said carrier.

Claim 16

An apparatus as set forth in claim 8, wherein said heating means heats said second heating element for a predetermined time period every time the resistance value of said second heating element becomes lower than a predetermined value.

Claim 17

An apparatus as set forth in claim 8, further comprising a switch, said heating means heating said second heating element for a predetermined time period every time said switch is turned off.

Claim 18

A direct-heated type gas-flow measuring apparatus comprising: a flow passage for the gas flow to be measured; a film resistor, disposed in said flow passage, for generating heat and detecting the temperature thereof, said film resistor being arranged in parallel to the gas flow; a shield, disposed on the upstream side of said film resistor near thereto along the same coaxial plane of said film resistor, for reducing the accumulation of deposits on said film resistor, said shield having substantially the same thickness as that of said film resistor, said shield comprising a heating element for burning off dirt, said heating element being of a streamlined shape in cross-section in that the portion on the upstream side is rounded and the portion on the downstream side is tapered; means for heating said heating element; feedback control means, connected to said film resistor, for controlling the heat generated by said film resistor so as to generate a control signal relating to the temperature of said film resistor; and measuring means for measuring the rate of the gas flow by receiving said control signal.

Claim 19

A direct-heated type gas-flow measuring apparatus comprising: a flow passage for the gas flow to be measured; a film resistor, disposed in said flow passage, for generating heat and detecting the temperature thereof, said film resistor being arranged in parallel to the gas flow; a shield, disposed on the upstream side of said film resistor near thereto along the same coaxial plane of said film resistor, for reducing the accumulation of deposits on said film resistor, said shield having substantially the same thickness as that of said film resistor, said shield comprising a heating element for burning off dirt, said heating element being of a streamlined shape in cross-section in that the portion on the upstream side is rounded and the portion on the downstream side is tapered; means for heating said heating element; feedback control means, connected to said film resistor, for controlling the heat generated by said film resistor so as to generate a control signal relating to the temperature of said film resistor; and measuring means for measuring the rate of the gas flow by receiving said control signal.

Claim 20

A direct-heated type gas-flow measuring apparatus comprising: a flow passage for the gas flow to be measured; a film resistor, disposed in said flow passage, for generating heat and detecting the temperature thereof, said film resistor being arranged in parallel to the gas flow; a shield, disposed on the upstream side of said film resistor near thereto along the same coaxial plane of said film resistor, for reducing the accumulation of deposits on said film resistor, said shield having substantially the same thickness as that of said film resistor, said shield comprising a heating element for burning off dirt; means for heating said heating element, said heating means heating said heating element for a predetermined time period every time the resistance value of said heating element becomes lower than a predetermined value; feedback control means, connected to said film resistor, for controlling the heat generated by said film resistor so as to generate a control signal relating to the temperature of said film resistor; and measuring means for measuring the rate of the gas flow by receiving said control signal.

Claim 21

A direct-heated type gas-flow measuring apparatus comprising: a flow passage for the gas flow to be measured; a film resistor, disposed in said flow passage, for generating heat and detecting the temperature thereof, said film resistor being arranged in parallel to the gas flow; a shield, disposed on the upstream side of said film resistor near thereto along the same coaxial plane of said film resistor, for reducing the accumulation of deposits on said film resistor, said shield having substantially the same thickness as that of said film resistor, said shield comprising a heating element for burning off dirt; means for heating said heating element, said heating means heating said heating element for a predetermined time period every time the resistance value of said heating element becomes lower than a predetermined value; feedback control means, connected to said film resistor, for controlling the heat generated by said film resistor so as to generate a control signal relating to the temperature of said film resistor; and measuring means for measuring the rate of the gas flow by receiving said control signal.

Claim 22

A direct-heated type gas-flow measuring apparatus comprising: a flow passage for the gas flow to be measured; a film resistor, disposed in said flow passage, for generating heat and detecting the temperature thereof, said film resistor being arranged in parallel to the gas flow; first and second shields, disposed on the upstream and downstream sides, respectively, of said film resistor near thereto along the same coaxial plane of said film resistor, for reducing the accumulation of deposits on said film resistor, said first shield having substantially the same thickness as that of said film resistor, said second shield comprising a heating element for burning off dirt, said heating element being of a streamlined shape in cross-section in that the portion on the upstream side is tapered and the portion on the downstream side is rounded; feedback control means, connected to said film resistor, for controlling the heat generated by said film resistor so as to generate a control signal relating to the temperature of said film resistor; and measuring means for measuring the rate of the gas flow by receiving said control signal.

Claim 23

A direct-heated type gas-flow measuring apparatus comprising: a flow passage for the gas flow to be measured; a film resistor, disposed in said flow passage, for generating heat and detecting the temperature thereof, said film resistor being arranged in parallel to the gas flow; first and second shields, disposed on the upstream and downstream sides, respectively, of said film resistor near thereto along the same coaxial plane of said film resistor, for reducing the accumulation of deposits on said film resistor, said first shield having substantially the same thickness as that of said film resistor, said second shield comprising a heating element for burning off dirt, said heating element being of a streamlined shape in cross-section in that the portion on the upstream side is tapered and the portion on the downstream side is rounded; feedback control means, connected to said film resistor, for controlling the heat generated by said film resistor so as to generate a control signal relating to the temperature of said film resistor; and measuring means for measuring the rate of the gas flow by receiving said control signal.

Claim 24

A direct-heated type gas-flow measuring apparatus comprising: a flow passage for the gas flow to be measured; a film resistor, disposed in said flow passage and arranged in parallel to the gas flow; first and second shields, disposed upstream and downstream, respectively, of said film resistor near thereto along the same coaxial plane of said film resistor, for reducing the accumulation of deposits on said film resistor, said first shield having substantially the same thickness as that of said film resistor, said second shield comprising a heating element for burning off dirt, means for heating said heating element for a predetermined time period every time the resistance value of said another heating element becomes lower than a predetermined value; feedback control means, connected to said film resistor, for providing power to and controlling the heat generated by said film resistor and providing a control signal relating to the temperature of said film resistor; and measuring means for providing, responsive to said control signal, an indication of the rate of the gas flow in said flow passage.

Claim 25

A direct-heated type gas-flow measuring apparatus comprising: a flow passage for the gas flow to be measured; a film resistor, disposed in said flow passage and arranged in parallel to the gas flow; first and second shields, disposed upstream and downstream, respectively, of said film resistor near thereto along the same coaxial plane of said film resistor, for reducing the accumulation of deposits on said film resistor, said first shield having substantially the same thickness as that of said film resistor, said second shield comprising a heating element for burning off dirt, means for heating said heating element for a predetermined time period every time the resistance value of said another heating element becomes lower than a predetermined value; feedback control means, connected to said film resistor, for providing power to and controlling the heat generated by said film resistor and providing a control signal relating to the temperature of said film resistor; and measuring means for providing, responsive to said control signal, an indication of the rate of the gas flow in said flow passage.