Direct-heated gas-flow measuring apparatus

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.ltoreq.50
• where "l.sub.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.

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.

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.

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.

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.