Apparatus for mass flow measurement of a gas

An apparatus for measuring the mass flow of a gas, said apparatus comprising:

• A. means for defining a fixed volume of space for containing a gas whose mass is to be measured;
• B. means for connecting said apparatus to a source of said gas so that gas can be introduced into said fixed volume of space;
• and
• C. a transducer assembly in fluid and thermal communication with the fixed volume of space, said assembly including (a) means for generating a first signal as a function of the pressure of said gas within said fixed volume of space, and (b) means for generating an output signal, in response to the first signal and as a function of the temperature of said gas within said fixed volume of space, representative of the mass of said gas in said fixed volume, wherein said means for generating an output signal comprises a voltage dividing network including (a) an input terminal for receiving said first signal, (b) an output terminal for providing said output signal, (c) at least one temperature-sensitive resistance element having a resistance value dependent on the temperature of the gas in said fixed volume, (d) at least one temperature-insensitive resistance element, coupled in series with said temperature-sensitive resistance element, having a resistance value substantially independent of the temperature of the gas in said fixed volume,
• wherein one of said resistance elements is connected between said input and output terminals so that said output terminal is disposed between said temperature-sensitive resistance element and said temperature-insensitive resistance element, and said means for generating said output signal includes means for measuring the signal level at said output terminal.

Apparatus for measuring the flow of a gas, said apparatus comprising:

• A. a source of a gas;
• B. a chamber in fluid connection with said source and having a gas inlet port, a gas outlet port and valve means for selectively opening and closing said ports to a flow of said gas, said chamber having a known constant volume;
• C. flow controlling means for conducting a controlled flow of said gas from said source into said chamber;
• and
• D. a transducer assembly comprising, in combination,
• i. pressure transducing means for measuring the pressure of said gas in said chamber and for providing a first signal representative of and proportional to said pressure, and
• ii. means, associated with said pressure transducing means, for modifying said first signal to obtain an output signal representative of the mass of said gas in said chamber,
• wherein said signal modifying means comprises a voltage dividing network having an input terminal, at least one temperature-sensitive resistance element and at least one temperature-insensitive resistance element electrically connected in series between said input terminal and ground, and an output terminal between said temperature-sensitive resistance element and said temperature-insensitive resistance element.

A method of measuring the mass flow of a gas, said method comprising:

• A. introducing the gas whose mass is to be measured into a fixed volume of space for containing the gas;
• and
• B. generating a first signal as a function of the pressure of said gas within said fixed volume of space, and generating an output signal, in response to the first signal and as a function of the temperature of said gas within said fixed volume of space, representative of the mass of said gas in said fixed volume,
• wherein the step of generating said output signal includes the steps of:
• generating said first signal as a voltage across a voltage divider including at least one temperature-sensitive resistance element having a resistance value dependent on the temperature of the gas in said fixed volume, and at least one temperature-insensitive resistance element, coupled in series with said temperature sensitive resistance element, having a resistance value substantially independent of the temperature of the gas in said fixed volume, said divider being connected to ground, and
• measuring the output signal at a point between said resistance elements and ground.

A method of calibrating a mass flow controller for use in controlling mass flow of a gas, said method comprising:

• A. connecting said mass flow controller to a source of gas;
• B. transmitting the gas whose mass is to be measured through said controller and into a fixed volume of space for containing the gas;
• C. generating a first signal as a function of the pressure of said gas within said fixed volume of space, and generating an output signal, in response to the first signal and as a function of the temperature of said gas within said fixed volume of space, representative of the mass of said gas in said fixed volume;
• and
• D. comparing the value of mass represented by said output signal with the corresponding measurement of said mass flow controller,
• wherein the step of generating said output signal includes the steps of:
• generating said first signal as a voltage across a voltage divider including at least one temperature-sensitive resistance element having a resistance value dependent on the temperature of the gas in said fixed volume, and at least one temperature-insensitive resistance element, coupled in series with said temperature sensitive resistance element, having a resistance value substantially independent of the temperature of the gas in said fixed volume, said divider being connected to ground, and
• measuring the output signal at a point between said resistance elements and ground.