Microcalorimeter sensor for the measurement of heat content of natural gas

A microcalorimeter for measuring BTU content of a gas sample, said microcalorimeter comprising:

• flow injection means for measuring out a precise predetermined amount of a sample gas and for diluting the sample gas with a carrier gas;
• at least two catalytic sensors positioned on an outlet side of said flow injection means for receiving the sample gas and the carrier gas and for producing output signals related to the BTU content of the sample gas, said sensors differing in at least one chemical or physical property for producing different signals in response to the sample gas;
• and
• signal processing means connected to outputs of said sensors for receiving said signals and for calculating the BTU content of said sample gas based on said signals.

A method of measuring BTU content of a gas comprising:

• providing a microcalorimeter comprising a catalytic sensor positioned in a combustion chamber, said sensor comprising a filament coated with a catalyst;
• applying a current to the filament to heat the sensor to an operating temperature;
• calibrating said sensor by the steps of
• passing a first calibration gas having a known BTU content over said sensor to obtain a first output signal,
• passing a second calibration gas having a known BTU content over said sensor to obtain a second output signal,
• comparing said first and second output signals,
• adjusting said operating temperature of said sensor and repeating said steps of passing and comparing until said first and second signals per known BTU content of said first and second calibration gases, respectively, are substantially equal;
• exposing said sensor to a sample gas to obtain a sensor signal;
• monitoring temperature changes or resistance changes in said sensor during the step of exposing;
• adjusting the current to said filament based on said temperature changes to maintain a constant sensor temperature or based on said voltage changes to maintain a constant voltage during said step of exposing;
• measuring voltage change across said sensor or change in sensor output signal required to maintain the constant sensor temperature or the constant voltage, respectively;
• and
• calculating said BTU content of said sample gas from said voltage change or said change in sensor output signal.

A method of measuring BTU content of a gas comprising:

• providing a microcalorimeter comprising a catalytic sensor positioned in a combustion chamber, said sensor comprising a filament coated with a catalyst;
• applying a current to the filament to heat the sensor to an operating temperature;
• calibrating said sensor by passing a calibration gas over said sensor to obtain a standard measurement;
• contacting said sensor with a sample gas to react said gas and cause a sensor signal;
• monitoring temperature or resistance changes in said sensor during the reaction of said gas;
• adjusting the current to said filament based on said temperature or resistance changes in said sensor to maintain a constant sensor temperature during said reaction;
• measuring voltage change across said sensor during the reaction of said gas;
• monitoring ambient temperature and pressure changes in said chamber during said step of adjusting;
• calculating a correction factor based on said ambient temperature and pressure changes in said chamber;
• calculating a BTU content of said sample gas from said voltage change and said standard measurement;
• and
• multiplying said BTU content by said correction factor to calculate actual BTU content of said sample gas.