Thermal conductivity detector

A method for determining the thermal conductivity of a sample fluid comprising the steps of:

• applying an alternating voltage to a sensor to vary a temperature of said sensor as a sample gas flows across said sensor, a resistance of said sensor being dependent upon a temperature of said sensor, a frequency of said alternating voltage being sufficiently low such that a temperature of said sensor substantially tracks said alternating voltage;
• measuring an electrical quantity that is related to an instantaneous temperature of said sensor;
• and
• determining a magnitude of said electrical quantity that has a frequency three times said frequency of said alternating voltage.

A method for measuring the thermal conductivity of a sample gas comprising the steps of:

• providing a resistive element in a cavity containing a sample fluid, said resistive element having a resistance which is dependent on a temperature of said resistive element;
• supplying a first amount of power to said resistive element required to cause said resistive element to be at a first predetermined temperature and measuring a quantity corresponding to said first amount of power;
• supplying a second amount of power to said resistive element required to cause said resistive element to be at a second predetermined temperature and measuring a quantity corresponding to said second amount of power;
• and
• determining a thermal conductivity of said sample fluid based on a difference in said first amount of power and said second amount of power.

A thermal conductivity detector comprising:

• a resistive element located in a cavity through which a sample fluid flows, said resistive element having a resistance which is dependent upon a temperature of said resistive element;
• control means, operably connected to said resistive element, for controlling a temperature of said resistive element to be a first predetermined temperature for a first period of time and a second predetermined temperature for a second period of time;
• and
• measuring means for measuring a quantity related to power dissipated by said resistive element at said first predetermined temperature and said second predetermined temperature.