Pulse modulated thermal conductivity detector
AssigneeHewlett-Packard Company
InventorRichard H. Kolloff
Life of this patent
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Abstract
A thermal conductivity detector comprised of a Wheatstone bridge having a filament in one arm thereof that is contained within a cavity through which the elutant from a column is passed and means for deriving an output signal from one diagonal of the bridge when the voltage applied across the other diagonal is changed from a small value to a large value. In one embodiment, the voltage applied across the one diagonal of the bridge is changed from a fixed low value to a fixed high value and the output signal is the change in the voltage appearing across the other diagonal. In another embodiment, the voltage applied across the one diagonal of the bridge varies from a low value to a value required to keep the bridge in balance, and the difference between these voltages is the output signal.
Claims12
A thermal conductivity detector comprising
- means defining a cavity through which fluids to be analyzed may be passed,
- means for alternately introducing different amounts of thermal energy into said cavity, and
- means coupled to said cavity so as to provide signals indicative of the respective difference in the thermal energy transmitted through the fluid therein for successive amounts of energy introduced into said cavity.
A thermal conductivity detector, comprising
- a bridge circuit having four resistive arms connected in series, one of said arms including a filament having a temperature responsive resistance,
- means defining a cavity having two ports therein so that fluid to be analyzed may be passed through the cavity,
- means mounting said filament in said cavity,
- means for successively applying voltages of different values across one diagonal of said bridge, and
- means for deriving signals from the other diagonal of said bridge indicative of the imbalance occurring in said bridge during the application of each successive voltage.
A thermal conductivity detector comprising
- a first resistor and a filament connected in series between two points, said filament and resistor meeting at a junction,
- second and third resistors connected in series between said two points, said second and third resistors meeting at a junction,
- a source of reference potential connected to one of said points,
- an operational amplifier having two inputs and an output, said output of said operational amplifier being connected to the other of said points, and one input of said operational amplifier being connected to one of said junctions,
- a source of voltage,
- a switch for connecting the other of said inputs to the other of said junctions when in one position and to said source of voltage when in the other position, and
- means coupled to said output of said operational amplifier for deriving the differences between the voltage appearing thereat for successive switch positions.
A thermal conductivity detector having
- means for successively introducing different amounts of thermal energy into a fluid to be analyzed,
- means for deriving a signal indicative of the thermal energy respectively transmitted through the fluid as successive amounts of energy are introduced thereto, and
- means coupled to said latter means for deriving an output signal that is a measurement of a parameter of the fluid.
A thermal conductivity detector comprising
- a first resistor and a filament connected in series between two points, said filament and resistor meeting at a junction,
- second and third resistors connected in series between said two points, said second and third resistors meeting at a junction,
- a source of reference potential connected to one of said points, an output,
- an operational amplifier having two inputs and an output, said output of said operational amplifier being connected to the other of said points, and one input of said operational amplifier being connected to one of said junctions,
- first and second sources of voltage,
- a switch for alternately connecting said first and second sources of voltage between said points, and
- means coupled to the output of said operational amplifier for deriving the differences between the voltage appearing at the output of said amplifier for successive switch positions.
A thermal conductivity detector comprising
- means defining a cavity having ports so that fluid to be analyzed can be passed through said cavity,
- means for successively introducing different amounts of thermal energy to fluid passing through said cavity,
- means for deriving signals indicative of the thermal energy flowing through said fluid for each amount of energy introduced, and
- means for deriving from said signals an output signal indicative of a parameter of fluid passing through said cavity.
A thermal conductivity detector comprising
- a temperature responsive resistance,
- means for successively applying different voltages across said temperature responsive resistance,
- means coupled to said temperature responsive resistance for deriving signals indicative of the value of its resistance during the application of each of the said voltages, and
- means for deriving the difference in the voltages produced in response to the application of each successive pair of applied voltages.
Dependencies are inferred from the claim text.