Fluid property sensor with heat loss compensation and operating method thereof
OwnerHeinz Plöchingerinventor
Life of this patent
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Abstract
An improved Pirani sensor uses a measuring element disposed within a fluid between a base plate and a cover. The measuring element is held by suspension members that are connected to the base plate. A heating element is thermally conductively connected to the suspension members. Using the sensor the characteristic of the fluid is determined by evaluating the heat transfer from the thermal element through the fluid into the cover when heating power is applied to measuring element. Parasitic conductive heat loss from the measuring element into the suspension members is compensated by applying power to the heating element.
Claims9
A method for measuring a characteristic of a fluid, comprising:
- suspending a measuring element within the fluid, the measuring element being held by suspension members;
- detecting an upper temperature threshold of the measuring element;
- applying measuring power to the measuring element during a heating phase until the measuring element reaches the upper temperature threshold;
- applying compensation power to one or more suspension heating elements which are thermally conductively connected to the suspension members;
- evaluating heat transfer from the measuring element into the fluid;
- and
- deriving the characteristic of the fluid,
- wherein the compensation power is selected to at least partially compensate parasitic conductive heat loss from the measuring element into the suspension members,
- wherein evaluating the heat transfer from the measuring element into the fluid comprises measuring a time tx required to heat the measuring element from a first temperature T1 to a second temperature T2,
- wherein following the application of measuring power during the heating phase a predetermined cooling phase wait period tw is applied during which measuring power is turned off or substantially reduced, and
- wherein at least one of the frequency 1/(tx+tw), the sum of tx+tw, or the ratio tx/tw is used to derive a pressure of the fluid.
A method for measuring a characteristic of a fluid, comprising:
- suspending a measuring element within the fluid, the measuring element being held by suspension members;
- detecting an intermediate temperature threshold of the measuring element;
- detecting an upper temperature threshold of the measuring element;
- applying measuring power to the measuring element during a heating phase until the measuring element reaches the upper temperature threshold;
- applying compensation power to one or more suspension heating elements which are thermally conductively connected to the suspension members;
- evaluating heat transfer from the measuring element into the fluid;
- and
- deriving the characteristic of the fluid,
- wherein the compensation power is selected to at least partially compensate parasitic conductive heat loss from the measuring element into the suspension members,
- wherein following the application of measuring power during the heating phase measuring power is turned off or substantially reduced during a cooling phase until the measuring element reaches the intermediate temperature threshold, and
- wherein a duration of the heating phase or a duration of the cooling phase or a sum thereof is used to evaluate heat transfer from the measuring element into the fluid.
A method for measuring a fluid characteristic, comprising:
- suspending a measuring element within the fluid, the measuring element being held by a suspension member;
- applying measuring power to the measuring element during a heating phase until the measuring element reaches an upper temperature threshold;
- turning off or substantially reducing the measuring power during a cooling phase subsequent to the heating phase, until the measuring element reaches an intermediate temperature threshold;
- applying compensation power to one or more suspension heating elements which are thermally conductively connected to the suspension member;
- and
- evaluating heat transfer from the measuring element into the fluid by determining a duration of the heating phase or a duration of the cooling phase or a sum thereof.
Dependencies are inferred from the claim text.