Automatic offset control for constant temperature anemometer

A device for continually adjusting a bridge circuit toward a balanced state in a high frequency response mode, including:

• a bridge circuit having several bridge arms and junction terminals including a drive terminal at a drive voltage, a base terminal at a constant base voltage, and first and second intermediate junction terminals at respective first and second voltage levels less than the drive voltage and greater than the base voltage;
• a sensing element in a first one of the bridge arms and having a sensing element resistance that varies with a parameter being measured by the sensing element, wherein the first and second voltage levels are equal whenever the measured parameter has a predetermined value, and wherein the first and second voltage levels are different from one another whenever the measured parameter has a value other than the predetermined value;
• a detecting means for receiving the first and second voltage levels and for generating an output voltage as a function of the difference between the first and second voltage levels;
• an offset voltage generating means for generating an offset voltage proportional to the output voltage;
• and
• a control means for combining the offset voltage and the output voltage, said offset voltage changing in response to changes in the output voltage to generate a modified voltage, and for providing the modified voltage to the drive terminal as the drive voltage.

A process for continually adjusting the temperature of a temperature responsive resistance toward a predetermined temperature in a high frequency mode, including the steps of:

• incorporating a temperature responsive resistance into a first bridge arm of a bridge circuit that includes several bridge arms and junction terminals;
• continually applying a drive voltage to a drive terminal of the bridge circuit, while maintaining a base terminal of the bridge circuit at a constant base voltage less than the drive voltage, to provide a first voltage level at a first intermediate junction terminal of the bridge, and a second voltage level at a second intermediate terminal of the bridge, said first and second voltage levels being greater than the base voltage and less than the drive voltage;
• selectively configuring the bridge circuit such that the first and second voltage levels are:
• (i) equal whenever the temperature of the temperature responsive resistance is equal to a predetermined temperature;
• and (ii) different whenever the temperature of the temperature responsive resistance is not equal to the predetermined temperature;
• continually detecting the first and second voltage levels to detect a difference in the first and second voltage levels, and generating an output voltage as a function of said difference;
• generating an offset voltage proportional to the output voltage, said offset voltage changing in response to changes in the output voltage;
• combining the offset voltage and the output voltage to generate a modified voltage;
• and
• applying the modified voltage to the drive terminal as the drive voltage.

A device for continually adjusting a bridge circuit toward a balanced state in a high frequency response mode, including:

• a bridge circuit having several bridge arms and junction terminals including a drive terminal at a drive voltage, a base terminal at a base voltage, and first and second intermediate junction terminals at respective first and second voltage levels less than the drive voltage and greater than the base voltage, wherein the bridge circuit is in a balanced state when the first and second voltage levels are equal;
• a sensing element in a first one of the bridge arms, said sensing element having a sensing element resistance that varies with a parameter being measured by the sensing element, thereby to vary the resistance in said first bridge arm and alter a difference between the first and second voltage levels;
• a detecting means receiving the first and second voltage levels, for generating an output voltage as a function of said difference between the first and second voltage levels;
• an offset voltage generating means for generating an offset voltage in response to receiving the output voltage, said offset voltage changing in response to changes in the output voltage, said offset voltage being proportional to the output voltage according to a ratio E.sub.B /E, where E is the output voltage and E.sub.B is the offset voltage;
• and
• a control means for combining the offset voltage and the output voltage to generate a modified voltage, and for providing the modified voltage to the drive terminal as the drive voltage.