| 摘要 |
A hot wire gas flow rate sensor having a bridge circuit with a sensing resistor avoids saturation of the signal processing circuitry at high gas flow rates by increasing a bias signal to a differential amplifier in the signal processing circuitry in a step-like manner as the flow rate responsive signal to the differential amplifier from the sensing resistor increases. The differential input signal to the amplifier is thus maintained at a level that avoids saturation of the amplifier. Appropriate scaling is provided to the output circuitry of the sensor in accordance with changes in the bias signal so that the sensor output correctly indicates gas flow rates. Compensation is provided for changes in gas composition and when the sensing resistor is changed by determining the voltage drop across a first sensing resistor with a gas of known composition at a zero gas flow condition. The voltage drop across a second sensing resistor at the zero gas flow condition for the gas is also determined. When sensing the flow rate with the second sensing resistor, the ratio of these voltage drops is applied to the flow responsive component of the voltage drop across the second sensing resistor. This compensates the flow responsive voltage drop component for changes in sensing resistor resistance. The voltage drop across the sensing resistor is determined at zero gas flow when the gas composition changes and ratioed to the voltage drop obtained with the known composition gas to compensate for changes in gas composition. |
