Downhole Pressure and Temperature Gauge Design

To measure the pressure and temperature in downhole of oil well for a long term, a pressure and temperature gauge was especially designed. In order to reduce the gauge power consumption, a set of low power ICs, such as the 87lpc764 CPU, the AD7705 with a PGA and a digital filter, 24LC1025 EEPROM, PCF8583 timer were adapted; in additional, the intermittent work, dormancy and wake up by the timer PCF8583 was a energy conservation strategy of this gauge. To simplify the circuit, the SPI bus and IIC was selected. A USB interface circuit was used to connect the gauge and the upper PC, so it was possible that the PC could write parameter to and read measuring data rapidly from the gauge. In the data processing aspect, a special verification model was designed to calibrate the pressure data with temperature, so pressure value of the gauge could meet accuracy in the operating temperature scope. After the above policies were applied, the pressure gauge possessed following characteristics: simple structure, low power consumption, high accuracy, and wide operating temperature. It could continuously measure the downhole pressure and temperature of oil well in long-term.