AD693循环供电4-20毫安传感器变送器

　　The AD693 is a monolithic signal conditioning circuit which accepts low-level inputs from a variety of transducers to control a standard 4–20 mA， two-wire current loop. An on-chip voltage reference and auxiliary amplifier are provided for transducer excitation; up to 3.5 mA of excitation current is available when the device is operated in the loop-powered mode. Alternatively， the device may be locally powered for three-wire applications when 0–20 mA operation is desired. Precalibrated 30 mV and 60 mV input spans may be set by simple pin strapping. Other spans from 1 mV to 100 mV may be realized with the addition of external resistors. The auxiliary amplifier may be used in combination with on-chip voltages to provide six precalibrated ranges for 100 Ω RTDs. Output span and zero are also determined by pin strapping to obtain the standard ranges： 4–20mA， 12 ± 8 mA and 0–20 mA. Active laser trimming of the AD693’s thin-film resistors result in high levels of accuracy without the need for additional adjustments and calibration. Total unadjusted error is tested on every device to be less than 0.5% of full scale at +25°C， and less than 0.75% over the industrial temperature range. Residual nonlinearity is under 0.05%. The AD693 also allows for the use of an external pass transistor to further reduce errors caused by self-heating. For transmission of low-level signals from RTDs， bridges and pressure transducers， the AD693 offers a cost-effective signal conditioning solution. It is recommended as a replacement for discrete designs in a variety of applications in process control， factory automation and system monitoring. The AD693 is packaged in a 20-pin ceramic side-brazed DIP， 20-pin Cerdip， and 20-pin LCCC and is specified over the –40°C to +85°C industrial temperature range.