谢谢楼上各位,今天我量过了,确实AI卡输出24VDC,我想应该是供给4~20mA回路输出用的吧,如果AI卡坏了,就没有4~20mA信号输出了。现附有原英文接线说明.
DC Main Power Supply
with 4–20 mA Loop
Power Supply
Wire the APEX and APEX Sentry Radar Gauges as shown in Figure 2-20,
using an 18–36 V dc main power supply. Loop power is required for the 4–20
mA/HART output. Use a 10.5–55.0 V dc secondary power supply for the 4–20
mA/HART loop output. Refer to Power Requirements on page 2-24 to
determine the power supply voltage required in the control room. Make sure
the main power to the gauge is off and the lines to any other external power
source are disconnected or not powered while wiring the gauge.