E3EFa HENF452750R1工业模块ABB

.也可以选择4至20 mA增强范围。选择此范围时，0 mA对应于–8000的计数，4 mA对应于0（零）的计数，20 mA对应于+32000的计数。增强范围使用与0至20 mA范围相同的硬件，但自动提供4至20 mA的范围缩放，但为4 mA至0 mA之间的输入电流水平向用户提供负数字值除外。这使您能够选择低报警限值，以检测输入电流何时从4 mA降至0 mA，其提供4至20mA应用中的开路故障检测。所有范围都有高报警限值和低报警限值。范围可以在pe LSB X=上配置，不适用于本讨论。电流输入和来自A/D转换器的数据之间的关系如下所示。4 A/D位（十进制）电流（mA）a4647 0 20 0 4000 4至20mA范围图12-1。A/D位与电流输入如果电流源反向输入或小于电流范围的低端， A 4 to 20 mA Enhanced range can also be selected. When this range is selected, 0 mA corresponds to a count of –8000, 4 mA corresponds to a count of 0 (zero) and 20 mA corresponds to a count of +32000. The Enhanced range uses the same hardware as the 0 to 20 mA range but automatically provides 4 to 20 mA range scaling with the exception that negative digital values are provided to the user for input current levels between 4 mA and 0 mA. This gives you the capability of selecting a low alarm limit that detects when the input current falls from 4 mA to 0 mA, which provides for open-wire fault detection in 4 to 20 mA applications. High and Low alarm limits are available on all ranges. Ranges can be configured on a pe LSB X=not applicable to this discussion. The relationship between the current input and the data from the A/D converter is show below. 4 A/D BITS (decimal) CURRENT (mA) a44647 0 20 0 4000 4 to 20mA RANGE Figure 12-1. A/D Bits vs. Current Input If the current source is reversed into the input, or is less than the low end of the current range,