The 'S', 'B', 'P', and 'I' suffixes in the 4/20 part number field are used to denote the monitor's display-readings capabilities. For example, the DMS-20PC-4/20S standard unipolar-reading model's gain and offset adjustments are optimized to display "000" with a 4mA input, and up to "1999" with a 20mA input. The DMS-20PC-4/2B bipolar reading model is designed to display a negative number with 4mA, "000" with 12mA, and a positive number with 20mA. The "4/20P" positive-reading model is optimized to display positive numbers with all inputs between 4 and 20mA.
The inverse-reading '4/20I' model is designed to display inverse readings, that is, a 4mA input will display a full-scale positive number, while a 20mA input will display "000". The '4/20I' model uses the same DIP-switch settings tables as its '4/20S' counterpart, the only difference is its full-scale and zero display-readings are reversed. For more information see product data sheet.