HART current ratio - What is this? in Allen Bradley Posted 1 January Hello fellas. I'm trying to learn to use the HART functions of a FLEX i/o 1794 input card, and I have most of it figured out. There is this setting though, called HART current ratio, which allows a selection of disabled, or 5% to 31%. I can't figure out what it does though. The "HELP" guide explains that it is a threshold percentage for forcing HART read back indication (Input signal deviation HART to analog) but I am quite unsure what this means. Is it the allowed deviation that the analog signal can have, compared to the transmitted HART data? Hope the question makes sense, cheerio.