Summing unit for 4 (optional 8) force transducers. The signals of 4 force transducers (4…20 mA, 2-wire) are added. The output delivers a sum signal (4…20 mA, 3-wire) which is proportional to the total load. The S-Box detects load limits and cable break of single ports and is suitable to force transducers with test signal (SIL).