I need to process two 4-20 mA signals from two pressure differential sensors (Dwyer MS-121-LCD) and average them so that their average will be the final signal to be translated as frequency (Max 60 Hz) in ABB ACS-510-01 VFDs in order to provide a pressurized air in stairwells for emergency situations and must be maintained at 50 pascals maximum and 12.5 pascals minimum if there are four fire exit doors opened. Any input will be great help. Thanks.