I am designing an electronic interface to SCADA. The SCADA typically takes 4-20 mA input for logging data to a central database. So I need to convert my voltage output from my instrument/device into current using a V/I convertor(like AD1B22). My instrument has just one analog out but I need 4 lines to interface to SCADA. For this I am using a 4:1 MUX. Now since these 4 lines should hold valid data at all times I need to latch in voltage values before converting them to current outputs. I was thinking of using sample and hold circuit to latch analog voltage values. When I looked at sample and hold circuit like AD585, the data sheet talks about droop rate(change in output voltage with time due to leakage capacitive current).
So I am thinking that the only way to latch analog voltage is to convert it into digital, then latch the voltage and convert it back to analog. Am I thinking on correct lines or not ? Any other ideas ?