Q: HIX Application - It appears that if the "Primary Master" loop (input loop side of the HIX) is broken or open circuited, the "Secondary" loop (output loop side of the HIX) will be 0mA. Is this true? Maybe I can put a zener across the primary process terminals to keep the current loop when the process opens? Also, are both or either loops bi-directional HART? I have a 4-20mA input signal that I'd like to share between two 4-20mA/HART process loops. Actually, we currently use another vendor's device to "split" one 4-20mA input to four process loops but it doesn't pass HART.
A: The HIX is an output loop powered device that is an analog circuit, so the output will follow the input as far down as possible. If the input goes to zero mA on the HIX input circuit, the output will go down to about 2mA, but not all the way down to zero. This is due to the active parts of the power supply circuit, on the output side of the HIX, that continue to consume some trickle power to keep the unit “alive”. Yes, the HIX supports bi-directional HART communication.
If you are looking for a single input, dual output device that passes HART, then take a look at the SST series. Utilizing two of these SST splitters will offer you the four process loops with HART pass through capability. This device also supports bi-directional HART communication.
The outputs of the dual output SST normally source the loop voltage, but there is an option to make both outputs “passive”.
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