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EHELP: How do I protect the STA from external voltage surges?

EHELP: How do I protect the STA from external voltage surges?

Q: We want to install an
STA / HLPRG / 3PRG / U / -AO [DIN] into our process and plan to use 4-20mA output loop voltage sourced by a DCS for the analog output, however this voltage may fault at up to 132 VAC. Should we design in fuse protection to the external voltage circuit upstream of the STA to protect it from these surges? Or does the STA include features that protect it from these faults?

A: A fuse will limit current but not excessive voltage. If the DCS cannot be configured for a sinking input, then we recommend using a “sacrificial” isolator.

To do this, connect the sourced output of the STA to the input of an output loop powered isolator. The output of the isolator goes to the sourcing input of the DCS. If there is a 132V fault voltage from the DCS, it will risk damaging the isolator and not the STA.

For information on the STA, download the data sheet.

Published: June 14, 2016
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Categories: E-Help, Applications
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