Problem: When sharing a Process Variable (PV) with multiple systems, the connection needs to be thought out carefully. Sending a signal to more than one PLC or receiving device needs to be considered just as thoughtfully.
Solution: In part 1 of this series, sharing one Process Variable (PV) was discussed. Creating a series connection for the 4-20mA signal through multiple receiving devices is not a best practice for sharing the PV signal. When sharing a Process Variable (PV) with multiple receiving devices or PLCs, the connection needs to be thought out carefully as well. Moore Industries has a clean and simple solution for connecting a PV to multiple devices.
Figure 1. Quad Isolator Using MIX
Note: The model used is the MIX / 4X4-20MA / 4X4-20MA / 12-42DC [DIN]
We recommend sharing the PV through a multi-channel isolator so that you can send your PV to more than one PLC. Moore Industries has multi-channel isolators, like the MIX, to help customers with their PV sharing, see Figure 1.
The MIX is a reliable and very economical 2 or 4-channel high-density loop powered signal isolator and converter. Only 25.4mm (1 inch) wide, the MIX delivers low cost I/O at 0.25 inch (6.35mm) per channel to substantially reduce installation, panel space, and instrument costs. The 2 or 4-channel MIX can take the place of four individual 4-20mA/4-20mA isolators.
By using the 2 or 4 channel MIX you no longer have to worry about lost signals, or broken current loops, when one of the receiving devices fails or needs to be replaced.
Read Part 2 of this series: Analog Isolation
Read Part 3 of this series: HART Functionality
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