In a blog posted late last month I addressed how to provide a 24VDC source of power to a three wire field device. In the past I have used a 24VDC High Side Discrete output to provide 24VDC to these types of devices. This solution can be implemented in most DCS and PLC systems. If you happen to be working with a DeltaV control system that utilized S-series Electronic Marshalling then a better solution has just been introduced. This new offering consists of:
- CHARM for 24 VDC Power
- The 3-wire DI Fused Injected Power Terminal block designed for use with all Isolated discrete Input CHARM types
As Klaus Erni, DeltaV HardwareProduct Marketing Manager, recently explained.
“With the help of the 24VDC Power CHARM, 3-wire Analog Field Devices like a Gas Detectors, can now be connected directly to a CHARM Solution by getting the Power from the 24 VDC Power CHARM, while the mA Loop is wired back to the AI 4-20mA HART CHARM. For 3-wire Discrete Field Devices, like proximity switches, a new Terminal Block has been developed, called the CHARM 3-Wire DI Fused Injected Power Terminal Block, to be able to land all wires from the proximity switch straight on the Terminal Block. This new Terminal Block also has a Fuse onboard and can be combined with all existing Isolated CHARM Types.”
It is nice to see this capability being introduced since it simplified wiring as illustrated below for a 3 wired field device.