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How to separate two devices on the same current loop

By Omniflex on

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This is a common question that is asked from plant personnel  especially where a DCS system and a PLC may function together with a transmitter signal being common from the field.

Putting the DCS and PLC in series into the current loop is the logical solution but there are some drawbacks or limitations. Often the PLC and DCS does not have isolated individual channels and you are sharing the input card with other devices from the plant. The volt drop across each input could be as much as 10V (500 Ohms) or at best 5V (250 Ohms) and then there may be other devices in the current loop, you very quickly run out of loop voltage which is typically 24V dc.

A quick fix is to install a Loop Splitter (Model No C2464B) One 4-20mA input and Two 4-20mA repeated outputs fully isolated from the field and from each other.

Link to PDF https://www.omniflex.com/pub/downloads/DSC2463B.pdf

Omniflex

The company was founded in 1965, formerly known as Conlog, specialising in process control, alarm/event management and instrumentation products and systems. In 1997, the original instrumentation business division of the company changed its name to OMNIFLEX Ltd.

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The company was founded in 1965, formerly known as Conlog, specialising in process control, alarm/event management and instrumentation products and systems. In 1997, the original instrumentation business division of the company changed its name to OMNIFLEX Ltd.

Omniflex works across all business sectors including pharmaceuticals, hospitals, oil, gas, nuclear, water, electrical distribution and energy monitoring.

The company has its offices in the UK, South Africa, and Australia, and the company’s products are sold on five continents. Product ranges include well-known brands such as OMNI SIL alarm annunciators, OMNITERM SIL signal conditioning, MAXIFLEX intelligent remote terminal units (RTU) and I/O systems and the MAXILARM/Omni 4000 alarm/event management systems.

We bracket ourselves as a ‘remote monitoring specialist’, using data acquisition systems, with better than 1mS timestamp at the IO point (from several I/O up to thousands of I/O),  alarm event management including multiplexing systems, telemetry systems, Data2Desktop using standard web browsers, over varying forms of media and high-integrity (SIL1) annunciator systems.

A particular area that Omniflex is also very strong in is obsolescence issues on old legacy alarm annunciators systems. We have, in most cases, a solution for replacement of Rochester, Highland and Robinson’s annunciator systems. Our alarm annunciator systems have been substantiated by Sellafield for and on behalf of all the nuclear operators.

An area that we can offer customers significant cost savings is through the use of our CONET networking technology, which is supported by many of our RTU / PLC products. Using our CONET network technology allows existing installed cabling to be used therefore significant cabling/installation costs can be avoided. A typical example of this whereby our customer in the nuclear industry used our CONET technology, retained their existing cabling and infrastructure, saved them in the region of £1m on cabling and scaffolding.

As a worldwide supplier, OMNIFLEX provides technical training, back-up and application engineering support to a variety of industry partners including local distributors, value-adding resellers and systems integrators, to provide superior levels of service to the end user.

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