Three-Way Isolating Signal Conditioner, 0(4)-20 mA In to 0(4)-20 mA Out, DIN Rail, DC Supplied

What this part is:
A Phoenix Contact MCR-C series signal conditioner — an analogue isolating amplifier for a current loop. It takes a 0(4)–20 mA input and reproduces it as an electrically isolated 0(4)–20 mA output, with galvanic isolation between input, output and the DC supply (Phoenix’s “three-way” isolation). It is a passive-signal conditioning module for the DIN rail, powered from a DC supply.

Correcting the source data:
Earlier copy on this listing described the unit as a PLC processor module. It is not a processor and not a PLC module of any kind: it has no backplane, no logic, no configuration and no programming. It is a two-terminal-pair analogue isolator that sits between a field instrument and whatever reads it.

Decoding the order code:
MCR — Phoenix Contact’s Modular Conditioning Range for analogue signals.C — the compact-housing MCR-C family, narrow DIN-rail modules.I/I — current in, current out. This is the field that decides fit: the sibling MCR-C-I/U variants are current-in, voltage-out, and are not interchangeable with this one.00 — the input/output range configuration. The 00 variant covers 0(4)–20 mA on both sides; the 40 variant in the same family is configured differently.DC — DC-supplied module.Phoenix Contact’s own order number for this unit is 2814508. Quote that number to any Phoenix distributor and it resolves unambiguously; the alphanumeric designation is often mistyped.

Published specifications:
Function: three-way isolating signal conditioner / isolating amplifier for analogue signalsInput signal: 0(4)–20 mAOutput signal: 0(4)–20 mAIsolation: galvanic separation between input, output and supplySupply: DCMounting: DIN rail, narrow compact housingManufacturer status: discontinued; Phoenix Contact’s nominated successor is MINI MCR-2-I-I, order number 2901998

What this does for you in practice:
Isolators exist to solve two specific problems, and they are worth understanding before you buy one. The first is the earth loop: when a transmitter’s 0 V and the receiving PLC’s 0 V are bonded at different points in a plant, current flows in the signal return and the reading wanders or picks up mains hum. Breaking the loop with an isolator fixes it properly, where fitting filters and re-routing cable usually does not. The second is protection and decoupling: a fault or surge on the field side cannot propagate into the control system through an isolated barrier, and one loop’s noise cannot contaminate another.

The third, quieter use is signal duplication and load matching — putting an isolator in line lets you drive a receiver whose input burden the transmitter could not otherwise support, because the isolator’s output stage is doing the driving.

Note what this module is not: it is not an intrinsically-safe barrier. If your instrument is in a hazardous area and needs Ex i isolation, you need a certified intrinsic-safety isolator (Phoenix’s MACX Analog Ex range or equivalent), not a general-purpose MCR-C. Do not use this module to cross a hazardous-area boundary.

Quantity and configuration:
One module, old stock, open box.

What is not included:
DC power supply, DIN rail, end brackets, marking labels, jumper or bridging combs, plug-in terminal blocks beyond those fitted, and documentation.

Installation notes:
Clip onto a standard 35 mm DIN rail and observe the terminal markings for input, output and supply — the entire benefit of the module is lost if the input and output commons get bridged downstream, which is easy to do accidentally in a crowded terminal box. Keep the analogue wiring in screened cable, screen earthed at one end only. Check the burden of your receiving device against what the output stage will drive, and confirm the loop’s zero (0 mA versus 4 mA live-zero) is the same on both sides of the isolator so a broken-wire condition still reads as a fault rather than as a valid zero.

Interchange guidance:
Direct interchange with other MCR-C-I/I-00-DC / 2814508 modules. Phoenix Contact’s own successor is the MINI MCR-2-I-I (2901998), which is functionally equivalent but physically a different, narrower module with a different terminal layout — plan on remaking the wiring rather than dropping it into the same footprint. Related but different parts, not equivalents: MCR-C-I/U-0-DC and MCR-C-I/U-4-DC (current-in, voltage-out) and MCR-C-I/I-40-DC (different range configuration). Match the I/I and the 00 as well as the MCR-C prefix.