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A level transmitter retrofit may fit the old mounting point while needing a different electrical circuit. Cable reuse should be decided from the selected electronics and the installed cable, not from the fact that both instruments report level. Confirm the route before purchasing a version that the existing wiring cannot support.
Start the Level Transmitter Retrofit With Two Circuit Drawings
Obtain the as-built circuit for the old instrument and the terminal drawing for the proposed replacement. Identify supply, signal, shield, junctions, barriers or isolators and receiver. Count usable conductors through the entire route; spare cores at one end do not prove continuity through every junction.
| Item | Evidence | Reuse limit |
|---|---|---|
| Circuit | Supply and input type at both ends. | A loop-powered input is not automatically suitable for separately powered serial electronics. |
| Cable | Construction, length, condition and available cores. | Check against the selected instrument's electrical requirements. |
| Junctions | Terminal allocation, seals and existing interfaces. | Hidden conversions or damaged joints may prevent direct reuse. |
| Protection | Approved installation drawing and applicable devices. | Retain the required system design; conductor count alone is insufficient. |
The METRAVON MV-RD12 can be ordered for a two-wire 4-20 mA/HART arrangement or an appropriate RS485 configuration. These choices must be made before declaring the old cable reusable. Adding a serial converter also changes the system and needs its own power, mapping and fault review.
Inspect and Test Without Damaging Connected Equipment
Have qualified personnel isolate and identify the circuit before tests. Use the site-approved method and equipment instructions for continuity or insulation checks. Do not apply an insulation tester across connected transmitter electronics, receiver cards or protection devices unless their documented procedure explicitly permits it.
Check the physical cable jacket, terminations and water exposure as well as electrical continuity. A cable that passes a simple continuity test can still have intermittent faults or an unsuitable construction for the new circuit. Record unresolved sections rather than describing an inaccessible route as checked.
Make the Quotation Reflect the Reuse Decision
List retained cable separately from new glands, junction work, isolators and receiver changes. Where route condition cannot be confirmed until shutdown, make that inspection an explicit hold point with a priced alternative. This prevents the installation team discovering an unbudgeted recabling requirement after the old device is removed.
Q1. Can the old wire colours be copied?
Use verified terminal functions, not colours alone. Previous repairs may have changed assignments. Identify both ends and label the final circuit against the approved drawing before energising it.
Q2. Does a successful local display check prove cable reuse worked?
No. Check the received measurement, fault behaviour and communication stability as applicable. The local display can operate correctly while the downstream circuit remains miswired or incorrectly configured.
Summary
Retain cable only after its construction, condition and circuit role have been established. Provide the old loop drawing, route details and desired output with a retrofit electronics enquiry so the supplied MV-RD12 version matches the installation plan.
