Identifying a Legacy Industrial Automation Part From Its Mar

Identifying a Legacy Industrial Automation Part From Its Marking and a Photo

An independent distributor and sourcing desk working in industrial automation can usually identify a legacy PLC, drive, HMI or sensor from the marking on its housing plus a clear photograph, but the two pieces of evidence carry different weight. The marking text — model string, series family, hardware revision code, date or batch stamp — is what gets read first. The photograph confirms housing shape, connector layout and accessory boards. Where the marking is incomplete, damaged, or replaced by a custom label, the inquiry has to go back for clearer evidence; in those cases identification is paused, not guessed.

The question a buyer actually types into a search box before reaching this page is short and direct: «Кто может опознать устаревшую деталь по маркировке?» — Who can identify an obsolete part from its marking? — and the honest answer is that identification is a layered process, not a single step. The same buyer, looking for a specific discontinued controller, will also ask «Можете найти компоненты по фото и маркировке?» — Can you source components from a photo and the marking? This article walks through what is read at each layer, what is left as unknown, and what evidence has to come back from the buyer before the desk can answer with anything firmer than "we believe this is…".

Why a photo alone is not enough

Most photos arrive on a phone camera at an angle, in uneven lighting, with the unit still half-wired into a control cabinet. From such a photo a desk can usually see the housing family, the connector style, the number of terminals, and any sticker a previous installer has applied. What a photo usually cannot show is the marking itself: the small laser-etched text on the front bezel of an Inovance H1U-2416MR-XP PLC, the revision dot on the side of an MD310T5.5B-TC drive, or the batch code stamped on the back of an IS620PS1R6I servo drive. A phone camera at arm's length will soften those characters to grey smears, and any desk that claims to read them in that state is reading a guess.

The practical rule on this desk is: the marking text comes first, the photo confirms. We ask for the marking text to be read off the housing and typed into the inquiry, even if the buyer also sends a photo, because typed marking removes the camera, the lighting and the operator from the chain of evidence. Once the typed marking is in, the photo is checked against it, and any disagreement — a different connector family, a different bezel colour, a different number of status LEDs — is a signal that the photo and the marking are describing different units, which happens when the wrong module was pulled from the cabinet.

The same rule applies when the marking has been damaged. A painted-over model number, a peeled label, or a grinding mark across a nameplate is not rare on a unit that has spent twenty years on a factory floor. The honest answer at that point is to say so, list what is still legible (often the series family, sometimes the voltage class, occasionally a partial order code), and ask for either a photo of the back of the unit or any documentation that was filed with the machine when it was installed.

The five fields we read off the marking

When the marking is legible, five fields are taken off it in this order. They are not always present, and missing fields are reported as missing rather than guessed.

1. Model string. This is the part-number string the manufacturer assigned: a string such as H1U-2416MR-XP, MD310T11B-TC, 6ES7315-2AH14-0AB0 or CSMSTRLE. The model string is the anchor of the whole identification — once it is in hand the desk can look it up in the original manufacturer's catalogue, in equivalent-listing tables, and in last-time-buy records. A misspelled or transposed model string is the single most common reason an inquiry stalls, which is why typed marking is preferred over a photo even when the photo is sharp.

2. Series family. Even where the full model string is illegible, the series family is often readable: S7-300, S7-1500, ET 200SP, FX5, MD310, IS620, KTP700, TeSys D. The series family narrows the search to a known platform with documented alternatives, even if the exact variant within that platform is unknown. A drive labelled "MD310" without the suffix still tells us which firmware family, which V/F curve set, and which keypad interface to expect.

3. Hardware revision code. Many control products carry a small FS number, hardware version letter, or dot-matrix revision code on the side or the back of the housing. This code is the single most-overlooked field, and it is the one most likely to decide whether an equivalent-listing entry actually fits. Two units of the same model string can differ on the revision code and behave differently with the same firmware, the same program, or the same peripheral; ignoring the revision code is how a line that looked fine on paper fails at commissioning.

4. Date or batch stamp. A date code in YYMM or YWW form, or a batch/lot stamp, narrows the unit to a manufacturing window. For legacy parts that window matters because firmware revisions and component changes inside a series family are not always uniform across years. The date stamp is also useful when a buyer has several identical-looking units in stock and is not sure which one came out of which machine.

5. Sub-model suffix. Many modern product codes carry a suffix that is not in the printed catalogue: a regional variant (CN, EU, US), a firmware-load identifier, a conformal-coating code, a customer-specific tag. The suffix often determines which firmware revision the unit ships with, which documentation applies, and whether the equivalent entry in the catalogue is even legal to claim against it.

A short worked example. A buyer sends a photo of an Inovance MD310 drive with the marking typed in as "MD310T5.5B-TC". The five fields read as: model = MD310T5.5B-TC, series family = MD310, hardware revision = the "B" suffix on a 5.5 kW unit, date stamp = whatever the buyer reads off the side label, sub-model suffix = "TC" indicating the factory-supplied variant with its standard control terminals. With those five fields, the desk can quote, can suggest alternatives within the MD310 family, and can warn the buyer if a different kW rating has a different control board. Without the revision and the suffix, the desk can quote but cannot warn, which is a worse position for the buyer.

What the photo is for

Once the five marking fields are in, the photograph has four jobs, and only four.

Confirming housing and connector family. A photo confirms that the unit is physically the one the typed marking describes. Two drives can share a model string but have different terminal layouts if one is a factory variant and the other is a contract-built version; a photo catches that within seconds.

Catching accessory and daughter-board content. Some units carry a daughter board under a removable cover, an option card in a slot, or a plug-in module on the side. The marking on the housing will not name these; only the photo, or a back-of-unit photo, will. For an IS620 servo drive this is the point at which the encoder interface card, the safety-option board or the fieldbus plug-in shows up, and any listing entry that ignores it is wrong.

Reading stickers the manufacturer did not print. Field-installed stickers — a panel-builder's loop number, a maintenance contractor's service tag, a previous owner's asset tag — are not part of the marking but they tell the desk what cabinet and what machine the unit came out of. That context can be more useful than the marking itself when the buyer does not have the original machine documentation.

Photographing damage, wear or repair marks. A unit with a repaired PCB, a replaced capacitor, a re-glued connector, or a heat mark on the housing is a different commercial object from a clean unit of the same model string, even when the marking is identical. The photograph is the only place that condition evidence lives before the unit is on the bench, and a desk that quotes without asking for it is quoting blind on a used or refurbished line.

When the inquiry has to go back

Four situations force the inquiry back to the buyer. None of them is a refusal; all four are a request for evidence that the desk cannot fake.

The marking has been ground off. A stainless-steel nameplate that has been mechanically ground is a deliberate act, and on this desk we do not pretend to read what has been physically removed. The honest reply lists what is still visible, which is usually the series family at best, and asks the buyer to send either the machine documentation or a photo of any other unit of the same model still in the cabinet.

The unit has been re-labelled. A sticker with another vendor's logo over the original marking, or a hand-written label with a different model code, is treated as a red flag. The unit may be perfectly functional but it cannot be quoted under the re-labelled code without confirming the original, which means the buyer has to send either the original paperwork or a back-of-unit photo where the PCB silkscreen often still carries the real part number.

The photo and the typed marking describe different units. This happens more often than expected — a buyer pulls the wrong module from a cabinet under time pressure and photographs the wrong face. When the photo and the typed marking disagree on connector family, terminal count, or bezel layout, the inquiry is paused, and the buyer is asked which of the two is the correct unit to identify.

The marking is legible but the part is outside our sourcing scope. Some products — safety-rated modules with functional-safety certification, medical devices with regulatory documentation, and items tied to end uses we do not serve — are not in scope of what an independent distributor sourcing desk sources regardless of how clearly they are marked. The inquiry is returned with an explanation of why, and where possible a pointer to the channel that does handle them.

What we do not guess, even when the buyer asks us to

Three pieces of information are deliberately not inferred from weak evidence, because a wrong inference costs more than a delayed reply.

The hardware revision. The revision code is read off the marking when it is legible; when it is not legible the desk reports it as unknown. We do not infer a revision from the date stamp, from the buyer's recollection, or from a previous quote on a similar model. The reason is mechanical: firmware behaviour, peripheral compatibility, and the validity of an equivalent-listing entry all hinge on the revision.

The firmware version. The firmware load on a refurbished or used unit is read from the unit itself once it is on the bench, not inferred from the model string. Two units of the same model string and the same hardware revision can carry different firmware loads if one has been field-updated, and a quote that assumes the wrong firmware is a quote that breaks at commissioning.

The condition of the unit. "Working when pulled" is not a condition we transcribe into a quote. Condition is reported per line as new, new surplus, refurbished or used, with the test record that supports the description, and the buyer is shown the photos that justify the label before the unit ships. The four words are not interchangeable; a used unit is not a refurbished unit, and a new-surplus unit is not a new unit.

For every identification that turns into a line on a quote, the desk asks the buyer — and the buyer should ask the desk — to verify the equivalent against the original manufacturer datasheet and the buyer's own qualification process before installation. Identification work is best-effort, not certified, and the final acceptance decision belongs to the buyer's engineering team.

When identification is not the bottleneck

Identification work can return a clean answer and still be the wrong tool for the problem. Three situations are deliberately handed back, even when the marking and the photo are unambiguous.

Safety-rated modules. For emergency-stop relays, safety PLCs, light curtains, guard-locking switches, and other safety-rated modules, identification is not the bottleneck; the bottleneck is the buyer's functional-safety process. We identify the part, source what can be sourced, and leave the certification determination to the buyer's safety engineer. Swapping in a different part here is not recommended — the safety case has to be rebuilt from scratch against the specific part, and a generic "this looks the same" answer is not safe.

Medical-device components. For medical-device components — patient-monitoring modules, diagnostic peripherals, imaging subsystems — identification is again not the bottleneck. We do not hold ISO 13485 and we do not certify a component for medical use; the determination belongs to the device manufacturer's quality system.

Authorisation, warranty, and certification papers from the original manufacturer. An independent distributor does not carry manufacturer-issued warranty, manufacturer-issued certificates of conformity, or manufacturer-issued authorization letters. Where the buyer's process requires those documents, the franchised channel is the correct channel; we identify, we source, we state condition per line, and we leave the paperwork that only the manufacturer can issue to the manufacturer.

How an identification inquiry moves through this desk

The path is short and visible. A buyer opens an inquiry through /inquiry with either a part number, a typed marking, or a photo with whatever marking is legible, and the desk comes back with a quote per line. The desk reads the marking, looks the model up against the original manufacturer's catalogue, and reports back what the unit is believed to be, what it is based on, and what evidence is still missing. If the unit is in current production in the franchised channel, the buyer is told so and pointed there; if it is out of production, the desk looks at remaining channel stock, at documented equivalent-listing entries, and at last-time-buy records. The quote that follows is per line: price, MOQ, lead time, condition — with each one stated individually rather than averaged. Buyers who send a multi-line BOM can request a quote for the whole list and we will treat it the same way; one line or forty, the per-line discipline is the same.

For an Inovance MD310T5.5B-TC the path is the same as for any other line. The marking text is the anchor, the photo confirms the housing, and the desk returns either a sourced unit, a documented equivalent within the MD310 family, or a clear statement that the line is not currently in our sourcing reach. For a buyer sending only a photo of an unmarked module the path stops earlier: the desk reports what can be read from the photo, lists what cannot be read, and asks for either the machine's spare-parts list or a clearer shot of the unit itself.

The takeaway

Identifying a legacy industrial automation part from a marking and a photo is a layered task, not a single act. The marking text — typed, not photographed — is the anchor. The photograph is the confirmation. Five fields are read off the marking (model, series, hardware revision, date or batch stamp, sub-model suffix), and missing fields are reported as missing rather than guessed. The inquiry goes back to the buyer when the marking has been ground off, when the unit has been re-labelled, when the photo and the typed marking describe different units, or when the part is outside what an independent desk sources. The desk identifies, sources, and states condition per line; it does not certify functional safety, does not qualify components for medical use, and does not issue manufacturer paperwork. Always verify against the original manufacturer datasheet and your own qualification process before installation. Send the typed marking plus a photo through /inquiry and request a quote once the line is confirmed; the rest of the work is on this side.

FAQ

Can a legacy automation part be identified from a photo alone?

Usually no. A photo confirms housing, connector layout and accessories, but the marking text — the model string, the hardware revision code, the date stamp — is what carries the identification. Typed marking plus a photo is the reliable combination, and the desk reads five fields off the marking in order.

What marking fields matter most when identifying an old PLC or drive?

The model string is the anchor. The series family narrows the platform when the full model is illegible. The hardware revision code is the field most often overlooked and most likely to decide whether an equivalent-listing entry actually fits. Date or batch stamps and sub-model suffixes round out the five fields the desk reads.

What should I include in an inquiry when I only have a photo of the part?

Send the photo plus whatever marking is legible on the housing, the PCB, and any accessory board; the machine the part came from; and, if available, the original spare-parts list or the machine's manual. The desk identifies what can be identified, reports what cannot, and asks for the evidence that closes the gap.

What happens if the marking on the unit has been ground off or painted over?

The desk reports what is still visible — typically the series family at best — and asks for either a photo of the back of the unit, the original machine documentation, or a photo of another unit of the same model still installed. A ground-off or painted-over nameplate is not read as a guess.

Do you identify parts from all brands, or only the brands on the catalogue page?

Identification is based on the marking and the manufacturer's own catalogue, so any brand with a documented model line can be identified. Sourcing is narrower and depends on what is currently in our channel reach; identification is reported regardless of whether the desk can source the line, so the buyer knows whether to look elsewhere.

How long does it take to identify a part and reply with a quote?

Single-line and short-list requests are usually answered the same working day; longer lists take longer because each line is sourced individually. We do not quote a fixed turnaround as a service guarantee — the response time depends on the list and on how quickly suppliers confirm, and is reported as the work proceeds rather than promised up front.

What if the photo and the typed marking describe two different units?

The inquiry is paused. This happens more often than expected when a buyer pulls the wrong module from a cabinet under time pressure. The buyer is asked to confirm which of the two is the correct unit, and the desk proceeds once the marking and the photo agree.

About the author. Written by the editorial desk of aoctrl.com, an independent distributor and sourcing desk working from China with buyers across overseas panel shops, machine OEMs, plant MRO teams, and repair shops — including buyers in Russia and the CIS. We are not an authorised distributor for any of the brands we handle; we identify, source, and state condition per line.

Last updated: 2026-09-20.

Data notes. Catalog references in this article are drawn from the aoctrl.com product index for Inovance MD310 series (MD310T11B-TC, MD310T7.5B-TC, MD310T5.5B-TC, MD310T3.7B-TC, MD310T1.5B-TC, MD310T2.2B-TC, MD310T0.7B-TC), Inovance IS620 servo drives (IS620PS1R6I, IS620PS2R8I), and Inovance H1U-2416MR-XP PLC. Stock, condition, MOQ and lead time are stated per line on the quote; nothing in this article is a fixed promise of availability. Process steps (typed-marking-first identification, photo confirmation, five-field read, per-line condition discipline, refusal of out-of-scope work) are taken from the published /procurement, /quality, /about, and /inquiry pages on aoctrl.com as of September 2026.