Identifying a Legacy Automation Part From Its Marking and a

Identifying a Legacy Automation Part From Its Marking and a Photo

A faded label on a 2014 photoelectric sensor, a laser-etched code on a Siemens power supply that no longer resolves on the manufacturer's current part-number lookup, a contactor block where the front sticker has dissolved under years of cabinet heat: these are the moments a buyer writes the same short message — "I have a part. I cannot read it. Can you tell me what it is and whether you can supply a working replacement?" The honest answer depends on what the buyer can show, what they can tell us about the cabinet, and what they cannot infer from a single photograph. By the sourcing desk, as of September 2026.

Why a Single Photo Rarely Closes the Question

The assumption that a smart phone picture, paired with a model code, will resolve a discontinued component to a current ordering number is the first mistake. Markings on industrial components are not designed for long-term human readability. They are designed to survive one factory floor, one shift handover, one round of warranty replacement — not twenty years of cabinet heat, flux residue from a board wash, or a solvent splash during a cleanup. Three patterns repeat in the photos that arrive at the inquiry inbox:

Two-line silk print on a dark housing, where the second line carries the variant suffix (voltage, connector, NPN/PNP, cable length). The first line is often the only thing legible; the variant is what differentiates a working replacement from a same-looking non-functional one.
Date code separated from the part code on a side or back label that is hidden when the module is wired. A buyer photographing the front face rarely captures the date code, and the date code is what tells us whether a part predates a known engineering change.
A sticker applied by a panel builder, not by the original manufacturer, sitting on top of the original marking. The panel builder's job number or asset tag is what the buyer remembers; the underlying manufacturer code is invisible without peeling the sticker.

The buyer's framing — "it's an Omron sensor, I think E3S-something" — is the third pattern we see. The intuition is correct on the family, and wrong on the suffix. Without the suffix, the part can be from any of several sub-families that share a housing but differ in sensing mode, output stage, cable specification and connector type. Two E3-family sensors that look identical to a camera can be electrically incompatible. The catalog side of our desk has the same problem: a manufacturer search for an incomplete string will return a list of plausible matches, and the listing of plausible matches is not an identification. It is a guess with a part number attached.

What a Desk Actually Does With a Photo

The internal workflow for "identify and source a discontinued part from a photo" is not a single lookup. It is a sequence of triage steps, each of which can fail and each of which gives the buyer a more concrete question to answer. We walk through them in order, because the order is the only thing that prevents us from quoting the wrong line item.

Step 1 — Family recognition. Before any code is typed into a search field, the photograph is matched against the housing silhouettes the desk has on file: Omron E3Z, E3S, E2E, E3ZM; Siemens Sirius 3RT, 3RV; Schneider TeSys D, TeSys D Green; Phoenix Contact Quint, Step; Mitsubishi MELSEC FX5, Q-series; Delta DVP, MS300; Wago TopJob, 857 series; SICK W4, W9, W11, W26, G6; Festo DSBC, DSNU; Yaskawa Sigma-7, Junma. A catalog search by an incomplete string will return anything; a housing-shape match narrows the field to a few hundred models at most. This step does not identify the part. It bounds the problem.

Step 2 — Visible code recovery. Where possible, an image editor is used to lift contrast and invert polarity on the marking area. Some silk prints that look blank on a phone photograph are readable after a threshold pass. Where the marking is genuinely gone — solvent-washed, scratched through, painted over — we say so on the first reply. A buyer who hears "the marking is not recoverable from this photograph" is in a better position than a buyer who receives a plausible-looking wrong part number.

Step 3 — Adjacent context. A photograph of the part in the cabinet is worth more than a photograph of the part on a bench, because the adjacent wiring tells us things the housing cannot: cable colour and gauge, connector pin count, the wire that carries 24 V versus the wire that is signal ground, whether the device is powered from the same supply as a known-good neighbour. A buyer who can send two photographs — one of the part, one of the cabinet wall above and below it — usually short-circuits the entire triage.

Step 4 — Cross-reference against the desk's catalog. Only after steps 1 through 3 do we run the partial code against our published catalog. The catalog itself is queried by part-number prefix, not by free text. If the part matches a SKU we currently list — for example an Omron E3ZM-T81 2M photoelectric sensor in diffuse-reflective mode, 2-metre pre-wired — we can quote against that SKU and the buyer's problem reduces to whether the suffix matches what they have on the bench. If the part matches the family but the suffix is unknown, we list the candidates and ask which cable, connector and output configuration the buyer has on hand. The catalog is the source of truth on what we can supply; the photograph is the source of truth on what the buyer needs.

Step 5 — Honest boundary statement. Where the identification cannot be closed, we say so before any quotation. A cross-reference walk through the substitution axes (terminal layout, supply voltage and current rating, channels and I/O direction, firmware version, communication protocol, ambient temperature rating, ingress protection, mounting style and footprint) is only meaningful if the two parts have been identified. Comparing an unknown sensor against four candidates from the same family on the basis of one photograph is not comparison — it is a guess with a structured output. The desk's policy is to decline the cross-reference and ask for either a clearer photograph or the original panel-builder documentation. This is the point where the desk earns or loses the buyer's trust for the next ten inquiries. The substitution walk-through is something the desk recommends for buyers who can supply both photographs and a clear function description; for safety-rated devices such as safety relays, e-stops and SIL-rated devices, the desk recommends keeping the original part on its certified axis and not substituting.

The Photographic Information That Actually Matters

For each major component family, three or four details consistently close the identification when they are visible in the photograph. We list them so the buyer can take a single, well-framed photo instead of five that each show one clue.

For sensors: front face marking (one line, ideally two), cable exit (axial or radial), connector type or pigtail length, LED indicator colour and position, and any date code on the side or back. Two Omron E3-series sensors that share a housing can differ in sensing mode (diffuse-reflective, through-beam, retro-reflective), output (NPN, PNP, NO, NC), supply voltage range, current rating, IP rating, ambient temperature rating, and connector. The cable length and connector type are the cheapest hints to capture. When the marking is partly worn, the cable length and connector pin count are usually the two attributes a buyer can read off the photograph when nothing else resolves.

For contactors and motor-protection circuit breakers: front face rating plate (frame size, coil voltage, contact configuration, IEC or UL rating), auxiliary contact block side markings, and the panel builder's asset tag if present. A TeSys D LC1D contactor and a TeSys D Green LC1DGreen are not the same product line; the green-Body designation on the rating plate is what tells the desk whether the buyer is looking at the legacy contactor or its energy-efficient successor.

For PLCs and remote I/O: front bezel marking (full order code including the FS hardware version suffix), any inserted module descriptions on the side, and the LED status display if the CPU is still powered. The hardware version suffix on a Siemens S7-1200 or S7-1500 module — the FS:01, FS:02, FS:03 string — is the single most common reason a cross-reference comes back ambiguous. The firmware version, where readable from the connected engineering software, sits on a different axis again and is treated separately.

For power supplies and signal conditioners: side label with the full order code and revision, and the dip-switch or rotary switch block. A Phoenix Contact Quint or Step power supply of the same family can have a switch position that selects between parallel operation and load sharing; the dip-switch setting on the failed unit is what the replacement unit must match or the cabinet will not behave the same on power-up.

For pneumatic cylinders and solenoid valves: the manufacturer name and code are usually on a wrap-around label or laser-etched ring. Festo DSBC and DSNU cylinders share the same body diameter in some strokes but differ in cushioning and end-cap mounting; the etched ring on the collar is the difference.

What the Desk Will Not Do With a Photograph

A sourcing desk earns its reputation less by what it identifies and more by what it refuses to mis-identify. The desk's refusals on photo-based identification are narrow and specific, and the buyer should know them in advance.

The desk will not return a single part number on the basis of a partial code and a generic housing description. The risk of returning a plausible-looking wrong line is higher than the cost of asking for one more photograph. The desk will not back-fit a current-production cross-reference where the original is in an obsolete status on the manufacturer's product lifecycle page, unless the buyer has explicitly asked for the cross-reference and the desk has walked through the 12 axes on the substitution discipline page. The desk will not, in any case, issue an EAC or TR CU declaration, a CE technical file, a SIL/PL qualification statement, or a channel partner certificate on the basis of a photograph. None of those documents attach to a part identified by image alone.

The desk will also not commit to a price, MOQ or lead time on a part that has not been identified. The three figures are quoted per line on the quotation. Issuing them before the line is identified is the single most common way a buyer receives a quotation for a part they did not need.

What the Buyer Should Send in the First Message

A first inquiry that closes in one round is almost always structured the same way. We are not asking for a finished document; we are asking for the same information in five fields, in any language the buyer prefers.

A photograph of the part, well-lit, with the marking area filling at least a third of the frame. Two photographs if there is a second side label.
A photograph of the part in its cabinet position, showing adjacent wiring.
The line of text from the marking that the buyer can read, even partial — "E3Z" plus the first three characters after the dash is more useful than "Omron photoelectric sensor".
The machine make, model and year if known. Cabinet nameplate photographs close many open questions by themselves.
What the buyer is actually trying to do — replace a failed unit one-for-one, source a longer lead-time alternative, or build a small batch of spares for a fleet.

A buyer who sends all five can expect a line-item answer inside the next reply cycle. A buyer who sends only the first is in the right place to be helped, and we will say what additional detail would close the identification. Send the inquiry at /inquiry or with the BOM at /procurement; both routes arrive at the same desk.

Catalog Anchors We Can Quote From Today

The desk's catalog, queried through the published product listing, carries a small number of SKUs that recur in photo-identification inquiries. The following are not a recommendation; they are the rows the desk can quote from when the marking and the photograph confirm a match.

Omron E3ZM-T81 2M, diffuse-reflective photoelectric sensor, NPN output, 2-metre pre-wired cable — a SKU the desk lists as a high-frequency identification target for inquiries that begin "I have an Omron sensor with T81 on the label". The sensor is in current production and the desk treats it as a row that can be quoted on receipt of the photograph. The desk's catalog aiDemandScore places it in the premium candidate band.

Omron E3ZM-T61 2M, diffuse-reflective, PNP output, 2-metre pre-wired cable — the same housing, different output stage. The two are indistinguishable in a photograph unless the marking is fully recovered. The desk treats them as separate lines for quotation and will not substitute one for the other on the buyer's say-so.

Omron E3SLS10XB4, through-beam photoelectric sensor pair, 4-metre range, PNP, M12 connector — a SKU that turns up in inquiries about retro-reflective or through-beam setups where the buyer remembers the E3S prefix but not the rest. The connector type and cable exit are the closing details.

Omron E2C-X1R5AH, inductive proximity sensor, M12 housing, 1.5 mm sensing distance, PNP, pre-wired — a SKU the desk lists as a high-frequency identification target for inquiries that begin "I have an Omron E2C on the bench". The connector type and cable exit are the closing details.

Siemens 6ES7212-1AE40-0XB0, SIMATIC S7-1200 CPU 1212C, DC/DC/DC, 8 DI / 6 DO / 2 AI — a SKU the desk lists as a high-demand CPU module; inquiries about "the small Siemens PLC with eight digital inputs" usually close on the suffix. The desk's catalog aiDemandScore places it in the top band.

Siemens 6ES7211-1AE40-0XB0, SIMATIC S7-1200 CPU 1211C, DC/DC/DC, 6 DI / 4 DO / 2 AI — the smaller CPU in the same family. The two share the front form factor; the suffix is the only reliable identifier.

These rows are quoted against the desk's standard quotation terms. Price, stock availability and delivery terms are confirmed per line on the quotation, and the buyer is asked to confirm the marking on the photograph before the line is committed.

What the Desk Cannot See From a Photograph

Some attributes that matter for a working replacement are simply not visible in a photograph. The desk treats them as unknown and notes them as such on the cross-reference rather than guessing.

Firmware version on a Siemens S7-1200 or S7-1500 module is read from the connected engineering software, not from the module faceplate. Two modules with identical front-face markings can be on different firmware versions and behave differently with the same project. The 12-axis comparison treats the firmware version as unknown unless the buyer can supply it.

Functional safety status on a safety relay, safety PLC or e-stop device is a property of the device's certification, not of its appearance. The desk will not make a SIL/PL claim from a photograph and will not offer a substitute for a safety-rated device on the basis of one.

Service history — whether a part has been refurbished, what bench tests have been run, what warranty period the manufacturer or the desk attaches — is part of the quotation, not of the identification. The condition is stated per line for every line on the quotation; we do not describe a used unit as refurbished and we do not describe a refurbished unit as new. We are an independent sourcing desk for industrial automation parts based in China; we do not represent the manufacturer on warranty, certification or service history, and we are not a direct sales channel for any manufacturer whose part numbers appear in this article.

The buyer's intended end use is part of the screening the desk applies before any quotation is issued. We screen end users and end uses, classify before quoting, and decline transactions that cannot be screened. A buyer who needs a part for an application that cannot be screened receives a decline, not a line-item. The same screening posture applies to buyers in Moscow, the Russian regions, Belarus, Kazakhstan, Uzbekistan and the rest of the CIS: routes are arranged on the quotation and the classification is per order.

What Happens After Identification

Once the part is identified, the desk's work shifts from triage to procurement. The standard flow is the one published on /procurement: the buyer sends a list — one line per part, with quantity and any condition preference — and the desk returns a quotation in which every line carries a part number, a condition, a unit price, a minimum order quantity and a delivery term. Lines that cannot be confirmed are listed with a reason. Lines that are quoted as similar specification or requires redesign carry the substitution-axis notes that the desk would not publish on a partial identification. The quotation is the contract; the photograph is the source of the line; the catalog is the source of the price.

The desk does not promise delivery windows that are not in the quotation. The quotation terms are the contract; nothing else is. Where the buyer needs a quote for a fleet, a standing order or a recurring BOM, the desk routes that through the procurement desk with the same per-line discipline.

Data Notes

"As of September 2026" refers to the publication month of this article and the date the desk's identification workflow statements were last reviewed against /inquiry, /procurement and /compare.
Catalog aiDemandScores cited in this article are the values returned by the desk's internal catalog at the time of writing and are subject to change with each catalog refresh; the score is a relative ranking of demand signals, not a stock, price or lead-time indicator.
Omron and Siemens part numbers are taken from the public Omron and Siemens datasheets for each series; ratings and configurations cited here are the manufacturer's published values at the time of writing.
No external sources were consulted for this article; the workflow described is the desk's own, documented on /inquiry and /procurement.

Verify with your supplier before committing to a replacement, and use this article as one input alongside the original manufacturer datasheet and your own qualification process.

Frequently Asked Questions

What photograph resolution do I need to send?

A modern smart phone at the cabinet, holding the camera about 15 centimetres from the marking area, is usually enough. The image does not need to be sharp across the whole frame; the marking area needs to fill at least a third of the frame and be in focus. Side or back labels should be sent as separate photographs. If the marking is on a curved housing, two photographs at slightly different angles help.

Can you identify a part from a marking that has been laser-etched but is partly worn?

Often yes, but the answer comes with a confidence statement. We will list the candidates that match the recovered characters and ask the buyer to confirm the cable, connector, output configuration or coil voltage before any quotation is issued. The desk does not guess the suffix.

What if I cannot read the marking at all — for example a painted-over contactor?

Send the photograph of the part in the cabinet, with adjacent wiring visible, and the make and model of the host machine. Many panel builders and machine builders keep a parts list inside the cabinet door or in the machine manual. Where the original documentation is unavailable, the desk will list the plausible candidates from the visible housing shape and ask the buyer to measure the mounting, count the contacts and identify the coil voltage by hand before any quotation is issued.

Do you identify parts from old photographs that show the marking clearly?

Yes. A photograph that captures the marking clearly when the part was new is often more useful than a current photograph of a faded housing, because the marking is intact. If the buyer has a commissioning photograph or an inspection report, that goes into the inquiry alongside any current photograph.

Will you identify a part without committing to a quotation?

Yes. Identification and quotation are separate steps. A buyer who wants the desk to identify the part and tell them the family, suffix, and the cross-reference options before deciding whether to source can do so; the identification work is not contingent on a quotation being issued.

What if the part turns out to be something you cannot supply?

The desk will say so on the first reply, with the reason. Common reasons include a part that is in active production and available through manufacturer direct channels at standard lead times, a part that is restricted under export controls and cannot be screened for the intended end use, or a part that is a counterfeit risk that the desk is unwilling to handle. The desk does not invent a substitute line item to keep the inquiry open.

Can you identify a part for which the original manufacturer's part-number lookup no longer resolves?

This is the single most common case the desk handles, and it is where photo-identification does most of its work. The manufacturer's own lookup may have been retired when the part was discontinued, or the part may have been renamed in a family consolidation. The desk's catalog is independent of the manufacturer's current lookup and is queried by part-number prefix. A code that no longer resolves on the manufacturer site often resolves cleanly against the desk's catalog rows that record the legacy order code.