Profile projectors and optical comparators: catalogue the measurement kit
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A profile projector or optical comparator should be sold as an identified measurement kit. The screen size alone tells only part of the story. Included lenses, stage movement, illumination, readout and accessories affect what the buyer is actually receiving.
Start by finding the model and serial number. Then identify each supplied lens and accessory. A fitted lens and three unidentified cases do not make a verified four-lens package.
Magnification changes the view
Higher magnification makes the projected image larger while reducing the field visible on the screen. Mitutoyo's profile-projector terminology guide gives the relationship as screen diameter divided by lens magnification.
For a hypothetical 500 mm screen:
- With a 10× lens, the calculated field diameter is 500 ÷ 10 = 50 mm.
- With a 20× lens, it is 500 ÷ 20 = 25 mm.
This illustrates why the lens list matters. It does not establish the usable measuring envelope of a particular projector. Stage movement, workpiece arrangement, working distance and the manufacturer's limits also need checking.
Use the manufacturer's terminology when recording image orientation and illumination. Do not assume that two projectors with the same screen diameter offer the same arrangement.
Make the accessory inventory match the machine
Keep the following information together rather than spreading it across a catalogue photograph and several boxes.
| Item | What to record | Matching evidence |
|---|---|---|
| Base projector | Make, model and serial number | Plate and relevant manual |
| Projection lenses | Marked magnification and identifying details | Manufacturer compatibility information |
| Screen | Size and documented type | Model-specific specification |
| Work stage | Documented travel and supplied fixtures | Matching specification and inventory |
| Readout or processor | Make, model, included cables and known function | Manual and service evidence |
| Illumination accessories | Identified supplied components | Relevant parts or accessory record |
| Reference scales or artefacts | Identity and condition | Their own reports where available |
| Covers and cases | Item association | Photographic inventory |
Do not place an accessory in the “fits” category merely because it was found nearby. If several inspection machines are leaving, compare their inventories before allocating the loose kit.
The gauge blocks, micrometers and gauges guide helps keep smaller measurement sets complete. If the report leaves an important condition question unanswered, use the specialist assessment brief to define the question for a suitable metrology provider.
Read the calibration evidence, not just the sticker
Match the report to the serial number. Record its date, scope, results and qualifications. Check whether it covers the supplied configuration or only a particular part of the system.
Mitutoyo's terminology guide distinguishes magnification accuracy from measuring accuracy. A listing should preserve that distinction. Likewise, a readout's displayed resolution is not a guarantee that the whole used instrument measures to that accuracy.
UKAS's metrology information explains the role of accredited measurement services. If a report is described as accredited, verify the relevant provider and scope. The presence of a recognised name on another document in the folder is not enough.
Where evidence is missing, say which evidence is missing. “Calibration report unavailable” is clearer than “calibration unknown”, which can leave the buyer uncertain whether the instrument or only its paperwork is in question.
Prepare for a sensible valuation enquiry
Retain dated photographs of the screen, stage, lens markings, readout and included accessories. Describe visible damage neutrally. Leave cleaning, optical adjustment and functional assessment to competent people following the relevant guidance.
The CMM guide covers a different measurement system with its own software and relocation dependencies. For torque wrenches in the same department, the calibration-certificate guide explains why each tool needs its own evidence.
Send the projector inventory and report details to UK Auction Group for a valuation discussion. The buyer should be able to tell which kit is included and which questions still need a metrology specialist.
More related topics are in the engineering and CNC hub.
Sources
This guide gives general information. Equipment-specific, legal, tax and safety decisions may need a qualified adviser or competent specialist. The guides do not promise sale prices, fees or results.