Below is a tailored evaluation guide you can use when inspecting a Starrett HDV horizontal digital video comparator (e.g. “HDV400-M3-2LED” style) in used / surplus condition. Because video comparators are precision metrology instruments (not “machines” in the machining-tool sense), the inspection emphasis shifts more toward optical, electronic, calibration, and environmental checks—alongside mechanical motions and structural integrity.

I cover:

1. What the HDV / digital video comparator is and key specifications
2. Major risk & wear points to check
3. Step-by-step inspection & test procedure
4. Decision criteria & red flags
5. Suggestions for negotiation leverage

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1. What Is the Starrett HDV / Digital Video Comparator & Key Specs You Should Know

This type of instrument blends the features of a horizontal optical comparator with a video / vision system. It projects, magnifies, images, and measures parts using optics + camera + software. The HDV series is a well-known example.

Key known / advertised specs for the HDV-400 / similar models you should validate:

Parameter	HDV-400 Typical Value	Comments / Source
Stage travel (X × Y)	400 mm × 150 mm (16″ × 6″)
Resolution / Scale	0.5 µm (0.00002″) via Heidenhain glass scales
Accuracy (X-Y)	E1 = 3.0 µm + L/33 (where L is measurement length)
Camera / Video System	5 megapixel digital camera, telecentric lens options, video edge detection (VED) capability
Illumination	LED surface and profile illumination, optional transmitted lighting, etc.
Focus Travel	Approximately 51 mm (2″) focus range
Load / Weight on Stage	Typically ~ 50 kg (110 lbs) maximum load
Optical Distortion	Very low distortion tolerances, ~0.001% in telecentric field of view

Because your specific unit is “HDV400-M3-2LED,” you should also verify:

• That the MetLogix M3 software is installed and operational
• That the 2 LED illuminations are working (surface LED, profile LED)
• That the camera, lenses, and telecentric modules are intact and not scratched / misaligned
• That the scale / encoder system (likely glass linear scales) is intact and functional

These spec values form your “target envelope.” Any deviations you measure (± drift, scale errors far outside tolerance) should raise concern.

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2. Major Wear / Risk Areas to Focus On

Because video comparators are optical-mechanical-electronic hybrids, the likely failure or degradation points include:

• Optical path & lenses — scratches, dust, alignment drift
• Camera sensor — dead pixels, sensor degradation, color balance drift
• Illumination system — LED aging, uneven brightness, flicker
• Linear scales / glass encoders — scale damage, contamination, misalignment
• Stage mechanics (X, Y, focus / Z) — backlash, stiction, wear in guides
• Electronics / controllers / software — corruption, board damage, failed components
• Calibration / reference standards — missing or invalid calibration records
• Environmental sensitivity — vibration, temperature drift, cleanliness affecting performance

Because optical and video systems are delicate, even small misalignments can degrade measurement accuracy severely.

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3. Step-by-Step Inspection / Test Procedure

Here’s an ordered checklist for when you inspect a used HDV / video comparator:

A. Pre-Inspection / Documentation Request

Before going onsite:

• Request system serial numbers, model plate photos, and specifications sheet
• Ask for calibration history / certificate, last calibration date, drift records
• Request the software version, backup of configuration / measurement programs
• Ask for photos/videos of the unit in operation
• Ask which lenses, camera modules, illumination modules are installed
• Ask for maintenance / repair logs (electronics, optics, stage service)
• Ask why the unit is being sold

If the seller can’t provide calibration records, that’s a red flag but not necessarily deal-killer (provided you can recalibrate afterward).

B. Structural / Mechanical Inspection

• Check the frame, base, optical housing for cracks, warping, damage
• Inspect protective covers, lens covers, dust seals, bellows
• Examine for signs of collisions, knocks around the optical path or stage
• Check that mounting and alignment mechanisms are intact

C. Stage / Motion & Scale / Backlash Tests

• Manually (or via motorized move at slow speed) move the X, Y stage through full travel — smoothness is key
• Place a calibrated reference gauge or precision grid and move stage; watch for jumps, slippage
• Use a dial indicator or high-precision probe to measure backlash / lost motion in X and Y (push-pull test)
• Reverse direction and check for hysteresis / deadband
• Check the focus (Z or lens movement) axis for smooth motion and backlash
• Use a known calibration grid / stage micrometer to check scale accuracy across travel

D. Optical / Video / Imaging Tests

• Inspect lenses and optics visually — look for scratches, dust, haze, fungus
• Turn on illumination (surface / profile / transmitted) and check uniformity, brightness, absence of flicker
• Capture static test images and check for artifacts, noise, dead pixels
• Use a calibrated grid or precision artifact to test distortion, linearity, edge detection precision
• Import a CAD / DXF overlay and test video edge detection (VED) to see if software alignment works properly
• Test magnification switching or lens changes (if dual-lens mount) for alignment consistency

E. Electronics / Control / Software Review

• Open electronics / control enclosure: inspect wiring, PCBs, connectors, power supplies for damage, heat marks, solder issues
• Boot up software / control: check that the software launches without errors, configuration loads
• Verify that the MetLogix M3 (or equivalent) software features (edge detection, CAD overlay, measurement routines) operate correctly
• Check logs / error history if available
• Test measurement routines (you might run a simple test program) to confirm repeatability

F. Calibration & Drift / Repeatability Tests

• Perform a repeatability test: measure the same feature multiple times, retract stage, re-measure — compute standard deviation
• Perform reversal / backlash verification: move to point, retract, return, measure deviation
• Measure at multiple positions across the field to check scale linearity / distortion
• After running for some time (warm-up), re-check calibration to see drift
• If possible, compare known, certified reference standards before/after to quantify error and stability

G. Environmental / Practical Checks

• Measure ambient temperature, humidity — compare to known tolerances for optical metrology
• Check vibration or shock in the floor area (is the comparator in a stable, low-vibration area?)
• Inspect power supply stability (voltage fluctuations, grounding)
• Confirm that spare optics, lenses, camera modules are available or included
• Check for mechanical cleanliness (no dust, foreign particles) around optical surfaces

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4. Decision Criteria & Red Flags

Here’s how to interpret your findings and decide whether or not to acquire the unit (or negotiate heavily).

Good / Acceptable Indicators:

• Stage motion is smooth, backlash minimal, linear scales read correctly
• Optical path is clean (no haze, dust, lens damage) and image quality is crisp
• Illumination works uniformly, no flicker or dead zones
• Camera and software (MetLogix M3) run properly, edge detection and overlays function
• Calibration checks show error within acceptable tolerance (e.g. less than a few µm over travel)
• Repeatability test has low standard deviation (< a few microns)
• Equipment has calibration records or certificates
• Spare optics / modules are included or available
• Enclosure / housing is intact, no damage or signs of abuse

Red Flags / Deal-Breakers:

• Cracked, scratched, or hazed lenses / optics
• Major drift or inconsistent calibration across the field
• Dead pixels, noise, or artifacts in imaging
• Stage motion is jerky, binding, or inconsistent
• Large backlash or subjectivity in motion
• Edge detection or overlay routines do not match or are unreliable
• No calibration history, or last calibration many years ago with no record
• Burned or damaged electronics / PCBs, corrupted software, failed power supplies
• Missing or proprietary optics that are extremely expensive or obsolete
• Environmental vulnerability (vibration, temperature instability)
• Seller refuses imaging tests, calibration verification, or access to software

Use any defects or degradation you see as negotiation leverage: demand discount, spare modules, recalibration service, or partial refund if performance doesn’t meet specs after installation.