Inline Diameter Gauging for Wire, Cable and Tube

Wire, cable and tube are the classic case for continuous diameter measurement: the product is long, it moves fast, and diameter drift is a defect you want to catch while the line is still running rather than from a reel that has already been wound. A transmitted-light gauge reads the shadow the product casts and reports diameter continuously. This page covers the range that a gauge such as the POMEAS LM-1030 covers, how to think about sampling rate against line speed, and the three limits that catch buyers out — ovality, transparent stock and pass-line wander.

The Range Window

The LM-1030 published measuring range is 0.3 mm to 30 mm, with a minimum detectable object of 0.3 mm. In practice that spans fine wire and filament at the bottom, through cable core and small tube, to larger hose and conduit at the top. Below 0.3 mm the shadow is too small relative to the receiver's pixel pitch to resolve reliably. Above 30 mm the product no longer fits the measurement window, and the answer is a larger-window instrument rather than a stretched installation — the principle options are compared in inline diameter measurement methods.

Sampling Rate Against Line Speed

The LM-1030 is published at 2400 samples per second. What that buys you is spatial resolution along the length: at 2400 samples per second and a line speed of 2 metres per second, one sample arrives every 0.83 mm of product. At 10 metres per second, one sample every 4.2 mm. Whether that is enough depends on the shortest defect length you need to catch — a short neck-down needs finer spacing than a gradual taper. Do this division before you buy, not after.

There is a second reason the sampling behaviour matters here. The gauge integrates continuously during exposure, so each reported value is an average over the exposure window rather than an instantaneous sample. A swept laser-scan gauge cannot see what happens between successive sweeps; this design does not have that blind interval. For a product with brief, intermittent diameter excursions — the failure mode that sampling at a bench tends to miss — that difference is the whole point.

Limit 1: Ovality Is Not Diameter

A single-axis projection gauge reads one diameter, along one direction, at one instant. If the product is oval and rotates as it travels, the reading will oscillate between the major and minor axis, and that oscillation is real information — but it is not the same as a roundness measurement, and a control plan that treats it as diameter will generate false calls. Options are to control rotation, to measure two axes at once with a multi-axis arrangement, or to accept diameter as a band. The distinction is set out in more depth in measuring shaft outer diameter.

Limit 2: Transparent and Translucent Stock

Transmitted-light gauging depends on a clean shadow. Clear tube, translucent hose and thin-walled transparent conduit do not reliably produce one — light passes through and refracts at the walls, and the apparent edge moves. This is a physical limit of the principle, not a specification shortfall. The workarounds and the alternative principles are covered in inline measurement of transparent and reflective parts. Confirm on your own material before committing to a projection gauge for clear product.

Limit 3: Pass-Line Wander and Swing

The product must cross the beam inside the measurement window. On a wire or cable line, swing and whip are normal, and if the product wanders laterally beyond the window the reading changes without the diameter changing. The transmitter-to-receiver distance for the LM-1030 is 160 ± 40 mm, which fixes the mounting geometry; the fixturing that holds the product inside the beam is part of the installation. Note that the HM series heads are stated to measure swing during rotation and workpiece position coordinates, which turns that wander into a measurable quantity on those models.

What Continuous Data Lets You Do

The value of gauging 100% rather than sampling is not primarily that you catch bad product — it is that you see drift early. A diameter trend that develops over twenty minutes points at a die, a screw or a temperature, and catching it there costs minutes of output rather than a scrapped reel. Planning what to do with that data, and how often a reading is needed to make it useful, is part of the cycle time and station count exercise.

When Offline Sampling Is Still the Better Answer

If the process is stable, the failure mode is gradual, and the product is not high-value, sampling at a bench may give equivalent control at lower capital and much easier calibration. Continuous gauging earns its cost when escape is expensive or when the process is genuinely unstable. The decision is worked through in inline versus offline optical measurement.

FAQ

What diameter range can be gauged inline?

The POMEAS LM-1030 publishes 0.3 mm to 30 mm with a minimum detectable object of 0.3 mm. Fine wire sits at the bottom of that window; larger conduit needs a wider-window instrument.

How many samples per second do I need?

Derive it from the shortest defect you must catch. At 2400 samples per second, a line running at 2 m/s gives one sample every 0.83 mm of product; at 10 m/s, one every 4.2 mm. If the defect you are hunting is shorter than that spacing, this rate is not enough.

Will it catch a brief neck-down in the product?

Better than a swept laser scan, because the gauge integrates continuously during exposure and has no blind interval between sweeps. Whether it resolves your specific neck-down still depends on the sample spacing calculation above.

Can it measure ovality?

Not from a single axis. Ovality shows up as an oscillating diameter if the product rotates, which is real data but not a roundness measurement. Control rotation or use a multi-axis arrangement if ovality is the tolerance you hold.

Does it work on clear tubing?

Not reliably. Transmitted light needs a clean shadow and transparent or translucent stock refracts rather than blocking. Test your own material before specifying, and see the dedicated page on transparent and reflective parts.

How far apart do the heads mount?

160 ± 40 mm for the LM-1030. That fixes the mounting geometry; fixturing the product inside the beam is a separate part of the installation.

What is the enclosure rating?

IP64 — protected against dust ingress and water splashing. It is not a washdown or immersion rating, so confirm against your cleaning regime.

Next Step

Send the product diameter range, line speed, material and the tolerance you have to hold, and we can confirm whether a transmitted-light gauge such as the LM-1030 covers the job. If your product is larger than 30 mm or needs full geometry rather than diameter, the HM series heads or a bench system such as IMAGE 3 may fit better.