A weight-per-meter control system does one thing: it keeps the material used per meter of cable on the target value. Put the same set of equipment on a fiber optic cable sheathing line, a submarine cable insulation line, a power cable insulation line and an automotive cable extrusion line, however, and the same control accuracy means different things on each. Fiber optic cable worries about a thin sheath being extruded unevenly; submarine cable watches whether the process is still stable after a long run; automotive cable watches how much transition scrap is produced in the few minutes of a construction change. The question, then, is why weight-per-meter control requirements differ between cable products that are all made on extrusion lines.
The answer lies in the product: the scale of the target weight per meter, the acceptance criterion, and how often someone has to intervene. Once those three are settled, there is a basis for deciding how large the hopper should be and how long the recheck interval should be.
What is measured and what is controlled: breaking kg/m into four quantities
Weight per meter here means the weight of material extruded per unit length. What is weighed is the material entering the extruder, not the cable core or the conductor; it is the amount of compound used, not the weight of the whole cable.
Weight per meter, reference wall thickness, wire diameter and material density are interlocked, and the conversion was set out in what a weight-per-meter controller is. A set of shop-floor readings: weight per meter 0.1413 kg/m, reference wall thickness 1.650 mm, wire diameter 17.50 mm, material density 1.42 g/cm³, wall thickness compensation 0.020 mm, screw speed 41.24 rpm, haul-off speed 60.013 m/min, extrusion output 508.70 kg/h, and the interface shows "auto control active".
The acceptance criterion then splits accordingly: fiber optic cable looks at sheath wall thickness and cable diameter, power cable at the insulation layer and sheath, automotive cable at wire diameter accuracy and stability over a small cross-section. The same deviation amplitude, on a thin sheath, has already consumed most of the wall thickness margin; on thick insulation it is still inside tolerance. This is also why the same weight-per-meter control system has to switch parameter sets when it moves to another product line.
Fiber optic cable: thin sheath, small cable diameter, control is about uniformity
The sheath of a fiber optic cable is thin, the cable diameter is small and the target weight per meter is low, with PE and PVC as the main materials. The thin sheath is not for saving material: it has to provide mechanical protection, water blocking and environmental resistance, and once uniformity suffers, the thinnest point fails first. The difficulty is one of scale: with a small target weight per meter, an absolute deviation is a larger proportion of it; with low extrusion output and low screw speed, pulsation in the low-speed section of the screw is more pronounced; with high line speed, a length measurement error is spread over fewer meters.
The control focus is accurate conversion and stability at low speed: cable diameter, wall thickness and density are switched for each construction, and the aim is not fast response but a reading that does not wander. Weight-per-meter control for fiber optic cable is difficult because of thin-wall conversion and low-speed conveying.
Submarine cable: high material throughput, long reel-change cycles, control is about whole-length consistency
Submarine cable is the other extreme: large cross-section, thick wall, high material throughput, long continuous production of a single length and long reel-change cycles; a deviation partway through affects a considerable number of meters. The hopper empties quickly, refilling is frequent, and every refill is a rhythmic disturbance.
Over several hours of continuous running, temperature drift and wear on the screw and barrel accumulate into weight per meter and only become visible in the later part of the run. The control focus is a large hopper and steady refilling: refill intervals must not be so close that they add up to a fluctuation, and the recheck interval and amplitude are tuned to the thermal inertia of the large machine. For the order in which to investigate drift, see troubleshooting weight-per-meter fluctuation.
Power cable: the insulation layer is critical, and eccentricity is the main defect
Here the control target is mainly the insulation layer. Insulation thickness determines electrical strength; extruding thick wastes material, extruding thin leaves insufficient withstand voltage, and the target is not to stay above the lower limit but to run close to the design value. Conductor wire diameter plus insulation thickness gives the insulated diameter, so when the conductor reel changes and the wire diameter changes, the conversion inputs have to be updated.
Weight per meter governs the total material used per unit length, which corresponds to average insulation thickness; it cannot govern eccentricity. Eccentricity is an uneven distribution of material around the circumference: the average thickness passes while one side is thin, and the problem lies in the die head, the die and concentricity. Medium-voltage cable usually has two lines, insulation and sheath; depending on whether single-channel or dual-channel control is configured, the two layers have separate parameter sets.
UHV cable: very large cross-section, very thick insulation, the narrowest process window
UHV cable (ultra-high voltage) magnifies the difficulty: a very large cross-section, very thick insulation and high value per length. Insulation can be tens of millimeters thick; extrusion output, melt pressure and thermal history all enter a narrow window, and a slight difference in temperature or screw condition shows up in weight per meter. One out-of-tolerance event scraps the whole length.
Thick insulation brings lag: after a speed change, the reading moves only when the melt has completed its residence time, and thermal inertia stretches the change further. If the interval is short, the system adds another correction to one that has not yet taken effect; if the amplitude is large, it overshoots the target in a single move. Tuning therefore runs opposite to a small machine: longer intervals and smaller amplitudes; start-up and end-of-run reference values are set separately.
Automotive cable: small cross-section, high line speed, most frequent construction changes
Automotive cable has the fastest rhythm: small cross-section, thin insulation, high line speed, dozens of constructions run in rotation, and several changes a day are normal. What it needs is not steady running but fast changes with little scrap — the transition section is inevitably non-conforming, and its length depends on how fast and how accurately the parameters are switched.
The difficulty is stability at small cross-sections: extrusion output is low, so low-speed screw pulsation is amplified; line speed is high, so one sample covers more meters; an outer diameter deviation directly affects crimping and assembly; the target weight per meter is small, so a wall thickness compensation of a few hundredths of a millimeter is a larger proportion. The control focus is "spec check", low-speed stability and material usage statistics per reel. More than half the competitiveness of automotive cable extrusion lies in those few minutes of a construction change.
Five product types in one table
| Cable type | Main control parameter | Control difficulty | Focus |
|---|---|---|---|
| Fiber optic cable | Sheath wall thickness and cable diameter | Small target value and thin wall, so the deviation is a large proportion | Accurate conversion, steady reading |
| Submarine cable | Insulation or sheath thickness, whole-length consistency | High extrusion output, frequent refilling, long continuous runs | Large hopper, refill disturbance, long-cycle drift |
| Power cable | Average insulation layer thickness | Eccentricity, conductor wire diameter variation, different parameters for the two channels | Average thickness close to the design value, dual-channel sets |
| UHV cable | Thickness stability of very thick insulation | High thermal inertia, narrow window, high cost per length | Longer intervals, smaller amplitudes |
| Automotive cable | Wire diameter accuracy and weight per meter at small cross-section | High line speed, frequent construction changes, transition scrap | Efficient spec check, low-speed stability |
There are four common points: the observed quantity is material used per unit length; the conversion interlocks weight per meter, wall thickness, wire diameter and density; a construction change switches the parameter set and performs "spec check" before entering auto; and data must be retained. The differences are in scale and rhythm: target weight per meter varies widely, while line speed and construction-change frequency run in opposite directions. The general part of cable weight-per-meter control lies at this level; the product-specific part lies in the parameters and tuning.
Why one system has to suit different products
The general part is genuinely general: the computing core is the same conversion and the same closed loop; what changes are the external conditions — the hopper follows extrusion output, the range follows the hopper, and the parameter set follows the product. Hopper volume is divided into five steps from 7–60 L, corresponding to NHY-M-7L, NHY-M-22L, NHY-M-48L, NHY-M-52L and NHY-M-60L; small-cross-section lines use a small hopper, which makes material changes and cleaning quick and keeps construction-change losses low, while large-cross-section lines use a large hopper, which lengthens the refill interval. The weighing unit range is divided into steps by model, and the correspondence is set out in full in technical specifications.
For a weight-per-meter control system, a construction change is the same sequence of actions: switch the parameter set, check weight per meter and wall thickness, apply wall thickness compensation, and carry out "spec check"; only after confirmation does the system enter "auto control active". "Wall thickness compensation" deals with a fixed conversion offset; "material usage statistics" record the weight, length and change time of each reel; the recheck interval and amplitude are tuned by machine model under "parameter settings". Weight per meter, screw speed, haul-off speed and extrusion output must be aligned on the same time axis, and the complete system is described in products and systems. The working temperature is −10 to +50 °C, humidity ≤ 90% R.H. non-condensing, power supply AC 220 V and power consumption about 50 W.
What to ask when selecting by cable type
When selecting a weight-per-meter control system, the questions have to land on the specific product.
- Target weight-per-meter scale and maximum extrusion output. These determine the hopper, the range step and the refill interval; use a 7 L hopper at a high extrusion output and refilling becomes so frequent that the intervals add up to a fluctuation.
- Which layer the acceptance criterion applies to. Fiber optic cable looks at sheath wall thickness and cable diameter, power cable at average insulation thickness, automotive cable at wire diameter accuracy; different criteria also mean different acceptance methods.
- Construction-change frequency and duration. If changes happen several times a day, check whether the operator can complete the switch and "spec check" independently; if they happen every few months, check whether the baseline values are complete.
- Whether two channels are needed. Whether the insulation and sheath lines are configured for single-channel or dual-channel control, and whether the two layers can each have their own parameter set.
- Who maintains the conversion inputs. Cable diameter, wall thickness, density and conductor wire diameter change with every reel; who enters them, and whether a wrong entry raises an alarm, affects use more than the algorithm does.
Only after these five questions should accuracy definitions and line interfaces be discussed; the questions to ask when selecting a model has a more detailed checklist.
Frequently asked questions
Can fiber optic cable and submarine cable use the same weight-per-meter control system?
Yes, but not the same hopper model or the same set of tuning parameters. Fiber optic cable uses a small hopper, submarine cable a large one; the recheck interval and amplitude are tuned to extrusion output and thermal inertia. The control logic and conversion core are the same; the differences are in the hardware step and the parameter set.
Can weight-per-meter control solve insulation eccentricity?
No. The weight-per-meter control system governs the total material used per unit length, which corresponds to average insulation thickness; eccentricity is the distribution of material around the circumference, and the problem lies in the die head, the die and concentricity. An average thickness that passes while the thinnest point is undersized is eccentricity; lowering weight per meter does not help and only makes the average thickness thinner.
How small a hopper should a small-cross-section product use?
A weight-per-meter control system selects the hopper by extrusion output. A small hopper cleans quickly and keeps construction-change losses low, at the cost of a shorter refill interval; the criterion is whether the refill interval can be long enough not to create a superimposed disturbance, not that bigger is always steadier.
Want to apply this to your line?
Describe your product construction, machine model and the problem you are seeing — we can give you a more specific assessment.
Contact us