Panel Meters for Rate, Totalizer with Functions A+B, A-B, AxB, A/B, A/B-1 Applications P/N L7000FFR

Ratio & Draw Panel Meter Frequently Asked Questions

Does this meter's arithmetic capability include A×B, or only A+B, A-B, A/B, and A/B-1?

Only A+B, A-B, A/B, and A/B-1 are documented as available on this specific meter configuration — A×B is not part of this product's function set, so an application specifically requiring a multiplication function (such as computing power from voltage and current) would need a different meter configuration.

What's the mathematical relationship between ratio and draw, and why does draw subtract exactly 1?

Draw is defined as A/B minus 1, which specifically expresses the ratio as a deviation from perfect 1:1 matching rather than as the raw ratio itself — a draw reading of 0 means A and B are running at exactly the same rate, a positive draw means A is running faster than B (elongation), and a negative draw means A is running slower (relaxation), which is a more directly useful number for tension and elongation control than the raw ratio would be.

Why does six-digit resolution matter specifically for draw measurement, more than for other functions?

Draw values in real elongation control applications are often very small percentages (a fraction of a percent difference between two closely matched roller speeds) — subtracting 1 from a ratio very close to 1.000000 leaves very little numeric "room," so the meter's six-digit resolution is specifically what allows a small, meaningful draw value to be resolved and displayed with useful precision rather than being lost in rounding.

Can the A/B ratio be applied to totalized volumes as well as instantaneous rates?

Yes — this is specifically documented for the fluid mixing application, where the A/B ratio can be displayed for totalized rate (delivered volume) in addition to instantaneous flow rate, letting an operator verify that the cumulative ratio of two ingredients delivered over an entire batch matches the target, not just the ratio at any single instant.

What does the 0.00001 to 100000 multiplier range on the ratio/draw result actually let me do?

This is a very wide scaling range specifically intended to bring the computed ratio or draw value into whatever display precision and engineering units are meaningful for the application — since raw ratios near 1.0 and draw values near 0 need very different scaling than, say, a mixing ratio deliberately set at 3:1, this multiplier lets the same underlying A/B calculation be displayed usefully across a very broad range of real-world ratio magnitudes.

Does the net inflow/outflow (A-B) application require both flow sensors to be identical in type and scale factor?

The documented application doesn't specify that they must be identical in sensor type, only that each channel be independently scaled to true engineering flow units before the subtraction — as long as both channels are correctly and independently scaled to the same engineering units (such as gallons/minute), A and B can come from different sensor types entirely.

Can the A/B ratio for coating thickness control be alarmed to catch a thickness deviation automatically?

Yes — this is specifically documented in the coating thickness application: displaying and alarming the A/B ratio (coating rate versus film speed) is how the system assures even coating thickness is maintained as film speed varies, using the meter's relay outputs to flag or act on a ratio deviation rather than requiring constant manual monitoring.

Why is Channel B's frequency ceiling (250 kHz) lower than Channel A's (1 MHz), and does that matter for ratio/draw applications?

This reflects a real hardware asymmetry between the two channels — for ratio/draw applications where both signals are expected to be reasonably close to each other in frequency (as in matched roller speeds or synchronized conveyors), this asymmetry rarely matters in practice, but it's worth confirming neither expected signal genuinely needs to exceed 250 kHz if it happens to be applied to Channel B.

Does the meter update the ratio/draw calculation at the same rate as a simple single-channel rate reading?

Update rate is tied to the same gate-time mechanism used for basic rate measurement, reaching up to 25 readings/second at the minimum 10 ms gate time — since the ratio/draw calculation is performed on the already-measured rates from both channels, it doesn't introduce meaningfully additional lag beyond the underlying channel measurement rate itself.

Can this meter's A/B ratio function be used for something other than flow or speed, like comparing two frequency-output sensors of a different kind entirely?

Yes — the underlying A/B calculation simply operates on whatever two scaled rates are present on Channels A and B, regardless of the physical quantity each channel's sensor actually measures. While the documented applications are flow, speed, and coating rate, the same

Web Tension & Draw Control Questions From the Field

What's the actual difference between "draw" and "tension" in a web handling process?

Documented converting industry terminology draws a clear distinction: draw is an equipment parameter defined by the velocity of the driven rollers (a speed relationship), while tension is a web property related to strain — the actual elongation of the material from its unloaded condition. Draw is what a speed-ratio meter like this one directly measures and controls; tension is the physical consequence that draw is being used to influence.

Is speed-ratio (draw) control considered a reliable way to control actual web tension, or is it just an approximation?

Documented industry guidance describes draw control as a legitimate and commonly used method specifically for situations where direct tension feedback (load cells or a dancer) isn't practical — such as closely spaced, high-wrap-angle driven rollers with no room for tension feedback hardware — but also notes that open-loop draw-based systems generally can't fully compensate for factors like speed changes, temperature, humidity, or web non-uniformity the way direct tension measurement can.

Why does "negative draw" make operators nervous, and is that concern actually justified?

Documented industry discussion specifically addresses this: negative draw (driving a downstream roller slightly slower than an upstream one) intuitively sounds like it should cause material to pile up, but documented analysis shows this isn't necessarily the case — if the incoming web already carries some elongation from tension, a small negative draw simply relaxes that elongation to a lower tension without necessarily causing slack, provided the negative draw doesn't exceed the web's existing strain.

Does a small tension swing actually translate into a meaningful thickness or coating variation in the final product?

Yes, and this relationship is specifically documented and quantified: a web tensioned to 1% elongation experiencing a 20% tension swing corresponds to roughly a 0.2% effective speed change at the coating point, which directly shows up as coating thickness variation in the final product — illustrating why draw and tension consistency matters even when the absolute magnitude of the swing seems small.

What accuracy can I realistically expect from open-loop, torque-based tension control compared to draw-ratio control?

Documented industry benchmarks specifically state that open-loop torque-based tension control (used in center-wind unwind/rewind zones) achieves accuracy in the range of ±10% at best — draw-ratio control between driven rollers is documented as a separate, commonly used approach for internal process zones where the web's own elasticity and the zone length permit establishing tension via speed differential rather than direct torque control.

In a multi-zone converting line, does draw control apply uniformly across the whole line, or only in specific sections?

Documented practice specifically describes most production converting lines as using closed-loop control (torque or tension-feedback based) on the unwind and rewind zones specifically, while using speed-ratio (draw) control across the internal process section between them — meaning draw control and direct tension feedback typically coexist on the same line, each applied where it's best suited.

What real physical process is draw control specifically well suited for, beyond simple line synchronization?

Documented converting applications specifically cite film machine-direction orientation (MDO) — where controlled stretching via a speed ratio between rollers is used to intentionally create desired material properties or thickness by a set percentage change in the web's length — as a process where draw control is directly the mechanism producing the desired product characteristic, not just a way of avoiding slack or tension spikes.

Does draw control require constant retuning as roll diameters change during unwind or rewind, the way torque-based tension control does?

Documented guidance distinguishes these cases specifically: torque-based control in center-wind zones must continuously adjust as roll diameter changes throughout a run (torque decreasing linearly as an unwind roll shrinks, or increasing as a rewind roll grows), while draw control between fixed-diameter driven rollers in the internal process section doesn't have this same diameter-dependent complication, since the rollers themselves aren't changing size during the run.