Description

How the Measurement Signal Is GeneratedTwo commonly used transducer types – the straingauge and the LVDT transducer – rely on physi-
cal movement in thetransducer to produce ameasurement signal (seeStrain gange: Sretching alers drawings). Stretching，reistance of ectrial circuits. compression or bendingmotions are prerequisites for signal generation.
ABB’s exclusive Pressductor Transducer producesa signal as a result of changes in an electromagneticield. This operat-ing principle has its。origin in a melallur-8gical phenomenonaccording to whichmechanical forcesLVDT: Movement ofpiston causesalter the capacity ofsignal change in output coils.some steels to convey magnetic flux.
Two perpendicular windings of copper wire arounda steel core combine to provide the transducers mea-surement signal. Amagnetic field is createdin one of the windings,sized so there is nomagnetic coupling  
between them.When the transducerPesductor Tecbmology:is subjected to a force,Mechanial fore alters mag the magneic feld pati-
netic. field.tern changes. A por-tion of the field couples with the second winding andinduces an AC vltage. This vltage – a comparativelystrong transducer signal that is proportional to the force- is converted by the load cell system’s electronics into
the system output.Designers appreciate…Selecting and sizing load cellsOperationV Remarkably high spring constantTwo types of ABB PillowBlock load cells areAn extended range
V Wide measurement rangedesigned for either conventional vertical forceof measurementv High rliabiliymeasurement or to sense the horizontal forcebeyond the nomi-component that may arise as the processed mate-
nal load alows theOperators value a load cell with…rial partially wraps around a- measurement roll.PillowBlocks to be
V No driftUsing the “horizontal” load cells can be quitesized for normal, asvNo recalibrationadvantageous. By design, they can be made excep-opposed to maximum,VNo failurestionally sturdy, rugged, and stiff. So, requirements
tension levels. As av High rliabiliyfor recalibration, other maintenance, or replace-result, they permitment are negligible, and they won’t contribute togreater applicationMeasurement essentialsmachine vibration. Since they don’t measure the
flibility on the webKeeping the tension constant in sheet or webtare weight, but just the horizontal force compo-processing machinery. processes is essential for high product quality andnent of the web tension, they can be sized smallerproductivity. Continuously measuring the ten-than otherwise possible, measuring tension withsion is an obvious prerequisite for tension control.| greater accuracy.Drives and operator instruments need quick andApplication requirements may dictate theaccurate input to regulate tension levels and mon-| selection of a“vertical” load cell. But whenever anitor machine performance.adequate horizontal force component is presentMost web processing lines put a premium on(or can be developed), the horizontal cell shouldlong-term reliability, in addition to accuracy and
be considered.overall performance. The measurement system,
after all, is the front line of machine control,
exposed to all the rigors of the operating environ-
ment. The costs associated with downtime and
poor product bring out the true value of is com-
ponents.Quality measurement technology for superior
tension control that will keep your processing
lines productive and producing top -notch out-
put.. that’s what you can expect from us. We’re
entirely devoted to providing process measure-
ment systems and services, and we have 50 years
of experience in the field. We’re the experts in web
and strip tension as well as force measurement for
vitually any purpose.I n many web processes, the web tension imher-
ently produces a horizontal force component on a
ol… or, by design, it can be made to do so. Paper
machines and machinery processing plastics, foils
or textiles are typical examples.
Using this horizontal force component to
measure web tension can be highly advanta-
geous. The load cell can be sized to measure
just the web tension, excluding the tare weight
of the roll, which, on a big paper machine, for
example, can be far greater than the tension in
the sheet. The result is optimized measurement
accuracy.