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Glossary

A

Absolute Pressure

The pressure measured using an ideal vacuum as a zero reference point.
Accuracy

The combined error due to nonlinearity, nonrepeatability, and hysteresis expressed as a percentage of full scale output.
Adaptive Tuning
A self-tuning function that continuously monitors the dynamics of a process and makes adjustments to the control parameters to maintain a pre-determined setpoint.
Adaptive-Tune
Dynisco`s continuous self-tuning algorithm based on the dominant poles theory. Available only in the Automatic mode of operation.
Agency Approval
Certification of conformity to the requirements of various independent testing agencies such as Underwriters Laboratories or the Canadian Standards Association.
Alarm
A point in a process if the value increases above (high alarm) or decreases below (low alarm), causes an action by an indicator or controller.
Alloy
Polymer blend having a modified interface and/or morpholog
Ambient Conditions
The condition(s) around the transducer (pressure, temperature, etc).
Ambient Pressure
The pressure of the medium surrounding the transducer.
Ambient Temperature
The average or mean temperature of the surrounding air which comes in contact with the equipment and instrument under test.
Amorpheus Polymer
A polymer having no crystallinity.
Amplifier
An electronic device which boots or increases a small signal to a higher level, usually for transmission, scale convenience, or noise immunity.
Analog Output
A voltage or current signal that is a continuous function of the measured parameter.
Anisotrophy
The situation where properties vary according to the direction in which they are measured.
ANSI

American National Standards Institute.
Apparent Shear Rate
The shear rate determined in capillary viscometers without making a Rabinowitsch correction for shear thinning.
Apparent Viscosity
The viscosity determined in capillary viscometry without making a Rabinowitsch correction for shear thinning.
ASTM

Abbreviation of American Society for Testing and Materials, an association for establishing standard testing and reporting procedures.
Auto/Manual Station

The controller function that allows the operator to select the Automatic or Manual control mode. In the automatic control algorithm the controller determines the control output. In the Manual mode, the operator determines the control output.

B

Back-Pressure

The resistance that reduces forward flow in an extruder.
Background Noise

The total noise from all sources of interference in a measurement system independent of the presence of a data signal.
Bagley Correction

A term used in capillary viscometry to describe the excess pressure drop in the entrance to the capillary due to extensional viscosity.
Boiling Point

The temperature at which a substance in the liquid state transforms to the gaseous state (commonly refers to the boiling point of water (100°C (212°F) at sea level).
Branched Polymers

Branched polymers have side chains attached to the molecular chain backbone.
Breakdown Voltage Rating
The AC or DC voltage, which can be applied across the insulation portion of a transducer without arcing or conduction above a specific current value.
BTU: British Thermal Unit

The quantity of thermal energy required to rise one pound of water 1°F at or near its maximum density (39.1°F) (1055J).
Burst Pressure

The maximum pressure applied to a transducer sensing element or case without causing leakage.

C

Calibration Cycle

Pressure calibration in both a descending and ascending mode.
Calibration

(1)A test during which known values of pressure are applied to the transducer and corresponding output readings are recorded under specified conditions.
(2)The matching of a pressure controller or indicator to the characteristics of a specific transducer. Most frequently done utilizing span resistor internal to the pressure transducer. Procedure is termed RCal.
(3)Adjustment of an instrument to standards of known accuracy and stability.
Capillary Rheometer

An instrument used to measure polymer melt viscosity. It consists of a heated reservoir used to melt the polymer, which is pushed by a piston and flows through a 1 to 2 millimeter diameter round die. Using the force required to move the piston and the corresponding volumetric flow rate, the viscosity can be determined. The Rabinowitsch correction is used to account for shear thinning effects while the Bagley correction is used to account for the excess pressure drop at the die entrance.
Carreau Model

A mathematical expression describing the shear thinning behavior of polymers. It is more realistic than the power-law model because it fits the data very well at both high and low shear rates. It is excellent for numerical simulations of flow processes.
Catalyst

A substance that changes the rate of a chemical reaction without itself undergoing a permanent change or becoming part of the molecular composition of the product.
Co-extrusion

The process used to form a multilayer structure from two or more polymers.
Coefficient of Friction

A measure of the resistance to sliding of one surface in contact with another.
Cogswell's Method

An approximate method for extensional viscosity measurement.
Commodity Resins
High-volume, low-priced resins like polyethylene, polypropylene, styrene, acrylic, or vinyl.
Compensation

The addition of specific material or device(s) to counteract a known error.
Compounding

The combination of polymers with other materials either by means of mechanical or dry blending or melt state blending.
Cone and Plate Instrument

A device to measure viscosity by determining the torque necessary to rotate a cone over a flat plate with molten polymer in between. The device can also be used to determine the (first) normal stress difference by measuring the normal force tending to separate the cone from the plate surface.
Configuration

Selection from menus, and switches or jumpers, those options on an instrument to be used in a specific process.
Consistency Index

In the power-law viscosity model which describes the reduction of viscosity as the shear rate increases (shear thinning), m is the consistency index which is a function of temperature. This corresponds to the value of the viscosity for shear rate.
Control Output

The output signal from a controller to the manipulated variable in response to input signals from the controlled variable. (See direct acting; reverse acting).
Controlled Variable
A process variable which is to be controlled at some desired value by means of error; i.e. cold junction compensation for thermocouples.
Controller
A device which manipulates one process variable (RPM, Heat, etc.) to result in a stable condition of a second (controlled) variable (pressure, temperature, etc).
Copolymer

Two monomers polymerized together to form a polymer.
Cross Model
A mathematical expression describing the shear thinning behavior of polymers. It is more realistic than the power-law model because it fits the data very well at both high and low shear rates. It is not possible to obtain analytical solutions with this model, but it is excellent for numerical simulations of flow processes.
Cross-Linking

Formation of a 3-dimensional network of polymer chains, which completely prevents flow.
Crystallinity
Ordered repeated structures (crystals) encountered in polymers below a certain temperature. Most polymers are semi-crystalline containing both crystalline and amorphous regions (see GLASS TRANSITION and MELTING POINT).
Current Loop

A two-wire loop in which the current through the wires is maintained according to a controlling device, usually a two-wire transmitter. The advantages of a current loop are longer distance signal transmission, better noise immunity, and the ability to power the two-wire transmitter throughout the same two wires. The most common current loop is 4 to 20 mA.
Cycle Time

The time usually expressed in seconds for a controller to complete one on/off cycle.

D

DC

Direct Current.
Dead Band

The range through which input can be varied without initiating observable change in output. (There is a separate and distinct input-output relationship for increasing and decreasing signals.)
Dead Volume

The volume of the pressure port of a transducer at room temperature and ambient barometric pressure.
Deborah Number

The ratio of a characteristic material time to a characteristic process time. As the characteristic material time we can use the relaxation time and as a characteristic process time the inverse of the shear rate. Under usual extrusion conditions the relaxation might be 0.1 and the shear rate 100 s-1 and thus De = 10 (0.1 divided by 1/100). When De << 1, the polymer behaves as a purely viscous fluid while for De >> 1 as an elastic solid. The phenomena of extrudate swell and melt flow instability are evidence of polymer elasticity.
Derivative PID Parameter (also called rate)

Reacts to the rate of rise, fall or recovery of a process.
Design of Experiments

A methodology for planning experiments where purposeful changes to the inputs (factors) to a process (or activity) are made in order to observe corresponding changes in the outputs (responses). A means of gaining knowledge about a process or activity with minimal effort.
Deviation

The difference between the value of the controlled variable and the value at which it is being controlled.
Differential Pressure

The static pressure difference generated by the primary device when there is no difference in elevation between the upstream and downstream pressure taps.
Digital Input

Auxiliary input to an indicator or controller which performs a function via switch closure or opening. Typically used to reset a latched alarm, or to duplicate a front panel function such as selection of automatic or manual control modes.
Digital Output

An output signal, which represents the size of a stimulus or input in the form of a series of discrete quantities.
Direct Acting

Control output action which increases as the process variable increases. In the case of an alarm, a direct acting alarm has its relay activated in an alarm condition.
Disturbance

An undesired change that takes place in a process(es) that tends to affect adversely the value of a controlled variable.
Drift

An undesired change in output over a period of time, of which change is not a function of the measurand.

E

Elongational Viscosity

The resistance to extension. For Newtonian fluids, the elongational viscosity is equal to 3 times the (common) viscosity (3 is known as the Trouton Ratio). Polymer melts are non-Newtonian and the elongational viscosity is usually between 3 and 100 times the viscosity. Melt strength is just a rough engineering measure of the elongational viscosity, determined from the force required to break an extruded strand of polymer by a pair of rollers (see MELT STRENGTH).
End Point

The output at zero pressure and full-scale pressure.
Engineering Resins

Resins for high-performance applications. This category includes polycarbonates (PC) and polyamides (PA) like nylon.
Environmental Conditions

All conditions to which a transducer may be exposed during shipping, storage, handling, and operation.
Error
The difference between the value indicated by the transducer and the true value of the pressure being sensed.
Error Band

The allowable deviation of output from specific reference norm.
Excitation

The voltage supplied by an indicator or controller to a transducer to provide its proper operating conditions.
Extrudate Swell

Whenever a polymer melt emerges from a die the diameter or thickness is always larger than the diameter (or gap) of the die. At usual production throughputs, diameter or thickness ratios range from 1.20-1.40 for PVC to 1.50-2.00 for commercial grade Polyethylenes and much more for some polymers containing a high molecular weight tail. It is an indication of the elasticity of the polymer. The more elastic polymers give larger swell. Of course, by pulling the extrudate the swell is reduced and of course extrudates can be drawn down to diameters (or thicknesses) much smaller than the die diameter or gap.

F

Fahrenheit
A temperature scale defined by 32° at the ice point and 212° at the boiling point of water at sea level.
Fail-Safe

See Reverse Acting.
Filter (Electrical)

A device to sort desired result from undesired. Electrically, a selective circuit which passes through certain frequencies, while attenuating or rejecting others.
FM-Approved

An instrument that meets a specific set of specifications established by the Factory Mutual Research Corporation which sets industrial safety standards.
Freezing Point

The temperature at which the substance goes from a liquid phase to a solid phase.
Full Bridge

A Wheatstone Bridge configuration utilizing active elements or stain gauges.
Full Scale Output

The electrical output of the pressure device with full scale pressure applied. Usually expressed in electrical units (mV/V, V, mA)
Full Scale Pressure

The maximum pressure under which applicable performance specifications apply.

G

Gain
The ratio of the change in output to the change in input, which caused it.
Gain Adjustment

Means of adjusting the full scale output of an amplified transducer.
Gauge Pressure

The difference between the local absolute pressure of the fluid and the atmospheric pressure at the place of the measurement.
Gels

In polymer science, a gel is defined as a 3-dimensional network of sufficient cross-link density that prevents flow. However, in extrusion practice the term "GEL" encompasses various visual defects in the final product, which sometimes appear as elongated ellipses and even includes various contaminants that are called "fisheyes" (see FISHEYE).
Glass Transition Temperature

The lowest temperature at which a polymer can be considered softened and possibly flowable. For HDPE and LDPE, it is 100°C and for PS +100°C.
Ground

The reference point of an electrical system, or alternatively, the local earth potential (earth ground).

H

Half Bridge

2 active elements or stain gauges.
HART Digital Communication

HART (Highway Addressable Remote Transducer), was originally developed by Rosemount and is now owned by the HART Communication Foundation (HCF). HART provides a standard twisted pair of wires with a 4-20 mA signal and digital capabilities for up to 15 additional signals (analog and digital) over the same twisted pair with two-way communication.
Heat
Thermal energy. Heat is expressed in units of calories or Btu`s.
Heat of Fusion

The heat required to mobilize the molecules of a solid polymer to produce a fluid melt i.e. the heat required to destroy the solid crystal structure without increasing the temperature. For amorphous polymers like polystyrene (PS) the heat of fusion is zero. For LDPE it is about 130,000 J/kg, which is roughly equivalent to the heat required to raise the temperature of 1kg of LDPE by about 50°C.
High Load Melt Flow Index

This is a melt flow index test that uses a higher than the usual (2.16 kg) weight. For PE, the HLMFI weight is usually 10 kg, but sometimes 21.6 kg.
Hysteresis

Deviation in output within the transducer range when first approaching this point with increasing pressure and then with decreasing pressure.

I

Indicator

A device which monitors and displays the condition of a process variable without exerting any control action. Indicators may be equipped with alarms or other auxiliary outputs.
Input and Output Resistance

The resistance measured across the input (excitation) and output (signal) terminals of an unamplified transducer.
Input Fail Safe

Direction in which signal is driven in the event of a sensor failure. Upscale will drive the signal fully upscale, and downscale will drive the signal fully downscale. The control output will respond as if the sensor has not failed.
Insulation Resistance

The resistance measured between specified insulated portions of a transducer when a specific DC voltage is applied at room conditions.
Integral

PID parameter (also called reset) which monitors and corrects the error signal between the setpoint and the process variable.
Intrinsic Viscosity

The limiting value of viscosity (at infinite dilution) of a polymer in a solution, which is used in the determination of an average molecular weight. The viscosity average molecular weight lies between the weight average and number average molecular weight (see also MOLECULAR WEIGHT).
Intrinsically Safe

An instrument which will not produce any spark or thermal effect, under normal or abnormal conditions, that will ignite a specified gas mixture.
ISO 9000

Family of standards concerned with "quality management". This means what the organization does to enhance customer satisfaction by meeting customer and applicable regulatory requirements.
ISO

The International Organization for Standardization, a worldwide federation of national standards bodies from some 140 countries. Equivalent to ASTM.
ISOTROPY

The situation where properties are independent of the direction in which they are measured.

J

Jumpers

Wire links that allow for changes to be made in input and output hardware configurations.

K

K-VALUE OF PVC

A measure of the molecular weight of PVC based on measurements of viscosity of a PVC solution. It ranges usually between 35 and 80. Low K-values imply low molecular weight (which is easy to process but has inferior properties) and high K-values imply high molecular weight, (which is difficult to process, but has outstanding properties).
Kelvin
(Symbol K)
The units of absolute or thermodynamic temperature scale based upon the Celsius scale with 100 units between the ice point and boiling point of water. 0°C = 273.16K (there is no degree [°] symbol used with the Kelvin scale).

L

Linear Polymers

Polymers can be classified as linear or branched. In linear polymers the monomeric units are linked together, linearly, with little or no long chain branching. In branched polymers, side chains are attached to the backbone of the molecular chain. High density polyethylene (HDPE) is linear while low density polyethylene (LDPE) is branched. Linear LDPE (LLDPE) is "stiffer" than LDPE in shear but "softer" in extension. In extension the LLDPE chains slide by without getting entangled (since the chain branches are very short).
Linearity (End Point/or Terminal)

Linearity as referring to a straight line between end points.
Linearity (or nonlinearity)
The maximum deviation of the transducer output from a defined straight line during increasing pressure in a calibration cycle.
Loop Gain

The product of the gains of all the elements in a loop.
Loop or Transmitter Power Supply

24 Volt DC (nominal) supplied by an indicator or controller power 2 or 4 wire transmitters.
Loss Modulus

An indirect measure of polymer viscosity using a cone-and-plate instrument subjected to dynamic (sinusoidal) deformation (see also STORAGE MODULUS).

M

Masterbatch

A concentrated blend of pigments, additives, fillers, etc. in a base polymer. Masterbatch is added in small amounts to large volume material (the same as or compatible with the base polymer) to achieve desired properties.
Maximum Diaphragm Temperature

The maximum temperature of the process media to which the transducer tip below the mounting threads can be exposed. Maximum strain gage temperature is the maximum environmental temperature at which the strain gage housing should be exposed.
Maximum Pressure

Pressure that may be applied to a transducer without changing the transducers` performance beyond specified tolerances.
Measurand

A physical quantity, property or condition which is measured. The term measurand is preferred to "input", "parameter to be measured", "physical phenomenon", "stimulus", and/or "variable."
Melt Flow Index

The number of grams of polymer that can be pushed out of a capillary die of standard dimensions under the action of standard weight (2.16 kg for PE, at 190°C). in 10 minutes (ASTM Standard 1238). The usual melt index range is from less than 1.0 (called fractional) to more than 25 (up to 100 for injection molding). For PP it is usually called MELT FLOW RATE and the standard temperature is 230°C.
Melt Fracture

At higher throughput rates, extrudates usually become highly distorted and the head pressure shows significant fluctuations. This phenomenon is known as gross MELT FRACTURE. It is possible with some polymers to obtain grossly melt fractured extrudates without sharkskin, i.e. the surface remains smooth and glossy but overall the extrudate is distorted (see also SHARKSKIN).
Melt Pressure Transducer

A device specifically designed to measure the pressure of molten polymers. This device produces an electrical signal proportional to the pressure of the molten polymers.
Melt Strength

A measure of the extensional viscosity of polymer melts. It represents the maximum tension that can be applied to the melt without rupture or tearing. Usually a capillary viscometer is used to extrude a polymer strand and the strand is pulled till rupture by a pair of rollers.
Melting Point

The temperature at which a substance transforms from a solid phase to a liquid phase.
Molecular Weight

Polymers are composed of long chain molecules. The monomer unit is repeated many times to give average molecular weights ranging from 50,000 to 500,000 for most common polymers. Of course, not all polymer chains are of the same length, so we have a MOLECULAR WEIGHT DISTRIBUTION (MWD). Different molecular weight averages are defined to express the breadth of the distribution. The number average molecular weight , Mn, is the sum of the individual molecular weights divided by their number. The weight average molecular weight, Mw, is the sum of the squares of the weights divided by the sum of the molecular weights. The POLYDISPERSITY INDEX (PDI) Mw/Mn (weight average / number average) would be 1.0 if all chains had exactly the same length (only theoretically possible). Usual grades of polymers have PI values from 1.5 to 30. Broad distribution polymers usually have lower viscosity, but higher elasticity.
Mounting Error

The error resultant from installing the pressure transducer, both electrical and mechanical.

N

NEMA-4

A standard from the National Electrical Manufacturers Association, which defines enclosures for indoor or outdoor use primarily to provide a degree of protection against windblown dust, rain, and/or splashing water.
Newtonian Fluids

Fluids which exhibit constant viscosities independent of the shear rate. Water, glycerin, oil and other small molecule fluids are Newtonian.
Noise

An unwanted signal which can contribute to errors in measurement. Examples are hum (power lines), radio frequency interference (RFI), electromagnetic interference (EMI), and broadband or white noise.
Non-Newtonian Fluids

Fluids having viscosities that depend on the shear rate. Polymer solutions and melts are non-Newtonian fluids. They also exhibit other non-Newtonian properties such as stress relaxation and normal stresses.
Normal Stresses

Polymer melts when sheared (i.e. when subjected to tangential forces) give rise to perpendicular (NORMAL) STRESSES. This means that when a fluid is flowing in a tube it is less compressed in the axial direction than in the radial direction. These NORMAL STRESSES are responsible for the phenomenon of EXTRUDATE SWELL at the exit of the die. Polymers containing a high molecular weight tail tend to give larger NORMAL STRESSES (i.e. they are more elastic).
Normally Closed

The state of a switching device (relay or SSR) whose non-powered state is connected.
Normally Open

The state of a switching device (relay or SSR) whose non-powered state provides no connection.

O

Output

The electrical signal, which is produced by a pressure applied to the transducer sensor.

P

PID

The control algorithm providing proportional control with automatic Integral and Derivative terms. Mathematically determines the control action to be performed.
Poiseuille Flow

The flow of a fluid caused by a pressure difference. The resulting velocity profile in a tube is parabolic for Newtonian fluids and somewhat "flatter" for polymer melts. The pressure drop is linear in the direction of flow for tubes or channels with parallel walls.
Polarity

In electricity, the quality of having two oppositely charged poles, one positive and one negative.
Polydisperity Index

The ratio of weight average to number average molecular weight (Mw/Mn) (see also MOLECULAR WEIGHT).
Positive Feedback

A closed loop in which any change is reinforced until a limit is eventually reached.
Potentiometer
A variable resistor often used to control a circuit.
Power Supply

A separate unit or part of a circuit that supplies power to the rest of the circuit or to a system.
Power-law Model

A simple mathematical expression describing the shear thinning behavior of polymers Where m is the consistency index, n is the power-law index, and the shear rate (for polymer melts 0.2 < n < 0.8). The power-law model does a good job in fitting high shear rate viscosity data but a poor job for fitting low shear rate viscosity data. In fact for the power-law model gives which is, of course, unrealistic. The usefulness of the power-law model is derived from the fact that several analytical solutions are possible and many practical flow problems occur at high shear rates where the power-law model gives a reasonable fit of viscosity data.
Pressure Flow

The flow of a fluid caused by a pressure difference. The resulting velocity profile in a tube is parabolic for Newtonian fluids and somewhat "flatter" for polymer melts. The pressure drop is linear in the direction of flow for tubes or channels with parallel walls. In the metering section of an extruder screw, pressure flow is the relatively backward flow of material down the screw channel caused by pressure in the head.
Pressure Range

The pressure values over which a transducer is intended to measure, specified by their upper and lower limits.
Primary Loop

The outer loop in a cascade system.
Proof Pressure

The maximum amount of pressure that can be applied to a pressure transducer without changing any specification. See maximum pressure.
Proportional Band

The PID parameter which determines the area in which the proportional control algorithm is operative.
Proportional Control

(1)Current or Voltage: Control algorithm which determines a continuous linear relationship between the input and the output.
(2) Time proportioning: Control algorithm that determines the time that a control output remains in the "ON" condition in a finite cycle. In this case, when the output is "ON", it is fully on.
Pseudoplastic Flow

This term is synonymous to shear thinning flow, i.e. viscosity decreases as the shear rate increases.
PSIA

Pounds per square inch absolute. Pressure referenced to a vacuum.
PSIG

Pounds per square inch gage. Pressure referenced to ambient air pressure.
PV-Process Variable

This is the controlled variable in a control situation or the monitored variable in an indicated situation.

R

Rabinowitsch Correction
When viscosity data are obtained from a capillary viscometer, they require a correction to account for the fact that the viscosity decreases as the shear rate increases. Without this (RABINOWITSCH) correction the viscosity is referred to as APPARENT VISCOSITY. Errors up to 10-20% in viscosity are common when this correction has not been made. For the power-law viscosity model the Rabinowitsch correction gives (i.e. for n=0.45 m(true) = 0.89 m(apparent)).
Random Copolymer

A random copolymer occurs when one of the two monomers polymerized together to form a polymer is in a random or statistical distribution in the polymer chain.
Range

The upper and lower pressure limits that a transducer is required to measure.
Rate Time

The time interval over which the system variable is sampled for the derivative function.
Reference Junction

The cold junction in a thermocouple circuit, which is held at a stable known temperature. The standard reference temperature is 0°C (32°F); however, other temperatures can be used.
Regrind

Waste material that has been reclaimed by shredding or granulating.
Relaxation

Whenever polymer melts are subjected to mechanical work they develop stresses which do not become immediately zero when the mechanical influence is removed. The time required for the stresses to relax is referred to as RELAXATION TIME. There is no universally accepted definition of the most characteristic relaxation time for a polymer melt. Some authors use the l of the Carreau or Cross viscosity models, but this is considered a poor choice by theoreticians. The best choice is perhaps the "longest relaxation time" determined in dynamic measurements as where G' is the storage modulus, h' is the dynamic viscosity and w is the frequency. Polymers with higher molecular weights have long relaxation times. When the polymer solidifies without the stresses having been relaxed, the product includes FROZEN-IN STRESSES which will be released when the plastic part is reheated. The accompanying changes in dimensions, shrinkage or warpage may be significant.
Remote Setpoint
An analog input to a controller which allows the setpoint to be changed by a remote device. This can be another instrument (cascading), a PLC, a computer or it can be done manually.
Repeatability

The ability of a transducer to reproduce output readings when the same pressure value is applied to it consecutively, under the same conditions, and in the same direction.
Retransmission Output
An analog output from an indicator or controller directly proportional to the value of the PV. Also called the recorder output. Reverse Acting Control output that decreases as the process variable increases. In the case of an alarm, a reverse acting alarm has its relay activated in the non-alarm state. This is also called a fail-safe alarm.
Reverse Acting
Control output that decreases as the process variable increases. In the case of an alarm, a reverse acting alarm has its relay activated in the non-alarm state. This is also called a fail-safe alarm.
RFI
Radio Frequency Interference.
Rheology
The science of deformation and flow of materials including polymers. Viscosity, elongational viscosity, normal stresses, relaxation time, G', G", etc. are rheological properties.
Room Condition
Ambient conditions used for test purposes.

S

Safe Overpressure
The maximum pressure that can be applied to a transducer without changing its performance beyond specified tolerances.
Self-Heating
Internal heating of a transducer as a result of power dissipation.
Self-Regulation
The property of a process or machine which permits attainment of equilibrium, after a disturbance, without the intervention of a controller.
Self-Tuning
Generic term for algorithms from a number of manufacturers which more or less succeed in tuning the PID parameters of controllers and control systems automatically. The term is non-specific, and individual manufacturers should be consulted regarding their algorithms
Sensing Element
The part of a transducer, which reacts directly in response to the pressure.
Sensitivity
The ratio of the change in transducer output to a change in the value of the pressure.
Sensitivity Shift
A change in the calibration slope.
Setpoint
An input variable which sets the desired value of a controlled variable.
Shear Rate
The velocity gradient, i.e., velocity divided by the gap measured in reciprocal seconds, s-1. In screw extruder channels, the shear rate can usually reach 100 s-1 or more. In flow through extrusion dies, it might reach 500 s-1 or more, and in injection molding more than 5000 s-1.
Shear Stress
A tangential force divided by the area (FORCE/AREA) on which it is applied. The shear stress is equal to the viscosity multiplied by the shear rate (measured in units of pressure, i.e., MPa or psi). At the die lips under usual production conditions, the shear stress may reach values of 0.2 MPa (29.0 psi) or more. The usually accepted value for the onset of sharkskin in capillaries is 0.14 MPa (20.3 psi), although higher values are reported in industrial production. With additives the critical shear stress value might be pushed up to 0.5 MPa (72.5 psi).
Shear Thinning
The reduction of the viscosity as the shear rate increases, which is exhibited by polymeric liquids. Shear thinning is due to molecular chain alignments in the direction of flow and disentanglements.
Shear Viscosity
The ordinary viscosity that is the ratio of shear stress to the shear rate (see also VISCOSITY).
Shield
A protective enclosure surrounding a circuit or cable which is to protect it from an electrical disturbance such as noise.
Shunt Calibration/Rcal
A method of generating an electrical output to match the electrical output that would be given in response to an applied pressure. This is accomplished using a resistor to unbalance the bridge electrically rather than with strain introduced by applied pressure. With standardized shunt or Rcal, the same point (generally 80%) is chosen on the calibration curve so that all similar transducers calibrate at the same point to facilitate interchangeability.
Signal Conditioner
An electronic network that permits adjustments to match a particular transducer to a readout device. Generally included are provisions for adjusting for zero balance and span or sensitivity.
Signal Conditioning
To process the form or mode of a signal so as to make it intelligible to, or compatible with, a given device, including such manipulation as pulse shaping, pulse clipping, digitizing, and linearizing.
SMART
Dynisco`s name for its proprietary two part self-tuning algorithm. It consists of TUNE and ADAPTIVE-TUNE.
Span
The algebraic difference between the limits of the range.
Span Turndown
The ability to re-range a transmitter to lower ranges. The re-ranging allows the 20 mA signal to be adjusted to the lower range which provides improved resolution.
SPE
Abbreviation for Society of Plastics Engineers.
SPI
Abbreviation for Society of Plastics Industry.
Stability
The ability of a transducer to retain its performance characteristics for a period of time and under a variety of conditions.
Static Calibration
 A calibration recording pressure versus output at room temperature. 
Static Error Band
The error band applicable at room temperature.
Static Pressure
The pressure of a fluid or gas at rest.
Storage Modulus
The ratio of shear stress to strain (deformation) when dynamic (sinusoidal) deformation is applied in a cone-and-plate rheometer. It relates to the elasticity of the polymer melt. G", the loss modulus, also determined in dynamic (sinusoidal) measurements relates to the viscous behaviour. So, G' and G" together give an idea of the dual nature of the polymer melt (partly elastic solid and partly viscous fluid). Measurements of G' and G" provide information on polymer structure and might be related to molecular weight distribution, cross-linking, etc.. Computer software like RHEOMWD can infer the breadth of the molecular weight distribution from G' and G" data.
Strain
A technical term synonymous with deformation.
Strain Gauge
A measuring element for converting force, pressure, tension, etc., into an electrical signal.
Surging
An instability of melt pressure and flow rate in an extruder, which can be detected by a pressure gage at the tip of the screw (or at the die adapter), or by dimensional product variations.

T

Temperature Effect on Span
The percentage change in rated output per degree change in ambient temperature.
Temperature Effect on Zero
The percentage change in zero balance due to a change in ambient temperature.
Temperature Range, Compensated
The range of ambient temperature for which Thermal Zero Shift is applicable (temperature error). Operation outside this range may require re-calibration.
Temperature Range, Operable
The range of ambient temperature, given by their extremes, within which the transducer is intended to operate.
Temperature Range, Storage
The range of ambient temperatures, given by their extremes, at which a transducer may be stored or transported.
Thermal Effect on Sensitivity
The change in transducer full scale output due to the effects of temperature only.
Thermal Effect on Zero
The change in transducer zero pressure output due to the effects of temperature only.
Thermal Mechanical Analysis
 Analysis In this technique, a sample is deformed under a static load as its temperature is being changed. Glass transition and softening points can be measured. The amount of orientation can also be measured by TMA. 
Thermal Sensitivity Shift
The sensitivity shift due to changes of the ambient temperature from room temperature to the specified limits of the compensated temperature range.
Thermal Zero Shift
An error due to changes in ambient temperature in which the zero pressure output shifts. Thus, the entire calibration curve moves in parallel displacement.
Thermogravimetric Analysis
This technique is used to measure a variety of polymeric phenomena involving weight changes, such as sorption of gases, desorption of contaminants (monomers, solvents, and additives) and degradation. In TGA, a sample is placed on a balance beam in an oven. From the weight versus temperature curves, kinetic and other studies are carried out.
Thermoplastics
Polymers that can be melted by heating and solidified by cooling and may be remelted repeatedly. PE, PP, PVC and all extrudable polymers are thermoplastics.
Thermosets
Materials that undergo chemical reaction and can be hardened by application of heat and pressure. They cannot be softened again to make them flowable. Typical plastics in this family are melamine, urea, epoxies and phenolics.
Transducer
In the broadest sense it is a device (or medium) that converts one energy form to another. Therefore, items such as a windmill, electric light, or an automobile engine could be called a "transducer" - but, in common practice, the term is generally applied to devices that take a physical phenomenon (pressure, temperature, humidity, flow, etc.) and converts it to an electrical output.
Transmitter
A device which translates the low-level output of a sensor or transducer to a higher level signal which is suitable for transmission to a site where it can be processed further.
Trouton Ratio
The ratio of elongational (extensional) viscosity to (shear) viscosity for Newtonian fluids is 3. Polymers do not obey this relation. Ratios can range up to 100 for melts and up to perhaps 10,000 for solutions.
TUNE
Dynisco`s one-shot algorithm that determines PID parameters based on a step change in output in the manual mode of operation.

V

Viscoelasticity
The dual nature of polymers, partly viscous fluid and partly elastic solid, is referred to as viscoelasticity. In flowing polymers viscoelasticity is responsible for time-dependent properties, such as stress relaxation, normal stresses, very large elongational viscosities, and numerous unusual phenomena such as extrudate swell, entry flow vortices and some flow instabilities.
Viscosity
The resistance to flow of a fluid (strictly speaking the resistance to shearing). It is defined as the ratio of shear stress (Tangential Force/Area) to shear rate (velocity/gap). The viscosity of a polymer decreases as the shear rate increases. This property is referred to as pseudoplastic behavior or shear thinning. The viscosity of a polymer at (near) zero shear for a polymer like PE might be 5,000 to 10,000 Pa.s while during flow in an extrusion channel it could be much lower (i.e. 500 Pa.s or less). Melt flow index corresponds to just one point on a viscosity curve (actually inverse). High viscosity implies low melt index and high molecular weight. Viscosity is measured in units of Pa.s or poise. 1 Pa.s = 10 poise. The viscosity of water is 10-3 Pa.s (1 centipoise) and for a typical polymer melt at least one million times larger (i.e. over 1000 Pa.s or 10,000 poise).

W

Weissenberg Number
The product of a characteristic material time and shear rate. It has the same meaning as the Deborah Number under certain conditions (see DEBORAH NUMBER).
Weissenberg Rheogoniometer
see Cone and Plate Instrument.
Weldlines
Weldlines are formed because of flow interruptions by obstructions in a melt flow field. Because of the high viscosity, the diffusion of polymer molecules, after they have been separated, is very slow and the weldline remains a line of mechanical weakness and may be visible to the naked eye. Such defects are common in injection molded products and are often encountered in extruded pipes, bottles, and film.

Y

Y2K
Potential for a computer or time/date stamped instrumentation to cease functioning at midnight on January 1, 2000. None of Dynisco`s present or past instrumentation is subject to the Y2K problem.

Z

Zero Adjustment
Means of adjusting the zero pressure output of an amplified transducer.
Zero Balance (offset)
The measured transducer output under room conditions with no pressure applied to the pressure port. For absolute pressure transducers, this value is measured at 0 psia. Gage and sealed pressure transducers have this value measured at atmospheric pressure.
Zero Shear Viscosity
The asymptotic viscosity value at zero shear rate (i.e., the maximum value). As the shear rate increases, the viscosity decreases due to alignments of molecular chains in the direction of flow and molecular chain disentanglements. The zero shear viscosity is proportional to the 3.4 power of the weight average molecular weight (i.e. h0 = constant * Mw3.4 for most common polymers). This means that if we increase the molecular weight of a polymer from 100,000 to 200,000 the viscosity will increase by 23.4 = 10.55 times. Obviously it is extremely difficult to extrude polymers having very high molecular weight.
Zero Shift
Any parallel shift of the input/output curve.