Glossary of Terms

Glossary of Terms for the Scale Industry

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S

Sampling Period
Time interval between observations in periodic sampling control system.

Scale
1) Change quantity by factor to bring its range within prescribed limits. 2) Device for weighing, comparing, and determining weight or mass.

Scale Averaging
Number of weight readings taken over period of time and averaged by dividing total accumulated weight by number of readings.

Note: Used when weigh vessel has mixer, blender, or some other device creating agitation during weighing process. Because center of gravity in weigh vessel is changing, displayed weight value tends to move up and down from actual weight in vessel. To dampen this effect, only average reading is displayed. This does not affect actual processing of weight signal.

Scale Capacity
Capacity of load cells only. Example: If four 1000 lb capacity load cells are placed under vessel, scale capacity would be 4,000 lbs. This does not mean you can move 4,000 lbs of material into vessel. You must also consider weight of vessel itself and supports that rest on load cells. This tare (or dead) weight must be included when determining required scale capacity. If vessel and supports weigh 1,500 lbs, then only 2,500 lbs of material can be moved into vessel before scale capacity is reached.

Scale Factor
1) Number used as multiplier, chosen so that set of quantities will fall within given range of values. Example: To scale 856, 432, -95, and -182 between -1 and +1, scale factor of 1/1000 is suitable.

2) Adjustable parameter in signal processor that creates match between actual input and indicated output. Scale factor (also called 'span') calibration results in determination of scale factor.

3) Slope of signal processor output (indicated weight) versus signal processor input (mV or counts). Transducer output, measured in mV or counts, is signal processor input.

Scale Factor Counts
Scale factor denominator, expressed in counts. Actually, change in counts that occurs because of change in load during calibration procedure. If scale factor is calculated, scale factor counts is calculated response of sensor/transducer array if given weight of material were placed in weigh vessel.

Scale Factor Weight
Scale factor numerator. Typical value for scale factor weight is full-scale live load of vessel, but because scale factor is ratio of weight per counts, smaller value of weight may be used.

Example: If only 30% of full-scale live load is used for calibration, scale factor weight is 0.3 x full-scale live load. Scale factor counts is also reduced to 0.3 of change in counts expected if full-scale live load had been used.

Sense Lines
In full bridge systems, these lines sense the excitation voltage at the load cell and return it to the power supply. The power supply then attempts to regulate the voltage to maintain a stable and accurate excitation voltage level at the load cell.

Sensing Element
Portion of device directly responsive to value of measured quantity.

Note: It may include case protecting sensitive portion.

Sensitivity
Sensitivity is the relationship under fixed conditions between a change in the output of a device to the change in input. The sensitivity of a sensor is the difference in its output values over a given range divided by the change in the value of the measurand.

That is, Sensitivity= output minimum output maximum / input minimum input maximum

The units in which sensitivity is expressed are defined by the above equation and consequently vary depending on the nature of the device and measurand. For example, there are sensors that measure the stress level in terms of psi. In this case the units of sensitivity would be millivolts per psi.

If the relationship between the measurand and the output is linear, then the sensitivity will usually be expressed over this whole range. If it is non-linear, the sensitivity characteristics of the device will vary for different values, and so the sensitivity will usually be quoted for several ranges. Note: Expressed as numerical ratio, with units of measurement of two quantities stated. Example: If load cell produces 360 mV when 2,000 lb load is applied, sensitivity is 360mV/2,000 lb = 0.18 mV/lb.

Shear
Strain or distortion in shape resulting from action of shearing stress. Component of stress on horizontal beam that is measured.

Shearing Strain
1) The angular distortion of an object under stress. 2) A measure of angular distortion also directly measurable, but not as easily as axial strain.

Shear Stress
Where normal stress is perpendicular to the designated plane, shear stress is parallel to the plane.

I Sigma
Range in which 65% of all samples values will fall.

II Sigma
Range in which 95% of all samples values will fall. This is industry standard.

III Sigma
Range in which 99% of all samples values will fall.

Specification
The specification of a device is a technical description of its characteristics, construction, performance and any other information relevant to its use.

Specific Gravity
Ratio of density of substance to density of another substance (usually water).

Stability
A measurement of how much the output from a device or system varies if, under fixed conditions, a constant input is applied over a long time. For weigh equipment it is the measure of ability to operate within tolerance over time.

Standard Deviation
Indication of how much individual sample values vary from mean (average). When standard deviation is small, most data values are near mean.

Strain Gage
1) Instrumental device used to measure dimensional change within or on surface of specimen. 2) A device that converts mechanical deflection to an electrical signal.

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