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Load Cell and
Transducer Glossary

Common frequently used terms related to load cells and force measurement

Accuracy

 Describes the closeness of agreement between a measured value and the reference value; it is often interpreted as a combination of the measurement trueness and measurement precision

Ambient Temperature

 The temperature of the medium surrounding the load cell; the temperature of the measuring environment.

Calibration

 Process that compares a measurement device—often referred to as the measurand or device under test (DUT)—to a reference standard; if the measurement device exhibits excessive measurement error, the measurement device is often adjusted to reduce this error

Calibration Curve

 A equation that characterizes the relationship between a sequence of applied loads and the resulting outputs from the measurement device; this relationship is typically expressed as a linear equation, series of linear equations, or polynomial equation

Capacity

 The maximum axial load a load cell is designed to measure within its specifications.

Compensated Temperature Range

 The range of temperatures over which the temperature drift specifications are valid; temperature drift is typically expressed by the Temperature Effect on Zero and Temperature Effect on Output terms.

Creep

 When a load cell is subjected to a constant / static load, Creep is the resulting change in load cell output that occurs over time; this value is usually measured at the load cell capacity when that load is applied for 30 minutes; the result is expressed as a percent of rated output over the loading period.

Creep Recovery

 The change in load cell signal occurring with time immediately after removal of a load which has been applied for a specified time interval, environmental conditions, and other variables remaining constant during the loaded and unloaded intervals. Normally expressed in units of % of applied load over a specified time interval. Normally the applied interval and the recovery interval are equal. It is common for characterization to be measured with a constant load or near capacity.

Creep Return

 The difference between load cell signal immediately after removal of a load which has been applied for a specified time interval, environmental conditions, and other variables remaining constant during the loaded interval, and the signal before the application of the load. Normally expressed in units of % of applied load over a specified time interval. It is common for characterization to be measured with a constant load at or near capacity.

Dead Load

 Loads that are constant over time, such as frames, structures, or other immovable objects. Other terms are permanent load or bearing load.

Deflection

 Expresses the change in the height of a load cell (measured along its loading axis) when it is loaded to its capacity

Drift

 Random change in the output of a load cell over time; can affect the zero point or output sensitivity of the load cell

Dynamic Load

 Loads that change rapidly, often bidirectionally (ascending and descending); examples include moving vehicles, machine vibration, wind gusts

Eccentric Load

 Any load applied parallel to but not concentric with the primary axis; applies a torque to the load cell measuring element

Error (Measurement Error)

 The measured value minus the reference value; typically applies the performance of a measurement device or measurement process

Excitation

 Excitation is the voltage or current applied to the input terminals of the load cell.

Full-Scale Output

 Also known as Rated Output or Sensitivity; the denominator term used to calculate a result that is expressed as a percent of full scale (%FS)

Hysteresis

 Performance specification that characterizes the difference between when a load cell is measuring ascending and descending loads.  In a typical calibration, a load cell is subjected to a series of ascending loads and, immediately after reaching full-scale, the load cell will be subjected to a single descending load point (often at 40% of scale); the difference between that measurement point on the way up and on the way down becomes the Hysteresis specification

Input Resistance

 Electrical resistance of the input to load cell bridge circuit measured across the positive and negative excitation terminals while the load cell is unloaded

Insulation (Leakage) Resistance

 The DC (direct current) resistance measured at 50 volts under standard test conditions between the bridge circuit and transducer, circuit and cable shield, and transducer element and cable shield

Load

 The force or weight applied to a load cell

Load Cell

 A precision, electromechanical spring element commonly constructed of alloy tool steel, stainless steel, or aluminum alloy; outputs a low-level voltage signal that is proportional to the applied load

Maximum Load

 The highest load in a specific test or application, which may be any load up to the load cell capacity; may not significantly exceed load cell capacity, upper limit is usually 110% of capacity

Measuring Range

 The difference between maximum load and minimum load in a specific test or application

Minimum Dead Load or MDL

 The smallest load for which specified performance will be met. It is normally equal to or near NO LOAD in single modea applications and is of necessity equal to no load in double mode applications.

Minimum Load

 The lowest load in a specific test or application, differing from no load by the weight of fixtures and load receptors which are attached plus any intentional pre-load which is applied.

Mode

 Also commonly referred to as Loading Mode; the direction of the load; tension and compression are loading modes

mV/V

 The ratio between the load cell signal (output) and the excitation voltage (input)

Natural Frequency

 Often termed the Ringing Frequency of the load cell; this is the frequency at which the load cell oscillates under conditions when unloaded; often used to as an implicit measure of load cell responsiveness in the time domain

No Load

 When the load cell is in its normal physical orientation, without any fixtures installed, and no external force is being applied

Non-linearity

 Characterizes the deviation a calibration curve has from a straight line; the straight line is drawn between the no-load and rated load points.

Non-repeatability (Repeatability)

 The maximum difference between load cell output readings for repeated rated loadings or unloadings under identical environmental conditions.

NTEP

 NTEP stands for National Type Evaluation Program, a certification organization created by the U.S. Department of Commerce’s National Institute of Standard and Technology (NIST) and the National Conference on Weights and Measure (NCWM).

Operating Temperature Range

 As referred to as the Safe Temperature Range; the temperature extremes within which a load cell will operate without permanent adverse change to its performance characteristics.

Output Resistance

 The resistance expressed in ohms of the strain gauge bridge circuit, measured at the positive and negative signal terminals with no load applied and input terminals open-circuited.

PLC (Programmable Logic Controller)

 An industrial computer designed to monitor and instruct manufacturing processes.

Primary Axis

 The axis along which the load cell is designed to be loaded; normally its geometric centerline.

Rated Capacity

 The maximum axial load that the load cell transducer is designed to measure within its technical specifications.

Rated Output (Sensitivity, Full-Scale Output)

 The algebraic difference of the load cell output at no-load compared to its output with the rated load applied, usually expressed in a ratio millivolts/volt (mV/V) of excitation. Also known as RO.
The excitation voltage, usually expressed in VDC, for optimal performance of the transducer to operate within its specifications.

Reproducibility

 The degree of agreement between the results of measurements taken under changing conditions or locations.

Resistance (Electrical)

 A measure of the opposition of the flow of electrical current in a wired circuit. Resistance, also called ohmic resistance, is measured in Ohms (Ω).

Resolution

 The smallest change in load which produces a detectable change in the signal.

Safe Overload

 Maximum (axial) load that can be (statically) applied without creating a permanent shift in performance, expressed as a percent of full-scale

Sensitivity

 See Rated Output

Signal

 The absolute level of the measurable quantity into which a force input is converted.

Span

 Another name for rated output.

Specification

 The error limits within which a load cell should function for a given technical parameter.

Strain Gauge

 A strain gauge sensor uses electrical resistance to measure deformation or displacement from applied stress or strain.

Temperature Range, Compensated

 The range of temperature over which the load cell is compensated to maintain output and zero balance within specified limits; range of temperatures over which the Temperature Effect on Zero and Temperature Effect on Span specifications apply

Temperature Range, Operating

 The extremes of ambient temperature within which the load cell will operate without permanent adverse change to any of its performance characteristics.

Temperature Shift (Effect) on Output

 The effect of temperature on a load cell’s sensitivity, usually expressed as a percentage of load per degree Fahrenheit (Celsius) change in temperature.

Temperature Shift (Effect) on Zero

 The change or shift in zero balance due to a change in ambient temperature and  causing the output curve to move up or down across the output axis.

Ultimate Overload

 The maximum load that can be applied without causing structural/catastrophic failure, usually expressed as a percentage of full-scale capacity.

Wheatstone Bridge

 A simple electrical circuit of four resistors connected as a quadrilateral used for measuring an unknown resistance.

Zero Balance (Zero Offset)

 The output signal of the load cell with rated excitation and with no-load applied; the amount of deviation in output between true zero and a real load cell with zero load and usually expressed in percent of rated output.

Zero Dead Band

 Another name for zero float.

Zero Float

 The shift in zero balance resulting from a complete cycle of equal tension and compression loads. Normally expressed in units of %FS and usually characterized at FS = Capacity.

Zero Return

 The difference in zero balance measured immediately before applying a rated load for a specified duration compared to the measurement after removal of the load and when the output has stabilized.

Zero Shift

 A permanent change in the no-load output.

Zero Stability

 The degree to which the transducer maintains its zero balance with all environmental conditions and other variables remaining constant.