Speaking to an expert in their field can be challenging, especially if you refer to various things differently. Learning the scale terminology used to describe the what you need, its performance, and how one operates can be challenging, especially with having to also learn the parts of a scale. I hope this blog sheds some light on some common key words used in the metrological industry day to day.
Learn some of the key terms relating to the quality of scale you need before you buy
More than likely, you’re going to need to know a few of these terms when determining the scale you need. Knowing these terms will prevent any miscommunication between you and the sales rep during the ordering process.
Accuracy – A term used to express the behavior of a measuring instrument showing its ability to indicate with sufficient exactness the true value of the magnitude to be measured.
Autorange – Automatic device for switching ranges in multiple-range scales and multiple-division scales. Imagine having two scales hooked up to it, each in different units, kilograms and pounds. Autorange would allow an indicator to switch between the scales and their units and preset division settings.
AZM (Auto Zero Maintenance) – Sometimes the accumulation of snow or the impact of rain can cause a scale to start reading weight. AZM compensates for that and can be set in the indicator to auto zero if the readout is below a predetermined weight.
Displayed Increment/Graduation/Increment Size – See d (division)
Division – ‘d’ is the simple way to express something like, “My scale is consistently 2d off.” ‘Division’ is typically used when indicating the scale capacity divided by the increment size. Example: A 500 lb scale that reads to .1 lbs has a Division of 5000 (or 5000d).
HMI – Human to Machine Interface. This typically refers to a monitor a user reads data about the state of a process and can physically control various parts of the process. If you have a touchscreen thermostat in your house or something similar, this can be considered a human to machine interface.
(Initial) Dead Load – Refers to the physical weight on the load cells before any weight is placed on the scale. Such as the weight of the platform, or the weight of an empty vessel. This is needed to know in the event of a scale or load cells being integrated into a system such as a conveyor or tank. The initial dead load will affect the max load requirements of the load cells when the largest weight of the product to be weighed is taken into consideration.
Max Load – The largest weight a scale can read.
Min Load – The smallest weight a scale can read.
Span – The maximum capacity of a scale subtracted by the minimum weight the module can measure.
Resolution/Readability – Generally refers to the smallest value the instrument can measure. Similar to d.
Stability (Motion) Detection – The ability for a terminal to determine that the load on the platform of the scale will not be affected by motion. This is mostly used so the indicator can tell the printer it is okay to print.
Tolerance – This one often gets confused with readability. The tolerance is simply the plus or minus factor that your weighments are allowed to be off. Example, if you’re baking a cake and you need a cup of sugar your tolerance could be plus or minus a teaspoon. Anymore would be too sweet, and too little would be not sweet enough.
Get to know the properties and functions of your new scale
Below is just some basic terminology used to describe different aspects of weighing. In the event of needing service, the service tech may need to know a few things using these terms.
Analog – Data displayed by continuously variable physical quantity, rather than discrete steps. Imagine a light bulb being powered by a bicycle. The harder I pedal, the brighter the light bulb gets. This is essentially analog communication.
Analog-Digital Converter – An electronic device designed to convert analog signals (voltages) in digital signals (units).
Digital – Information in discrete quantities. Let’s go back to the light bulb analogy. Before, the speed of my pedaling controlled the strength and quality of the output of the light. With digital communication, as soon as I begin to pedal or reach a certain speed, the electric bridge opens and the full power is sent to the light bulb. Think binary. It either is on, or it isn’t.
Gross Weight – The weight of an object or sample (net), including its container or packaging (tare).
Net Weight – The weight of a material or product after the packaging or container has been removed (tare).
Tare Weight – The mass of the packaging or transport container of the material weighed.
Zero – Current empty weight with no product or packaging/containers on the platform
Understand what your service technicians are doing and monitoring
Because of environmental influences and digital interference, scales need to be inspected and calibrated every so often. Here is a list of terms to help you understand the performance of a scale and how it’s tested
Calibration – If you start seeing weight readings that are unusual, your weigh module probably needs to be calibrated using certified test weights. What’s happens is the terminal sends out a voltage to the load cell(s), the weight applied to the load cells bends them and returns a varying voltage to the terminal based on the flexure of the load cells. The terminal then reads this difference and calculates a weight. The load cells, wires, and platform can all be affected by things like vibration over time, temperature, digital frequencies, and even humidity. This will cause a variance in voltage and the scale will need to be recalibrated under the current circumstances.
Cornerload Test – Wherever a weight is placed on the platform of a scale, the same weight should be read. This test checks to see if each corner of the platform reads the same weight. This ensures the load cells are all working and positioned correctly.
Creep – This is something that happens when a load is placed on the scale and left there for some time. Eventually, the weight reading starts to increase or decrease. A creep of .02% within 15 minutes is generally acceptable.
Drift – When the measuring device is constantly being loaded, drift is used to describe a consistent or noticeable increase in weight outside of what is to be expected over time. Often times confused with creep. Although similar, drift occurs when weight is continuously added.
Hysteresis – The difference between the load cell output readings when weight is applied, versus when it is removed. Example: If I put 50 lbs on a scale, and it read 51 lbs, then I put 100 lbs and it read right on. I would then proceed to remove 50 pounds to get back to the expected weight of 50 lbs, but it instead read 49 lbs. I would have a Hysteresis of 2 lbs at 50 lbs.
Linearity – Is the expected weight of increased and decreased loads. If I put 200 lbs of weights on the scale in 50 lb increments, I should expect that each one of those increments weighs exactly 50, 100, 150, and 200 lbs. This is simply referred to as “non-linearity” when that expectation is not met.
Non-Axial Loading – This occurs when a weight isn’t applied to a weigh module at 90 degrees. This can cause load cells to shift and deflect which can cause inaccurate readings.
Overload – Simply any load that exceeds maximum capacity of the balance.
Repeatability – The effectiveness of a scales ability to reproduce the exact same results when a known weight is applied, removed, and reapplied multiple times.
Reproducibility – Similar to repeatability, except this typically means that the accuracy of a scale based off of test results within 1 standard deviation, will be identical when tested at a later time or different place after calibrated.
Shift (Test) – See Cornerload.
Feeling ambitious, or want to impress our service techs? Check out these more technical terms that are typically used by our technicians.
Cal. Initial – This is defined as the empty “counts” at calibration. Meaning, the raw reading each load cell is giving off before any mass is applied or weight is calculated.
Counts – Raw counts processed by the transducer (PowerCell or Junction Box) after being compensated for temperature, creep, and hysteresis.
Factory Mutual – An agency that performs product tests and approvals. In our case, X company lightning tested and approved our PowerCell PDX load cells to 80,000 amperes. Twice that of a typical lightning strike.
Flexure – Typically used to describe how an analog load cell bends. At least two sides of a load cell contain strain gauges that measure how much the steel block is bending during a load.
Raw Counts – If we get down to it, “weight” is just a concept. Raw Counts are the units that are actually measured. See ‘Counts’. A raw count is before temperature, creep, and hysteresis compensation.
Span Factor – The multiplier to convert counts to weight.
Transducer – A device that converts an input (electrical or non-electrical) to an electrical output. Like a strain gauge.
UL (Underwriters Laboratory) – An agency that performs product tests and approvals.
Weight – Counts that have been combined, filtered, processed, and scaled to the unit of measure.
Wheatstone Bridge – The electrical jargon of how a strain gauge works and is built. A null-type resistance-measuring circuit in which resistance is measured by direct comparison with a standard resistance.
Zero Register – Contains the current empty counts.
Now you know the language us scale guys use during the buying process, after the buy process, and even when your scale is being serviced. Knowing some of these terms, or at least having a place you can reference them, should help close the language barriers between you, your production crew, and your scale service providers.
Want to or need to know the general parts of a scale? Click here!