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Scale Components & Features
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© r i g h t o n s c a l e s . c o m
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 Specifications Explained
There are two main specifications for all scales including infant and toddler scales. For example, it is common to see a scale listed with specs of 44 lbs x 1/2 oz.
This means the scale has a Maximum Capacity of 44 lbs with an Accuracy of 1/2 oz (0.5 oz)
Max Capacity
This is the most weight a scale is designed to weigh at one time. If more than the max weight is placed on the tray at one time (even if the scale is off) damage will occur to the Load Cell. When in use, most scales will display "EEEEE" or similar to indicate too much weight.
How do I know How Much Capacity I Need? That's purely up to you and how heavy your weighing subject is.
Accuracy
Also referred to as resolution and readability. This is the smallest amount of weight the scale is able to see, which determines how accurate the scale is.
See the following examples of various scale accuracies, and how a scale with that particular accuracy registers weight.
0.002 lbs Accuracy: 0.002, 0.004, 0.006, 0.008, 0.010, 0.012...
0.01 lbs Accuracy: 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, 0.11...
0.05 lbs Accuracy: 0.05, 0.10, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40, 0.45, 0.50...
0.1 lbs Accuracy: 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1...
0.5 lbs Accuracy: 0.5, 1.0, 1.5, 2.0, 2.5, 3.0...
1 lbs Accuracy: 1, 2, 3, 4, 5...
Note that pounds (lbs) are used in the above example. Scales often weigh in many different weighing modes (ounces, pounds, kilograms, etc). A scale's specifications will always provide the Max Capacity and accuracy in each weighing mode the scale has.
How do I know How Much Accuracy I Need? That's purely up to you and how accurate you need to make your measurements. As mentioned above, be sure the posted accuracy for the scale you are purchasing matches the amount of precision you need to make your measurements to.
Note that as accuracy increases so does price. Also as accuracy increases, Maximum Capacity of the scale generally decreases.
Also see our handy Weight Converter.
Resolution: See Accuracy
Readability: See Accuracy
Calibration
People new to digital scales often have the most questions regarding calibration and calibration masses. Most infant scales like the Salter 914 come pre-calibrated from the factory and are ready for use right out of the box. Almost all health scales are not designed to be re-calibrated by the user.
The info below pretains to other digital scales which can be calibrated by the user.
Over a period of time and after being subjected to a lot of bumping around (like during shipping) a scale's readings may drift slightly.
When is re-calibration required? For example, if we place a 5 lb mass on the tray of a scale with 0.1 oz accuracy and it's more than 0.3 oz off we recommend re-calibration. Anything within three divisions is usually fine.
Also note that Air Currents, Vibrations, and other Environmental Factors can interfere with your scale's readings.
What does calibration do? Calibration requires a calibration mass or masses. The calibration mass required for each scale varies, and the user manual will tell you exactly what mass is needed.
When a scale is re-calibrated correctly it is resetting the scale's computer to the reference weight you are placing on the tray. In other words, by placing the cal mass on the tray you are reminding the scale exactly what that 100g mass weighs. By doing so, it will reset itself according to the cal mass and its readings will again be right on the money.
Optional Calibration Masses. Some scales include the calibration mass with the scale. With other models, the calibration masses are an optional accessory. People always want to know if they should spend the extra money for the cal mass or not.
For scales will smaller calibration masses like a few hundred grams, the masses are relatively cheap and do not add much to the shipping weight of your order so we suggest you do pickup the cal mass.
However, some scales require expensive weights that are also very heavy to ship. In cases like these we remind customers the scale comes pre-calibrated and ready to go, and that the calibration masses are not a necessity.
Calibration Gone Bad. Some customers assume that all scales need to be recalibrated as soon as they come out of the box, or even before each use which is not true. In the worst cases these customers may not even have the correct calibration mass or may have no masses at all. Then top it off by not reading the calibration instructions and you have one messed up scale. Improper calibration will render your scale useless. Always be sure to follow the instructions in your User Manual.
Scale Components
Liquid Crystal Display (LCD) & Backlit LCDs
Almost all modern scales employ an LCD (Liquid Crystal Display) for the readout. LCD displays are inexpensive, reliable, consume a minimum of power and provide very high contrast readouts which are easy to read.
You will see Backlit LCDs offered on some models. Standard LCDs cannot be seen in darkness. But by adding a backlight, the entire display behind the numbers is illuminated, usually in a blue color. This allows the display to be seen in total darkness.
A downside to a backlit LCD is that the backlight does consume quite a bit more power when it is on, thus draining your battery faster than a non-backlit display. Manufactures have come to a compromise with this issue. By limiting the time the backlight remains on, usually to about 3 seconds after a weight is registered, the power drain is minimized. Some backlit models have a button to turn on and off the backlight, and others allow you to program how long the backlight remains on. With the backlight is off, the LCD operates just like a normal LCD. So turning off the backlight does not turn off the entire LCD.
Batteries & AC Adapters
Almost all bathroom scales will run only from batteries. Infant and larger models will usually have the ability to run from AC adapter in addition to batteries.
Battery Types: There are two main types of batteries found in today's scales.
Alkaline: The first is the standard alkaline batteries which everyone is familiar with. Common alkaline batteries found in scales are AAA, AA, 9v, and C sizes. The benefit to these batteries is they are relatively cheap and most people have these batteries around the house. Alkalines do tend to have a shorter life span compared to the next type of battery, the lithium button cells.
Lithium Button Cells: Are found in many digital scales today. They offer a longer battery life compared to alkaline batteries. A pocket scale using lithium batteries can offer around 200 hours of usage on average, while Alkalines will tend to offer slightly less.
Lithiums are also very thin, allowing the scale to be made smaller.
In the past lithium batteries used to be difficult to find in stores when the time came to purchase a replacement. However, now a large selection of lithium batteries can be found in many national chain stores such as Home Depot, Wal-Mart, Radio Shack, drug stores and many other places. Lithiums still tend to cost slightly more than alkaline batteries so keep that in mind.
How long will my batteries last? That all depends on how often you use the scale and how long the scale is left on using battery power. Battery life will also depend on the scale model you are using and the type of batteries.
Also, batteries tend to loose their charge faster in hotter Temperatures. Manufactures always recommend that you remove the batteries from your scale if you are planning to store it for a long period of time. This will prevent any corrosion and preserve the life of your battery.
AC Power: AC power is nice to have if you plan on using your scale near an electrical outlet, or require prolonged uses of your scale. A lot of larger digital scales today will offer AC power along with battery power so you have the best of both worlds.
If your scale is able to run from AC power and the adapter is not included we highly suggest you purchase the correct corresponding AC adapter that was designed for your scale. Otherwise, using an adapter of the wrong voltage or connector can permanently destroy your scale and void your warranty.
Auto Power Off
Scale manufactures have developed the auto-off feature in order to prolong battery life and to prevent the scale from inadvertently being left on. If your scale were accidentally left on, your battery would be fully drained for the next time you tried to use it.
Auto-off is usually set to a two or three minute interval where if the scale does not register any input or change in weight, the scale will shut down. Some models have the auto-off programmable so you can set the time interval, or set it to disable auto-off all together.
Load Cells & Strain Gauge Transducers
The strain gauge, also known as the load cell, is the heart of any scale. This is the actual sensor component that registers the weight on the tray and converts that into an electrical signal which is then passed along to the other parts of the scale for processing.
Strain gauges come in two types, they are compression or tension.
A compression strain gauge is based on how much the cell compresses when pressure is applied, while a tension strain gauge is based on the slight change in shape of the cell caused by the weight.
The gauges are developed from an ultra-thin heat-treated metallic foil and are chemically bonded to a thin dielectric layer. The precise positioning of the gauge, the mounting procedure, and the materials used all have a measurable effect on overall performance of the load cell.
How does it work? Electricity is passed through the strain gauge. As weight is applied, the shape of the gauge changes. The change in shape also affects its resistance to the electric current being passed through it. By knowing precisely how much the electrical impedance changes in proportion to the weight being applied, the processing components are able to interpret the impedance change from the load cell into a weight, which is then displayed on the readout.
Exceeding the maximum capacity of a scale will almost always permanently bend the load cell. This means the load cell will not flex back to its original state when the weight is lifted as it was designed to do, thus overloading your scale and making it unusable.
Tare/Zeroing Function
Most digital scales have a tare function, also referred to as zeroing out. Pressing the tare button at any time will return the scale display to zero. The most common use for tare is to zero out a Weighing Container or Expansion Tray.
Different scale models may use different terms for the same thing such as "zero", "tare", or just the character "Z" or "0" on the button itself. Scales that do not have a tare button may require you to turn the scale off, place the weighing bowl on the platform, then turn the scale back on. This will zero out the weighing tray, as the scale will go to 0.0 when it is powered back up. This is common in some of the kitchen scales like the Salters.
Expansion Trays
Using a weighing container or expansion tray allows you to expand the usable area of the scale's tray, and allow your scale to weigh more of your sample at one time.
Anything can be used for your weighing container, as long as the weight of your container and the weight of what you plan to weigh do not exceed the maximum capacity of your scale.
You will see listed in the specifications of some scales "tare to capacity by subtraction". This means the scale will Zero Out up to the Max Capacity of the scale
Auto-Zero
Some very sensitive scales may have an auto-zero function. Because they are so sensitive, scales like these tend to be a bit "jumpy" and will often fluctuate slightly from zero when nothing is on the tray. In order to correct this an auto-zero function keeps the scale at zero if it is within a few Divisions of zero in order to provide a steady zero reading.
The downside to auto-zero is if you are slowly adding a small amount of weight at a time to the tray, the scale may keep auto-zeroing as you add weight, resulting in an inaccurate reading. Please refer to the user manual for your scale for more information about the auto-zero function if your scale is equipped with this feature.
Environmental Factors
Temperature Range
Digital scales consist of many electrical components, many of which utilize electrical resistance to provide accurate readings. The resistance of metal changes with temperature. Scales are designed to work best within a set temperature operating range which is usually posted with the scale's specifications.
Overall, scales work best at room temperature. Extreme heat or cold will affect your scale and most likely result in inaccurate readings. Extreme heat (like being left in direct sunlight) for example, will also render the LCD of a scale unreadable if it is heated up past a certain point. For best results treat your scale like the sensitive measuring device that it is, and always allow your scale to turn on and "warm up" before use in cold environments.
Air Currents
Scales are very sensitive, and will display any mass applied to the weighing tray. This includes mass applied by air currents. Very accurate scales such as those with an accuracy of 0.01 oz or more are most susceptible to air currents and other environmental factors. This will cause the readout to be "jumpy" and it will have a difficult time showing zero, or the weight of the sample on the tray.
Very sensitive lab balances often have a windscreen around the tray to prevent ambient air currents from interfering with the readings. And in the most sensitive scales, the weighing tray may even be in a vacuum chamber to prevent the weight of any dust particles from messing up your readings.
Vibrations
Vibrations and Air Currents are the two biggest problems people encounter with scale inaccuracies. It is common for us to get phone calls or e-mails from customers who are using their scale for the first time and are complaining the scale is jumping all over the place and will not provide an accurate readout.
It usually turns out the scale is being used in a location full of vibrations and air currents. Vibrations will travel from the surface the scale is sitting on and be transferred to the scale tray, which then reflects these vibrations on the display.
There is nothing wrong with the scale in this case, it is accurately displaying the weight and fluctuations it is getting from its weighing tray. Do not underestimate the accuracy of your scale, it will register many things you are not aware of in the environment.
RF Interference
Anything that emits Radio Frequencies (RF) can cause interference with your scale. This includes, but is not limited to, cell phones, cordless phone, TVs, computer monitors, and pretty much all electrical devices. A good rule of thumb is to not use you scale within proximity to any other electrical device.
One of our customers found that he was getting interference throughout his entire house, due to the high-voltage power lines which crossed over his house.
Static Electricity
Not as big as a concern as the other factors above, but as with any electrical device, the build up of static electricity within your scale's components can interfere with your readings and in the worst cases destroy or damage some of your scale's components. If you feel your scale may be suffering from a static electricity build up, a solution is to gently rub it with an anti-static dryer sheet which will discharge the static.
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