|
Scale Information Database
When selecting a scale, there are certain things you should
keep in mind in order to find the weighing device the best suites you. There
are certain terms that are used in the weighing industry to describe a scales
specifications. Here are some useful scale terms to know:
Capacity
- This is the maximum weight that the scale can accomodate at one time. Your
heaviest item that you place on the scale should determine what capacity you
need. For instance, the AMW-500
has a 500g capacity. This scale would be suitable for weighing small items that
weigh less than 500g.
 Top
Accuracy - The scales
accuracy is the smallest increment of weight that the scale displays (display
accuracy). For the AMW-500,
the accuracy is 0.1g.
This means that the scale counts up in increments of 0.1g ( 0.1, 0.2, 0.3, 0.4g......and
so on). Another scale may have an accuracy of 0.5g, meaning it would count up
by 0.5g like: 0.5, 1.0, 1.5.... Therefore, you would never see the display show:
1.4 or something. Accuracy and capacity,
are the two most important specs for selecting your scale. They will also play
a big role in how much the scale will cost. A scale that is 1000g x 1g is going
to be cheaper than a scale which weighs 1000g x 0.1g. Therefore, you should
select a scale based off of the measurements you require.
Accuracy is also written as Resolution or Readability.
Weighing Platform
- The size of the scales weighing platform (also
written Weighing Tray) is another thing to consider when purchasing
your scale. You want to have a large enough tray area to hold most of your sample,
but it is ok if some of it hangs over the side as long as it is balanced and
centered on the platform. Also your sample should never rest against anything
other than the scales weighing tray, otherwise your readout will be inaccurate.
You can also buy expansion trays with many scales, but some even come with them
(such as the Blade
Series). When you use expansion trays, the Tare function
is used to reset the scale to zero after adding the tray.
Top
Expansion Tray
- An expansion tray effectively increases the scales weighing
platform size, and allows for easy management of items that would otherwise
fall off the scale.
Top
Tare - Tare is used to reset
the scale to zero. This can be used to weigh items using a container that you
set on the scale. To use the Tare function, place the container or tray
(tare item) on the scale and press the Tare button. Your scale should go to
zero allowing you to now add items to the container and only see the weight
of those items within it (net weight).
Top
Calibration - Calibration
is the process of adjusting a scales precision using known weights (calibration
weights). Calibration should only be performed if your scale is not weighing
properly. After calibration, the scale should display the exact weight that
is placed on the tray (within a certain tolerance), and also go to Zero when
removing any weight. Some scales do not offer calibration (such as most postal
scales). Typically, a scale calibrates at two points: zero and at the end
of its span (span calibration). So, for the AMW-500,
calibration starts with nothing on the scale (to get the zero weight), then
the scale will ask for a 500g weight. Other scales might have linear calibration,
which calibrates at 3 points (zero, center span, end span). You should check
your users manual for calibration instructions.
Top
Calibration Weights
- Calibration weights are known masses such as a 100g
or 500g
weight. It is important to use the correct calibration weight when calibrating
a scale. Otherwise, your scale could become highly innacurate. For instance,
if during calibration, the scale asked for you to place 200g
weight on the tray, and you placed 100g
instead, your weight readouts on the display would show at twice what their
actual weight was. For instance, if you placed 1g on the scale it would say
2g, 4g would say 8g, and so on. Obviously, this is not how you would want your
scale to perform. Check availability of weights with your scale supplier, or
check here for our Calibration
Weights section. Calibration weights do not always come with a scale.
Top
Calibration Certificate
- A Calibration Certificate is a certified document provided by a local weighmaster
which provides proof of calibration along with information
about when/where the calibration was performed, and with what weights. This
service must be performed within the state that you will be using your scale.
Cal Certs. are required for scales which are used to sell goods based on weight.
If you are selling goods with your scale, it must be Legal for
Trade and have calibration performed regularly.
Legal for Trade / NTEP Approved-
If you will be selling goods based off of weight with a scale, it must be Legal
for Trade. This status is given to scales that meet certain guidelines and restrictions
mandated by the Department of Weights and Measures. This helps insure that consumer
is protected against overcharge.
Top
Linearity - Linearity
is a scales ability to produce the same accurate readout throughout the entire
span. Linearity is mostly listed on specification sheets for the high-end precision/industrial
scales and not for scales such as pocket
scales. To test linearity of a scale, you would use multiple weights, each
of which are a fraction of the scales total capacity. When placed on the scale
together, the weight should equal the sum of each individual weight.
Top
Repeatability -
Repeatability, like Linearity, is a specification most seen on precision/industrial
scale spec. sheets. It refers to the scales ability to display the same
weight consistently for an object and return to zero each weighing cycle.
Top
Strain Gauge Load Cell
- Most digital scales use a load cell to convert weight to a digital signal.
Load cells typically consist of a block of metal with a strain guage attached
that can detect the slight variations in stress on the metal. The strain guage
detects the change in electrical resistance and converts this to a digital signal.
The scales microprocessor converts this signal to a weight and displays it on
the LCD.
Top
Capacitance Load Cell
- In a capacitance cell, two thin metal waffers are set at a small distance
apart. As weight is added to the scale, the pressure pushes the two plates closer
together. The signal is sent to a microprocessor which then converts it into
a weight readout. Capacitance cells aren't quite as poular as load cells, but
are used in the 1479V
from Tanita.
Capacitance cells are designed to be more durable than strain
gauge load cells, but are also said to not be as accurate.
Top
|
