Considerations for Buying a Scale
Buying a weighing product involves more than a summary
comparison of capacity and price. This article reviews some
major points to consider when buying a scale.
When buying a scale, there are several criteria that are important
to help you find the right product for your needs. Often
price is considered as the deciding point, but in order to get the
most out of any scale, you should consider the total value that the
scale will bring to your operation. If the scale is key to
the efficiency and profitability of your business, and especially
if it is used to manufacture or package your products, in the long
run a low cost scale can often be far more expensive.
Capacity
A primary criterion is the total weight of what you will
measure. A common mistake is to buy a scale with the same
capacity as the weight of the item you will usually weigh.
While this may seem the right choice, and may help you buy a less
expensive scale, it is important to remember that there are several
specifications that cover the capacity of the scale. A scale
may be rated to 100 lbs., but how much extra weight can be added
before the scale is damaged? OHAUS products routinely offer a
150% overload rating, so that a 100 lb scale can handle a load to
150 lb before there is a possibility to casue damage to the
weighing device. More importantly, how will the weight be
added to the scale? Some operations routinely drop items or
bags on a scale, which increases the force which the scale
experiences (also known as a dynamic load). So the same 100
lb scale will handle a 90 lb load placed normally on the scale, but
might be damaged if the same load is dropped 5 feet onto the
weighing platform. A way to ensure that the scale is able to
withstand the loads placed on it is to buy a scale twice the
capacity of the weight you expect to place on it, so a 100 lb scale
would be better suited to handle 50 lb loads precisely, rather than
a 60 lb scale. While the heavier scale might cost more
initially, it will be better suited to the needs of your
operation.
Weighing Unit
Another issue to think of is which weighing unit will your
operation use? Pounds, kilograms, ounces? The weighing
unit used will also vary depending on what you are weighing:
- Avoirdupois - Pounds, ounces, tons, grains, etc.
- Metric -- kg, g, mg, metric tonnes
- Jewelry -- Grains, pennyweights (dwt), Troy Ounces (ozt),
carats (ct), etc.
- Custom units
In some instances, the weighing unit will already be decided by
a legal requirement, in others it will be based on the needs of
your operation. Is there a need to change units quickly, or
do you need to use only one unit? When buying a scale, it is
important to ensure that you understand this issue and buy the
scale that fits your operation.
Readability
Another major factor is the readability of the scale, or how
precisely it has to read. This is often confused with the
accuracy of the scale (which is actually the combination of the
scale, how it is set-up, how it is used, and how well it is
maintained). Many large capacity scales only require a
readability of 0.1 lb, while a bench scale used for QA/QC on a
processing line might have to be accurate to 1g (about 0.002 lb).
Built into this issue is how reliable the weight reading has to
be, which may be legally prescribed and is affected by the item
being weighed. A general rule of thumb is to buy a scale
which is 10 times the precision you need (for example, buy a scale
that reads to 0.1 lb if you need 1 lb of readability), or to have
an approved/certified scale installed. If the weighing
process has to be legally approved or certified, the scale will
have to meet legal standards which will define a level of
reliability for the readability of the scale. Even if your
operation does not have this legal requirement, using an
approved/certified scale will ensure a higher level of
performance.
Object Size, Shape and Movement
Most items weighed on a scale do not require special
consideration, but your process may require additional features on
the scale to accurately weigh. Is the object, like a shipping
box, often so large as to obscure the display? Is the object
moving, like livestock, or is the environment causing the object to
move, like with a conveyor belt? Is the object round,
requiring you to box the product? Understanding exactly what
the object is to be weighed is a key factor to consider.
Modes/Software
Once you have decided the capacity and readability you will need,
the next step is to decide what modes or software you will need in
the scale to meet your application. Most scales are used for
straight weighing, possibly with some additional filtering to
mitigate environmental issues like vibrations, etc. Some of
the most common weighing applications are:
- Parts Counting
- Checkweighing
- Percentage Weighing
- Dynamic Weighing
- Display Hold
- Totalization / Accumulation of data
- Statistics output
- Retail Price Computing
- Legal for Trade
- GMP or GLP for Traceability
When buying a scale, decide if the scale has to more than one
application, and make sure that the way the scale actually works
fits your operation. Many scales will offer parts counting,
for example, but each will operate differently and may offer
software to increase the accuracy of your counting, all of which
will affect how accurately you count in your day-to-day
business. When buying a sale, your local dealer can help you
buy the right scale for your application, and will help you set-up
the scale properly.
Environment
Another issue is the general environment in which you use your
scale. Almost any scale will work well in a laboratory
environment, but there are definite characteristics for a scale
that can work in harsh industrial environments or outdoors. A
common specification for industrial scales is the NEMA or IP
rating, which will tell you how well the scale will handle dust,
dirt, water and other materials trying to ingress into the
scale. In the US, the NEMA rating will tell you how resistant
the scale is to ingress and to the effects of corrosion, while the
international IP rating will give information about ingress
only. Beyond this distinction, scales that are rated IP65 or
NEMA4 or higher will be washable and resist infiltration of dirt
and water.
Along with water resistance, many scales used in food processing
and foodservice require additional listings or
certifications. NSF provides a range of standards for food
safety, and lists/certifies foodservice equipment. In
addition, scales may be USDA-AMS accepted for use in food
processing applications, and often equipment is required to support
HACCP systems for food safety. Understanding which of these
food safety standards apply is critical to ensuring that you have
the right scale for your operation.
Temperature
Another environmental factor will be the temperature range, which
is especially critical as the materials which make up the weighing
sensors in the scale will be affected by both the ambient
temperature as well as any rapid changes in temperature. Most
applications will not require special consideration beyond ensuring
that the scale has equalized with the ambient temperature, but if
your scale will be used in a difficult environment consult your
local dealer to ensure that scale you buy fits the situation.
Connectivity
Connectivity with computer systems and printers is increasingly
required in many situations for traceability and process
control. Most scales offer an RS232 port for connection to a
printer or PC, though many also have the option of USB, RS485/422,
or other standards. If connectivity or printing is also a
requirement of your application, choose the right scale.
Often your local dealer can integrate the scale into your process
and can also act as a consultant to help you get the most out of
your scale investment.
Support
As with anything else, the warranty is important to understand how
much the manufacturer will stand behind their product. Most
manufacturers will warranty their products against defects in
design or manufacture for a set period of time, although these
issues will present themselves relatively early in the ownership
term. Some manufacturers will have longer warranties, some
shorter, but in most cases the warranty will not cover damage cause
by misuse, accidents, or normal wear-and-tear.
Just as important as the warranty is the support that the
manufacturer provides. Is there information easily available
on the web? Can you get a new manual quickly by
download? Is there additional information on how to use the
product, like a quick start guide? Is there in-person tech
support through either a telephone call or an on-line chat?
Also important is how much support you need the dealer to
give. Do you need the dealer to help you set-up the scale and
calibrate it for optimum accuracy? Can they help you
integrate the scale into your process? Can they provide
scheduled calibrations? Can the dealer get spare parts easily
for repairs? Is the dealer an authorized dealer, or are they
reselling products they have bought through another dealer?
Conclusion
Many factors go into buying a scale, especially if your business
depends on it for your profitability. As with any piece of
equipment, the value - and not the price -- of the product will
determine if it ends-up being a good investment for you. By
carefully looking at your needs and the abilities of the scale, you
will be able to make the right choice.
Related links
- NSF
www.nsf.org
- USDA-AMS
www.ams.usda.gov
- HACCP
http://en.wikipedia.org/wiki/Hazard_Analysis_and_Critical_Control_Points
- IP
http://en.wikipedia.org/wiki/IP_Code
- NEMA
http://www.nema.org/
- NTEP - For more information, please go to
http://www.ncwm.net/ntep/
- Measurement Canada - For more information, please go to
https://strategis.ic.gc.ca/eic/site/mc-mc.nsf/eng/Home