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What to consider when buying a Scale

What to consider when 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.

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?  Some products (Ex. 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 cause 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.

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.

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.

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.

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 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.

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?  

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.