When selecting a scale, there are certain things to keep in mind in order to find the weighing device that best suites you.
Legal For Trade
If you will be selling goods based on 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 NRCS (National Regulator for Compulsory Specifications) and SANAS (South African National Accreditation System) to promote fair trade and to protect public health and safety
Calibration is the process of adjusting a scales precision using known weights (mass pieces). Calibration should only be performed if your scale is not weighing accurately. 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. Typically, a scale calibrates at two points: zero and at the end of its span (span calibration).
This is the maximum weight that the scale can weigh at one time. Your heaviest item that you place on the scale should determine what capacity you need.
The accuracy that the scale weighs in.
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.
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).
A Calibration Certificate is a certified document provided by us that provides proof of calibration along with information about when/where the calibration was performed, and with what weights. Cal Certs. are required for scales that 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.
The scales accuracy is the smallest increment of weight that the scale displays (display accuracy). 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 that weighs 1000g x 0.1g. Therefore, you should select a scale based on the accuracy and capacity you require. Accuracy is also written as Resolution or Readability.
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 gauge attached that can detect the slight variations in stress on the metal. The strain gauge 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.