Everyone knows them from visiting the post office. But parcel scales are also used in other areas of daily life. They belong to calibration class M III. By law, a parcel scale must be calibrated if the price/charge is determined by the weight. Post offices, courts, customs, etc. would be examples of this. Parcel scales can be used for shipping as well as in trade, commerce and industry. After official verification it is prohibited by law to calibrate with calibration weights. The first calibration is valid for 2 years. After that, annual recalibration is necessary.
The practical piece counting and percentage function makes this scale indispensable for many applications. The percentage function shows the deviation of the respective sample from the reference weight. As with other balances, calibration must of course be carried out before the balance is put into operation for the first time. Unfortunately, this is not possible later.
What makes parcel scales so valuable?
Decision criteria are:
the package size and thus the weighing range
digital or mechanical - today almost exclusively digital (savings, more practical)
the number of load cells
freestanding or built into a table
the transverse load and leverage effect
the taxiway or the ball table
the overload protection
the possible electrostatic charge caused by the packaging - Recommendation: extra grounding of the platform of the balance
further processing of the weighing data - integration into the dispatch system, checking for completeness, monitoring of the highest payload of the delivery vehicles
The package size is the most important criterion for the selection of the package scale. The platform size should never be smaller than the package. The weighing process and the associated precision depend on how well the parcel is supported. This is the only way the sensors, the measuring cells can record and process the weight. There are models with only one measuring cell in the middle and those with four in each corner of the platform. The first variant is the cheaper one. Parcel scales are usually in continuous use. Therefore the price should not be the first priority when deciding to buy. Reliability and longevity are the top priorities for users.
A freestanding parcel scale is often used for other purposes. This damages the longevity of the scale. This can be remedied by sinking the scale into the work table. However, in this case it is advisable to install path limiters as mechanical overload protection. Overdimensioning the maximum load would be another alternative. The higher the maximum load on the weighing surface, the worse the resolution. Not to mention the measurement uncertainty. Heavy packages pushed and pulled on the package scale cause transverse loads and leverage effects. However, the load cells are not designed for this. For this case there are the "runways" or the ball table (airport, large post offices). This looks like an assembly line, but with rollers.
Every parcel scale for commercial use should have overload protection. Electrostatic charges caused by packaging negatively influence the precise weighing result. Separate grounding of the platform is the only viable solution.
To be able to process the data further, the scale must be loaded with CSV files. This process is relatively simple. These are created with Excel, for example. The transfer of data can be done on a case-by-case basis or continuously. The occasional data transfer takes place either by pressing a button directly on the package scale or via an external button. The latter is the better variant. The continuous, automatic data transfer takes place when a stable weight value is available. With some variants, data retrieval is possible by control command. The system can be connected via Modbus, USB, LAN or RS232.
Of course, the digital connection to a PC requires some effort. Therefore independent "Plug and Play" possibilities are becoming more and more popular. This requires parcel scales with scanner, a database and printer. The data is scanned, the weight is stored e.g. on a USB stick. Many parcel scales have data interfaces for printer and PC connections. There are also models that have internal software. This enables direct connection to UPS, GLS or DHL.
Which variants are available?
Parcel scales with removable stainless steel weighing plate. USB parcel scales are particularly suitable for shipping and offer many functions. The weighing ranges go up to 200 kg. Readability is possible in the range 0.5 g to 50 g. Some offer bidirectional USB interfaces, piece counting function or multiple tare. For the piece counting function, however, the package scale requires a reference quantity. Some parcel scales have an integrated spirit level and lockable, adjustable feet for levelling. Stands can be separated from the platform and recessed into the table. Cables are usually plugged in for easy handling. Plastic-coated steel platforms are easier to clean. Stainless steel platforms are rust-free. The IP67 protection rating indicates that the package scale is dust-tight and can even sometimes be completely submerged under water (to a depth of 1 m!).
There are also built-in package scales for level installation. On request, the version with a mounting frame is also available. There is also the possibility to install the package scale in the floor. Loading with any means of conveyance is easily possible with this scale. By default, parcel scales work with 240V mains power. If the parcel scale has a very small division, it can also be used as a letter scale. The displays usually have practical backlighting. Smaller scales often have a carrying handle on the side so that they can be easily transported. Some also offer battery operation. The choice between battery or mains operation provides additional safety and guarantee for the ongoing operation. Large parcel scales weigh up to 300 kilograms and have a 100g graduation. The display unit of the digital scale usually has a wall mount. If these devices work in battery operation, they have an operating time of approx. 60 hours. The automatic switch-off function has proven to be very practical.
Used for the intended purpose, regularly cleaned and serviced, parcel scales have a very long service life.