Parcel Scales

How to make a decision about what model of scales to purchase?
It may be quite a challenge to decide what to buy, especially when it goes about such a delicate device as scales. From the one side, weight remains weight and some customers may ask whether it really matters what model of scales to purchase to fulfill a weighing task.

We in PCE Instruments are sure that making a choice of the measuring or weighing device is a serious task and plays an important role. That is why, in case of doubts or questions, you are welcome to contact us: you may use either consulting hotline of PCE Instruments 02903 - 976 99 – 50 or email.

Our specialists are ready to share their knowledge with you and find the solution for your task together with you. Even if you have got some unusual task requiring a special approach, we are ready to take the challenge. Please, describe what you need, and we’ll find a way to create a new design and adapt the software especially for your requirement.

A few recommendations below may help you to make the right choice, and we invite you to read this short text before making the final decision about selecting and purchasing a new measuring device.

If the decision is not easy, first of all, try to make it clear for yourself, what you need, by considering the following:

- Is there any need in verification of the weighing procedure (is there a requirement from the legal authorities)?
- Determine the materials to be weighed (Max. / Min. weight)
- What are the sufficient values for accuracy / resolution / repeatability?
- Are there special requirements to the size of the platform?
- What are the desirable functions the scales should perform?
- Should the data from the scales be further processed after weighing or not?
- Desirable price range

Is there any need in verification of the weighing procedure (is there a requirement from the legal authorities)?

Sometimes, there is an opinion that it is always better to have something than not to have, if it goes about extra papers, documents, proofs and similar. In case of parcel scales, it is not quite the case. Verification is a special procedure which will not particularly influence the precision and accuracy of your scales and it may turn out that for your tape of application, it is absolutely unnecessary. That is why, before making a decision, determine what the main purpose and place of application will be and as a confirmation, you can consult the verification office in your area.

As a customer, you may have a desire to get extra security and confidence that the device you are purchasing is an accurate and reliable weighing instrument. We fully understand that, and in case you find out that a verification is not mandatory, we offer you a good option: calibration certificate. The latter is an official document containing all the necessary information about the measurement deviations, errors, repeatability and other parameters, and thus, you will get a better idea about your device and what to expect from it.

Determine the materials to be weighed (Max. / Min. weight)
Since parcel scales are expected to give quite precise results, the resolution and accuracy are the parameters to care about. They are connected with the weight that will regularly be put on them. Since with the increase of the weight the parameters may change and get worse, it is desirable to avoid overloading of a certain model of scales with the weight which the device is not suitable for. So, your further task is to determine the minimum and maximum weight of the parcels which you are going to weigh. If there is a possibility that a need to weighing bigger load may arise in future, the scales can be modified by adding a few better load cells – this will solve the problem with resolution and accuracy but will also influence the price of the device. That is why, weigh determination is an essential point to think about.

What are the sufficient values for accuracy / resolution / repeatability?

One of the most frequent mistakes is a confusion between resolution, accuracy and repeatability and the role these parameters play in the process of weighing. Depending on what an accent is made on, the parcel scales can be adjusted correspondingly. In case of this type of scales, resolution is very important. In general, there is a similar principle as for other types of scales. If the measuring accuracy is not specified, the rule for the parcel balances is that the measurement deviation is the resolution value multiplied by 3 or 4. A buffer "factor 10" for the parcel scales can be arranged by the user, which, in any case, will give him confidence in measurements. Example: If the balances have the resolution 0.1 g, then a measurement deviation of approx. ± 0.3 g ... ± 0.4 g has to be assumed (unless otherwise described). However, if the user wants to have the measuring accuracy of 0.1 g, then he should look for a balance with the resolution of 0.01 g (factor 10).

As stated above, calibration certificate may provide an operator with all the information concerning deviation, repeatability and similar.

For sure, multiple weighing and use over longer periods of time lead to drifting of the scales and the measuring error becomes bigger. A solution may be to have a personal weight set, with the help of which the parcel scales can be regularly checked and, on demand, adjusted.

Are there special requirements to the size of the platform?

Platform size plays an incredibly important role in the weighing platform, as well as how well the load fits on the platform. Maximum load and accuracy are connected with the platform size and that is why it is another issue to solve. When weighing an attention should be paid to the position of the load (parcel) on the platform. Leverage effect may occur, if the parcel is not placed correctly or does not quite fit, and this may be compensated by the cells of the scales, but for sure, it is better and recommended to place the parcel correctly from the very beginning, with the center of gravity in the center of the platform. In general, the smaller the weighing platform is, the more accurate the scales / balances are. For various weighing tasks, there may be various solutions found, like, for example, weighing of suspended loads, but if it goes about platform, it is definitely a point which should not be underestimated and neglected.

What are the desirable functions the scales should perform?

This question can and should be answered only by the user / the operator, who is going to use the particular scales regularly. A certain model of scales may have numerous functions, which is not always necessary for all the users. In addition, one may function may be needed sometimes, but for different applications (like for example, piece counting function), and it is important to consider this to make an absolutely right choice. A long list of functions is not always the best solution for a certain user. That is why we recommend, first of all, to clearly define what you are going to use the device for and only then make a decision. The device you choose, should meet exactly the requirement you have, otherwise, no matter, how interesting it may from the purchasing aspect point of view, it may turn out to be inapplicable for your weighing task.

Should the data from the scales be further processed after weighing or not?

Modern weighing equipment is often digital, which means that there are many possibilities which they offer, besides direct weighing, for example, there may be analogue outputs, interfaces, USB or LAN interfaces, possibilities for connection to printer or scanner, saving the data to the USB stick for further processing on the computer, data storage and many others. In fact, to produce the scales with all these elements is much easier and cheaper than to install them later on a ready-made device. It may seem to the customer that certain functions are not necessary at the moment; at that point, we ever recommend to think a bit forward and try to predict if there is any possibility that some of the above-mentioned features might be necessary in the future. Preliminary installation may turn out to be very helpful and you will save the extra costs later.

Desirable price range

If you have succeeded in answering all the questions and in making it clear what model of the parcel scales you need for your weighing tasks, it may turn out that there are a few models available that may meet your requirements, but that are from different price ranges. Then, you should carefully study the technical specifications and select the device which will really facilitate and accelerate the weighing process and improve your performance. Not always it is the most expensive model, but not always – the cheapest. Saving money just by buying the cheapest device is not a correct solution, and that is why we recommend to look at this problem from different angles and make an investment into a device which will bring use and good result in future, but not save a bit of money right now.

First of all, there is the question of platform size. If possible, the dimensions of the platform should not be smaller than those of the parcels to be weighed. This is particularly important for the parcel scales equipped with only one measuring cell located in the centre of the platform. In these models, uneven loading can cause leverage forces that can lead to incorrect measurement results and damage the load cell. Other models of the parcel scales have four load cells installed in each corner of the platform instead of one load cell in the centre of the platform. The model of the parcel scales with one load cell is in most cases cheaper than the parcel scales with four load cells. However, the purchase price should not be the most important selection criterion. Rather, durability and reliability in the conditions under which the parcel scales will be used should be taken into account.

Day after day and week after week, the parcel scales often go through a serious test in the manufacturing, order picking or shipping. Thousands of weighings have to be performed. With an appropriate preparation, even inexpensive parcel scales can meet these demands. One way to reduce the risk of overloads and lateral forces is to embed the parcel scales in a worktable. On the one hand, this measure prevents the misuse of the parcel scales and, on the other hand, it reduces the effect of horizontal forces on the platform and thus on the load cell located underneath. Depending on the design of the parcel scales, mechanical travel limiters can also provide protection against overloading of the load cells. Another possibility would be to oversize the maximum load, e.g. to choose the parcel scales for 150 kg maximum load even if only parcels up to 50 kg are weighed. In the case of this solution, it must be taken into account that the resolution and the measurement error deteriorate with increasing maximum load.

Before selecting the parcel scales, it should be checked due to which arrangement of the scales and with the help of which additional measures the weighing processes can be carried out as ergonomically as possible and without unnecessary transverse loads for the scales. In the case of very heavy parcels that have to be brought onto the platform per hand, there is a high probability that the parcels will be pushed onto the platform. However, the load cells are not designed for the transverse forces that occur during pushing. Possible solutions that also reduce the load on the employees and thus simplify the weighing processes are, for example, swivelling hoists, roller conveyors etc. Parcel scales can also be integrated directly into the roller conveyor systems.

Depending on the size and weight of the items to be weighed, the package scales is placed on or in the floor or arranged in a working table. If only very small packages are weighed, compact scales can also be used as the package scales. Mostly, however, the platform scales are used as the parcel scales, where the platform can be installed separately from the display and control unit. The housing and electronics in many models of the modern digital parcel scales are designed to compensate for vibrations to a certain extent. Many of these models of the parcel scales have the option of setting a filter value in the operating menu. To avoid electrostatic charges that can be caused by packaging material, for example, we recommend grounding the platform of the parcel scales separately.

Special functions in the parcel scales
The standard functions in the scales include zero setting and the tare function. Most scales also have calculation functions. The totalizing and piece counting functions are among the most frequently encountered functions in the parcel scales. The totalizing function allows several weighings to be combined. This is useful, for example, if the total weight of a consignment or the weights per load carrier must not be exceeded. With the piece counting function, the quantity of similar parts, such as screws of one type, can be determined quickly and easily. This facilitates the checking of multi-piece packages and the inventory of small parts. Two other functions that are useful for operational use and in research are the percentage and limit value functions. Due to the percentage function, it can be determined with the package scales how far the individual items or packaging units deviate from the specified reference weight. If the deviation is too high, the affected parts can be sorted out before further processing or dispatch. The parts with too heavy or too little weight can thus be separated more quickly and then recycled separately. The limit value function can be used in a similar way: after defining the upper and lower limit value, it is displayed whether the weighed part is too light, ok or too heavy.

Special functions in the parcel scales include the so-called animal weighing function for dynamic weighing, adjustable filters for reacting to fluctuating ambient conditions and internal databases for the product data. In some models of the parcel scales, the internal database can be easily loaded with the help of CSV files. These CSV files can be created with the popular spreadsheet programs such as Excel or exported from merchandise management or warehouse management programs.

If other units are required instead of the internationally used units grams and kilograms, care should be taken to ensure that the parcel scales offer the option of converting to these units. A clock built into the scales makes it possible to assign the weighing time and date to each stored or printed weighing result.

Interfaces for the parcel scales
Once the design and functions of the parcel scales have been selected, it must be clarified whether the measurement data will only be read or whether it will be passed on to other devices for printing or storage and the requirements for the measurement data must be determined. The main question to be clarified is the further processing of the weighing data. Many users want or need to log the weighing results. For this reason, the parcel scales usually have a data interface for connecting a printer or PC.

Many of our customers intend to integrate the parcel scales into the existing shipping system in order to be able to add the weights of the weighed parcels to the shipping documents. With special software, the weighing results of the parcel scales can be transferred directly into company-specific application programs or into the parcel service software of DHL, GLS and UPS. This is to prevent the errors in the transfer of the weighing results and to shorten the processing time. During weighing, a check for completeness can then also be carried out, if necessary, by means of the TARGET-ACTUAL weight comparison. In addition, it is possible to take the maximum load capacity of the delivery vehicles into account when compiling the deliveries. Various types of interfaces can be used to connect the parcel scales to the computer, for example RS232, USB, LAN or Modbus. After a successful connection, the transfer of the weighing results can be triggered by pressing a button on the parcel scales. If this is the solution desired, we recommend checking whether the connection of an external push-button would facilitate the process. The other possibilities to trigger the data transfer are, for example, continuous data transfer, automatic data transfer when the weight value is stable and, in the case of any parcel scales with a bidirectional interface and also query of the weighing data via the control commands.

The connection of the parcel scales to a computer involves a certain amount of effort, and not every weighing station is suitable or intended for an immediate transfer of the data to a computer. For this reason, the demand for PC-independent "plug and play" solutions has also significantly increased lately. With these solutions, the parcel scales can be equipped with an internal database and provided with the connections for scanners and printers. With the help of the scanner, the user can quickly and securely send information about the product to the parcel scales and then save it together with the determined weight on an adhesive label and/or on a USB stick.

Here is an example:
The user scans a barcode with the product number 272035. The parcel scales then search in the internal database for the information stored about the product. In this case, the parcel scales have the stored the article description "guide sleeve" and the unit weight. After the user has placed the parts to be weighed on the parcel scales, a label with the important information such as the article designation, article number, number of pieces, piece weight, etc. can now be created. The results are printed once again as a barcode so that the data can be scanned and processed quickly, securely and easily elsewhere.

In addition to the interfaces for transmitting the weighing data to printers or computers, the parcel scales can also be or be equipped with analogue or switching interfaces for process control. Via these interfaces, the weighed parcels or parts can be, for example, automatically sorted on the conveyor systems according to weight and forwarded further.

Here is another example:
Data transfer to transport service providers such as DHL, UPS, DPD, GLS, Schenker via the shipping interface
For many companies with high shipping volumes, it makes sense if every parcel scales in the shipping department can be integrated into the existing shipping system in such a way that the weights of the parcels are transferred directly to the shipping documents when they are weighed. This may prevent the errors in the transfer of the weighing results and considerably reduce the processing time. To do this, the parcel scales must be connected to the computer via an interface. Special software programmes for scales make it possible for the data transferred from the parcel scales to be immediately transferred in the appropriate format to the desired location in the company's shipping programme or in the software used by the parcel service or the forwarding agents.

Before converting the shipping process, it should be determined for how many weighing stations the data transfer to the shipping software is desired and whether the scales of different types have to be integrated. There are software solutions available that only support single parcel scales and others that can receive the data from several scales simultaneously, even if they are not of the same type. Often the manufacturers of the scales offer different solutions and support the user in selecting the appropriate model.

When weighing, a check for completeness can be made immediately, if necessary, by comparing the weight with the stored data. The weight determined by the parcel scales is compared with the sum of the stored individual weights of the parcel contents and packaging material. If there are major discrepancies, the parcel can be checked again before it is handed over to the parcel service. This reduces the number of incorrect deliveries with too much or too little goods. It is also possible to take into account the maximum load capacity for pallets or for certain delivery vehicles when compiling parcels for deliveries.

Various types of interfaces can be used to connect the parcel scales to the computer, for example RS232, USB, LAN or Modbus. After a successful connection, the transmission of the weighing results via these interfaces can be triggered by pressing a button on the parcel scales or on an external button mounted at a suitable location. Other possibilities to trigger the data transmission are, for example, the automatic data transfer when the weighing value is stable and, in the case of the parcel scales with a bidirectional interface, also the querying the weighing data by pressing a key on the connected computer.

Mandatory verification of parcel scales
Verification is intended to ensure that no party is disadvantaged or even endangered in medical areas because of the incorrect weighing results. If you would like to have more information on the verification of scales or do not know whether you actually need calibrated parcel scales, you can contact your local verification authority. If you are sure that a calibrated parcel scale should or must be used, you must state this when ordering. In addition, for the most scales there is a requirement for the postcode and the town name to be specified for correct setting, as the weighing result is influenced by the gravitational value at the installation location. The more accurately the parcel scales can display, the smaller the local scope of the verification is. The verification is valid for 2 years. The operator is obliged to timely register the scales with the local verification authority for renewed verification.

According to the EU Directive 90/384/EEC, the scales must be verified if it is used, for example, as follows:

- In the course of trade, when the price of the goods is determined by weighing.
- For official purposes such as the determination of fees and penalties.
- For court opinions.
- In the manufacturing of the pre-packaged goods.

Information on volume weight
For optimizing the storage and freight space, it is not only the weight of the packages that is important, but also their volume. Service providers who charge for the transport of goods based only on weight would not be able to use the freight space effectively for large but light consignments. In order to be able to take the volume of the goods consignments into account when calculating the price, many service providers work with size limits. For large packages, the value of the volume weight has also been defined. This value is a "substitute weight" in order to take the size of the freight appropriately into account when calculating the price for the transport. To obtain the numerical value, the volume in cm³ of the consignment (i.e. length in cm * width in cm * height in cm) is divided by a divisor defined by the service provider. Only the higher of the two values, i.e. either the weight or the volume weight, is used to calculate the freight charges.

There are some special parcel scales that are equipped with additional devices for registering the parcel dimensions. When it goes about large parcel quantities, they not only facilitate the preparation and allocation of the shipments for dispatch, but also the effective storage of parcels. In the parcel scales with volume measurement, the length, width and height of the individual parcel are automatically recorded via laser distance meters, camera systems or light grids. Thus, the weight and volume is determined for each parcel. Some systems also allow dynamic measurement on the belt systems and result-dependent sorting of the parcels.

Many users transfer the weights determined with the parcel scales to application programs on the computer. There, the data is not only stored for documentation purposes as with an inventory list, but it is also immediately available for delivery notes and invoices or for order and material planning. The more weighing data has to be recorded, the greater the advantages are when the values do not have to be entered via keyboard but can be transferred directly from the parcel scales to the user software. This not only speeds up the process, but also prevents input errors.

Whether for incoming goods, for recipes, for order picking or for outgoing goods, the direct connection of the scales used to the ERP system considerably simplifies the recording of the weighing data. In order to not only show the weighing results on the display, but also to send them, the parcel scales must be equipped with a suitable data interface. RS232 and USB interfaces are relatively often already built into the scales as standard.

For the RS232 interface, the appropriate cable and the adapter from RS232 to USB are usually available as accessories with the scales, so that it can be connected to the computer without any problems. If you want to use a different type of interface, such as Ethernet, WiFi or Bluetooth, there are far fewer scales models to choose from. Alternatively, the scales with RS232 or USB interfaces can be connected to the Ethernet network via an interface converter, and RS232 or USB Bluetooth adapters enable wireless transmission to computers with Bluetooth.

The content of the transmission protocol of the parcel scales often contains additional information that should not be transferred to the ERP system. For this reason, software that filters the data immediately is required for the direct transfer of the weight values into application programmes. Many manufacturers offer such programmes for their scales. After the scales and computer have been connected and the appropriate settings have been selected, the scales software runs in the background. It ensures that the data for the weight sent by the parcel scales arrive at the current cursor position in the ERP programme like a keyboard entry.

Anyone who uses parcel scales generally assumes that the displayed weighing result is correct. However, depending on the type of the construction and the conditions of use, there may be more or less significant deviations between the displayed value and the actual value. These deviations can be determined relatively easily for all types of package scales that can be calibrated by means of weighing known weights.

Calibration weights
There is a wide range of test weights for different accuracies as single weights or multi-part sets, for different milligram, gram or kilogram values. The number and type of weights used should be selected according to the resolution of the package scales and according to the specific requirements for weighing accuracy. However, gross deviations in the results can be quickly detected even without special calibration weights. For example, containers can be tared and then filled with a known amount of water, or a suitable object can be additionally weighed on the comparative scales that have been proven to be accurate.

ISO and DAkkS calibrations
Where very high demands are made on the accuracy because of the product safety, the accuracy of the measuring instruments often has to be fully documented. One way of proving compliance with the accuracy tolerances of the package scales is to obtain device-related certificates of ISO or DAkkS calibrations. These calibrations should be carried out at regular intervals in approved in-house calibration laboratories or by external calibration services.

Calibration and adjustment
Not every tested parcel scales achieves the desired accuracy in the weighing performed during the calibration. Often, however, the affected scales can be readjusted to achieve the required accuracy through mechanical adjustments or by making adjustments via the device menu. When selecting the package scales, attention should be paid to which adjustment functions it offers. Often the adjustment function is referred to as calibration in the descriptions of the scales, even though the weighing result is influenced by the function. It is important for the user to know whether only one weight or several weights can be adjusted at a time and whether the weights used can be freely selected.

Should the calibrated parcel scales also be calibrated?
In the areas of application where weighing errors can lead to financial or health damage, the calibrated parcel scales must be used. With the verified scales, measurement errors are limited by official regulations and official monitoring. Of course, the calibrated parcel scales can also be calibrated. Additional calibration is particularly recommended if the accuracy is to be checked at shorter intervals than during the verification. The verified parcel scales cannot be adjusted without breaking the calibration seal. It must then be recalibrated and sealed. If the seal is damaged, it may no longer be used for weighing subject to verification.