Platform Scales

While looking for a suitable model of platform scales, one may see how many different scales that can be used for weighing are available. With this purchase advice, we would like to give you an overview of different designs and functions to make the process of selecting the right platform scales easier.

First and foremost, the question of the platform size is crucial. Platform scales can have different platform sizes. The platform sizes are designed according to the sensors installed there and, if possible, should not be smaller than the goods to be weighed.

Criteria for selecting the right platform scales:

- What is the measuring task like? (Type of scales)
- Is the weighing operation legal-for-trade/subject to verification? (Legal requirement)
- What are the ambient conditions?
- What is the heaviest item to be weighed? (Maximum weight)
- How light is the lightest item to be weighed? (Minimum weight)
- What is the desired accuracy? (Resolution / repeatability / accuracy)
- What is the aim of the weighing? (Functions)
- Should the measurement data be further processed after weighing? (Interfaces)

Due to the different applications, platform scales have a very wide range of use. Due to different shapes, functions and accessories, standard platform scales can easily be adapted to the needs of the respective place of use.

- What is the measuring task like? (Type of scales)
First of all, the user should define the application of the platform scales, which means to primarily determine the main task field. Enquiries about the platforms scale can be used to cover all the task at the enterprise are not quite correct.

With this knowledge, the user can make a preselection of the platform scales. First and foremost, PCE platform scales are robust and durable.

The platform scales consist of an evaluation unit (display) and an external platform (weighing plate). The platform is mainly mounted on or in the work table. The platform size plays a particularly important role in the platform scales. There are two types of the platform scales, which should be used according to the specific application. The less expensive platform scales have only one weighing cell (single point) in the middle of the platform. However, this construction is significantly higher compared to the platform with 4 load cells, as the struts of the construction have to be more stable. The single point weighing plate is limited in size, as the leverage forces could otherwise easily damage the cell. In the case of the platform scales with 4 load cells, one is more flexible in the platform size, as the load is distributed over 4 points and thus larger platform dimensions can be made possible. When choosing the right platform scales, the price should play a subordinate role, as the fulfilment of the application requirements should be in the foreground. The platform scales are secured differently against transverse and leverage forces and should be selected in accordance with the requirements at the place of use in order to be able to guarantee a durable working application.

- Is the weighing process legal-for-trade/subject to verification? (Legal requirement)
If the shape and design of the platform scales have been specified in more detail, further requirements must be clarified. An important piece of information that strongly influences the selection of the appropriate scales is the question of “legal-for-trade” or “mandatory for verification”. The legal-for-trade weighings must be carried out with the calibrated platform scales; otherwise there is a risk of fines in the event of non-compliance. The calibrated platform scales are mandatory where a price is determined through the determined weight.

However, if the weighing values are intended for internal purposes, verification is not mandatory and should be avoided if possible. Verification restricts some functions of the platform scales that may not be compliant with regulations, but may prove to be very helpful in the work environment.

- What are the ambient conditions?
Once the legal-for-trade requirement of the platform scales has been clarified, the ambient conditions at the place of use should be determined. Platform scales can be found in a wide variety of areas, so that different requirements are made for the material and the technology. For example, there may be a specific requirement for the alloy used, as is often the case in the chemical industry. In the food industry, for example, the industrial scales made of stainless steel with a high IP protection class are required, which are also HACCP-compliant. In foundry operations, for example, there are special requirements for heat protection and in potentially explosive areas only platform scales with an appropriate explosion protection may be used.

- How heavy is the heaviest product to be weighed? (Max.)
- How light is the lightest product to be weighed? (Min.)
- What is the desired accuracy? (Resolution / Repeatability / Accuracy)
Once the previous general conditions have been clarified, the next step is to select the platform scales that match the goods to be weighed. In most cases, depending on the application, the aim is to achieve the largest possible weighing range (MAX) with the best possible resolution and the smallest possible measurement deviation. Taking into account the operating environment and the aspects already described, certain compromises may have to be made when selecting the platform scales.

- What is the aim of the weighing? (Functions)
As the platform scales are used in various fields, they have a variety of functions. Functions that are particularly on demand in industry include the totalizing function, container weighing function, batching function, TARGET and ACTUAL monitoring function, counting function. Some functions are programmed into the platform scales according to the customer specifications and thus fulfil the individual requirements of the customer.

- Should the weighing data be processed further after weighing? (Interfaces)
In most cases, the platform scales are extended with the help of additional interfaces. Depending on the customer's requirements, we can equip the platform scales with a bidirectional RS232, USB, LAN, RS485 interface or with a 0-10 V, 4-20 mA analogue output as well as several switching contacts for dosing and monitoring functions. The selection of these options should be made also with consideration of the future before ordering, as retrofitting of the platform scales is associated with considerable costs.

Since every industry has its own special requirements for the platform scales and the internal process sequences can also differ greatly, PCE Instruments offers the option of manufacturing an individual model of the platform scales. This is individually tailored to the customer's requirements and includes both design and software adaptations. If no platform scales from the standard range are suitable, please contact our technicians. However, the above-mentioned selection criteria for the platform scales should already have been thought through so that the project can be implemented cost-effectively and promptly.

The verified scales must be used in many areas of the food processing industry. What to pay attention for when selecting and using the verified platform scale is explained in the separate section - Platform scales with verification. When weighing food, there is also almost always the requirement that the surfaces that come into contact with the food can be cleaned easily and in accordance with the respective hygiene specifications.

Due to the hygiene requirements, the platform scale models are often used in the food industry where the surface of the weighing platform is made of smooth and easy-to-clean material. The surfaces made of stainless steel, ceramics or suitable plastic must often not only be resistant to moisture, but also withstand corrosive effects from cleaning agents or acids and alkalis used in the production process.

On many models, the platform is removable and can be cleaned separately. In other types of the platform scales designed for continuous use in humid environments, the entire housing is made of robust, rustproof material and the sensitive electrical and electronic components are enclosed in a waterproof housing. These types have high IP protection ratings and some of them can even be cleaned with steam jets and high-pressure cleaners.

The separate evaluation and display unit of the platform scale is connected to the housing via a fixed or detachable cable in such a way that it can be positioned independently of the housing at different heights and inclinations to suit the work process. Due to the nature of the goods to be weighed and the environmental conditions in the food industry, whether in the laboratory, in storage or processing rooms, outdoors or on conveyor lines, it is often advantageous to position the display and control panel slightly away from the weighing platform.

In the food industry, the platform scales as table or floor scales are often recessed at the same height in work tables or in the floor to facilitate the work processes. It is even more effective if the scales can be integrated into an existing or planned roller conveyor line. Then the weight of the foodstuffs can be checked practically on the way and the goods do not have to be lifted or driven onto the scales.

For the applications in the food industry, the scales can be adapted to the respective requirements with special equipment and accessories. These can be, for example, process and data interfaces, stored product databases, connections for printers and scanners, but also special protective or retaining brackets, separate weighing trays or protective covers for the operating unit.

In the food industry, weighing is often required for filling, mixing, portioning or packaging processes. For some processing steps, these processes, including weighing, can be largely automated. The scales used are equipped with analogue or switching interfaces for this purpose, or they transmit the weighing values directly to a computer. In other processes, a large part of the operations and weighing is carried out manually, but simplified by special menu functions of the platform scales used.

Useful additional functions include:

- Adjustable tare values for different containers or packages
- Recipe weighing function, for example for sausage, meat, baked goods, sauces, soups, teas
- Totalizing function for adding up several individual weighings
- Dosing aid function, e.g. with limit values or piece counts,
- Upper and lower limit for portioning and filling
- Continuous container weighing for monitoring the fill level
- Percentage function for displaying the percentage deviation from the target weight (e.g. for checking prepackages)
- Statistical functions for evaluating weighing data
- Integrated product database
- Product-related price calculation
- Label printing for products or packages
- Transfer of the weighing data directly into the user software
- Motion compensation function, e.g. for weighing live animals or on ships  

Not all the user requirements can always be met with the series-produced platform scales. Many manufacturers therefore offer customization options for some of their models. Among other things, dimensions can be changed or alternative interfaces can be installed.

In all the areas where the platform scales have to be cleaned frequently or come into contact with moisture or aggressive media for other reasons, stainless steel versions are the best choice. Stainless steels are quenched and tempered steels that are specially treated and often enriched with additives in the manufacturing process to achieve certain properties. The current steel list contains 159 unalloyed and 1315 alloyed stainless steels. In a common parlance, stainless steel is often equated with rust-resistant steel. However, rust-resistant steels are only a subgroup of stainless steels. Rust-resistant steels contain at least 10.5 per cent chromium and no more than 1.2 per cent carbon. However, the grades with higher chromium contents and additional alloying components are often used. Especially if the platform scales frequently come into contact with acids or dissolved salts, the resistance of the steel grade used to the products used should be clarified before purchasing new scales.

However, it is important to pay attention not only to the material of the housing, but also to how well the platform scales are protected against the ingress of water and foreign bodies. This protection can be classified according to EN 60529 (VDE 0470-1) and is known internationally as IP protection class or IP protection rating. The higher the two digits are, the better the protection of the enclosure against the ingress of foreign bodies and water is. Here, the first digit stands for the foreign bodies – IP6X means, for example, dust-proof and protected against contact. The second digit of the IP code stands for the protection against the ingress of water. The platform scales with IPX7 are protected against temporary submersion, with IPX8 against permanent submersion and with IPX9 even against cleaning with a high-pressure cleaner

Stainless steels are easy to clean, compared to the other materials, and are therefore preferred wherever hygiene regulations have to be observed. The stainless steel platform scales can be used in the food processing and chemical industries, in laboratories, in commercial kitchens, in laundries and dry cleaners. Also, the application outdoors, for example in a field, a pasture or a company storage area is possible, without the platform scales having to be elaborately protected from moisture.

The platform scales are one of the most commonly used types of scales. As with the compact scales, the material to be weighed is put on the weighing surface from above. The weighing cells are therefore subjected to pressure. However, the platform scales differ fundamentally from the compact scales in that the display and control unit are not placed together with the weighing platform in one housing. The multitude of the available models can be subdivided according to different criteria. If you are looking for the platform scales, it makes sense to choose a model the features of which have already been optimised for the intended use or for future conditions of use.

Platform scales as bench scales
Everyone has certainly used or at least seen the platform scales placed on a table or at table height. Be it in the post office or at the parcel service to check the weight of the parcels or in the supermarket at the meat or cheese counter, when weighing fruit and vegetables in the self-service area or at the checkout. The weighing platform can be placed on counters or work tables or, for special requirements, it can be embedded or integrated into the work surface. The display and control unit is either attached to a stand or wall or placed on the table. Most models can be mounted in various ways and the inclination can be adjusted. This makes it easy to adjust the position, regardless of whether the platform scales are operated while sitting or standing.

Platform scales as floor scales
When the goods with large dimensions or high weight, that are not moved at table height, need to be weighed, the platform scales placed on the floor with a suitable weighing range and large platform are often used. Floor scales are used, for example, as scales for people, animal scales, pallet scales, parcel scales or container scales. The drive-on platform scales are usually very flat and equipped with ramps or they are embedded into the floor. When selecting the maximum load of the drive-on scales, it is essential to take into account the load caused by the means of transport. Even if a pallet truck is not weighed later, it will put a load on the weighing cells when it is driven onto the platform.

Platform scales as animal scales
For weighing live animals, there are scales that are equipped with a special filter function. This animal weighing function compensates for fluctuating weight values caused by the movement of the animals. For weighing animals that are to walk on the platform scales by themselves, there are models with cage attachments. This ensures that the animal is completely on the platform during weighing. In general, the models offered as animal scales are very robust and usually also easy to clean.

Platform scales with several platforms
For some applications, it is practical to have several platforms of different sizes and weighing ranges connected to a common evaluation and operating unit. For example, for piece counting, the reference weight can be determined on the smaller platform with the better resolution and then the number of pieces in the large collection container can be determined on the other platform with the higher maximum weight. However, several platforms on one evaluation unit can also be useful for other applications.

Platform scales in U-shape or with two weighing beams
The U-shaped scales have been developed for easy weighing of Euro pallets moved by pallet trucks and other pallets with similar dimensions. With these, the fork of the lift truck or forklift can simply be moved between the two legs of the U-shaped housing and lowered there. The load cells of the U-shaped scales are therefore only loaded by the weight of the pallet. The lowering also means that there are no lateral forces.

This is also an advantage of the platform scales types where the goods to be weighed are placed on two beam-shaped weighing surfaces. In contrast to the U-shaped scales, where the distance between the two legs is fixed, the distance of the weighing beams can be changed and thus adapted to the goods to be weighed. They require little space and can be moved quickly and easily.

In many companies and institutions, it is intended to use the new platform scales not only at a fixed location, but occasionally or more frequently at different locations. For this purpose, it is convenient if the scales can be easily transported by one person and can also be operated without being connected to the mains. If the platform scales are to be used in very different climatic conditions, care must be taken to ensure that the design is adapted to this. If unsuitable models are used in damp, very hot or very cold environments, electronic parts may be damaged or the weighing results may no longer be determined with sufficient accuracy.

Battery and mains operation
If the platform scales are to be used frequently in locations where the connection to the mains is difficult or impossible, the models equipped with rechargeable batteries are recommended. For most applications, the models with battery and mains operation are particularly practical, as the battery is charged as soon as the scales are connected to the mains. As a rule, the scales equipped with battery or rechargeable battery show the current charge status by means of a changeable battery symbol on the display, so that weighing does not have to be interrupted abruptly.

Transport facilitation
For fast and uncomplicated moving of the platform scales, it is advantageous if it is designed to be light and compact. It should also be easy for one person to lift and carry without any risk of injury. This is not possible with the models that are too large or too heavy. However, the transport can be facilitated by placing the carrying handles and rollers on the scales housing. Then even heavy and bulky scales can be moved safely, if necessary, without great physical effort or additional means of transport, because it can be easily pulled across the floor.

The evaluation and control unit is usually connected via a flexible cable with a plug-in connection to the part of the platform scales in which the load cell and platform are installed. If desired, the cable can simply be unplugged and both parts can be transported separately. Permanently connected indicator parts can be locked to the housing or can simply be placed on the platform or taken in hand for a change of location.

Mobile truck scales
Mobile platform scales can also be used for weighing vehicles. Whereas with permanently installed truck scales the complete vehicle is often moved onto a very large platform, mobile weighing systems for vehicles consist of several platforms that are connected to the same evaluation unit. There are different options for size, load capacity and number of platforms.

The minimum equipment of the mobile truck scales includes two weighing platforms and the evaluation unit. This allows the vehicles to be weighed axle by axle and the total weight can be calculated as the sum of the axle loads. The individual platforms must be positioned according to the track width so that the vehicle tires can stand completely on the weighing platform. If there are more than two platforms, the axle spacing of the vehicle must also be taken into account when placing them.

The police also frequently use such types of the mobile platform scales in the cases of suspected incorrect loading or overloading. For example, these are the case during large-scale checks on motorways, during which the vehicles to be checked are checked in parking lots with suitable space. For applications where the location has to be changed frequently or the position of the individual platforms has to be changed in relation to each other, solutions are particularly suitable where the wheel loads are sent wirelessly from the platforms to the evaluation unit.

The verification of the measuring instruments and measuring tools serves to protect the consumers. It is intended to ensure that in trade and when calculating customs duties, the fees or penalties are calculated based on the correct measurement results. But also in the medical and pharmaceutical sector, verification is mandatory for the measuring instruments in hospitals, doctors' practices and laboratories where the measurement values have an impact on medical treatment. Surely everyone has checked the calibration mark on a beverage glass – consciously or unconsciously. With the help of this mark, the buyer can immediately see whether the ordered and calculated quantity of the drink – for example 0.2 or 0.3 litres – has been filled into the glass. In contrast, in the case of the goods that are weighed on the platform scales, it is not apparent whether the weight is correctly displayed. Therefore, for the scales used in legal metrology, regular inspection by the authorized for this purpose body is mandatory. In Germany, the responsibility for monitoring lies with the local calibration offices.

The place of installation influences the accuracy of the weighing result for the platform scales that determine the mass with the help of the weight. After all, the weight results from the mass multiplied by the location-dependent acceleration due to gravity. Only the scales that always compare the mass to be determined with a known mass are independent of the force of gravity. This applies, for example, to the Justitia beam balances with its symmetrically suspended weighing pans. Also, modern electronic platform scales, which have an internal reference weight and an automatic self-adjustment function, also weigh independently of the place of installation.

The force of attraction of large masses is generally referred to as gravity. It acts not only on the earth, but also on other celestial bodies. In the gravity-dependent platform scales, the more divisions there are, the stronger the influence of gravity is and thus, the more accurately the scales indicate. Therefore, the geographical area in which it may be used – the zone of use – then becomes smaller. In Germany, for example, the verification can be with the gravitational value g = 9.81 m/s² completely for the Federal Republic of Germany, for the two federal states of Baden-Württemberg and Bavaria-North with g= 9.8081 m/s² or for a specific place of installation, such as Meschede, with g = 9.811523 m/s². If the scales are to be used at another location or outside the permissible zone, it must be recalibrated and then calibrated for the new regional area of validity.

The calibration periods are specified for all the measuring instruments in the Measuring and Calibration Ordinance (MessEV). In general, the verification period is two years. However, unlike the main inspection and exhaust emission test for motor vehicles – i.e. the technical inspection for motor vehicles – it is always valid until the end of the year in which the prescribed period expires. This means that irrespective of the day in 2020 on which the platform scales were inspected at the Calibration / Weights and Measures Office, the verification is always valid until 31.12.2022 in the case of a 2-year period. According to Annex 7 of the Measuring Ordinance, different verification periods apply to the following non-automatic weighing instruments:

– platform scales with a maximum load of 3000 kg or more (except building material scales) 3 years
– platform scales as non-self-contained fine or precision scales 4 years
– commercial scales as platform scales with less than 350 kg maximum load 4 years
– platform scales for weighing people in hospitals (except bed scales) 4 years
– personal scales that are not installed in hospitals; verification is unlimited
– baby scales 4 years
– container trolleys for liquefied gases with shock-free application and removal 4 years
– platform scales as cattle scales in farms 4 years

Not each model of the platform scales is legal for trade. For this purpose, certain requirements must be met in the design. Above all, it must be ensured that the scales cannot be manipulated after calibration without damaging a calibration seal. The users who have to use the verified platform scales for their weighing operations must make sure when selecting new scales that it is already verified or conformity-assessed with a verification mark. Whether and when the scales have been verified can be seen on the type plate. Each time the scales are verified, a sticker indicating the year and the name of the verifying authority is affixed there. The following information must be permanently and tamper-proof displayed on the type plate or on the display or housing of the verified or conformity-assessed platform scales:

• Manufacturer's brand or name
• Model designation for the scales
• Number of the EC pattern approval
• The serial number of the scales
• Accuracy class It is indicated in Roman numerals from I to IV and is enclosed in an oval frame.
• Maximum load “Max” The weighing results above the maximum load may not be used, usually an overload symbol is displayed instead.
• Minimum load “Min” The weighing results below the minimum load, even if displayed, must not be used for legal-for-trade measurements.
• Division value / graduation value “d” The division value corresponds to the possible display steps and thus to the reading accuracy.
• Verification value “e” The verification value for the platform scales of accuracy class III corresponds to the division value "d". In accuracy class II, the verification value often corresponds to 10 times the graduation value and in accuracy class I, the   calibration value can correspond to 100 times the graduation value. The additional decimal places are marked as additional digits in the display – similar to the last digit in the electricity meters.
• The temperature limits within which the scales maintain the specified accuracy.

The platform scales that have been placed on the market with conformity assessment according to Directive 2014/31/EU is considered to be verified. It bears the CE mark and, directly behind it, the metrology mark M with the last two digits of the year of marking. The M and the year are framed by a rectangle. The EU declaration of conformity is mandatory for all conformity-assessed platform scales. If the declaration of conformity has been issued for a series of scales, it can also be provided as part of the operating instructions.