Industrial Scale for Process or Legal-for-Trade Applications: Correctly Distinguishing Resolution, Weighing Range and Approval

→ Product category: Scales / Industrial Scales

 

An industrial scale is required to weigh components up to:

50 kg

.

The user requires:

1 g resolution

and also wants to transmit the weight values to a PLC.

Is a scale with:

Max = 50 kg

and:

d = 1 g

therefore sufficient?

These specifications alone are not sufficient for a reliable selection.

First, it must be clarified how the weight value will be used.

Is it intended for:

internal process monitoring

or:

a legally regulated or billing-relevant weighing application?

Further parameters must then be distinguished:

Max = maximum capacity

Min = minimum load

d = readability / scale interval

e = verification scale interval

internal resolution ≠ accuracy ≠ legal metrology scale interval

Additional factors include:

• platform size,
• load distribution,
• force introduction,
• overload reserves,
• environmental influences,
• weighing electronics,
• interfaces,
• calibration or legal metrology requirements.

A scale is therefore not selected solely according to the required kilogram capacity. The complete measurement task, including the mechanical installation and the legal use of the measurement result, is decisive.

Complete industrial weighing systems can be found at ICS Schneider under Scales / Industrial Scales. Load cells and other mechanical sensors can be found under Force, Weighing, Speed and Torque Sensors.

Process scale or legal-for-trade application?

The most important question is often asked too late:

What will happen with the measured weight?

Typical process weighing

A weight value may, for example, be used for:

• internal dosing,
• machine control,
• determining the fill level of a vessel,
• process monitoring,
• internal quality control,
• trend recording.

Typical legally relevant weighing

By contrast, the weight may be used directly for:

• sales by weight,
• billing between business partners,
• calculating a price based on mass,
• certain legally or officially regulated applications,
• certain prepackaging or weight-labeling processes.

The technical difference is significant

For a pure process scale, the measurement task can be optimized more strongly for:

• process accuracy,
• dynamics,
• interfaces,
• machine integration

.

For legally regulated weighing, the metrological regulations applicable to the specific application must additionally be fulfilled.

When is a scale subject to legal metrology requirements?

Whether a scale is subject to legal metrology requirements does not depend solely on the instrument itself.

The decisive factor is:

the specific intended use

Example 1

A company weighs raw material exclusively for internal production control.

The measured value has no influence on billing.

This is a typical:

process weighing application

Example 2

The same material is billed between supplier and customer according to the determined net weight.

The same measured value therefore acquires a:

commercial or legally relevant function

Important

It is not the designation “industrial scale” that determines whether legal metrology requirements apply, but the use of the measurement result.

Distinguishing automatic and non-automatic weighing instruments

The operating principle of the scale is also legally relevant.

Non-automatic weighing instrument

With a non-automatic weighing instrument, operator intervention is required during the weighing process.

Example:

place component on platform → read weight

Automatic weighing instrument

An automatic weighing instrument determines the mass within an automatically executed process.

For example:

product moves along conveyor → scale determines weight → product is automatically accepted or rejected

Typical automatic applications

• checkweighers,
• sorting scales,
• weight labeling,
• automatic filling,
• certain belt and totalizing scales.

Why this distinction is important

Different regulatory requirements and approval bases apply to non-automatic and automatic weighing instruments.

A request should therefore not only state:

scale must weigh 50 kg

but also:

manual or automatic weighing?

Distinguishing legal-for-trade capable, conformity-assessed and verified

These terms are often used synonymously in everyday practice.

Technically and legally, however, they are not identical.

Legal-for-trade capable

This generally describes an instrument version designed or approved for a corresponding legally regulated weighing application.

For a new instrument

the relevant conformity assessment procedure for the complete scale is required for legally regulated use.

During subsequent operation

national verification periods and regulations governing continued use may also apply.

Important

A single legal-for-trade capable component does not automatically turn a self-built weighing system into a legally compliant scale for regulated use.

Calibration is not legal verification

These two terms must also be clearly distinguished.

Calibration

During calibration, the indication of a measuring system is compared with traceable reference values.

The result can, for example, be documented in a:

DAkkS calibration certificate

.

Legal verification or statutory metrological control

has a different purpose.

It concerns compliance with legal requirements for the intended regulated use.

Therefore

calibrated ≠ legally verified

and:

DAkkS calibration certificate ≠ legal metrology approval

Conversely

a legal-for-trade capable or verified scale can also be calibrated additionally if, for example, a quality assurance system requires detailed information on the actual measurement deviation.

Correctly determining maximum capacity Max

The maximum capacity:

Max

is one of the most important selection parameters.

Typical mistake

The product itself weighs a maximum of:

50 kg

so a:

50-kg scale

is selected.

However, the following may be overlooked

• container weight,
• fixtures,
• transport aids,
• adapter plates,
• dynamic loads.

Example

Product:

45 kg

Container:

8 kg

Fixture:

2 kg

Total load:

55 kg

The scale sees the gross load

Even if the display after taring shows:

0,000 kg

the load cells are still mechanically loaded by the container.

Why tare does not increase maximum capacity

A tare function changes the zero point of the display.

However, it does not change the mechanical load on the weighing system.

Example

Scale:

Max = 60 kg

Container:

20 kg

after taring:

Display = 0 kg

Remaining mechanical capacity

is not once again:

60 kg

but correspondingly lower.

Key point

Tare creates display capacity, but no additional mechanical load capacity.

What does minimum load Min mean?

Legal-for-trade scales frequently also specify:

Min

Minimum load

identifies the lower limit from which the scale may be used for the intended legally regulated measurement task or from which the corresponding metrological requirements apply.

This does not mean

that the display necessarily shows nothing below Min.

However

for legally relevant determination of weight, a displayed value below the permissible minimum load must not simply be treated as a regular legal-for-trade weighing result.

Example SFE 30K-2NM

ICS specifies:

Max = 30 kg

d = 10 g

e = 10 g

Min = 200 g

Consequence

A product weighing:

50 g

cannot therefore be considered legally correctly weighed merely because the display shows a value.

What does scale interval d mean?

The scale interval or display increment:

d

describes the smallest step of the weight display.

Example

With:

d = 10 g

the display may, for example, show:

12,340 kg

12,350 kg

12,360 kg

However

A display in 10-g increments does not mean that the scale measures with an accuracy of ±10 g under all conditions.

What does verification scale interval e mean?

For legally regulated scales, the:

verification scale interval e

is additionally specified.

The verification scale interval

is the scale interval relevant for legal metrology assessment.

Frequently

the following applies:

d = e

but the two terms must nevertheless be distinguished technically.

Example

For the SFE series listed by ICS, separate columns are specified for the corresponding legal-for-trade models, for example for:

• readability d,
• verification scale interval e,
• minimum load Min

.

Do not confuse resolution and accuracy

One of the most common misinterpretations is:

more digits on the display = more accurate scale

This is incorrect

Resolution initially only describes how finely changes can be displayed or processed internally.

Actual measurement quality is additionally influenced by

• linearity,
• repeatability,
• hysteresis,
• temperature behavior,
• corner load,
• mechanical force introduction,
• zero-point drift,
• filtering,
• environmental conditions.

Example

A system may internally resolve:

1.000.000 parts

.

This does not automatically mean that it achieves:

1 ppm accuracy

.

Why internal resolution is not the usable resolution

Modern weighing electronics use very high-resolution A/D converters.

Example SIWAREX WP351

ICS specifies an internal resolution of:

±20.000.000 parts

At the same time, ICS specifies for legal-for-trade applications

among other things:

3 × 6000 d

for a multi-range/multi-interval scale.

This clearly shows

internal digital resolution ≠ permissible scale division

Why is high internal resolution useful nevertheless?

It enables, for example:

• clean filtering,
• small usable signal changes,
• good control performance,
• precise dosing cut-off,
• diagnostics.

However, the resulting weight value must not simply be displayed with an arbitrary number of meaningful digits.

Number of scale intervals and weighing range

A simple parameter is:

n = Max / e

for the number of verification scale intervals in the corresponding weighing range.

Example

SFE 6K-3NM:

Max = 6 kg

e = 2 g

therefore:

6000 g / 2 g = 3000 scale intervals

Another example

SFE 300K-1LNM:

Max = 300 kg

e = 100 g

therefore likewise:

300.000 g / 100 g = 3000 scale intervals

Consequence

With the same number of usable scale intervals, a larger weighing range results in a larger weight increment.

Max should therefore not be selected unnecessarily high.

Multi-range and multi-interval scales

With a very large load range, there is often a conflict between:

high maximum capacity

and at the same time:

very small scale interval

One possible solution

is to use multi-range or multi-interval scales.

Example principle

A system could operate with a smaller scale interval in the lower range and a coarser interval at higher loads.

Advantage

This allows a larger overall range to be used without unnecessarily sacrificing resolution in the lower load range.

However

the specific switching logic and approval are instrument-specific.

Distinguishing load cell class and complete scale

For self-built weighing systems, a load cell with:

OIML R60 C3

is often selected.

Example

The:

SIWAREX WL260 SP-S SB

listed by ICS is available in accuracy class:

C3 according to OIML R60

.

ICS also specifies use in class III commercial scales.

Important distinction

The approval or accuracy class of an individual load cell is not automatically the approval of the complete scale.

The complete system additionally includes

• platform,
• force introduction,
• mechanical stops,
• wiring,
• junction box,
• weighing electronics,
• software,
• display.

Each of these components

can influence the actual weighing result.

Selecting the correct platform size

A platform scale must not only have the correct maximum capacity.

The dimensions must also suit the load

A container should:

• rest securely on the platform,
• not tip over,
• not permanently protrude excessively,
• not introduce impermissible moments into the load cell.

Example

A small single-point load cell may have sufficient load capacity.

However, a significantly oversized platform creates higher bending moments and corner-load stresses.

Manufacturers therefore often specify

for platform load cells a:

maximum permissible platform size

Corner load and off-center loading

Ideally, the load would always act exactly along the intended force introduction axis.

In everyday operation, however, a component is often positioned:

• to the left,
• to the right,
• at the front,
• at the rear

of the platform.

A suitable platform scale

must handle such changes in position within its specified limits.

Typical test

A defined weight is applied successively:

• in the center,
• at different corners or positions

.

If the indication varies significantly

the following should be checked:

• leveling,
• platform mechanics,
• load cell installation,
• mechanical stress,
• corner-load adjustment.

Mechanical force introduction

A load cell does not measure abstract “weight”.

It responds to the mechanical load applied to its measuring body.

Ideally

the force acts:

in the intended measuring direction

Problematic influences include

• lateral forces,
• bending moments,
• torsion,
• mechanical stress,
• mechanical friction points.

Particularly with vessel scales

connected:

• pipes,
• hoses,
• cables,
• agitators

can transmit additional forces to the weighing system.

Avoiding transverse forces and mechanical stress

A common error pattern is:

scale empty → zero point correct

vessel connected → zero point shifts

Possible cause

A rigid pipe pulls or pushes on the weighed vessel.

The weighing system then measures

not only:

weight force

but also additional mechanical reaction forces.

Therefore

flexible connections must not only be present, but must also be:

sufficiently mechanically flexible

.

Installation surface and leveling

A platform scale requires a stable mechanical base.

Unfavorable conditions include

• soft floors,
• unstable positioning,
• uneven feet,
• mechanical stress in the frame,
• vibrating machine foundations.

Leveling

is particularly important because the load cell is designed for a defined direction of force.

For mobile scales

the following should be checked after relocating the scale:

• stability,
• leveling,
• zero point,
• if necessary, a check weight.

Considering dynamic loads and overload

A scale with:

Max = 100 kg

is not automatically suitable if a:

100-kg component is regularly dropped onto the platform from a height of several centimeters

Distinguish static and dynamic loading

During impact, significantly higher forces can occur briefly.

Therefore consider

• mechanical overload capacity,
• impact loading,
• drop height,
• mechanical stops,
• transport operation.

In practice

An adequate reserve in maximum capacity is useful.

However, an unnecessarily large scale is also disadvantageous because usable resolution typically decreases.

Temperature, vibration and air flow

Even a correctly installed scale can be influenced by its environment.

Temperature

affects, among other things:

• load cell,
• electronics,
• mechanics.

Vibrations

can prevent a stable weight indication.

Air flow

is particularly relevant for:

• small loads,
• large lightweight components,
• high-resolution scales

.

Other influences

• moisture,
• dust,
• cleaning agents,
• electromagnetic interference.

Correct load cell wiring

Load cells often provide very small electrical signals.

Typical strain-gauge load cells, for example, operate in the range of:

mV/V

This makes signal transmission sensitive

to:

• EMC interference,
• potential differences,
• poor shielding,
• contact resistance,
• moisture in junction boxes.

Do not modify cables unnecessarily

For certain load cell designs, the connection cable is part of the specified measurement chain.

For multi-cell scales

the following are often used:

• summing boxes,
• junction boxes,
• digital junction boxes

.

Important

Mechanically perfect load cells cannot produce a stable scale if the millivolt signals are transmitted electrically in an unsuitable manner.

Interfaces and PLC connection

In industrial systems, a weight display alone is often not sufficient.

Additional interfaces may include

• RS-232,
• RS485,
• Ethernet,
• PROFINET,
• Modbus TCP,
• Modbus RTU,
• analog output,
• digital inputs and outputs.

Clarify before selection

Should the PLC only:

read the weight

or should it also:

• tare,
• zero,
• dose,
• control limit values,
• read status information?

Also consider the data rate

A static shipping scale does not require an extremely fast measurement update rate.

For automatic dosing, however:

response time and update rate

can be decisive.

Correctly classifying checkweighing

The term:

checkweighing

does not automatically mean:

legally regulated checkweigher

Internal checkweighing

For example:

A company checks internally whether a component weighs approximately:

12,5 kg

.

The result is used exclusively for internal process evaluation.

Automatic legally regulated checkweigher

In an automated production line, by contrast, a weight value may be used for legally relevant sorting or a prepackaging task.

Therefore

the following must be assessed together:

• intended use,
• degree of automation,
• legal function of the result

.

Correctly designing process weighing

If there is no legal metrology requirement, a scale can be optimized specifically for the process.

Typical requirements

• high repeatability,
• fast settling,
• small dosing increments,
• PLC connection,
• robust mechanics,
• high degree of protection.

Dosing example

A valve is to close when:

24,950 kg

is reached.

The static display alone is not sufficient here

Additional relevant factors include:

• measurement filtering,
• sampling rate,
• switching delay,
• product overrun,
• vessel mechanics.

Measurement uncertainty and process capability

For industrial applications, the theoretically smallest display increment is often not the decisive factor.

More important is:

How reliably can I distinguish a real process value?

Example

A scale displays:

0,1 g

increments.

Under real conditions, however, the same device under test fluctuates by:

±1,5 g

An additional decimal place

is then only of limited benefit to the process.

The following should therefore be considered

• repeatability,
• linearity,
• long-term drift,
• temperature,
• installation conditions,
• measurement uncertainty.

Systematic selection of an industrial scale

1. Define the measurement task: Weighing, counting, dosing, checking or billing?
2. Clarify legal use: Is the weight commercially, officially or otherwise legally relevant?
3. Determine whether weighing is automatic or non-automatic: Operator intervention or automatic weighing?
4. Determine maximum gross load: Add product, container, fixture and auxiliary equipment.
5. Consider dynamic loads: Estimate impact, loading and overload.
6. Define the smallest required usable weight increment: Do not specify only a desired display resolution.
7. Check minimum load: Particularly for legal metrology applications.
8. Distinguish d and e: Consider readability and verification scale interval separately.
9. Check number of scale intervals: Evaluate the relationship between weighing range and required interval.
10. Consider a multi-range solution: For a large load range combined with high resolution.
11. Determine platform size: Consider the dimensions of the largest item to be weighed.
12. Evaluate load position: Centered or frequently off-center loading?
13. Check force introduction: Avoid lateral forces, bending and friction points.
14. Check installation location: Evaluate floor, foundation, vibration and leveling.
15. Define the environment: Consider temperature, dust, moisture, cleaning and degree of protection.
16. Select material: Steel, stainless steel or hygienic design appropriate for the environment.
17. Select load cell concept: Single-point or multi-cell solution according to the mechanics.
18. Select weighing electronics: Consider measuring rate, filtering, I/O and diagnostics.
19. Determine interfaces: Define PLC, MES, ERP, printer or PC connection.
20. Define calibration requirements: Consider factory or DAkkS calibration.
21. Define legal metrology requirements: If required, select only a version suitable for the specific regulated application.
22. Evaluate the complete system: Do not consider only the load cell or display individually.
23. Define test procedure: Check zero point, repeatability and several load points.
24. Check corner load: Test different load positions on platform scales.
25. Define documentation: Document instrument version, calibration, approval and test intervals.

Typical errors with industrial scales

Observation	Possible cause	Recommended check
Scale has many decimal places, but results still vary	Resolution confused with accuracy	Check repeatability and environmental conditions
Weight depends on the position on the platform	Corner-load error or mechanical stress	Test the load at several positions
Scale reaches overload with a full container	Tare weight was omitted when selecting Max	Calculate maximum gross load
Small products are below the permissible minimum load	Weighing range selected too large	Consider a smaller scale or multi-range system
Display drifts after connecting a pipe	Mechanical force shunts	Check pipe connections or flexible connections
Value changes when the cable is touched	Cable strain or electrical contact problem	Check cable fastening and connection
Display fluctuates while machine is running	Vibrations	Check installation location and filtering
Weight jumps when a frequency converter is operating	EMC interference	Check shielding, cable routing and grounding
Display is no longer correct after relocation	Leveling or installation conditions changed	Re-level the scale and check with a test weight
Empty scale does not return exactly to zero	Mechanical friction or stress	Check platform for free movement
Load cell is C3, but complete scale is not legal-for-trade capable	Component approval confused with system approval	Check complete configuration and weighing electronics
DAkkS certificate is available, but scale may not be used for billing	Calibration confused with legal verification	Check legal requirements for the intended use
Automatic checkweigher was selected like a static platform scale	Dynamic and regulatory requirements were not considered	Design automatic weighing process separately

Practical example: selecting a 30-kg platform scale

A manufacturer wants to weigh containers with product fillings of:

2 … 24 kg

.

The container weight is:

4 kg

Step 1: Determine gross load

Maximum load:

24 kg product + 4 kg container = 28 kg

Step 2: Weighing range

A scale with:

Max = 30 kg

is generally better matched to the application than an unnecessarily large 150-kg version.

Step 3: Resolution

Assume the required weight discrimination is:

10 g

It is then not sufficient merely to check whether:

d = 10 g

is available.

Repeatability and process conditions must also meaningfully support this requirement.

Step 4: Legal use

Variant A:

The weight is used only to monitor an internal filling process.

In this case:

process measurement

is the main focus.

Variant B

The customer pays exactly according to the net weight determined on this scale.

The specific scale must then be designed for the corresponding legally regulated use.

Step 5: Example SFE 30K-2NM

ICS specifies for this version:

Max = 30 kg

d = 10 g

e = 10 g

Min = 200 g

Step 6: Platform

It must additionally be checked whether the:

300 × 240 mm

platform is suitable for the container.

Step 7: Environment

If the scale is used in an industrial area with dust and splash water, the IP65 version of the SFE series is an additional relevant selection feature.

Result

Only the combination of gross load, scale interval, minimum load, platform size, environmental conditions and legal use determines whether the selected 30-kg scale is actually suitable.

Suitable ICS products for industrial and legal-for-trade weighing systems

SFE Platform Scale with Legal-for-Trade Approval [M]

For conventional industrial platform weighing, ICS offers the:

SFE Platform Scale

ICS specifies, among other things

• IP65 protection against dust and splash water,
• stainless steel weighing plate,
• stainless steel display unit,
• checkweighing function,
• hold function,
• legal-for-trade versions [M],
• optional DAkkS calibration certificate.

Available ranges on the ICS website

extend, depending on the version, from:

Max = 6 kg

to:

Max = 300 kg

Examples

Model	Max	d	e	Min
SFE 6K-3NM	6 kg	2 g	2 g	40 g
SFE 30K-2NM	30 kg	10 g	10 g	200 g
SFE 60K-2NM	60 kg	20 g	20 g	400 g
SFE 100K-2LNM	150 kg	50 g	50 g	1000 g
SFE 300K-1LNM	300 kg	100 g	100 g	2000 g

Why this series is particularly illustrative for this topic

The product data directly shows the relationship between:

weighing range → readability → verification scale interval → minimum load

Further information can be found under SFE Platform Scale at ICS Schneider.

SIWAREX WP351 – Weighing Electronics for Process and Legal-for-Trade Applications

For weighing systems integrated into machines and plants, ICS offers the:

SIWAREX WP351

ICS specifies, among other things

• internal resolution ±20.000.000 parts,
• digital output response time < 1 ms,
• 3 × 6000 d multi-range/multi-interval scale,
• 0,4 µV/e,
• integrated web server,
• various communication interfaces.

Legal-for-trade capability

ICS specifies legal-for-trade capability according to:

• OIML R-51,
• OIML R-61,
• OIML R-76,
• OIML R-107.

Typical applications according to ICS

include, among other things:

• precision mixing,
• filling,
• bagging,
• checking,
• dosing.

Particularly important for this article

The WP351 clearly demonstrates:

A very high internal electronic resolution must not be confused with the permissible or practically usable scale interval of the complete scale.

Further information can be found under SIWAREX WP351 at ICS Schneider.

SIWAREX WP231

Another legal-for-trade weighing electronic module listed by ICS is the:

SIWAREX WP231

ICS specifies

• integration into SIMATIC S7-1200,
• operation also possible without SIMATIC CPU,
• Ethernet,
• RS485 with Modbus,
• 4 digital inputs and outputs,
• analog output,
• accuracy 0,05 %,
• internal resolution up to 4 million parts,
• update rate 100 Hz.

Application

The WP231 is particularly suitable for static scales and machine-integrated weighing systems in which weight values are to be transferred directly to the automation system.

Further information can be found under SIWAREX WP231 at ICS Schneider.

SIWAREX WL260 SP-S SB – Platform Load Cell

For building compact platform scales, ICS offers the:

SIWAREX WL260 SP-S SB

ICS specifies

• rated loads of 6, 12, 30 and 60 kg,
• accuracy class C3 according to OIML R60,
• use in class III commercial scales,
• up to 3000 scale intervals,
• stainless steel,
• hermetically sealed,
• degree of protection IP68,
• maximum platform size 350 × 350 mm.

Typical applications

ICS specifies:

• platform scales,
• small belt scales,
• checkweighers,
• dosing applications.

However

The OIML R60 class of the load cell does not replace the assessment or approval of the complete weighing system.

Further information can be found under SIWAREX WL260 SP-S SB at ICS Schneider.

Which solution is suitable?

Application	Suitable ICS solution
Manual industrial platform weighing	Consider SFE platform scale according to Max, d and platform size
Legal-for-trade platform weighing	Consider SFE version with legal-for-trade approval [M] according to the application
Weighing system directly integrated into SIMATIC S7-1200	SIWAREX WP231
Highly dynamic or demanding automatic weighing application	Consider SIWAREX WP351 according to the application
Custom compact platform scale up to 60 kg	Consider SIWAREX WL260 SP-S SB as load cell
Pure internal process weighing	Design weighing range, resolution, mechanics and interface according to process requirements
Legally regulated or billing-relevant weighing	Select a complete suitable and conformity-assessed/legal-for-trade system configuration

An overview of the complete product group can be found under Scales / Industrial Scales at ICS Schneider.

Conclusion

When selecting an industrial scale, the statement:

“We need to weigh up to 50 kg.”

is not sufficient.

First, the use of the weight value must be clarified

The decisive question is:

internal process information or legally relevant weight determination?

Next comes the weighing range

The maximum capacity must be designed for the:

maximum gross load

.

Tare, container and fixture continue to load the load cell even when they have been zeroed on the display.

Resolution is not accuracy

The following must be distinguished:

• internal resolution,
• readability d,
• verification scale interval e,
• actual measurement deviation.

For legal-for-trade scales, Min must also be considered

A displayed weight below the minimum load must not simply be treated as a regular legally valid weighing result.

Mechanics are just as important as electronics

Even a highly accurate load cell delivers poor results in the presence of:

• lateral forces,
• mechanically stressed installation,
• unsuitable platform,
• unstable foundation,
• rigid pipe connections.

Approval of a component alone is also not sufficient

A:

C3 load cell

does not automatically turn a self-built structure into a complete legal-for-trade scale.

For practical applications

Determine intended use → distinguish process weighing from legal metrology weighing → determine automatic or non-automatic function → calculate maximum gross load → consider minimum load → define required weight increment → distinguish d and e → do not confuse internal resolution with accuracy → define platform size → check load position and force introduction → consider overload and dynamics → define environment and degree of protection → select load cell and electronics concept → define interfaces → define calibration or legal verification requirements → test the complete scale under real operating conditions.

FAQ: Selecting an Industrial Scale for Process or Legal-for-Trade Applications

What is an industrial scale?

An industrial scale is a robust weighing system for production, logistics, testing or process applications. Depending on the design, it can be configured as a platform, floor, counting, crane, vessel or automatic scale.

When do I need a legal-for-trade scale?

This depends on the specific use of the weight value. Particularly relevant examples include weighing processes in which mass is used for commercial billing or other legally regulated purposes.

Is every scale used for incoming goods subject to legal metrology requirements?

Not automatically. The decisive factor is the legal or commercial function of the determined weight.

What is a process scale?

A process scale provides weight information for control, monitoring, dosing or internal quality control within a technical process.

Can a process scale still be legal-for-trade capable?

Yes. A weighing system can technically be designed for legal-for-trade applications even if it is currently used exclusively for internal process purposes.

What does Max mean on a scale?

Max denotes the maximum capacity of the respective weighing range.

Does the container weight have to be included in Max?

Yes. Mechanically, the complete gross load consisting of product, container and any additional fixture acts on the scale.

Does taring increase the maximum load capacity?

No. Taring only resets the display. The mechanical load remains present.

What does Min mean?

For corresponding legal-for-trade scales, Min denotes the minimum load of the approved weighing range.

Can the scale still display a value below Min?

Yes, technically a value may still be displayed. However, this does not automatically mean that the value may be used for legally regulated weighing.

What does d mean?

d is the scale interval or smallest digit increment of the weight display.

What does e mean?

e is the verification scale interval used for metrological assessment of a legally relevant scale.

Are d and e always the same?

No. Although d = e applies to many industrial scales, they are technically different parameters.

What does scale resolution mean?

Depending on the context, this can refer to displayed resolution, internal resolution or counting resolution. The term should therefore always be specified more precisely in an inquiry.

Is a scale with a 1-g display accurate to 1 g?

Not automatically. Repeatability, linearity, temperature, mechanics and other influencing factors determine the actual measurement quality.

What is internal resolution?

It describes how finely the weighing electronics can internally process the electrical input signal in digital form.

Why do weighing electronics have millions of internal divisions?

High internal resolution provides reserves for filtering, control, linearization and small signal changes. It does not mean that the weight can be displayed or legally used with the same number of divisions.

What does n = Max / e mean?

This can be used to determine the number of verification scale intervals in the corresponding weighing range.

Why should I not select Max unnecessarily high?

An unnecessarily large weighing range often results in a coarser weight interval for a comparable number of divisions and therefore reduces usable resolution for small loads.

What is a multi-range scale?

A multi-range scale has several weighing ranges with different limits or scale intervals.

What is a multi-interval scale?

With a multi-interval scale, the scale interval changes within the total weighing range depending on the load zone.

What does C3 mean for a load cell?

C3 denotes an accuracy class according to OIML R60 for corresponding load cells.

Is a C3 load cell automatically legal-for-trade capable?

The load cell may be suitable for constructing corresponding legal-for-trade systems. However, the complete scale must meet the respective requirements as an overall system.

What is a single-point load cell?

It is designed for platform scales and can compensate for off-center loads within the specified platform size.

Why is the maximum platform size of a load cell important?

A larger platform creates higher moments and changes the mechanical loading of the load cell.

What is a corner-load error?

This describes a change in the indicated weight when the same load is applied at different positions on the platform.

Why must a platform scale not be installed under mechanical stress?

Mechanical stress can transfer additional forces to the load cells and thereby influence zero point, linearity and repeatability.

Why do pipes influence a vessel scale?

Rigid pipes can transmit forces to the weighed vessel that act on the load cells in addition to the actual weight force.

Why is leveling important?

Load cells are designed for a defined loading direction. An inclined installation can generate additional force components.

Can vibration influence a scale?

Yes. Mechanical vibration can cause an unstable indication and can particularly affect automatic dosing or checkweighing processes.

Which degree of protection should an industrial scale have?

This depends on dust, moisture, cleaning procedures and the installation location. For industrial wet or cleaning areas, IP65 or higher degrees of protection may be relevant, for example.

What is checkweighing?

During checkweighing, the measured weight is compared with predefined limits, for example for portioning, sorting or quality control.

Is checkweighing automatically subject to legal metrology requirements?

No. The specific application and use of the measurement result are decisive. However, corresponding metrological requirements apply to certain automatic legally regulated checkweighers.

What is a non-automatic weighing instrument?

A weighing instrument that requires operator intervention during the weighing process.

What is an automatic weighing instrument?

A weighing instrument that determines mass within a predefined automatic sequence without operator intervention during the actual weighing process.

Is calibration the same as legal verification?

No. Calibration documents the measurement deviation relative to traceable references. Legal verification or statutory metrological control concerns compliance with legal requirements.

Does a DAkkS calibration certificate make a scale legal-for-trade capable?

No. A DAkkS calibration certificate is not a substitute for the required legal metrology conformity.

Can a legal-for-trade scale additionally be DAkkS-calibrated?

Yes. This can be useful particularly for quality assurance and measurement uncertainty assessments.

What is the SFE platform scale?

The SFE listed by ICS is an IP65 platform scale for industrial applications that is available in different weighing ranges and with legal-for-trade approval [M].

Which weighing ranges are available in the SFE series?

Depending on the version, ICS lists maximum capacities from 6 kg to 300 kg.

Which values does ICS specify for the SFE?

Depending on the model, the data includes maximum capacity Max, readability d, verification scale interval e, minimum load Min and platform size.

What is the SIWAREX WP351?

The SIWAREX WP351 is a high-resolution weighing electronic module listed by ICS for various manual and automatic weighing applications.

What internal resolution does the WP351 have?

ICS specifies an internal resolution of ±20 million parts.

Does that mean 20 million legal-for-trade scale intervals?

No. ICS specifies 3 × 6000 d for the corresponding legal-for-trade multi-range/multi-interval function. The internal electronic resolution must therefore be clearly distinguished from the legal metrology scale interval.

What is the SIWAREX WP231?

The WP231 is a weighing electronic module for SIMATIC S7-1200 which, according to ICS, can also be used without a SIMATIC CPU and provides Ethernet and RS485 interfaces.

What is the SIWAREX WL260 SP-S SB?

It is a stainless-steel platform load cell with IP68 and C3 according to OIML R60, which ICS lists for platform scales, checkweighers and dosing scales, among other applications.

Which rated loads are available for the WL260 SP-S SB?

ICS specifies 6, 12, 30 and 60 kg.

Which platform size does ICS specify for the WL260 SP-S SB?

A maximum platform size of 350 × 350 mm is specified.

Where can I find industrial scales at ICS Schneider?

An overview can be found under Scales / Industrial Scales at ICS Schneider.

Where can I find load cells and force sensors at ICS Schneider?

An overview can be found under Force, Weighing, Speed and Torque Sensors at ICS Schneider.

Where can I find the SFE platform scale at ICS Schneider?

Further information can be found under SFE Platform Scale at ICS Schneider.

Where can I find the SIWAREX WP351 at ICS Schneider?

Further information can be found under SIWAREX WP351 at ICS Schneider.

Where can I find the SIWAREX WP231 at ICS Schneider?

Further information can be found under SIWAREX WP231 at ICS Schneider.

Where can I find the SIWAREX WL260 SP-S SB at ICS Schneider?

Further information can be found under SIWAREX WL260 SP-S SB at ICS Schneider.