Industries

Weighing in the Chemical Industry and Hazardous Areas (ATEX)

Updated September 15, 20264 min readBy WPL Industries Engineering

Short answer

Chemical plants weigh raw materials, recipe components and filled containers, often where flammable gas, vapour or dust can form an explosive atmosphere. The operator classifies these zones, and the complete weighing installation must suit them. WPL supplies weighing electronics and software for Ex zones, SSP platforms with an optional ATEX load cell, and recipe and filling software.

What is weighed in chemical production

Chemical plants weigh raw materials at intake, components during recipe dosing, and drums, cans and containers during filling and final checks. Many of these steps take place where flammable gases, vapours or dusts are handled, so the weighing equipment must also suit the hazardous area it stands in.

WPL Industries, established in 1994, develops weighing electronics for different Ex zones and software that runs on Ex terminals. A typical WPL system for checkweighing and filling combines a PC-based touchscreen, with graphics and traceability reports, with dedicated microcontroller weighing electronics that handle the measurement itself.

Step	Typical load	What the weight is used for
Intake of raw materials	Bags, drums, containers	Stock, supplier checks
Recipe dosing	Components from grams to hundreds of kilograms	Correct composition, batch records
Filling	Cans, drums, containers	Stated quantity, product cost
Checkweighing	Finished packs	Rejecting under- or overweight packs, reports

ATEX weighing: hazardous area zones in plain words

A hazardous area zone describes how often and how long an explosive atmosphere can be present at a place, and it determines which equipment may be used there. Directive 1999/92/EC defines six zones, three for gases, vapours and mists and three for combustible dusts:

Zone (gas / dust)	Explosive atmosphere present	Equipment categories allowed
Zone 0 / Zone 20	Continuously, for long periods or frequently	Category 1
Zone 1 / Zone 21	Likely to occur occasionally in normal operation	Category 1 or 2
Zone 2 / Zone 22	Not likely in normal operation, and then only for a short time	Category 1, 2 or 3

In practice, zone 0 is found inside tanks and vessels, zone 1 around filling points and openings that are used regularly, and zone 2 in the wider area around them. The dust zones follow the same logic for places such as powder hoppers and bag emptying stations.

Rules for equipment and workplaces in Ex zones

Two EU directives work together: one covers the equipment, the other the workplace where it is used.

Directive 2014/34/EU (the ATEX equipment directive) applies to equipment and protective systems intended for use in potentially explosive atmospheres. The manufacturer assesses conformity for an equipment group and category and marks the product accordingly.
Directive 1999/92/EC sets the duties of the employer: assessing explosion risks, classifying places into zones and recording this in an explosion protection document.

Three consequences matter when you buy a scale:

The operator classifies the zones. A scale supplier cannot decide the zone; it follows from your own risk assessment.
The complete installation counts. The load cell, junction box, cables, indicator, PC terminal, printer and any interface to the control system must all be suitable for the zone where each part is installed.
One certified part is not enough. An ATEX load cell makes the load cell suitable for a zone; it does not by itself make the whole scale suitable.

WPL weighing equipment for chemical and Ex applications

WPL combines standard platforms and software with electronics chosen for the zone, and advises per project which components and certificates are available.

SSP stainless steel platform scale: a bench platform from 1.5 to 60 kg with an ATEX load cell available on request. The indicator, cabling and other parts of the configuration are selected separately for the zone.
R10 weighing indicator: an AISI 316 stainless steel housing, checkweighing with plus and minus tolerances, a filling application, four relay outputs, 13 digital I/O channels and fieldbus options such as Profinet and Modbus TCP. Ask WPL whether it can be used for your location, or which alternative electronics apply for the zone.
WeightControl Formula: step-by-step recipe weighing with totals and percentages, batch scaling, PDF and CSV batch records, and user roles. It can be adapted for ERP, MES or LIMS.
WeightControl SQC: statistical control of fill quantities for products sold in prepackages under Directive 76/211/EEC, with tolerance zones, trends and reports.

Both software modules require WeightControl Base; all modules are listed under weighing software. For dosing and filling lines, see gravimetric filling and dosing systems. Every WPL scale can be supplied with an EURAMET cg-18 calibration certificate as an option; EURAMET cg-18 calibration explains what it covers.

Recommended WPL set-up for chemical plants

A practical set-up keeps the measurement close to the product and the operator screen where it is easy and safe to use.

Position	Task	Suggested equipment
Laboratory or safe-area weighing room	Small components, samples	SSP with R10 indicator and WeightControl Formula
Dosing point inside an Ex zone	Components per batch	SSP with ATEX load cell; indicator or terminal selected for the zone with WPL
Filling station	Cans and drums to target weight	Filling electronics and touchscreen software with traceability reports, specified per project
Quality control	Sample checks on filled packs	WeightControl Base with SQC

What to prepare before requesting a quote

A clear description of the zones and the process lets WPL propose components that fit your site.

The zone classification of every location where a part of the system will stand, and whether gas or dust is involved, taken from your explosion protection document.
Whether the indicator, PC or printer can be placed outside the hazardous area.
The heaviest load, the smallest quantity to weigh and the platform size; capacity and readability helps here.
The chemicals and cleaning agents the scale meets; see stainless steel grades.
Which data must be recorded and where it goes, such as a batch report, ERP or PLC; see weighing data logging and scale API integration.

For projects beyond standard products, see custom weighing solutions or request a quote.

Frequently asked questions

Is an SSP with an ATEX load cell an ATEX-certified scale?

No. The ATEX option on the SSP concerns the load cell only. The junction box, cables, indicator and any terminal or printer must each be suitable for the zone where they are installed. Describe the zone classification and the planned location of every component, and WPL will advise which parts and certificates are available.

Who decides which zone applies at my weighing point?

The employer or operator of the site. Under Directive 1999/92/EC, the employer assesses the explosion risks, classifies the places where explosive atmospheres may occur into zones and records this in the explosion protection document. The equipment supplier uses that classification to select suitable components.

Can the weighing indicator stand outside the hazardous area?

Often that is a sensible layout, because fewer components then need to be suitable for the zone. Whether it works depends on the distance, the cable route and how the load cell circuit is protected. Include a floor plan with the zone boundaries in your enquiry so WPL can assess it.

Can recipe weighing records go to our ERP or LIMS?

WeightControl Formula exports batch records as PDF or CSV and can be adapted for ERP, MES or LIMS. It runs as a module on WeightControl Base. Describe the target system and the data fields you need, so the integration can be specified.