From weighing scale to in-line weighing

May 11, 2021 Jos Abbing

Using a flow meter instead of a weighing scale for high accurate dosing

If we talk about dosing ingredients, like flavourings and fragrances, often the first measuring instrument to come in mind is the weighing scale, independent from whichever industry you work in. But why not use a flow meter instead? 

I hear you think… a flow meter? Yes, a mass flow meter is an in-line weighing method and can offer several benefits compared to a conventional weighing scale, especially when it comes to processes including dosing ingredients.

Dosing liquid vaccine in bottle with flow meter

Inline weighing makes it possible to dose additives very fast and gives you the possibility for a semi-continuous process.  I’m interested to hear if I have convinced you to use a flow meter instead of a weighing scale after reading this blog.

Mail Jos

Features Weighing scale

  • Static measurement
  • Step-by-step dosing
  • Batch process

Features Mass flow meter

  • Inline measurement
  • Parallel dosing / cluster dosing
  • Semi-continuous process

Weighing Scale versus mass flow meter

Let’s start with the scale: a scale offers a static measurement. It will need a few seconds to settle to stabilize for good accuracy and repeatability. When a liquid is sloshing and needs to settle, additional time can be needed. 

In the dosing process the ingredients are dosed step-by-step as in a sequential process. It is not possible to add multiple additives at the same time using only one weighing scale.

Multiple mass flow meters used for dosing ingredients
Multiple mass flow meters used for dosing ingredients

You can, when using a flow meter as inline weighing method. If you combine a mass flow meter with a pump or valve, you can dose multiple ingredients simultaneously. This way you create a semi-continuous dosing process instead of a batch process. Besides that, by using this combination of flow meter/pump you create a direct controlled process, meaning the flow meter can adjust the pump speed directly. 

I agree with you; a batch process is somewhat easier to engineer. However, you need to control, produce, and check each batch with risks in batch-to-batch inconsistency, production losses, availability, and required storage space for (premixed) additives. Changes in product can lead to considerable overhaul and set-up costs.  

Semi-continuous processes inherently offer a good possibility to reduce waste or excess inventory and to complete more products in less time. Spotting errors and correcting them as well, are simplified because this is done directly, even during the dosing cycle itself. This enables a more continuous process.

Spraying oil on backing trays in food production
Spraying oil on backing trays in food production

Dosing process with a scale

To enable a fast filling time with a scale, high concentrate-additives are often pre-mixed in a batch tank before it is dosed into the production process. Between different batches, the premix tanks and parts of the bottling system must be emptied and cleaned to prevent cross-contamination and ensure hygienic standards.

It is also important to prevent any (mechanical and physical) contact with the scale during the weighing procedure in order not to disturb the accuracy of the scale.

Sequential dosing process
Sequential dosing process

If you mix a dozen of ingredients or you have a long processing time in your dispenser, ingredients will evaporate to some extent. The evaporating rate depends on the size of the bottle opening, temperature, and type of carrier liquid.

Use of volatile, hazardous or smelly additives result in potential environmental odour nuisance and sometimes more severe health, safety and environment (HSE) risks. Additional safety-, ventilation and mechanical measures are often required to contain such “source of release”. 

Let’s compare this with the in-line weighing method using flow meters:

Benefits of in-line weighing with mass flow meters

1. Faster dosing 

Inline mass-dosing does not need premixing. It offers true ‘on demand bottling’ in the final stage of the production process or even directly into the destination container or bottle. Small doses of additives in milligrams or grams can easily be added in less than a second. Changes are easy to implement, even during production cycles.

Modern (mass) flow meters with integrated high-speed dosing (PID) controllers are very accurate. They can be used as inline scale from kilograms down to milligrams directly controlling a valve or pump. They enable smooth and easy dosing of single- or multiple ingredients in parallel, fast and with the highest repeatability.

Read more about fast batch dosing in our blog ‘Additive dosing solutions for fast batch dosing’.

Blog about batch dosing
Fast dosing of bottles

2. System availability

Overall system availability is increased because traditional batch-related cleaning is not required to the same extend as before. Batch-to-batch deviations are prevented due to the nature of an inline process. The dosing quality is excellent because delicate corrections are executed during the dosing process itself, e.g. to cope with pressure, viscosity, and temperature changes. 

Example of dosing liquids with on-board firmware on mass flow controller
Example of dosing liquids with on-board firmware on mass flow controller

3. Semi-continuous (cluster) dosing of ingredients

A unique feature of inline mass dosing is the possibility to dose multiple ingredients in one clustered dosing step, in parallel, resulting in a semi-continuous process set up.

The integrated high-speed on-board dosing controller uses intelligent dosing firmware to enable the highest accuracy and speed with automatic correction mechanisms without a direct need for a complex PLC program.

4. Risk reduction

Since the dosing process can be done very fast, strong reduction in evaporative releases can be realised. This can result in a considerable risk reduction, even up to relaxation of the safety measures as described before. 

Off course, just like many other technologies; mass flow-based inline dosing is somewhat depending on specific system parameters. Your process parameters will determine which of the mentioned benefits are applicable to you.

Bronkhorst can help you

Have you become curious which benefits apply to you? Most projects we execute will start with system configuration advice, a basic demonstration, and a proof of concept, just contact us and learn about your benefits!

Video explaining the principle of bypass technology: High-speed batch dosing using mass flow controllers

Would you like more information about flow meters and controllers?

Select the right flow meter Ask for advice

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