What is the difference between an analytical balance and a precision balance?

An analytical balance provides readability of 0.1 mg or better, while a precision balance typically reads to 0.001 g or 0.01 g. Analytical balances include draft shields and are designed for highly sensitive measurements. Precision balances handle larger samples and are less affected by environmental conditions.

What readability do I need for my lab application?

You need a readability that is at least one-tenth of your smallest sample weight or required measurement increment. For example, measuring 100 mg samples may require 0.01 mg readability, while gram-level work may only need 0.01 g. Selecting higher readability than necessary increases cost without improving results.

Do lab balances need to be calibrated?

Yes, all lab balances require regular calibration to maintain accuracy. Calibration ensures measurements remain traceable to certified standards. Internal calibration simplifies this process by automating adjustments, while external calibration requires manual verification with certified weights. In regulated environments, calibration records must be documented and retained.

What is the difference between readability and repeatability?

Readability is the smallest increment of weight a balance will display. Repeatability is the degree of agreement between multiple measurements of the same mass, on the same balance, under the same conditions.

What is the best way to clean my balance to ensure accurate readings?

Inspect and clean before each use. A flannel cloth or soft brush works well for dusting and light cleaning. Use a non-abrasive cleaner for light spills, and a dry flannel cloth for glass parts. Set a regular maintenance schedule for deep cleaning to ensure optimal performance and instrument longevity.

Can vibration affect the accuracy of my balance?

Yes — even slight vibration from a heavy footstep can affect accuracy. Place the balance on a sturdy benchtop away from high-traffic areas such as hallways, elevators, stairways, and doors. If that placement is not possible, an anti-vibration table should be considered.

Flowmeters: Variable Area & Laminar DP| Cole-Parmer Blog

The Essential Guide to Variable Area and Laminar Differential Pressure Flowmeters: What You Need to Know

Accurately measuring the flowrate of fluids and gases is essential across various industries, from bioprocessing workflows to industrial gas monitoring. Understanding the difference between mass and volumetric flow, as well as the advantages of different flowmeter types, helps ensure precise measurements for efficiency and safety. In this article, we’ll explore mass vs. volumetric flow, variable area and laminar differential pressure (DP) flowmeters, and essential flow conversion factors to simplify your calculations.

In this article you’ll learn:

Mass Flow vs. Volumetric Flow: Understanding the Difference
Variable Area Flowmeters: Direct Read and Correlated
Laminar Differential Pressure (DP) Flowmeters
Flow Conversion Factors & Standard vs. Actual Flow Measurements

Mass Flow vs. Volumetric Flow: Understanding the Difference

Flow measurement is a critical factor in many industrial and scientific applications, but not all flow measurements are the same. The distinction between mass flow and volumetric flow is essential when selecting the right flowmeter for a given process. While volumetric flow measures the physical volume of fluid moving through a system, mass flow accounts for the actual mass of the fluid, which remains constant regardless of temperature and pressure changes.

What is Volumetric Flow?

Volumetric flow measures the volume of a gas or liquid that flows through a system in a certain amount of time, expressed in units like liters per minute (L/min or LPM), cubic meters per second (m³/s), or milliliters per minute (mL/min). This type of measurement is highly dependent on external conditions: gases, for example, expand or contract with changes in pressure and temperature, altering the measured volume without changing the actual quantity of gas present.

What is Mass Flow?

Mass flow measures the actual quantity of fluid, liquid or gas, moving through a system in a certain amount of time, expressed in kilograms per second (kg/s), pounds per hour (lb/hr), or standard liters per minute (SLPM) for gases. Unlike volumetric flow, mass flow remains constant even when pressure and temperature fluctuate, making it ideal for applications where precise amounts of material need to be delivered.

Flow Type	Best For	Example Applications
Volumetric Flow	Liquids or gases when temperature and pressure are stable	Water distribution, HVAC airflows, food and beverage production
Mass Flow	Precise gas flow measurement, varying temperature/pressure conditions	Clinical research gas delivery, semiconductor manufacturing, chemical processing

Understanding whether your application requires volumetric or mass flow is essential to choosing the right type of flowmeter and ensuring accurate, reliable measurements.

Variable Area Flowmeters

Cole-Parmer variable area flow meter

A variable area flowmeter, commonly known as a rotameter, is a simple and reliable device used to measure gas or fluid flow rates. It consists of a tapered tube with a float inside that moves up and down based on the flow rate. As the media flows upward, the float rises until the forces acting upon it (velocity, gravity, and buoyancy) reach equilibrium. The height of the float corresponds to the flow rate, which can be read on a scale.

Variable area flowmeters are widely used because they are mechanically simple, cost-effective, and require no external power. They are particularly well suited for low-flow liquid and gas applications where real-time monitoring is needed.

Variable area flowmeters come in two primary types: direct read and correlated flowmeters.

Direct Read Flowmeters
- Have a scale that is pre-calibrated for a specific media (e.g., air or water) at a given temperature and pressure.
- Allow users to read the flow rate directly from the scale, eliminating the need for conversions, charts, or additional calculations.
- Simple to use but limited in flexibility, as they must be recalibrated or replaced if used with different media or conditions.
Correlated Flowmeters
- Do not have a direct flow scale; instead, they provide a dimensionless scale (e.g., 0 to 100) that requires a separate correlation chart or equation to determine the actual flow rate.
- Can be used with multiple fluids or gases by applying conversion factors based on specific operating conditions.
- Offer greater versatility but require additional calculations for precise readings.

Variable area flowmeters are used in various industries due to their simplicity and versatility. Some common applications include:

Water treatment plants – Monitoring chemical dosing and water flow rates.
Laboratories and research – Low-flow gas or liquid measurements in experimental setups.
HVAC systems – Monitoring airflow in ventilation systems.
Industrial gas flow measurement – Ensuring controlled delivery of gases in welding and manufacturing.

Variable area flowmeters are an excellent choice for applications where simplicity, affordability, and visual flow monitoring are priorities. While they may not offer the precision of digital or mass flowmeters, they remain a reliable and widely used option in many industries.

Advantages	Disadvantages
Simple and inexpensive – No external power or complex electronics required. Easy visual flow indication – Provides real-time feedback. Low maintenance – Few moving parts, reducing wear and tear. Works with a variety of fluids – Suitable for gases and liquids.	Limited accuracy – Not as precise as digital or mass flowmeters. Vertical installation required – Must be mounted upright to function properly. Media-specific calibration – Requires recalibration or conversion for different media and operating conditions. Sensitive to viscosity changes – Higher viscosity fluids may affect accuracy.

Laminar Differential Pressure (DP) Flowmeters

Alicat Scientific laminar differential pressure mass flow meter with a digital display

Laminar differential pressure (DP) flowmeters are precision instruments used to measure flow rates of both liquids and gases by utilizing the principles of laminar flow. Unlike conventional DP flowmeters that rely on turbulent flow conditions, these flowmeters use a laminar flow element (LFE) to create a controlled pressure drop, which directly correlates to the flow rate. This ensures high accuracy, repeatability, and stability, making them ideal for low-flow applications where precision is critical.

Laminar DP flowmeters operate based on Poiseuille’s Law, which states that in laminar flow conditions, pressure drop is directly proportional to volumetric flow rate. These flowmeters contain a laminar flow element (LFE)—a set of parallel, small-diameter flow channels that ensure the fluid moves in a predictable, non-turbulent manner.

Key Components:

Laminar Flow Element (LFE): Creates a uniform, non-turbulent flow to ensure accurate pressure drop readings.
Differential Pressure Sensor: Measures the pressure drop across the LFE and converts it into a flow rate.
Electronics & Signal Processing: Modern versions include digital compensation for temperature and pressure variations to enhance accuracy.

While laminar DP flowmeters can measure both liquids and gases, their design and function differ slightly depending on the medium.

Gas Flow Measurement:
- Commonly used in applications requiring precise low-flow gas measurements, such as research gas monitoring and industrial gas flow control.
- Requires correction for temperature and pressure changes to maintain accuracy.
- Often used with standardized flow conditions (e.g., SLPM instead of LPM) to ensure consistent readings.
Liquid Flow Measurement:
- Used in high-precision liquid dosing, fuel flow monitoring, and chemical processing.
- Less affected by pressure and temperature variations than gas flow but may require viscosity compensation for different liquids.
- Offers excellent repeatability, making it suitable for pharmaceutical and laboratory applications.

Advantages

Disadvantages

Highly accurate and repeatable – Ideal for precision flow measurement.
Works with both gases and liquids – Versatile across industries.
Low-pressure drop – Reduces energy consumption and system impact.
Stable over a wide range of environments – Provides reliable data across different operating conditions.
Compact and durable – Often used in portable or embedded systems.

Limited to low and medium flow rates – Not suitable for high-flow applications.
Sensitive to contamination and particulates – Requires clean fluids to maintain accuracy.
Viscosity-dependent for liquids – May need adjustments for different fluid properties.
Higher initial cost – More expensive than simple variable area or traditional DP meters.

Flow Conversion Factors & Standard vs. Actual Flow Measurements

This table provides quick reference for converting between common flow rate units used in different industries, also you can use our flow-meter conversion tool.

Measurement	Convert To	Multiply By
Gallons per minute (GPM)	Cubic meters per second (m³/s)	0.00006309
Gallons per minute (GPM)	Liters per minute (L/min or LPM)	3.785
Liters per minute (L/min or LPM)	Cubic meters per hour (m³/h)	0.06
Liters per minute (L/min or LPM)	Cubic centimeters per minute (cc/min or CCM)	1,000
Milliliters per minute (mL/min)	Liters per minute (L/min or LPM)	0.001
Cubic centimeters per minute (cc/min or CCM)	Liters per minute (L/min or LPM)	0.001
Cubic feet per minute (CFM)	Cubic meters per hour (m³/h)	1.699
Cubic feet per minute (CFM)	Liters per minute (L/min or LPM)	28.3168
Cubic feet per minute (CFM)	Cubic centimeters per minute (cc/min or CCM)	28,316.80
Pounds per hour (lb/hr)	Kilograms per hour (kg/hr)	0.453592
Cubic meters per hour (m³/h)	Liters per minute (L/min or LPM)	16.667

Understanding Standard vs. Actual Flow Measurements
- When measuring gas flow, it’s important to distinguish between actual and standardized flow rates.
  - Actual Flow Rate (LPM, CFM, etc.): Measured under the actual temperature and pressure conditions in a system. This can fluctuate based on environmental changes.
  - Standard Flow Rate (SLPM, SCFM, etc.): Corrected to a standard reference temperature and pressure, ensuring consistency across measurements and industries.
- Common Standard Conditions:
  - Standard temperature: 0°C (32°F) or 20°C (68°F), depending on the industry.
  - Standard pressure: 1 atmosphere (101.325 kPa or 14.7 psi).
  - Since gas expands and contracts with temperature and pressure changes, standard flow rates allow for accurate comparisons between different operating conditions.

Find the Perfect Flowmeter with Cole-Parmer

Choosing the right flowmeter is essential for accurate and reliable fluid measurement, and Cole-Parmer offers a wide selection of high-quality flowmeters to meet your needs. Whether you’re looking for variable area flowmeters, laminar differential pressure flowmeters, or other precision instruments, we provide top brands like Cole-Parmer and Alicat, known for their accuracy and durability. Our team of experts is here to help you select the best flowmeter for your specific application, ensuring optimal performance and efficiency. Shop our entire collection of Flowmeters today.

References

Alicat What is the difference between mass flow and volumetric flow?

Alicat Engineering Units

Aalborg Rotameter Technical Information