Physical Influences Caused by the Sample

Physical Influences Caused by Your Sample

Physical Influences Caused by Your Sample

Even the slightest change to environmental conditions or physical variables can cause balances, especially semi-micro, micro or ultra-micro, to react. These reactions can cause variations in the readings and produce poor results. Physical influences can also cause changes in the sample and/or container. Below are the main problems caused by physical influences on your sample or containers.

Issue: Container or Sample Was Not Allowed to Acclimate to Current Temperature

What You See: Poor repeatability, unexpected weigh results, readout drifts when sample is placed on pan even though the display is stable when balance is at zero

How to Fix: Condition the sample or container to environment

Issue: Sample is Evaporating or Hygroscopic (Sample Can Easily Retain Moisture)

What You See: readout increases and decreases, readout drifts even thought display is stable when balance is at zero

How to Fix: cover the container to prevent evaporation, do not handle container or sample with care fingers

Issue: Container or Sample is Electrostatically Charged

Static electricity occurs more at very low humidity and when sample/container has low electrical conductivity and large surface area.

Examples: Plastic or glass containers, powdered substances.

What You See: The weight readout drifts in one direction, repeatability of readouts.

How to Fix: Increase humidity in room, use metal container, use metal foil to shield sample, use accessories such as an ionizer blower to neutralize static electricity, find a draft shield with a built-in ionizer.

Issue: Container or Sample is Magnetic

Magnetic materials such as iron, nickel, etc generate force fields and these fields can act/push on the weighing pan or chamber.

What You See: Weight values are stable but non-repeatable, different value are displayed depending on positioning on pan.

How to Fix: Use a nonmagnetic objects to increase distance of the sample from pan (upside-down beaker), demagnetize your sample / container if possible, use mumetal foil as shielding, use special anti-magnetic weighing pans.

Issue: Gravitational Acceleration – Changing Location of Balance and Not Recalibrating or Adjusting

What You See: The balance readout is substantially different at new location.

Science Behind This: Degree of dependence on altitude. A 3-meter increase in height will affect weighing results. 200.0000 g balance if moved up 3-meters will read 199.9997 g.

How to Fix: Anytime the balance is moved, always adjust and calibrate using a certified test weight.

Selecting Your Sample Containers:

  • Optimize containers as needed – provide covers, select a material best suited to your application.
  • Make sure weighing pan and container are clean and dry.
  • Graduated flasks are more suitable than beakers with wide opening.
  • Use containers with small openings.
  • Always use smallest container feasible.

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