Physical Influences Caused by the 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.