Introduction | Radiation Force Balances | Measurement | Additional Information | Further Reading

Setting up and alignment - Environment

An enclosure around the balance
and a solid base can reduce effects
from vibration.

Draughts and vibration

Due to the relatively small changes in mass that are being measured it is necessary to limit disturbances from other sources other than the balance and transducer. The most significant source is vibration through the surface that the balance is positioned on and from draughts around the balance. Vibrations within the vicinity are reduced by limiting movement in the local area from persons or objects (doors being opened). Ensure the balance is isolated on a flat, stable surface with enough space around it for positioning a transducer and clamp. All other test equipment necessary for the measurement should ideally be positioned on a separate table from the balance to avoid vibration. If the balance has a circular spirit level (usually at the rear) then adjust accordingly to level the balance. Once levelled assemble with the water tank, gantry (where applicable) and target.

The effects from draughts can be reduced by using an enclosure. Some balances come with small glass enclosures that may be adapted. For a simpler and cost effective method, a cardboard box can be used. The enclosure should totally surround the balance but not be in contact with any part of it.

Bubbles

Bubbles may occur more readily if the target or transducer have not been pre-soaked and once the balance is set up they may be difficult to check for due to the resultant restricted visibility. Depending on the space available in the tank, a dentist's mirror can be used to check any surfaces not in view. If bubbles occur they can be removed from the target using a soft brush and from the transducer face with something that will not damage the surface. An alternative, non-contact method would be to rotate the transducer as it is lowered into the water tank to ensure that it breaks the water surface at an angle, avoising trapping of air under its flat surface. This method may be most appropriate if the transducer under test has a concave front face.