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Setting up and alignment

Target and transducer preparation

Subtle changes can occur in a target the longer it is left in water medium. For an absorbing target The effects of surface tension on the target and the transducer can cause bubbles to adhere to the surface. The target and the front face of the transducer shouldbe soaked for at least a couple of hours (or preferably overnight) to adjust to the ambient temperatures, to accomodate water uptake, to reduce the effects of surface tension allowing wetting of its surface.

The transducer is aligned over the
target (absorbing) and secured with
cable ties and a laboratory clamp.

Transducer alignment

The transducer should always be held in a retort stand with a clamp which will allow the orientation and positioning of the transducer to be altered in two main respects:

• The transducer is positioned over the apex of the convex cone or centered over the absorbing target
• The face of the treatment head is parallel to the base of the cone or absorbing target.

The second requirement is difficult to check and depends on the correct setting up of the gantry/target arrangement which could in principle be assessed through other measurements.

It is clearly important to ensure that the target and gantry assembly are not mechanically stressed either in use or when dismantled to ensure that the relative orientation of the float (for a reflecting target) is undisturbed. Typically, a visual alignment of the position and orientation of the transducer may be achieved to ± 3 mm and ± 3°. An allowance should be made in the uncertainty budget for the maximum expected deviation. It should be noted that, typically, the transducer will be positioned about 5 to 10 mm away from the apex of the cone or the absorber.