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

Rf Pickup

The weighing mechanisms of radiation force balances, particularly those that employ compensation techniques to derive the force being measured, can be susceptible to stray water-coupled RF fields.

Some ultrasonic transducers of drive systems generate stray RF radiation in the low MHz frequency ranges, especially dual frequency physiotherapy devices. In extreme cases, these circumstances can lead to significant measurement errors. To minimise the likelihood that measurements are being affected by such fields, it recommended that if there is a continuous electrical signal path from target to balance (e.g. a reflecting target, and metal gantry keying in to the balance mechanism), an insulating fixture (such as a washer) be included in the interface between the target/gantry arrangement and the connection to the balance pan.

In most implementations, it should be possible to check whether measurements are being affected by checking the difference in power when introducing a small piece of expanded polystyrene between the transducer and the target. The measured power should drop to zero when the polystyrene is in place.