Looking Under the Bridge

摘要

There is a need to somehow look "under the bridge" at each individual element of a Wheatstone bridge in normal transducer operation to understand the details of what is going on electrically in a transducer. Fortunately, a simple technique is available to accomplish these observations. The measurement circuit topology of choice for observing small changes in variable-impedance transducer elements has long been the Wheatstone bridge. This topology presents a continuous differential signal that is a function of the various impedance levels and especially of the impedance variations in all four arms of the bridge circuit. However, the bridge topology does not usually inform the observer what individual sensing elements are contributing to the overall differential output. Single-element impedance variations can be identified using the bridge topology only when it is arranged in advance that only one element in the bridge will vary, an awkward situation when attempting to identify what is really happening to each individual element of a transducer in operation. There is a need to somehow look "under the bridge" at each individual element of a Wheatstone bridge in normal transducer operation to understand the details of what is going on electrically in a transducer. Fortunately, a simple technique is available to accomplish these observations.