TYPES AND WORKING PRINCIPLES

A position transducer, often called a pin or referred to by some as a TOAD (Time of Arrival Detector unit), is a small coaxial probe that produces an electrical signal when impacted at its sensing end by a fast moving object, or when exposed to either an ionization or shock front. Two types of pins are commonly used. They are the switch type and the piezoelectric type. The switch types require an excitation source and consist of ionization pins and shorting pins. The piezoelectric pins do not require an external excitation source. Being small and rugged, several pins can be accurately positioned in space or within a material, thus providing an accurate means for detecting the time-of-arrival of a shock or ionization front, or of a fast-moving object. Their outputs can be amplitude- or polarity-coded and multiplexed into a single output line, (see Dynasen's Pin Mixer information) thus providing a simple technique for measuring material and shock velocities, impact planarity, or triggering instrumentation.
A graphical representation of the three types of transducers is shown below.