A multiwire proportional chamber has been employed in a fast logic system to select a trigger according to the number of outgoing particles in π+N→N+3π, (5π, 7π) interactions. Efficiencies of 99% in the selection of events with numbers of particles ≥1 and ≥2 have been achieved with two planes in coincidence at 90°. The present paper describes the multiwire proportional chamber and the associated electronics and discusses their behaviour.
