What are the common types of counters used in PLC programming?

Common PLC counter types: CTU (Count Up) - increments on each false-to-true transition of input until preset reached. CTD (Count Down) - decrements from preset value. CTUD (Count Up/Down) - can count both directions with separate inputs. Counters have accumulated value, done/enable bits, and reset inputs. Applications include: counting parts, tracking inventory, limiting operations, and totalizing events. For high-speed counting (encoders, flowmeters), dedicated high-speed counter modules handle pulses faster than scan cycle.