Apparatus is disclosed for sensing impact events in reciprocating machinery. The apparatus establishes first and second reference or threshold voltages, where the second reference voltage is greater than the first reference voltage. The number of impact events (N.sub.1) in a time window that exceed the first reference voltage and the number of impact events (N.sub.2) in a time window that exceed the second reference voltage are counted and an output current is generated representative of the number of such impact events. If no impact greater than the lower threshold voltage is received during a given time window, the apparatus detects and stores a peak voltage corresponding to the impact having the greatest magnitude received during that time window. Apparatus according to the present invention produces an output current based on the magnitude of that peak voltage.