supply 60 must be lowered by control unit 70 for these injections otherwise band broadening due to excessively large injection slugs is the result another consideration is the time it takes the voltage of power supply 60 to drop from the high voltage value to ground in the present example it takes approximately 2 seconds for the voltage of power supply 60 to drop from 30 kv to 0 kv a faster drop can be facilitated by operation of grounding box 62 but this has a tendency to interfere with control unit 70 and over the course of a several hour run would cause unnecessary wear on the solenoid in grounding box 62 therefore prior to each movement of valve 10 to the inject position there is a 2 second interval during which no data is collected and the voltage of power supply 60 is allowed to drop from the run voltage to the injection voltage this 2 second high voltage slew time interval is constant regardless of any other run parameters at the end of the 2 second interval valve 10 is turned to the inject position and the electromigration injection is begun and continues for the length of time entered by the user no data is collected during the injection period at the end of the injection time valve 10 is returned to the 34 run 34 position voltage is returned to the run voltage value and data acquisition is resumed in that order this entire sequence of 2 second interval injection time and data collection time takes place during the user entered 34.