0-500v 0-400mA continuously adjustable, with flow-limited and digital two-way time-control device of 0-99.9 hours, protection function: giving an alarm when it is over-voltage, over-current, over-load, variable-load , no-load or leakage, two non-uniform electric fields in different directions are used alternately , so that DNA molecules keep continuously changing directions when squeezing through the gel sieve. And then the resolution of DNA molecules is obtained.