My PV 150 turns off too soon while testing, and I have to keep switching it on again?

The auto-shutdown can be altered by the user, between 1 minute and 10 minutes. Follow this sequence to adjust it: Turn the PV150/200/210 unit off. Press and hold the NULL key, then power on the instrument while still holding the NULL key. The display will show “OFF” on line 1, and the turnoff time on line 2 (in minutes). Keep holding the NULL key and press the Viso key. Each press of the Viso key will increment the turnoff time. Increment beyond 10 to set the time back to 1 minute. Release all buttons when the desired shutdown time has been reached.