What you call the amount of radiation is the selection of the time in ms, apparently the timer is digital with display and buttons to increase (+) and decrease (-) time, your problem could be that the mask covering these buttons It is very tight and is pressing the buttons altering the selected, or it could also be that in the electronic card of the timer the signal of raising and lowering the time is altering or entering noise. For more details I would recommend that you put the brand and model of the equipment, since the control of the time varies according to the brands and models.