A method includes acquiring imaging data of a scene using an imaging tool. According to one aspect of the present invention, a positive blowdown signal is presented to indicate to the operator that the alarm probe is in steam; performing blowdown until this indicator turns on helps ensure that the alarm probe is working properly. The final part provides field shielding as provided by the nickel alloy shell, low stray field provided by the non-magnetic alloy, good vacuum performance, and tight mechanical tolerance control.