supereterodina, fonorivelatore.... Jesus, what was the deal with this localization?? Did they just take an electrical manual and threw in words from it into the script at random??
..... yeah, I'd go with "transducer", too, seems appropriate.
"Transducer reading : 5...."
You're doing a great job, erri_wan, I wish I could help more.
And kudos for translating "Il secondo tragico Fantozzi" into english, that must've been one hell of a job!