In article .com,
"terryS" wrote:

Came across a couple of those RF antenna current meters. Typical they
have a scale up to three of five amps. One is US and other is UK war
surplus.
AIUI the meter movement is driven by a small DC current produced from
the output of the thermocouple.
The thermocouple being heated by the RF current. Looks like the meter
itself is a one or five milliamp movement. Can anyone comment/advise?
Thanks.


The British ones (black bakelite cases) almost always have the thermocouple
built into the meter. They will usually be marked "Thermocouple" or "For
Radio Frequency Only" on the dial, and the resistance is usually shown
as well.

Be careful: the thermocouple is *VERY* delicate and will not stand up
to overload - the nichrome wire melts and it's useless thereafter.
(I've blown up an ex-Admiralty plug-in meter that was scaled 0-500mA
but had "requires x20 shunt" pencilled very faintly on the back.)

Chris.

--
If it doesn't contravene the Criminal Justice Act (1988) it has no place
in a kitchen. -- Peter Corlett in the scary devil monastery.