panel meter การใช้

The signals were summed through a detector ( normally a panel meter with or without some level of amplification ).
Beginning with the TR-3, Drake adopted a scheme for illuminating tuning dials and panel meters on its equipment using small incandescent bulbs behind greenish-blue transparent plastic filters.
When zero current was noted by changing the value of the standards and looking for a " null " in the panel meter, it could be assumed that the current magnitude through the unknown was equal to that of the standard and that the phase was exactly the reverse ( 180 degrees apart ).