U7-1 has a gain of 25 and the amplifiers that follow, U7-7 and U8-6, have a constant gain of 10
when properly adjusted with RV6 and RV7. The output of U7-1, U7-7 and U8-6 are each
connected to one contact of the "Current" switch. The other contact is connected to its
counterparts
so that the selected output is applied to the true RMS-DC converter, U11, when
"Amps" is selected with the "V/I" keypad.
A 200mV input from U7-1 produces 5 volts at the output of U7-7 and 2mV produces 5 volts at
the output of U8-6. The full-scale voltage applied to the true RMS converter in any range is 5
volts.
The output of the true RMS converter appears across the divider composed of R36, RV14 and
R37. The potential at the arm of RV14 is 200mV and is applied to the amps/volts DVM, U13,
through a section of RL8 relay when "Amps" is selected.
Figure 7-3 | Simplified Current Amplifier
33
