Figure 2-9. Measuring circuit, simplified schematic diagram

The detector circuit converts the dc error voltage

into an ac voltage which is amplified until it

moves the balancing motor. The resulting motion

is imparted by mechanical coupling to the wiper

arm, which is another point of dc balance, At this

point, there is no longer any driving power and

the motor stops. This balance point is adjusted by

the calibration controls to give a chart trace that

may be translated into meteorological data.

a. The 030 millivolts of dc signal developed

across resistors R203 and R207 is applied through

the normally-closed contacts of REC. TEST

switch S204, on the control panel, through the

damping filter (which consists of R333, R334, and

R335 and three-section capacitor C315) to the vi-

brating reed of inverter G301. This voltage is al-

Figure 2-10. Reference adjust circuit, simplified

ternately applied to the two ends of the primary

schematic diagram.

"windings of transformer T302, 60 times a second

as the reed vibrates in synchronism with the ac

The balancing circuit sets in motion the action

applied to its operating coil. It is assumed that the

necessary to rebalance these potentials once a dif-

signal voltage at this instant is slightly greater

ference has occurred, and thus cancel the error.