Figure 3-25.--Stabilization control-signal flow.

The op-amps used in this system are integrated

Figure 3-25 shows the signal flow in the servo loop.

circuit types using a configuration as shown in fig-

For example, in gyro normal mode, the gyro is powered

ure 3-26.

through the gyro power switch and the gyro erection

amp. The gyro synchro signal is converted to dc in the

An op-amp is a very high gain device, whose output

gyro demodulator and goes through the stab-lock relay

is the amplified difference between the inverting and

into the servo amplifier. The servo amplifier drives the

noninverting inputs. If feedback is added, the op-amp

servo valve that moves the cylinder to correct platform

will try to keep the voltage difference between the two

position. Any servo errors are compared in the error

inputs near zero.

circuit and trigger the error relay if the errors are large

The most common form of op-amp is the inverting

enough. The error relay will turn on the NOT READY

amplifier, as shown in figure 3-27. With the nonin-

light and turn off the GSI light. Stab-lock mode is similar

verting input tied to ground, the inverting input will be

and can also be followed on figure 3-25.

close to ground and is referred to as a virtual ground.

The higher the amplifier gain, the closer the point will

OPERATIONAL AMPLIFIERS

be to ground and for all computations it is assumed to

be ground. If an input voltage (Vin) is applied to the

circuit of figure 3-27, a current will flow in Rin. The

Operational amplifiers (op-amps) are used through-

amplifiers will amplify and invert the current and pro-

out the stable platform system as amplifiers, oscillators,

vide an output voltage. The output voltage will cause a

and comparators. To understand the different circuits,

current to flow in RF that will exactly cancel that flowing

you need to have a basic understanding of op-amps. An

through Rin. If the currents do not cancel, the difference

operational amplifier is a high gain (10,000 or greater),

between them will be amplified until they do.

highly stable, dc amplifier. It is used most often to

perform analog computer functions such as summing

Multiple input circuits are similar to the inverting

amplifier circuit. The gain of each input is controlled by

Figure 3-25.--Stabilization control-signal flow.

3-18