Ac Metering Circuits

TM 11-6625-646-15

through multiplier resistor R305.

a. Twenty-six volt ac from power transformer T501

f. When FUNCTION switch S7 is at PEDAL

is connected to the primary of reference voltage

transformer T401. The output of transformer T401, is 5

POT. OUPT, the simulated feedback being fed from the

volts centertapped to the negative side of FUNCTION

moving contact of PEDAL POT resistor R502 to the yaw

meter M1. This output is applied to a demodulator

channel of the SAS amplifier is connected to meter M1

consisting of diodes CR401 through CR404 and test

through multiplier resistor R401.

voltage input transformer T402. On one half-cycle of

reference voltage, diodes CR401 and CR402 conduct.

1-32. Ac Metering Circuits

On the alternate half-cycle, diodes CR403 and CR404

(fig. 1-4)

conduct. When a diode pair is conductive, the circuit is

During ac metering functions, the voltage to be

closed through the associated half of the input

measured is connected through a calibrating resistor

transformer secondary to the positive side of meter M1.

and FUNCTION switch wafers S7C and S7D to test

In effect, the positive side of meter M1 is switched from

voltage input transformer T402 of the function meter

one half to the other half of the secondary of input

rectifier (para 1-33). The dc output of the meter rectifier

transformer T402 at the power frequency rate. Without

is applied across a meter shunt and through FUNCTION

an ac voltage in the primary winding of transformer

switch wafers S7A and S7B to FUNCTION meter Ml.

T402, the output to meter M1 is theoretical zero, a

For each position of switch S7, the calibrating resistor

series of self-canceling pulses of negligible amplitude

has a value which, together with the value of the meter

which have no effect on the meter indication.

shunt, results in the meter indication within the red or

green sector of the scale.

b. When ac test voltage is applied to the primary

of transformer T402, the voltage applied to meter M1 is

a. When FUNCTION switch S7 is at AC PWR, the

the output of one half of the secondary winding during

26-volt output of the secondary winding of test set power

its positive or negative half-cycle and the output of the

transformer T501 is connected to input transformer

other half of the secondary during its corresponding half-

T402 through calibrating resistor R406.

cycle. The output of transformer T402 at the center tap

b. When FUNCTION switch S7 is at YAW, ROLL,

is a series of positive or negative pulses, depending

or PITCH FEEDBACK POT. EXCITATION, the primary

upon the phase of the ac voltage being measured. This

excitation voltage (from the SAS amplifier), normally

dc output voltage is applied across meter shunt resistor

applied to the primary feedback variable resistor in the

R407 and through the ac test positions of FUNCTION

corresponding extensible link, is connected to input

switch S7 to the positive terminal of FUNCTION meter

transformer T402 through switch S5 and calibrating

M1.

resistor R402, R403, or R404, respectively.

c. When FUNCTION switch S7 is at SEC.

1-34. Miscellaneous Test Circuits

FEEDBACK POT EXCITATION, the secondary

excitation voltage (from the SAS amplifier), normally

1-35. ASE Mode

applied to the secondary feedback variable resistor in

These circuits not applicable to the CH-47 SAS

the extensible links is connected to input transformer

amplifier.

T402 through calibrating resistor R405.

1-36. Half-Gain Mode

1-33. Function Meter Rectifier

(fig. 1-5)

(fig. 1-4)

During normal operation, each SAS amplifier operates

In the meter rectifier (phase-sensitive demodulator), the

at half gain. During bench testing,

ac voltage to be measured is converted to a positive or

negative dc voltage. The polarity of the dc output

voltage is a function of the phase of the ac input

voltage.