TM 11-6625-539-14-4
EL6625-539-14-4-TM-5
5-3. Beta Function Circuit
quired base current from the device under test to
a. A simplified schematic diagram of the beta
flow through resistor R30. The output voltage at
function circuit is shown in figure 5-3. The circuit
AR3, therefore, is proportional to the base current
is shown for the NPN transistor, but it also
of the device. When this voltage is applied to
applies to a PNP when the polarity is reversed
meter amplifier AR4, it drives the meter to indi-
through POLARITY switch S2.
cate the beta of the device under test. RANGE
switch S3 selects the required sensitivity level to
b. The beta circuits are automatically energized
provide full-scale deflection at 5 mV, 50 mV, and
w h e n the BETA is selected on FUNCTION
500 mV to correspond with full scale beta ranges
SWITCH S1. No additional front panel adjust-
of 100, 1000, and 10,000.
ments are required.
e. Since beta is an inverse function, and the
higher beta transistors read less than full scale,
switches Z1A and Z1B to produce a square wave
transistors with betas from 1 to 10,000 may accu-
at C6. The square-wave peak-to-peak level is equal
rately be tested.
to the difference between circuit common and the
output of AR2 through CR6. Amplifier AR2 ampli-
5-4. Ohms Function Circuit
fies the square wave and drives the emitter of the
a. A simplified schematic diagram of the ohms
device under test to produce a collector current
function circuit is shown in figure 5-4. A voltage
which flows through resistors R4 and R6. The
divider consisting of resistors R10, R13, R15, R16,
values of R4 and R6 are such that the input of the
and R20 produces a 10 mV source for the meter.
sense amplifier AR1 is satisfied when an average
I CES ZERO/OHMS ADJ controls are adjusted to
collector current of 1mA flows. In this manner,
provide full-scale meter deflection when the unit
the sense amplifier AR1 controls the emitter drive
is not connected to the equipment under test.
signal, forcing the device under test to conduct at
RANGE resistors R19, R22, and R25 provide ohms
1mA. Variable resistor R6 provides an adjustment
ranges of 100 ohms, 1 kilohm, and 10 kilohms at
of the current level during NPN calibration. Vari-
center scale. The meter amplifier AR4 monitors
able resistor R3 provides the adjustment during
the voltage divider formed by the range resistor
PNP calibration.
