Heathkit IT -3120 User Manual

Page 34
,
R x S
~
100m A
I
~
)
IA
I
~ R2
) I . 5V
I A
10 0mA
I Om A
I
fil A
SET BE l A
I
I
'>
J
I
R4 RIO R 11
R1
~ R 2
~
R3
'> '>
~
1 5000
~
I S 'I
) 150
"
)
1 50
) 1 660
"
I
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~ ---------- --~~+-------------------.------~ +
B 2
B 1
1. 5V
I. SV
10 n1 A
1 mA
R3 ~ R 4
1 5V
) 1660
BETA
Figure 8
BETA
This circuit is similar to the beta cal circuit except that the
meter is now in the base circuit dnd resistor Rl0 is in the
collector circuit. See Figure 8. Also, because the shunt
resistor that was previously across R lOis now across the
meter , only 1/10 the current is required for full -scale meter
deflection_
Since
beta, by definition, is collector current (Ic)/ base
current (fb), these currents could be measured and the ratio
computed to obtain beta . However, the meter scale takes
into account the currents and their ratio, and reads directly
in terms of beta.
For example , when the 10 mA current range is selected , and
the Beta Cal control is adjusted to place the meter pointer
over the CAL Xl0 mark (full scale), a collector current of
10 mA flows through the device. Now, when the meter is in
the base circuit, assume that almA current flows. The
meter pointer will deflect full scale (1 mAl and indicate a
beta
of 1 times a multiplier of 10 (CAL Xl0). Thus , beta =
10 . The same result can be obtained from the formula :
IC = 10mA= 10
IB 1 mA
lebo, lees, AND leeo
Leakage currents are measured by placing a battery and the
meter (and its shunt resistance) in series with two of the
transistor leads. The meter indicates leakage current from 0
to 1 ampere , depending on the current range selected . Since
the leakage currents are quite small, usually measured in
microamperes (pA), the transistor must be removed from
the circu it.
lebo is the measurement of the cu rrent that flows between
the collector and the base of the transistor with the emitter
open (unconnected) . See Figure 9.
lees
is the measurement of the current that flows between
the collector and the emitter of the transistor with the base
connected to the emitter . See Figure 10.
Ieeo is the measurement of the current that flows between
the collector and the emitter of the transistor with the base
open (unconnected) . See Figure 11.

Heathkit IT -3120 Specifications

General

Brand	Heathkit
Model	IT -3120
Category	Test Equipment
Language	English