whenit is necessary to convert them into dB values. Represented electrically, Fig. 7 may otherwise be
(1) dB measurement on 50V, 250V and 1000V ranges as Fig. 8 where the section on the right of the N
For measurement on the 10V range, the dB scale and P terminals enclosed in the dotted line corre-
(-10dB-+22dB) is read directly, but, when measu- sponds to the internal circuit of the tester.
red on the 50V range, 14dB is added. On the 250V
range, 28dB is added to the reading on the scale, I N: i
and on the 1000V range, 40dB added. ICEO!c M !
Thus, the maximum dB readable is 22+40=62{dB) LEAK ~ + !
measuredonthe1000Vrange. '~-- B IV =- !
As transistor tester °,/("", NPN-TRE . !
. Preliminaries ~ P' i
This instrument uses its resistance range for transis- k:EO . ' '-'
tor tests, and so the pointer must be exactly adjusted FIg.8
to zero before connecting a transistor for measurem- (3) In Fig. 8, the current flowing across the P and N
ent, for which the P and N terminals are shorted toge- terminals is IcEo(reverse leakage current) of the
ther and the pointer is adjusted by 0.0.ADJ. TR, and the quantity of the leakage current is
. Measurement of IcEo(leakage current) read on the LEAK scale in mA.
(1) A small-size TR ( hereinafter a transistor is referr- (4) For a Si TR, this current is too small to read.
ed to as TR) is checked on the X10.o.(15mA) (5) There will be some leakage current read even for
range, and a large-size TR on the X 10 range. a good quality Ge TR, though there is some diff-
(2) An NPN TR is connected as shown in Fig. 7-A, and erence subject to its type. It will be 0.1mA -2mA
a PNP TR, in Fig. 7-B. for a small- and medium-size TR, and 1mA-5mA
A. B. for a large-size one.
~~0 ~::~c~ ~~0 (6) If the reading falls within the red LEAK zone of
0"1 0'. the ICEOscale, the TR tested is passable but if
N~N'" . .'@ p@ @ p@ It goes beyond the zone coming near to the full
-~ + -~ + scale, the TR is definitely defective.
1... I... (7) Leakage current is little to do with voltage value
~c r ~E r showing constant current characteristic but it is
_TR --TR -'
Fig.7 a great deal subject to temperature. Be aware of
E C Ltemperature rise while testing; it reads twice as
much for +10 DC.
-16 - - 17.-
