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Sec tion I
Paragraph 1 -2
For flat frequency response th e shunt input impedance
of the as sociated voltmete r or oscilloscope should be
greater than l OOK ohms in pa rallel w ith 25 pf or
made ro appear that value to the 456A.
Lower shunt resistance w ill change the accu rac y
equally at all frequenci es , due ro th e low output im
pedance (about 200 ohms) of the Model 456A.
Different shunt capacitances have no effect on the low
frequency respon se , but can affec t the high frequency
gain as shown in figu re 1-3.
100 UUF
- 4
LOAD
-6
IMC
fREQUENCY
F igure 1-3.
Typical Change in F requency
Response w ith Load Capac itanc e
The Model 456A output contains a dc componen t of
approximately
1 vdc which mus t not be loaded ex
+
ces sively (less than lOKohms sh unt load is excess ive).
Almost a ll ac vol tmeters and oscilloscopes h ave a
dc blocking capacitor in the input circuit ro take care
1-2
1 0 UUf
LOAD
40 Ullf
LOAD
IOMC
30Me
of this requiremen t .
DO NOT USE THIS INSTRU
MENT WITH RECTIFIER TYPE METERS .
loading in th is type of in s trument is excessive and
may affec t the reading.
1·2.
P O WER REQUIREM E N T S .
The Model 456A is available eith er as a batte ry
powered or ac powe red instrument.
�
Supply (
s roc k # 456A-95B) fits into the space nor
mally occupied by the ba ttery supply and takes th e
place of i t
e lectrically.
be ordered sepa rately.
When the 456A is powered w ith its ow n internal ba t
teries it is independent of power l ines .
us ed in the field with battery operated VOl tmete rs,
tfi;
Mcxiel 403A A C Voltmete r, or battery
s uch as the
powered oscilloscopes.
usefu l in the laboratory whe re complete is olation is
desired.
While ba ttery operated the 456A may be
used w ith th e chassis off ground w ith out difficu lty .
This type of operation may a ls o be des ired ro isolate
pow er lin e hum in a system where several ins tru
ments are used.
Wh en the 456A is u s e d with th e ac power supply the
chassis is automatically grounded th rough the third
prong in the power plug. The three conduc tor �ower
c able s u pplied with the i nstru ment is terminated in
a polarized, three-prong male connector rec omm ended
by the Na tional Electrical Manufa cturers ' Association
(NEM.f.). Th e third conduc tor grou nds the ins trument
chassis for protection of the operating personnel.
W ARNI NG
When using a three-prong to two-prong adapter
ground the third lead (green wire) externa lly.
Model 456A
The
The AC Power
Th e ac power su ppl y must
It ma y be
Batte ry opera tion is also
00395-1
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