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Model 456A
2-1 .
GEN ERAL.
The Mcxlel 456A must be used with an ac voltmeter
or an oscilloscope . Figure 2-2 shows a typical setup .
2-2.
O PE R AT I N G I N ST R U C TIO N S .
Connect the shielded plug of the Model 456 A OUTPUT
cable to a voltmeter or oscilloscope of appropriate
ra nge.
The conversion ratio is millivolts out equals
milliamperes in.
Thus the voltmeter should read in
millivolts the expec ted mill i amperes being mea s ured.
The current range of the Model 456A is less than
I
1 milliampere to
ampere. The
Vacuum Tube Voltmeter is ideal for this mea suremen t
as it covers the entire range and has a 3/4 inch spac
in g input jack.
WARNIN G
00 NOT PLUG THE OUTPUT CABLE OF
THE 456A INTO A SOURCE OF AC OR DC
VOL TAGE.
Doing. so will burn out the tran
sistors and perhaps other c omponents.
The spacing of the pins on the OUTPUT cable fits all
standard 3/4 inch connectors , such as on Hewlett
Packard voltmete rs , wav e-analyzers , and oscillo
scopes (when used with AC-76A adapte r) . S e e table
1-2 for a list o f Hewlett-Packard instruments s uitable
for use with the Model 456A.
�
The
Mcxlel 400D has an additional ou tput terminal
for viewing the Voltage being mea sured with an oscil
loscope .
This ma y be very useful , for example,
measuring the cu rrent a t which a tra n s is tor s tans
clipping.
The Model 456A may be used to measure very low
curren t , even below the noise level of the probe , if
s ome provision is made to fi lter out the noise. The
I/jJ
Mcxlel 302A Wave Analyzer is ideal for this purpose,
p articularly if the BFO of the
s ignal source (see figure 2-1).
Tunsisler under lest
-.",
-
.---
---_
�� A
-J.p -
CURRENT
PROBE
Figure 2- 1 .
Probe can be used with
to measure distortion in current waveforms
or to measure small audio curren t, as
described in text
00395-1
SE CTION II
O P E R ATING
I NST RUCTIONS
It;!!
Model 400D/H/L
302A
is used as the
302A
-hp-
WAVE ANALYZER
I
/
BFO OUTPUT
/
20'" - � �C
It;!!
30
2 A
In
this manner, currents even below 1 0 microampe res
ca n be measured.
2 - 3.
OPERAT I N G T HE PRO BE.
The probe jaws may be operated w ith one hand. While
holding the probe handle in the palm , squee ze the
flanges together with the finge rs .
open the jaw s .
Move the probe to the v icinity of the
insulated wire being mea s u red and slowly releas e the
flanges until the jaws fit over the wire .
CAUTION
Do NOT let the jaws snap clos ed as they may
be
damaged .
Clip the probe over the wire with the arrow on the
probe in the direc tion of conventional current flow
for a positive-going ou tput signal. This procedure is
important when u s ing an oscilloscope but it ma y also
be importan t when using this probe to measure uns ym
metrical waveforms with half-wave rectifier type
·
meters .
All Hewlett
1 - 2 a re full-wave rectifier types so you will get the
same reading whichever way the probe is clipped over
the wire.
Howeve r , with half-wave type mete rs
the readi ngs may be differen t. This action is a limi
tation of the m eter and not a fault of the Mcxlel 456A.
Refer to the Operating a nd Servicing Manual for the
meter or change to one of the recommended meters .
2-4 .
I N CREAS IN G T HE S ENSITIVITY .
Sensitiv ity of the Model 456A may be inc reased by
looping the wire ca rrying the cur rent to be meas ured
th rough the jaws more than once. The reading on the
meter or oscilloscope will be multiplied by the number
of times that the cu rrent passes th rough the jaws . To
obtain the true reading divide the c u rrent indication
by the number of tu rns enclos ed by the ja w s . The
series loading effect of the probe on the circuit being
measured is then multiplied by the squa re of the
number of t u rn s .
This effect may have to be taken
into account (see pa ragraph 2-50).
2-5.
MEASUREME N T P R E CAU TIO NS.
Bes t performance will be achi eved by observing the
following precautions:
P ROBE HANDLING
A .
1) Do not snap the ja ws closed by letting go of the
probe flanges abruptl y .
shield or the jaws.
2) Do not d rop the probe . The ja ws a re made from an
Sec tion Il
Pa ragraphs 2- 2 to 2 -5
This action will
This action may damage the
2- 1
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