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HEWLETT-PACKARD


V " f T E C H N I C A L
JOURNAL
I N F O R M A T I O N F R O M T H E - h p - L A B O R A T O R I E S
)l. 10, No. 9- 10

PUBLISHED BY THE HEWLETT-PACKARD COMPANY, 275 PAGE MILL ROAD, PALO ALTO, CALIFORNIA MAY -JUNE, 1959



A Clip -On Oscilloscope Probe
for Measuring and Viewing Current Waveforms
A though current is a fundamental quantity tion the general problem of measuring alter
in electronic circuitry and accurate knowl nating currents is made much more convenient
edge of it is valuable, it is a quantity that has by a new oscilloscope probe which permits
always been rather inconvenient to measure both viewing and measuring alternating cur
and in at least one important case quite diffi rents merely by clipping the probe around the
cult. This is the case of alternating currents in current conductor. The probe operates with the
circuits elevated from ground. Here, to use a -hp- Model 150A Oscilloscope and a new plug-
current meter involves at best the trouble of in amplifier to measure and display currents
opening the circuit, while the meter, when con over an amplitude range from 1 milliampere
nected, will usually not indicate such often- to 15 amperes peak-to-peak and over a fre
needed information as the current's peak value. quency range from below 500 cps to 8 mega
At the same time to measure the current wave cycles. In the case of sinusoidal currents, wave
form in such circuits with an oscilloscope has forms down to about 50 cps can be displayed.
required the combination of a suitable circuit Electrically, the probe consists of a wide-
resistance to connect across and an oscilloscope range current transformer with a split core
with a differential input of adequate range, a which is mechanically opened and closed by
combination often not available. flanges on the probe body in the manner proved
These problems are overcome and in addi popular in other -hp- probes. When the probe




PLATE
VOLTAGE




Fig. 2. Oscillogram illustrating type of dis
play obtainable with new probe and plug-in
unit. V pper trace shows plate current waveform
in an oscillator circuit, while lower trace shows
oscillator plate voltage.



Fig. 1 (at left). N'e/i' current probe and plug-
in unit for Model 1 W A Oscilloscope enable al
ternating currents as small as I ma and up to 8 me in frequency to be measured merely by clipping probe on conductor.
Unit also simultaneously roltage channel and dual-trace provision to permit foliage to be measured simultaneously with current.



P R I N T E D I N U . S . A . C O P Y R I G H T 1 9 5 9 H E W L E T T - P A C K A R D C O .