HP 428B, Operating And Service Manual, Page: 9 / 52

Model 428B
SECTION I
GENERAL INFORMATION
1-1. INTRODUCTION
1-2. The -hp- Model 428B Clip-On Milliammeter measures
the magnetic field, which exists around the wire carrying dc
current. Operating the instrument is simple. After zero
setting, the two jaws of the probe are clamped around wire
(arrow on probe head indicates direction of conventional
current flow) and the meter will indicate the current.
1-3. There are nine current ranges starting from 1 mA to 10
amp full-scale deflection. The sensitivity can be increased
even further by looping the wire several times through the
opening in the probe. The current indication is virtually
insensitive to superimposed ac signals and the series
loading of the circuit is less than 0.5 pH. A large amount of
feedback provides great stability.
1-4. OTHER PROBE HEADS.
1-5. Other probe heads are available to extend the
usefulness of your Clip-On DC Milliammeter. Write to the
nearest Sales and Service Office (listed in Appendix C) for
further information. At the time of publication of this manual,
the following accessory probe heads were available:
a. -hp- Model 3528A Large Aperture (2-1/2
inch probe head).
b. -hp- Model 3529A Magnetometer (1
gauss = 1 amp).
c. -hp- Model C11-3529A Magnetometer
(1 gauss = 1 mA).
1-6. Write to the nearest Sales and Service Office
(listed in Appendix C) stating your complete
requirements for information concerning special
applications.
1-7. INSTRUMENT AND MANUAL
IDENTIFICATION.
1-8. Hewlett-Packard uses a two-section serial
number. If the first section (serial prefix) of the serial
number on your instrument does not agree with
those on the title page of this manual, change
sheets supplied with the manual will define the
differences between your instrument and the Model
428B described in this manual. Some serial
numbers may have a letter separating the two
sections of the number. This letter indicates the
country in which the instrument was manufactured.
Figure 1-1. Model 428B Clip-On Milliammeter
2