2-1
SECTION 2 – GENERAL DESCRIPTION
PRINCIPLES OF OPERATION
2-1
Locating short circuits
The TONEOHM 550A Shorts Locator is a precision milliohmmeter incorporating:
•
A resistance-dependent, variable-frequency audio tone output.
•
A liquid crystal display (LCD) screen providing an indication of the
resistance being measured.
•
Kelvin probes to minimise measurement errors.
•
Low probe tip injection voltage to safeguard sensitive semiconductor
devices
The variable-frequency audio tone output of the TONEOHM 550A makes it especially
suitable for locating for short circuits between the tracks of a PCB where hairline
bridges between tracks may be hidden beneath components or even buried below the
surface of the board.
Using the TONEOHM 550A the technician can locate a short circuit between two tracks
of a printed circuit board tracks by positioning the two Kelvin probes on the two tracks
and listening for an audio tone. A tone indicates the presence of a short circuit between
the tracks.
The frequency of the audio tone is dependent on the resistance between the two Kelvin
probes.
Moving one of the probes along its track will cause the resistance between the probes
to change and cause a corresponding change in the frequency of the audible tone.
By moving the probe along the track until the tone reaches its highest pitch the
technician will quickly locate the precise position of the short.
Summary of Contents for Toneohm 550A
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