Global Specialties 4005 - Manual - Manual (Page 22)

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F. LOW-PASS FILTER: If necessary, engage the LPF (low pass filter) switch. This will route the
input through a low pass filter (-3 dB point of approximately 100 KHz) prior to passing through
to the frequency counter. This helps eliminate counting errors in low frequency measurements
by minimizing effects of high frequency noise present on the input.
CAUTION
1. APPLICATION OF INPUT VOLTAGES HIGHER THAN THE LIMITS LISTED IN THE
SPECIFICATIONS SECTION MAY DAMAGE THE COUNTER. BEFORE APPLYING ANY SIGNAL
TO THE INPUTS, MAKE CERTAIN THAT IT DOES NOT EXCEED THESE SPECIFIED MAXIMUMS.
2. FREQUENCY COUNTER GROUND POINTS ARE CONNECTED DIRECTLY TO EARTH
GROUND. ALWAYS CONNECT FREQUENCY COUNTER GROUND ONLY TO GROUND POINTS
IN THE CIRCUIT UNDER TEST
NOTE
THE OVERVOLTAGE CATEGORY OF THE EXTERNAL FREQUENCY INPUT TERMINAL IS “CAT
II ”. IT IS PERFORMED ON CIRCUITS DIRECTLY CONNECTED TO THE LOW VOLTAGE
INSTALLATION.