GW Instek GFC-8131H - Manual (Page 6)

FREQUENCY COUNTER
USER MANUAL
10
(4) LP FILTER
An unstable reading is caused from measuring noise of low frequency
signals on channel A. The LP FILTER minimizes high frequency noise,
permitting the counter to measure only the desired low frequency
component.
For more stable reading, insert a 100kHz low pass filter into the channel
A input circuit by pushing in the LP FILTER button.
(5) Attenuator
An attenuator is provided in the channel A input circuit for measuring
large signals and for providing additional overload protection.
Reduce the input signal by 20 times by pushing in the ATT button. It is
recommended that when measuring signals of unknown amplitude, this
button should be pushed in for protection. If the amplitude is too low,
the button can be released for greater sensitivity.
FREQUENCY COUNTER
USER MANUAL
11
6. MAINTENENCE
The following instructions are executed by qualified personnel only. To
avoid electrical shock, do not perform any servicing other than the operating
instructions unless you are qualified to do so.
6-1.Standard method for calibration
(1) Input offset voltage adjustment
Push the TRIG LEVEL knob and turn it to the central position.
Connect a 10MHz sine wave to channel A input BNC.
Adjust SVR102 and decrease amplitude of 10MHz sine (typically
20mVrms) to the minimum allowable to maintain display.
(2) Standard oscillator adjustment
Connect a standard reference frequency (10MHz, temperature stability
＜0.2ppm) to channel A input.
Adjust the GATE TIME control for 8 digital display.
Adjust SVC201 for the most accurate display of the reference
frequency.
(3) Hysteresis Bias voltage adjustment
Set the LP FILTER to ON and set the COUP to DC position. Push the
TRIG LEVEL knob and turn it to the central position.
Connect a 1Hz sine wave 30mVrms to channel A input BNC. Adjust
SVR103 to the minimum allowable to maintain display.