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3-11-2. Continuity Measuring Circuit
The continuity measuring circuit sets the reference voltage at U3-3 by R20, R21,
R23. When resistance is connected to the input, the voltage is applied R18 by
the voltage from R17. The attenuated voltage by R22 is linked to U3-2 through
R24 and connected to R72.
AT this time, if the U3-2 voltage is lower than the reference voltage of U3-3,
U3-1 turns to the high state and puts U4-1 in the high state through R26, the
input of buzzer circuit, and then sets the buzzer in motion by operating U4
oscillation circuit.
3-12. FREQUENCY MEASURING CIRCUIT
When the frequency described in the specification is input by using the
frequency generator, the frequency is applied to U7-3 through R52, C25. At this
time, if the signal of frequency is higher than that of U7-2, the signal of U7-1
turns to the high state and becomes the trigger signal of U8-2 by being
differentiated by C26, R55. When the trigger signal is applied to U8-2, U8
monostable multivibrator with U8-3 output generates the square wave of 20kHz
with time constant of R59, C27 and 200kHz with time constant of R58, C27.
The generated square wave 20kHz and 200kHz through the analog switch of U9-12
and U9-13, respectively, and the attenuated signal by VR14, R65 through the 10-
time amplifying circuit are connected to R72.
3-13. FRONT PANEL FUNTION AND RANGE DISPLAYING LED DRIVER CIRCUIT
The signal of the driver circuit of LED displaying the front panel range is made
by combination of function and range switch selection and U17, U18 IC. Function
LED signal is made by combination of R96 and the function switch.
3-14. HOLD CIRCUIT
If the HOLD switch on the front panel is pressed, the value on display is held
by connecting U10-25 to GND. At this time, over-range value does not appear. In
addition, the hold LED on the front panel is displayed when supplied with power
through R33.
