Pointer frequency meter - capacitance meter. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Measuring technology
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Pointer frequency meter - capacitance meter consists of an input device, a Schmitt trigger, a differentiating circuit, a waiting multivibrator and a measuring device.
The input device is made on the transistor V1 according to the emitter follower circuit to increase the input resistance. Diodes V2, V3 protect the input from overloads. The Schmitt trigger is assembled on elements D1.1 and D1.2. The rectangular pulses generated by the trigger are differentiated by the C3-R8 chain, through the V4 diode they go to the waiting multivibrator (D1.3, D1.4), start it and then go to the device. The higher the frequency, the more the instrument needle will deviate. The subrange is selected by pushbutton switches S2-S5.
With the ratings of the elements indicated in the diagram, the following frequency subranges are obtained: 20 ... 200 Hz, 200 ... 2000 Hz, 2 kHz ... 20 kHz, 20 kHz ... 200 kHz (with an input voltage of at least 0,5 V ).
If instead of capacitors C4-C7 in the waiting multivibrator, you turn on a capacitor of unknown capacity (to the input Cx) and press the button S1, and apply a known frequency to the input of the device, the readings of the device will be proportional to the value of this capacitance.
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