Practical Circuit for Measuring Capacitor Capacity with a Pointer Multimeter
Want to use the pointer multimeter to determine the good and bad 400 microfarads of capacitors, you can use the multimeter suitable resistance file to measure the two pins of the capacitor, according to the amplitude of the pointer swing can know the capacitor is good or bad. Generally good capacitor pointer can point to the maximum value (or close to the maximum value), if the capacitor breakdown damage, the pointer points to the minimum value, if the pointer stays in the middle of a certain value, it shows that the capacitor has a certain leakage. If the questioner would like to use an ordinary pointer multimeter to measure the capacitance, you can use the LM358 operational amplifier according to the circuit shown in the following figure can be connected to measure the capacity of 400 microfarads of capacitance.
Here an internal operational amplifier is used to connect an inverting proportional amplifier. The closed-loop amplification of the circuit is - (R/Xc), where Xc is the capacitance of the measured capacitor. We know that the capacitive reactance of a capacitor Xc = 1/2πfC, and if the frequency f is 50 Hz and C is 400 microfarads, then the capacitive reactance Xc = 7.96 Ω.
In measuring the capacity of 400 microfarads, we can find a 6V power transformer, the secondary output of 6V AC voltage through the resistor divider into a 100mV/50Hz sine wave as a signal source, 400 microfarads connected to the position of C in the figure, so that the pointer multimeter AC voltage file to measure the output voltage of the operational amplifier Vout, and then after a simple calculation can be know the capacity of the measured capacitor. Assuming that Vin is stable 100mV, measured Vout = 1000mV, according to the above formula can be seen, the capacitance of the capacitor Xc = 7.96Ω, and then again according to the capacitance of the capacitance of the formula can be known to the capacitance of the capacitor capacity.
Now most of the digital multimeter is used to measure the capacitance of the above method. Due to the frequency and amplitude of the sinusoidal signal source in this circuit and the value of resistance R and the digital multimeter capacitance file is not the same, so it can not read the capacitance. General digital multimeter with a signal source of 40mV/400Hz sine wave signal, R's value is not the same as the above resistance, so the output voltage of the amplifier and the measured capacitance is the same as the capacitance, can be read directly. The power supply voltage of the above measurement circuit can be ±5V.
