Hi all,
Let's discuss why we use these excitation voltage, we are late
.
First of all, we need to admit that many capacitance measurements do use 1Vrms as the test standard in the data sheet.
This value looks accurate, but it's not that accurate. Because there is usually a resistor connected in series between the excitation voltage source and the DUT, at this time the real voltage on the capacitor is related to the capacitance value and the series resistance.
Imagine if there is no series resistor, a 1000uF capacitor, superimposed on a 10kHz, 1Vrms signal, the current will be 62.8Arms, which is ridiculous. (If I am wrong, please help me point out). So I think that 1Vrms is not so strict sometimes, Especially for those capacitors whose capacitance is above 1uF.
But the RMS value is more suitable for the expression of energy, and the Q value is the ratio of energy.
One of my impression is that capacitors that require high excitation voltage often do not require high precision. I don’t know if it is accurate. If there is a more correct expression, please correct me.
Another point is that using a higher excitation voltage can obtain a higher signal-to-noise ratio, which is very meaningful for those measurement systems with a large noise floor, in this situation, higher SNR means the measurement can be more accurate, but it is not very meaningful for ST42, the noise floor of ST42 is very low.(you can verify the measurement results of 0.1Vpp, 0.5Vpp and 1Vpp, the difference is very small, higher voltage does not bring higher accuracy).
ST42 is a very small portable device, too high excitation voltage will consume more power consumption.
Another point is that we need more complex circuits (default operating voltage 3.3V) in order to achieve 1Vrms (2.8Vpp), and may introduce high noise(boost type switch power), we think the gain is not very big.
The first impression of ST42 for users is that it is suitable for measuring SMD components, because it is in the form of tweezers. When measuring on PCB, the most noteworthy thing is whether the excitation voltage will cause errors due to excessive excitation. The user's intuitive experience of Vpp must be clearer and more direct than Vrms.
The last question, why do you need 0.1Vpp and 0.5Vpp? I understand that 0.25V is a relatively marginal voltage value. There will be leakage current of some devices at this voltage that will affect the measurement accuracy, and it does not have to be completely turned on. (0.3V for Schottky diode and 0.7V for silicon diode in the book) will affect the measurement. From this point of view, as long as the measurement accuracy is not affected, the smaller the voltage is, the safer it is.
I don't know that if this reply would stop the argument. I suggest that everyone communicate calmly, because only through calm discussions we can discover more details hidden behind ST42 and the valuable content behind them