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| LCR Tweezers test and analysis (HP-990, DT71, ST5S...) |
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| Shannon:
Hi fabriciofx, I designed this Calibration board by myself and manufacturing it by my Chinese Friends. Those resistors are 0.1% 25ppm, caps are 5% (1% caps are expensive for few parts). it's quite convenient. If possible, I will manufacture some of them for those who are interested. |
| Shannon:
Smart tweezers st5s is a well-known commercial precision measuring tweezers. I believe it is a real pure AC inspired LCR meter, rather than the two products mentioned above. It's time to take a look at st5s, which is generally recognized as the best tweezers. As I said, ST5S is a very high precision, and it's very convenient to use, so the price is beyond my plan. The price on Amazon is $311, and the shipping cost is $46. OMG. I thought it was very expensive many years ago, but it's still very expensive for me now Finally, through the second-hand platform, I bought a second-hand st5s for $120. I thought it was quite worthwhile. Although it was not very good, the button cap was missing, and the tweezers arm was bent. It seemed that its owner didn't care about it. He tried to bend the tweezer's arm to make the tweezer's point aligned. When I got this tweezer, I really liked its performance. It was very powerful and accurate. When I found that it supported ESR and |Z| measurement, I could confirm that this LCR meter really used pure AC signal for measurement, because if the test methods in hp-990 and dt71 were used, it was impossible to measure the ESR characteristics of capacitance, which was great, makes me know the quality of the capacitors. The test frequency supports four frequency points: 100Hz, 120Hz, 1kHz, 10kHz, and supports the automatic identification of components. Dt71 also supports the identification of component types, but st5s can automatically adjust the frequency of the excitation signal to measure the device under test. The main parameter display is standard 4 bits, so the display range is from 0000 to 9999, and the highest resolution is close to 0.01%. The subparameter index is also 4 bits, but there is no clear description of the performance of the subparameter. If the main parameter is very accurate, the accuracy of the subparameter is usually very high. The chapter "how it works", clearly states that st5s uses Kelvin 4-wire measurement method to measure, and finally sees the necessary conditions to realize precision measurement. It is worth emphasizing that st5s supports two kinds of excitation amplitude, which is very good because when measuring SMD components on PCBA, these components are usually connected with the pins of semiconductor devices. If the excitation amplitude is too large, the measured impedance is the result of connecting the diodes inside the semiconductor devices in parallel, so the excitation signal with low voltage amplitude is very useful, which does not exceed that of semiconductor devices At the same time, the parameters of the device can be measured. St5s supports excitation signals of 0.5vrms and 1Vrms, and the accuracy of excitation voltage is 2%. |
| Shannon:
The resistance index is very good. There is a note below the index, which indicates that the range of 1 ~ 100ohm is minus the offset impedance. The best index is 0.2% + 3counts, and the accuracy under different frequencies is clearly marked, except for 120Hz, because the index of 120Hz is very close to 100Hz. Compared with the test results and indexes, the resistance indexes are all within 0.2% + 3 of the best indexes, which is unbelievable. When testing the capacitance, in addition to the capacitance value, the equivalent RP or equivalent RS parameters of the capacitance can be obtained through the sub-parameters, and the quality of the capacitance can be detected. In addition, through st5s, it is found that the ceramic capacitance will change in the measurement process, which should be due to the piezoelectric effect of the ceramic capacitance, resulting in a small change in the capacitance value. St5s can detect this slow change phenomenon. The figure below is the waveform of the excitation signal. The device to be tested is the probe of the oscilloscope. The input capacitance is about 10PF. The default test frequency is 10kHz. The waveform is a very beautiful AC 10kHz 0.5Vrms sine signal. The internal circuit looks very complicated, salute to the designers. |
| Shannon:
ST5S summary: This is the best commercial LCR tweezers I have ever used Advantages: 1. Very, very accurate 2. The function is very powerful, which can be compared with the standard LCR meter 3. Support Kelvin measurement 4. Compact design Disadvantages: 1. A little expensive 2. The structure design is the best LCR tweezers I have ever used, but there is still a gap between real tweezers 3. Although it is very accurate, it does not support self-calibration, which may be a disadvantage |
| tautech:
For 15 years I have used the earlier ST3 and even back then the cost was a disincentive to purchase although with a quality tool the initial cost hurt is now long forgotten. They are my goto component tester as with that cost also provides you an ESR tester ....another piece of equipment you don't need to buy. :phew: Some think tweezers are only suitable for SMD and to that I say BS as the tweezer legs can be spread to cover most through hole devices. Would I buy another ? In an instant ! |
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