Schematic ?
Before I designed the 5 Transistor ESR meter, I designed and built an ESR meter using a digital panel meter.
The design is unusual in that it uses 10kHz, instead of the more usual 100kHz. By using a synchronous rectifier to measure the in-phase component of the capacitor impedance.
QuoteSchematic ?
Sure.
Before I designed the 5 Transistor ESR meter, I designed and built an ESR meter using a digital panel meter.
The design is unusual in that it uses 10kHz, instead of the more usual 100kHz. By using a synchronous rectifier to measure the in-phase component of the capacitor impedance.
Jay_Diddy_B, thanks, that looks interesting.
Now, as usual, incoming bombardments of noob questions :
- What is so special about that "synchronous rectifier" method compared to others common "cheap DIY" ESR measurement techniques ?
- Why 10 KHz ? How about other frequency like 100 KHz ? or lower ?
- Any pre-adjustments or tunings required when finished building it ?
10KHz was chosen as a compromise. 100kHz is the traditional frequency used for ESR measurements. At a 100KHz I would have needed some faster op-amps and a better analog switch.
There are several weaknesses in this design:
1) The amplitude of the square wave is dependant on how close the op-amp can swing to the rail.
2) The amplitude of the sine wave depends on being in the center of the band pass filter.
3) I tweaked the value of the R23 to obtain the calibration.
This circuit has a nice linear response. It is a true ESR meter, it is not an impedance meter. It use as nice low voltage test signal to allow in circuit measurements. It will work with a DMM, but you have to multiply the voltage read by 10x to get ohms.
Thanks for the signal's scope shot, that helps me to further getting a grip on this circuit.
Btw, I have to be honest with you, that most of my questions are from an enthusiast level perspective, which emphasizing more at practicality point of view. Its not I'm lazy to learn in depth on how it works, its just it will take much longer time for me to catch up since without any strong foundation of electronics knowledge, and experiences like you EE or pro do. While the main interest is still on building it, hope you can bear with me here.
More ..10KHz was chosen as a compromise. 100kHz is the traditional frequency used for ESR measurements. At a 100KHz I would have needed some faster op-amps and a better analog switch.How fast op-amp needed at 100 KHz ? Any example of popular op-amp ? Non the exotic one if possible, please.There are several weaknesses in this design:
1) The amplitude of the square wave is dependant on how close the op-amp can swing to the rail.
2) The amplitude of the sine wave depends on being in the center of the band pass filter.
3) I tweaked the value of the R23 to obtain the calibration.So I'm assuming from above points, this circuit has a fixed test frequency ?This circuit has a nice linear response. It is a true ESR meter, it is not an impedance meter. It use as nice low voltage test signal to allow in circuit measurements. It will work with a DMM, but you have to multiply the voltage read by 10x to get ohms.Will a cheap say like common low offset op-amp, set up as 10X gain connected at TP7 enough for that ? cmiiw
Have no intention to derail the discussion from this fine circuit, just curious about another diy esr meter circuit that output to DMM -> here (scroll down abit at the bottom), or link to the schematic -> here for better view.
Does it use the same/similar synchronous rectification method ? The reason I bring this out because I see it uses switches to switch the test signal back & forth like yours.
How fast op-amp needed at 100 KHz ? Any example of popular op-amp ? Non the exotic one if possible, please.
Will a cheap say like common low offset op-amp, set up as 10X gain connected at TP7 enough for that ? cmiiw
Have no intention to derail the discussion from this fine circuit, just curious about another diy esr meter circuit that output to DMM -> here (scroll down abit at the bottom), or link to the schematic -> here for better view.
Does it use the same/similar synchronous rectification method ? The reason I bring this out because I see it uses switches to switch the test signal back & forth like yours.
This is the ESR meter mention by BravoV:
QuoteThis is the ESR meter mention by BravoV:
Could you build a flip/flop from the spare gates? Or to build an oscillator from the spare flip/flop. Saving one IC.
I can not see a way to reduce the IC count.
Here is a LTspice model for a 100 kHz version. This uses LTC6244HV dual op-amps. These have 50MHz GBW and 35V/us Slew rate.
I really think that there is little advantage over using 100 kHz instead of 10 kHz.
A 10x simple op-amp could be used for 10x correction, but unless you have a 24 rail, you will limit the maximum resistance that can be read.
Yes, the use of the analog switch to form a synchronous detector is similar. It applies a square wave current to the capacitor. In this circuit there is a trade off using analog switches at low signal levels and then dc amplification versus amplifying the ac signal and then using the analog switches.
It would be interesting to build a model of this circuit.
The test results from LTspice:
I really think that there is little advantage over using 100 kHz instead of 10 kHz.
Ok, I keep hearing this, is there any examples where 100 KHz has the advantage over 10 KHz ?
I'm still lost in understanding that circuit, what this test result is telling if you don't mind explain a bit ?
Using a 100kHz has advantages if you design an ESR meter that measures the impedance of the capacitor instead of the ESR. This determines how effective the meters work for low value capacitors.
If the meter is able to measure the in-phase component of the impedance, which is the ESR, then the frequency does not need to be as high.
The test result has the value of the test resistor on the X axis and the output voltage or meter reading on the Y axis. What you are looking for is a straight line that goes through 0,0. This tell you that the meter is linear and has the capability to measure low values of ESR accurately. You can also change the value of the capacitor in the simulation. A good ESR meter will be able to measure the ESR of a low value capacitor correctly.
In the 10 kHz digital ESR meter that I post I can correctly measure a 4.7uF capacitor with an ESR of 1.2 Ohms. This is good enough for me.
Here is the same capacitor in an HP 4274A Multi-Frequency LCR meter (5 1/2 Digits 0.1% , around $1000 to $1500 for a used one, the 16047D Test Fixture is worth about $250.00):
Here is a quick analysis of the VK5JST ESR meter. The operation of this meter is very similar to the 5 transistor design at the start of this thread. It place the rectifier inside the feedback loop of an op-amp. This type of circuit has the advantage that the signals are larger for small ESRs than they are for higher values.