ESR meter with extended scale.

[iet]

Basic information here.
https://electronicsdesignfun.blogspot.com/p/esr-meter.html
The meter is adapted to the tester body.
The front panel contains a zero regulator, a power switch, and a graduated scale. The calibration was done using SMD resistors with low inductance.
Scale: 0.005-5 Ohm.
Some changes have been made to the original scheme.
U1-LM833
Resistors:R4-5.6k,R5,R6-0.1,R8-20k,R11-100k
D1,D2-1N5817
The transformer is wound on a ferrite ring
Supply voltage:9v
Frequency:100 kHz
Vpp:100mV

[enut11]

Interesting adaption for an old analog multimeter. How does the scaling work?

[iet]

How does the scaling work?

The values on the ohms scale of the multimeter are indicated in red.
The ESR values in mohms are indicated in blue.

[iet]

As you know, the ESR of a capacitor can react to the heat of your hands. And the result may not correspond to the actual value. In addition, to obtain the most reliable result, very reliable contact between the probes and the legs of the capacitor is necessary.
Therefore, a simple device was made to install and measure the ESR of capacitors.

[iet]

I made a small modification to the ESR meter.
I used larger cross-section wires. I used elements with greater temperature stability in the 100 kHz generator circuit. Previously, the generator frequency drifted to 100-200 Hz during several hours of operation. Now the frequency is stable at 100 kHz.

[enut11]

@iet. Thanks for the update. It will be one of my future projects when I get the time. Thanks for sharing.
enut11

[iet]

Always positive to help in any way I can.
I would like to say a little more about the components used.
There are no special requirements for resistors and capacitors, except for the generator circuit. More stringent requirements for diodes and especially for the operational amplifier.
The best Schottky diodes are the 1N58 series..., but there may be others.
The stretch and linearity of the scale depend to some extent on them.
The most requirements are for the operational amplifier. It must be LM833 or similar in characteristics. I advise you to pay attention to the frequency range that is indicated in the datasheet.
It is optimal when it is 8-16 MHz. The slew rate is of secondary importance.
It should also be noted that the actual characteristics of the op amp from different manufacturers may differ slightly.
Additionally, different op amps have different maximum gain values depending on the supply voltage.
As for microammeters, everything is very simple. The more sensitive it is, the better.

[iet]

Probes.
The main requirement for them is minimal resistance and good contact.
The best solution would be a wire cross-section of 2x2.5 mm. An audio wire is perfect here. There is no need to separate the wires, this reduces interference. A length of 40 cm is optimal.
Solder the probes directly to the transformer.

[iet]

Anyone who doesn’t like a multimeter with long probes can make an ESR meter in the form of tweezers. The prototype was the MS8911 tweezers, I used spare tips from it. At the bottom I attached a socket for a 9V battery.
The microammeter can be installed in any convenient place.

[iet]

Measuring ESR of capacitors.

[iet]

I redid the power supply for the tweezers. Instead of a socket and a 9V battery, I made a homemade socket for two CR2450 batteries. Now the supply voltage is 6V. Everything works well due to the high gain of the op-amp.
The tweezers have become somewhat lighter and more convenient.
A 1mA milliammeter is attached to a small movable stand. It can be installed in any suitable place on the table and you can choose any angle of inclination.

[iet]

In this design, the scale is quite stretched near zero and slightly compressed to 1 Ohm. At the same time, good linearity is maintained.
Here are some ESR measurements of capacitors.

[iet]

Now we can measure SMD calibration resistors with low inductance with tweezers.
We make sure that there is no need to draw a new scale.

[iet]

Once the design was complete, it was time to evaluate the effect of the inductance of the resistors on the calibration of the ESR meter scale.
Three resistors with the same resistance of 100 mOhm were studied.
With increasing inductance, the deviation from the actual value on the scale increased.

[iet]

So the moment came when I decided to measure a very low ESR. I had to buy capacitors from Panasonic-Conductive Polymer Aluminum Electrolytic Capacitors. SP-Cap GY 820 uF, 2v.
These capacitors have a max. ESR of 3mOhm.
The measurement gave a result of approximately 2 mOhm, which in principle coincides with the data from the datasheet.
https://api.pim.na.industrial.panasonic.com/file_stream/main/fileversion/8713

[AlienRelics]

Nicely done.

[enut11]

Well done @iet. May have to bring this project forward.😀

[iet]

Thank you everyone for your words of support.
I will try to add important things and develop the topic naturally if I have time.
Tweezers does the necessary job of estimating the ESR of used capacitors, even if there is no data in the datasheet.
Several Nichicon GU, 330 uF-420 v capacitors were removed from the board. The measured ESR was approximately 185 mOhm. This is a good value for this type of capacitor.

[iet]

Using the capabilities of tweezers, you can easily measure the resistance of SMD fuses.
Fuse 5A, resistance 11 mOhms.
https://www.bourns.com/docs/product-datasheets/sf-2410hi-t.pdf?sfvrsn=4d8a79f6_11

[iet]

Microammeter 100 µA. The scale is larger and more stretched, which is naturally more convenient for reading in general and for those with poor eyesight. I did the markings manually, which is fine for me.

[iet]

If necessary, you can make a more accurate scale, 15,25,35 mOhms, etc.
This matters when we select from a batch of new capacitors those that are closest in value. Or we select the best from used capacitors.
But our goal is not super accuracy, but an extended scale for all types of capacitors (electrolytic, tantalum, solid polymer).

[Uky]

Nice project.

 

Just one comment. (Not that it affects the performance very much but...)

U2A, a diff amp with G=10. Note that Zin differs between the two inputs.
If wanting to perfect the design, an Instrument OPAmp could be considered.

I am in need of an ESR meter myself so I will use this design as the starting point.

 

[iet]

If wanting to perfect the design, an Instrument OPAmp could be considered.

Thanks for the tip.
I continue to improve my ESR meter.
I received the ordered NE5532P. I received even greater gain, which made it possible to reduce the resistors in the load of the transformer by half. At the same time, the scale stretch near zero doubled. Now 5 mOhms corresponds to the 10 mOhms mark. Power supply is 6 V. Full scale is 500 mOhms.

[Wolfgang]

Hi, I made an autoscaling ESR meter with autorange using an Arduino and an AD8307.
Works fine, look here:

https://electronicprojectsforfun.wordpress.com/homebrew-scpi-controllable-instruments-with-arduino-controllers/an-autorange-cap-esr-meter-with-scpi-connectivity/

[hugo]

Hi, I made an autoscaling ESR meter with autorange using an Arduino and an AD8307.
Works fine, look here:

https://electronicprojectsforfun.wordpress.com/homebrew-scpi-controllable-instruments-with-arduino-controllers/an-autorange-cap-esr-meter-with-scpi-connectivity/

I believe you that it works fine, however where are the schematic and the arduino source code?