ESR meter with extended scale.

[iet]

Hi, I made an autoscaling ESR meter with autorange using an Arduino and an AD8307.

Hi, nice project.
I finally adjusted all the operating modes of the circuit.
The scale is very stretched near zero and moderately compressed near the maximum value.
Scale: 0-0.08 Ohm.
U1-NE5532P
Resistors:R4-5.1k,R5,R6-0.05,R8-20k,R11-100k
D1,D2-1N5817
Supply voltage:5v
Frequency:100 kHz
Vpp:70mV

[iet]

An extended scale near zero has undeniable advantages over a compressed one. This part of the scale is used to measure capacitors with very low ESR. These are mainly modern series of solid polymer and tantalum capacitors.
We can also use this section of the scale to measure the ESR of capacitors connected in parallel.

[iet]

I replaced the 100k adjusting resistor.
Now it works vertically and takes up less space. The previous resistor was a little old and the zero adjustment was not as smooth as I would like. Now everything is fine.

[iet]

The ordered op amp OP275 arrived. It was purchased purely out of interest in comparison with other op amps in order to remove all questions and doubts. Summary.
There are no advantages over the NE5532P. The performance is identical.
But OP275 needs 10V power supply. The oscillogram is slightly distorted. Most likely this is due to the fact that JFET transistors are used there.
In addition, it is much more expensive.
The NE5532P is definitely unrivaled.
Regarding TL072. With this circuit design it does not work. At a voltage of 9V, the needle deviates by only one division.

[iet]

Recently some missing resistor values ​​arrived and I finished calibrating the scale of the ESR meter, which uses the NE5532P op-amp.
To be honest, I didn’t even expect it myself.
The result was a very stretched, linear scale with a range of 1-100 mOhm.

[iet]

It is very important to know the ESR value of capacitors in any connection without removing them from the board. Also, searching for documentation on them does not always lead to success. Therefore, we can now trust our calibrated scale, which naturally speeds up the work.
We must ensure that the capacitor is suitable for further use in our projects without removing it from the board.

[iet]

In my work, sometimes it is necessary to make measurements with high accuracy, and to do it quickly and as efficiently as possible. Some things have to be done directly on the boards, without desoldering the components.
Therefore, we studied the issue of purchasing a second tweezers with higher characteristics. In the end, I chose the LCR Pro1 Plus.
In addition, I naturally wanted to check the measurement results with my 100 kHz tweezers. The results delighted me, which means my time was not wasted.

[iet]

I used digital tweezers to measure the resistance of the smd fuse and the esr of two 220 uF SP-CAP capacitors connected in parallel. Naturally, good contact is needed and this is provided by high-quality tips. I would even make the tips even more rigid, because sometimes sufficient effort is needed to obtain a reliable result.
I also measured a capacitor from Panasonic SP-Cap GY 820 uF.

[iet]

Made a slight upgrade to my tweezers.
With the same dimensions, the new board added a connector for external power. The microswitch is half the size and is used when powered by batteries.
All resistors, except the power bus, have a 1% tolerance. The 1nF capacitor was selected for the lowest losses.
Resistors R5, R6 0.1 Ohms were replaced with smd ones. The freed up space can be used for ferite rings of larger diameter.

[iet]

The second tweezers are made a little differently. Of course, you can buy ready-made gold-plated tips, but this greatly increases the cost of the design. In the process of working with two tweezers, I decided to try to make my own tips from available materials. I experimented with different materials, but in the end I chose copper plates.
The tips must be thin enough, while maintaining good rigidity and stability and have low resistance. Copper plates are perfect for these requirements. The only possible inconvenience is sometimes rubbing the surfaces with fine emery cloth. As you know, copper also comes in different qualities, so it is necessary to use plates well-known manufacturers, such as flexible multi-plate electrical busbars.
Another significant difference from the first tweezers is the distance between the tips. 2 cm and 4.5 cm, respectively. This allows you to measure capacitors of different types with radial leads.
In addition, having a low-impedance range, it is more convenient to look for short circuits on boards at more distant points.

[iet]

I finally resolved the issue of powering the tweezers. Now it is combined. From an external power supply and from a 3.7 V lithium battery. This became possible due to a significant reduction in the resistance of the tip-transformer circuit. The amplifier works perfectly at a voltage of 3.7 V and even when the supply voltage is reduced to 3 ,3V. Thus, it became possible to use a lithium battery. There was a slight conflict here, because it was necessary to use two 3V batteries, and the amplifier did not work with 3V.
In addition, purchasing a lithium battery is much more economical than periodically purchasing 3V batteries.
On the board, instead of a microswitch, there is a micro-connector for connecting the battery. A charger micro-board is screwed to the side. The battery itself is attached to the bottom. I’ll see how long it will last for continuous operation.
A steeper stand for the microammeter is used. It rotates around its axis and tilts to the required angle.
The 50 µA microammeter AIME60005 from Welleman was ideal. With dimensions of 60x47 mm, it has excellent sensitivity.
Scale 0-500mOhms.
The scale was calibrated so that 30mOhms coincided with 30uA. This simplifies the rest of the calibration.
The rest of the parameters are the same. Frequency is 100 kHz, test voltage is even lower - 40 mV.

[iet]

The maximum voltage of a fully charged lithium battery is 4.2 V. This is good. This means that the tweezers can confidently work within the voltage drop range of 4.2-3.3 V. The only inconvenience in this situation is the minimal adjustment of the R11 zero. Now we will monitor how much it will be over time reduce the voltage drop at rest and in working condition. What is the point of this? Very simple. A 400 mA lithium battery is used, taking into account the price and size.Let's see if there is a need to install a more powerful battery. Or vice versa, just 100-200 mA is enough .It will be even cheaper in price.
As I already said, the distance between the tips of the tweezers is 45mm. Here is a good example of measuring a 10000 uF capacitor. Its length is 40 mm.ESR 22 mOhms.

[iet]

Well, after 72 hours, the voltage of the lithium battery decreased by 1V. And at 3.2V, the tweezers no longer work. And this takes into account the fact that it was at rest most of the time.
We can already draw some conclusions. With periodic use, a 400mA battery should last for 2-3 days. With intensive use, you will need a more powerful lithium battery in the range of 1000-2500 mA. Therefore, those who want to repeat this design can use these data to choose the optimal lithium battery for yourself.
Several repeated measurements with the new scale.
Very clear and easy to read scale.
Many times measured solid polymer capacitor.
Low impedance capacitor.

[iet]

I installed a microswitch in the power supply circuit from the lithium battery. The energy savings of the lithium battery have increased significantly. Now you can turn off the power to the tweezers after each measurement.
The changes also affected some resistors for calibrating the scale. I used resistors of smaller overall dimensions and, accordingly, lower inductance. The previous 100 mOhms  resistor had an inductance of 10 nH, the new one has 5 nH. The calibration of the scale has become even more accurate.
Added a new smaller resistor 10 mOhms.

[iet]

After the final settings and calibrations of the tweezers, I made a calibration test board from different solid polymer capacitors.
I used copper wire of the appropriate thickness as pins. This method turned out to be very effective and does not require large financial costs.

[iet]

Small microammeters are good. They take up little space and can be moved to any point on the table. But to get greater resolution of this meter, you need a more extended scale. I bought a large microammeter. It was easily adapted to this circuit.
With this microammeter, I managed to obtain a resolution of 1 mOhm in the range of 0-60 mOhms. This is an impressive result, which once again proves the great capabilities of this circuit. I finished calibrating the scale.
The value on the left is uA. The value on the right is mOhms.
|0-250|5-200|10-150|15-100|20-80|25-60|30-55|35-50|
|55-30|60-25|65-20|70-15|75-10|80-7.5|85-5|90-2.5|100-0|