A useful attachment to a multimeter for measuring low-resistance resistors
When remaking computer power supplies, you need to make a resistor up to one ohm. I managed to buy Manganin. Some people use stainless steel. To select the desired segment, you need to know its resistance. I make resistors of the order of 0.01-0.05 Ohm. Measuring resistance with a regular Ohmmeter is not easy. For a more accurate measurement, you need to measure the voltage drop across a piece of metal.
I drew a simple and understandable diagram.
About the scheme
The plus power of the power supply goes to the linear stabilizer. I'll use an adjustable one, but you can use a permanent stabilizer. Whether it's 5-6-8 Volts. Not important. The main voltage must be stable. We install a 100 ohm resistor in the positive gap. We will use it to adjust the current in the circuit. We connect a millivoltmeter to the output of the stabilizer. We connect the measured resistor in parallel to the millivoltmeter.
Components
To make the design, I chose a case from a Krona battery.
Compact and convenient body.
I will use a linear stabilizer LM317 - http://alii.pub/5w6tni Having previously calculated the divider resistors.I set the output to just over 5 Volts.
Since I plan to connect the set-top box directly to the millivoltmeter, I will make convenient contacts. I will use the contacts from the “ШР” connector.
To connect the measured resistor, I will take screw contacts. They were just like that, and I’ll use them.
Assembly
Contacts from "ShR" I used screw contacts. I made holes in the housing and inserted wires from the cable into them. I used copper wires and soldered them to the contacts. From the inside of the core I twisted and soldered pieces of wire. Accordingly, I do not connect the two contacts.
I solder everything by surface mounting, not forgetting about insulating the components. I soldered the resistors on the stabilizer.
I connect all the wires and components. I install it in the case. You can connect a battery, but it will quickly run out. Still, it will be enough for a certain number of measurements. Using the adjusting resistor we set the current to 0.1 Ampere. Just by setting a limit multimeter into current mode and turning up the required current. We will carry out the measurement in volts measurement mode.
Let's test
We fasten the measured resistor. We supply power to the console. It can be from the crown, but fresh. I'll apply voltage from the power supply. The millivoltmeter shows a drop of 20.8 mV.
Using Ohm's law we derive the result. Top line, voltage drop across the measured resistor. Bottom line, set circuit current.
The calculation turned out to be correct, with a small degree of error.
So you can easily and quickly measure the resistance of a resistor. If you don’t need a body, you can make it a canopy. I'm used to making a complete design. I'm thinking of fixing the contacts, additionally, with thermal glue.
