Introduction: Current Sensing Circuit
In this simple tutorial, I am going to explain how to measure a current in your circuit. ALL that is here and more you can watch it on my channel VEGEtek on youtube (episode 003).
Teachers! Did you use this instructable in your classroom?
Add a Teacher Note to share how you incorporated it into your lesson.
Step 1: Ways to Measure Current
Ways to measure current:
1- Indirect method: such as current transformers (in the figure) and Hall effect sensors, which relies on Faraday's law of induction to sense current in a circuit and convert it to a proportional voltage.
These methods are suitable more for high current systems.
2- Direct method: which relies on Ohm’s law which states that V = I x R.
This method is suitable for low currents and widely used in electronics devices.
Step 2: Measuring Current by Multimeter
Measuring current using a
1- cut the circuit.
2- use the “current” multimeter input jack, not the voltage one.
3- put the probes as the figure to close the circuit.
Step 3: High-side and Low-side Sensing
High-side and low-side sensing
Direct sensing has 2 methods: High-side and low-side sensing. It depends on the position of the shunt resistor with respect to the load.
This op-amp configuration is called “differential amplifier” which it amplifies the voltage difference between its inputs.
Step 4: Differential Amplifier
The op-amp will amplify the voltage difference between its two inputs according to this equation (also in the figure):
V_output = R3/R1 (V2-V1)
If all 4 resistors where the same value
(like 10k) this will be a unity gain differential amplifier which the output voltage is: [ V_out = V2 – V1 ] since R3/R1 = 1/1 = 1. This will give the voltage difference directly as it is.
However, it is common to have a gain of 10 or so in such practical circuits because the voltage difference may be so small, for example:
If shunt resistor is 0.1 Ohms (very common) and the current is 1A, this will result in 1 x 0.1 = 0.1v across shunt resistor, this will mean 0.1v output of the differential amplifier when unity gain is used, so it is 0.1v per 1 A. While using a gain of 10 will mean 1v per 1A which is a lot easy and practical.
Step 5: Video Tutorial With Example
This is the video tutorial that I made:
Please view the video and go apply what I explained in it. I also attached the slides for those who want them!
Please like, share, and subscribe to my channel: https://www.youtube.com/channel/UCXodUSRG2__hTpW4...