Understanding the datasheet of INA225


I was reading the datasheet of INA225 then I saw this page and I got confused.

Q1: I should use 36V zener diode right?

Q2: Are the diodes used for overvoltage protection?

Q3: If we assume that the zener diodes are 36 volts, both lines(IN+ and IN-) should be 36 volt when the input voltage is above 36 volt right?

If I am right what is the purpose of the diodes and why do we add them?

To protect the device against high-voltage, short-duration, low-energy spikes.

You will find answers to your questions and programming tips in the following Table
of Fig-1.


I didn't see anything relevant to input voltage or zener diode can you help me?

So I can not measure beyond 36 volts right?
They are just for protection.

Simple answer: no. It's very clearly outlined in the datasheet that you can't.

Slightly more complex answer: you can, but you have to make sure that the voltage across the INA225 never exceeds 36V - you could, for instance, lift the INA225's GND to whatever level necessary, galvanically isolate the device from its control circuitry/microcontroller and have it measure currents in lines that are way above 36V. Just as long as you never exceed the 36V limit of the INA225 itself.

The setup is:
1. Install protective 2x36V zeeners, 2x10 Ohm/2x1.6W resistors, and 16 mOhm shunt.

2. (1) 2200 W heater at 220V AC supply voltage. Be sure that the neutral point of the AC supply is solidly grounded. Otherwsie, use 220/220V/3 kW isolation transformation for experiment. After that you can leave the system on the floating 220V supply.

(2) Practicall, you may not be able to arrange such a huge setup. In that case, use 220/220V-500W isolation transformer and a 3x100W filament lamp to feed line current of 1.364 A current.

3. Measure AC voltage across shunt/cathod-points of zeeners using a DVM, you shoud see very close to 160 mV under Step-2(1) setup and 13.6 mV under Step-2(2) setup.

4. Measure volatge (DC) at Vout terminal (with gain 25) of INA225, you should see very close to 4V under Step-2(1) setup and Vout (record the reading).

5. Feed this 4V /Vout to an analog channel of the ADC of UNO and map it to show 10.00 A /1.364 A on the display unit.

Practically, you may not get a shunt of 16 mOhm; in that case, what shunt do you have?

Safety Warning!!! As you will be working with 220V which is very lethal. So, take enough protection to get away from possible eletrocution.

Uh...weren't you the guy who warned the other day against using a computer power supply because of the risk of accidents?

I am using a 5mOhm shunt.

Which one is true?
Difference between IN+ and IN- should not exceed 36(I mean voltage drop across the resistor) or IN+ and IN- should not exceed 36v.

No I am not.

Sometimes, you have to work in a hazardous environment and you are safe as long as you know that there are safety risks and you undertake appropriate protection.

Difference between IN+ and IN- should be around 160 mV when you feed 10 A AC current through 10 mOhm shunt. Are you an electronics graduate? How much do you about operational amplifier?

Well, duh. Point is, one day you're saying people shouldn't be using a ATX power supplies because they're supposedly dangerous, the next day you're giving vague (for novices) instructions on dealing with 230V to a random person online who's asking fairly basic questions, from which you can easily derive that they probably are NOT aware of the necessary safety precautions.

I find that kind of funny/ironic.

I know, the reply was not to you.
Please be careful about the ideas of @GolamMostafa. I don't recommend doing what he says. I also doubt it's necessary in your case. What do you need this INA225 for anyway?

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You should have enough congnitive skill to extract the essentials from the details.

No I am not.

I can analiyse simple op amp circuits.(The circuits that use resistor only)

I found this on the datasheet. I can measure the current independent of the supplied power right?

Sorry sir

I don't have enough equipment to do it and I am not an engineer nor engineering student but the example that @GolamMostafa gave really helped me.

I am trying to meassure the current with high accuracy.

1. Make a setup of 5 mOhm hunt, 2x36V Zeeners, 2x10ohm/1.6W resistors, and INA225 with 5V bias.

2. Connect 300W/220V filament lamps as load.
3. With DVM, measure AC volatge across the shunt.
4. With DVM, measure DC volatge at Output terminal of INA225.
5. Calculate load current/shunt current as: 300/220 = 1.36 A.
6. Feed Vout into A0-point of UNO and map it to show 1.36 A on the Serial Monitor.
7. Remove one 100W lamp. Check that Serial Moniotr shows: 0.91 A.
8. Keep only one 100W lamp. Check that Serial Monitor shows: 0.45 A.
9. Disconnect all loads. Check that Serial Monitor shows: 0.00 A.

Yes, of course :wink:
The question is: in what kind of system? What kind of current range are you measuring, and at what voltage? Can you share some details about the circuit this current sensor will be part of?

I did this test with a DC source and an led. I saw voltage changing when I change the current.