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# digital current meter

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#### Mojalco

##### New Member
hi everyone! i'm working on a project that would measure the total current up to 250 Amperes maximum. I plan to use a current transformer and read the corresponding current measurement through the use of a ADC0832 Analog to digital converter. Then i'll use an Atmel 89C51 to process the data an display the measurment in a LCD. Could anyone be willing to help me find a more appropriate circuit that i use to measure the readings from the current transformer to my analog to digital converter circuit...

I suppose you have considered the alternative method: 250A shunt and ordinary digital mV meter? A lot cheaper than a current transformer, A/D converter and whatnot but, perhaps, you have a good reason to go the current transformer way? Just curious.

this project will be used to measure the total load current that lsupplied by a generator. So a current transformer is much more suitable for rugged environment and for this kind of applications.

I suppose you have considered the alternative method: 250A shunt and ordinary digital mV meter? A lot cheaper than a current transformer,

This made me ponder... if you use a current transformer, and connect a shunt of fairly low, known resistance, across the CT terminals, then you could use a digital mV meter across the shunt. Hey presto, calibrate your shunt, such that 1 mV = 1A (primary), you got a 250A ammeter

Say you use a 800/5 CT (quite common):
At 250A primary, secondary current is 250/(800/5) = 1.5625A
If 1mV = 1A (primary), then shunt resistance = 0.250V/1.5625A = 0.16 ohm
Of course this is a theoretical value, might need to be adjusted in practice.

Well, I wanted to build a DC ammeter so I can use it in conjunction with my audio amp. See a MultiMeter doesn't give you something you can work with. If you wanted to integrate it into a system or something, you can't because you can't very well tell your STAMP or something to just read the multimeter. So is it possible to create using a transfomer and A/D and what way is going to make it the most accurate?

imeg4fun12 said:
you can't very well tell your STAMP or something to just read the multimeter.

Agreed, but in this case, you are just using the multimeter as an ADC. As suggested, you can use a 250A shunt and use your basic stamp to measure the voltage across the shunt. Most shunts are designed so that their full scale corresponds to 50mV.

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