DC Current Measurement

Most dc current meters use a hall effect sensor. You can find lots of suppliers by googling. Fluke and Omega offer several models.

You can also find suppliers of current measuring sensors on GlobalSpec.

There are two generic ways I can think to measure current. First you can use a current sensor such as a Hall Effect sensor or current transformer. I have used LEM current sensors; they are very nice but expensive. The other method would be to use a resistor and measure the voltage drop across it. This method can be very inexpensive but you do have to burn the power in your resistor. You can use very small resistors like an .o1 ohm or a .1 ohm resistor and your resistor will burn .25 or 2.5 watts. If you want to measure the voltage drop across the resistor at 25 volts you might need to get a high common mode voltage diff amp. You also can use two p-channel BJT's in kind of a current mirror configuration to do the high voltage measurement and then just use a regular op-amp for the measurement.

I have also done some signal processing techniques to measure current using a loop of wire in the current path and estimating the current with a dsp. This is a lot more complicated but pretty cheap. So you could look into doing so thing like this too.

What kind of bandwidth do you need for your current measurement? If you can say what this current measurement is for I might be able to give other suggestions.

I want to measure the current of drill.this is my project at university and i must have a collection of all of the ways of current measurement and after that choose the best one and then use it for my project .but the current of drill is ac and imust convert it to dc current.please help me. thanks

If you are in India then come to my place. I have sensor, ADC board and I can teach you how to record the current waveform as your drill machine works with no load to full load. You can find my address on my website link below.

thank you very much that you reply to my question.I not in india .but I really love india.if you can please send me all of the ways of current measurement that we have .just the subjects .if you do this work for me i think i can start my project .thanks

For DC current measurement Hall Effect sensors work great. Try www.allegromicro.com and they may give you few samples for free.

very common way is to use current shunt resistance to measure the DC current together with one monitoring IC like the following

http://docs-europe.electrocomponents.com/webdocs/0283/0900766b80283d32.pdf

Serendipity strikes again. I am in the design phase of a specialized battery charger at this very moment. For the current sensing side I decided to go with a hall effect sensor rather than the series resistor mainly because I don't like the idea of using a resistor. I picked up some UGN3503U hall effect sensors for less than AU$4-00 each. While they are more expensive than a resistor they are not as expensive as you would think. Here is a link to the data on them to give you some background

http://www.allegromicro.com/datafile/3503.pdf

and shows you an how to use them as a current sensor. These are discontinued now but I am certain you would be able to get and equivalent for probably less than I paid.

Hey!!! the poster has nicked my avatar!!! Grrrrrrrrrrrrrr

Anyway, the simplest and cheapest way to measure the 5 amps is to buy a cheap moving iron ammeter rated at 5 amps and stick it in-line... problem solved.

Now stop pinching my avatar or I will.... errrrmmmm get cross!!

John

Dear John

You have your twin awatar now. I hope this get solved as I look for that dancing puppy to locate your links.

Most cheap (and all expensive) digital multimeters will have a 10A range. I got a multimeter for $10AU, and see ads for less than $20AU frequently. All multimeters will be fine at 25 volts. Quick fix.

Greg

I have used a DC current sensor (hall effect) from Veris Industries with range 0-50 Amp DC with output 0-5 VDC inserted in a data logger brand Pace Scientific as input.Its looked so simple,you can also make recording data from this.

Please check this website via google.