non- contact current sensor baised on Rogowski coil

[abadi250]

hiii guys

im doing my FYP on amplify the voltage from a rogowski coil

just to make it short
i have already design the coil
which can detect a 300k frequency and gives Vp-p = 55mV Ac
now, i have to design an amplifier that can give an actual value.

so, i designed the amplifier in both way which are non inverter and inverter
but in both cases my result was an expected
which is Zero volt.

im suing ic- LT1014
and my ( Rf = 100 K ohms , Ri = 1 K ohms )
so, my Gain is ( G = 100 )
but i still get the wrong result .

i got a helped before, but unfortunately i couldnt find the ICs
because its not available in the market

is it my mistake is
using LT1014 ???? or what ????

 

[ark5230]

Rogowsky coil works with varying signals. When you connect the amplifier, if there is input at the input of the amplifier bu no output, you need to check amplifier, else see if you are using the coil in the expected fashion.

 

[abadi250]

i have already tested the coil with 1M hz and give ma 40 mv

so, thats mean the coil is working
but the problem is from the amplifier
and im wondering what king of Ic i have to use
???????????????

 

[karesz]

Check pls the "Gain, Phase vs Frequency" on pp8= at 1MHz it has a gain of -4dB!!
These is a very prec./good OpAmp, but practically only for DC/low frequency jobs...
K.

 

[abadi250]

i really didnt get what does you mean

can you explain more ???

 

[karesz]

And I really didnt get what you wish really know!?
If you dont have some amplified signal by your OpAmp at 1MHz & I told; pls check datasheet, thes type has -4dB (~50%:-() at these frequency and you dont get it: its not my mistake_sorry! :-(
Thes IC has a signal damping in that case (setted gain is 100x, but the stage brings only ca. 0.5!), you can see on the datasheet..
Best greetings!
K.

 

[FvM]

You didn't give a specifiaction for your intended amplifier. Most Rogowski coil applications are targetting to frequency
independant sensitivity, which requires an integrator characteristic. Depending on the intended frequency range, I would prefer
either a faster or a lower noise voltage OP than LT1014, at best both in one.

 

[abadi250]

To karesz
so, my ic is consider as the worst and it doesn't work with my coil ,,,,,, ok, what amplifier you suggest to use ?

To FvM
i have already ordered a new one which is LT1630, but im really afraid it doesn't work even that the slew rate is 10 V.

but to be honest each time im learning something new

do you have another idea ??

 

[FvM]

Also LT1014 can be expected to work. But again, you didn't give any specification and you didn't tell your circuit
(except two resistance numbers). In my opinion, you didn't ask an actual question, that could be answered.

 

[ark5230]

abadi250

If you could give some feel of how is your circuit, what you wish to measure. Is your signal undr measurement really that high frequency. Also before you resolve the issue, i am afraid, the problem of stray pickup becomes serious and please confirm that what you have been measuring so far is really the signal you intend to see and not stray pick up. This is because the signal is week.

 

[abadi250]

sorry for late reply
that is my circuit and shows all the details
and my problem is the ic LT1230,

and today i find that there is an IC with the same function, and its LT1229

do you think its gonna work ?

 

[FvM]

I'm unable to identify an "integrator" in this circuit. Also I don't see the purpose of the two high-passes. Usual integrating Rogowski
amplifiers are fine with one or two OPs and have bandwidths of e.g. 1 Hz .. 1 MHz.

P.S.: See attached an example of an effective Rogowski integrator with DC feedback.

 

[abadi250]

but the OPA227 got a low slew rate which is 2.3V

is that enough ???????

 

[FvM]

is that enough ???????

Cool down. A single question mark should be sufficient to mark a question.

The slew-rate is O.K. for my application, I don't know with yours. You should calculate. I didn't want to suggest particularly OPA2227 for your application rather than the circuit. You can use many other OPs as well.

 

[abadi250]

hehehe
thanx bro

what am going to do is like this
im going to use your circuit but using my IC

let me try it and come back with a good news

thanx a lots

 

[FvM]

Yes, the application requirements can be actually very different.

My requirements have been
- wide bandwidth (1Hz .. 1 MHz)
- moderate power bandwidth (≈ 100 kHz)
- low noise

If you are targetting to higher power bandwidth, you need an amplifier with higher slew rate. Because the low frequency noise will
be most likely higher, you may want to raise the lower cut-off frequency. You don't find much amplifiers with good low frequency
noise behaviour and high bandwidth. If I had to redesign my amplifier for higher bandwidth and power bandwidth, I would
possibly use an OPA1611.

If you don't need to reproduce current waveforms and measure several decades of frequency, you don't need an integrator of course.

 

[abadi250]

bro
i want to ask
if my coil only detect 30 K Hz and above

how to make it to detect lower than that ?????

is it independent on the coil only , or i can on the amplifier to detect it ????

 

[FvM]

The coil don't set a lower cut-off frequency for the measurement. The amplifier does (and must do), however. As said, the
above integrator achieves a flat frequency response with about 1 Hz lower cut-off frequency, that is set by the dimensioning
of the DC feedback loop.

 

[abadi250]

great
i think i got it now

ok, now you are using high pass filter to cut off the low frequency

but, i want to use bandpass filter

becouse mine project is from 100 Hz to 1M Hz

so, i have to cut-off below 100 Hz and above 1M Hz

what do you suggest for me ????

 

[karesz]

Hi,
You can not have a bandpass filter for 100Hz-1MHz, these is reason for coupling as highpass (as mentionend Frank & Brian too) & a lowpass filtering...
K.