current peak detector

[tom_hanks]

Hi there,
Can any one suggest a technique to detect the current peak consumption. my system is running a motor on the interval of 100ms.
in every cycle, motor consume some current, i want to find out the maximum value of the current in one cycle.

or other way is to calculate the avg of current in one cycle...

what do u think is appropriate?

any circuit ?

depends upon answer i am ready to donate the points

 

[Siniša]

Put resistor in series with motor. Amplify voltage across resistor with opamp. Detect peak of that voltage with some standard peak detector that suits you the most. (plenty of links on web) You can use also specialized integrated IC for that purpose, like Analog Devices PKD01. If AC current is detected, build precision full wave rectifier with opamps. Float if circuit is connected to mains.
For Q (or I*t ) you can use integrator circuit with opamp. Use opamp with low input bias current and quality capacitors for accuracy.
RMS value is litle harder to obtain, for that I would suggest small voltage light bulb in series with motor. Light bulb should be selected for maximum motor current and desired integration time. Shunt resistor or more bulbs can be used to extend range. Photoresistor can detect output that can be calibrated for particular narrow range (e.g.8-10A). For wide range of currents microcontroller would have to be used for linearisation of curve.

 

[nguyennam]

For measuring the peak current, you should connect a low value resistor in series with the motor, or use a current transformer, and any OP AMP connected in "peak detector circuit", or "sample-and-hold (S-H)" circuit. You can get these types of circuits anywhere in Op amp datasheet, or any Op amp user's manual, Electronic books.

To measure the avr, or rms current use the common instruments.

nguyennam

 

[waxtomato]

I am trying to make a simple answer.

insert a serial resistor , monitor the voltage curve by any oscillograph which can capture wave faster than 100kHz, you will see it

 

[tom_hanks]

SINISA..THANKS FOR REPLY I CHKED THE PKD01, BUT IT NEED -15V...
WHICH I CANNT PROVIDE...

NOW I AM THINKING TO USE A PIC WITH CURRENT SENSE AMPLIFIER....
SO PIC CAN STORE THE VALUE AND OUTPUT THE PEAK OUT OF IT...


ANY WAY YOU ARE HAVING GOOD FIGURE

 

[tronoty]

If you need it just for testing, use a current probe and an oscilloscope. AEMC makes some of the best DC current probes and they are very reliable.

I like this one especially:
Model SL261 [Catalog No. 1201.51]

https://www.aemc.com/products/html/view.asp?id=202&dbname=products


Hope this helps

Tronoty

 

[spbhu]

current mode opamp!

 

[Meridian]

SINISA..THANKS FOR REPLY I CHKED THE PKD01, BUT IT NEED -15V...
WHICH I CANNT PROVIDE...

NOW I AM THINKING TO USE A PIC WITH CURRENT SENSE AMPLIFIER....
SO PIC CAN STORE THE VALUE AND OUTPUT THE PEAK OUT OF IT...


ANY WAY YOU ARE HAVING GOOD FIGURE

I'm not sure, but a PIC is not a proper device to store data, if at all possible. Why not use a usb flashdrive to store that data *or* write it to a PDA directly using a op-amp?

The circuit was used to measure foot-pressure at two locations in a shoe, but the same can be adapted for your purpose in my opinion. For the op-amp, you can use the LMC271, or TLC271. It is just used as an impedance buffer so almost any low voltage/single supply device should work okay.

 

[grittinjames]

first step is to get a proportional voltage to ur current .then the task is easy . just make a peak detector for that vtg
u can use ct or series resister for getting proportional vtg

Hi there,
Can any one suggest a technique to detect the current peak consumption. my system is running a motor on the interval of 100ms.
in every cycle, motor consume some current, i want to find out the maximum value of the current in one cycle.

or other way is to calculate the avg of current in one cycle...

what do u think is appropriate?

any circuit ?

depends upon answer i am ready to donate the points

 

[rfzheng]

it is a useful question

 

[ldanielrosa]

Allegro makes hall effect current sensors for a few different ranges, from 5A to 200A. I believe all of them use a 5V supply, isolated from the current being measured. The output is about half the supply voltage at zero current detected, and varies linearly.

The upside is a very low loss and electrically isolated sensor, but the downside is the necessity for an ADC. If you are in the right area, you can request free samples.

https://www.allegromicro.com/en/

 

[pravin_dwaramwar]

use ct (Current transformer ) to get samples of current.
Use ADC with PC
Use FFT (Fast fourier Transform) to get fundamental component and get its peak value.

 

[masthdn]

Here is a simple way to measure maximum current.

By a Voltmeter measure voltage of cap.
Regard.[/img]

 

[TERADYNE]

i also have this question :how to measure the IC current limit

 

[maha123]

Best way to measure current (both DC or AC) is LEM current sensor. It have both contact and non contact types.
So Please try for a suitable lem current sensors

 

[xshou]

The question is kind general. Typically current under concern needs be converted to voltage before a peak detector ckt (either based on feedback or just like a rectifier). Just remember log amp typically can take current input and offer ~90dB DR.

To make the i-v conversion, there are quite a few solutions. IR drop; current mirror (check ONSEMI); high side current monitor (Maxim and LTC get some parts); or build up your own transimpedance amplifier; hall devices or current transformers are good for scope measurement.