How do I know the current's ampere value when it fluctuates rapidly?

[kurisu]

What "ampere value” is measured by a d-c ammeter when the current fluctuates rapidly?

 

[Baluncore]

Welcome to PF.
The reading will depend on the type of meter used, and the period of the measurement.
What type of meter ? What is the source of the varying current ?

 

[kurisu]

Welcome to PF.
The reading will depend on the type of meter used, and the period of the measurement.
What type of meter ? What is the source of the varying current ?

I'm using Analog dc ammeter. What do you mean by varying current?

 

[Baluncore]

Why does the current fluctuate rapidly ?

 

[berkeman]

What "ampere value” is measured by a d-c ammeter when the current fluctuates rapidly?

I'm using Analog dc ammeter. What do you mean by varying current?

Do you know what the frequency of these fluctuations is? Is it at the 50Hz / 60Hz AC Mains line frequency? Or at some higher frequency?

Can you see the needle indicator of your DC ammeter wiggling? Is that why you think there is an AC component? Does your meter have an AC current setting? If so, what do you read for the AC value? What DC value do you read for your current?

Does your meter look anything like this one below? What is the model number of your meter?

https://www.newark.com/tenma/72-8170/multimeter-analog-6-functions/dp/20M0354?gclid=CjwKCAiA8Jf-BRB-EiwAWDtEGqtVGYX1P8SiBhcL00BGwmfFw7sAuI9-9KGvu5fORjTtK_hctG1LdhoCtd4QAvD_BwE&mckv=scsU2PYU8_dc|pcrid|434136793584|plid||kword||match||slid||product|20M0354|pgrid|100464452106|ptaid|pla-901419072416|&CMP=KNC-GUSA-GEN-Shopping-NewStructure-Test-Measurement

 

[maxwells_demon]

Basically, there are lots of ways to measure current. There's 1) instantaneous current, 2) rms (root-mean-square current), and 3) average current.

If your dc ammeter's readings or pointer varies too much from one point in time to the next, then what you might be reading is instantaneous current.

You should determine based on the circuit you have if this would be an expected response. If not, you may want to consider the possibility that your dc ammeter may need replacement.

 

[maxwells_demon]

Or that you should have set your ammeter to ac instead of dc. but highly dependent on what your situation is and what you're trying to do.

 

[sophiecentaur]

I'm using Analog dc ammeter. What do you mean by varying current?

You seem to be having a problem deciding on what your question is. That often happens. If you give us a bit of context it would help greatly. Have you connected your ammeter in the power feed to a device or, are you trying to find out how long a battery will last when different devices are connected sporadically?

 

[tech99]

What "ampere value” is measured by a d-c ammeter when the current fluctuates rapidly?

The average current.

 

[DaveE]

Unfortunately the real answer to this question is harder than most people realize. It's really all about the nature of the measuring instrument.

First, for the most complex current waveforms engineers would use oscilloscopes and current probes to create a graph of the instantaneous current vs. time. Then there are some calculations you can do to assign parameters, like DC (average), RMS, AC, peak, peak to peak, etc. Whether these parameters are of any value depends on both the nature of the waveform and what you care about.

This of course is too difficult to do in many cases, frankly a waste of time and effort, for simple case. So people sell various meters to do this process for you. Here's the part people often get wrong; they assume all meters do the same thing. They don't. Your volt meter or current meter could use different technologies and have different performance. This can be true of meters that look nearly identical. Each (good) meter will come with a set of specifications that will describe how it does the measurements and with what sort of accuracy. This is the ultimate answer to your question.

For common applications (electricians, field service techs, etc.) people get away with guessing or just not knowing. However, in the R&D labs I worked in with complex circuits (analog, SMPS, etc.) the good EEs knew about the various meters, their specifications and their quirks. We had our favorites, but also sometimes would just grab whatever was closest when we knew it didn't matter. I would also fairly often measure the same thing with different meters just to see if they agreed. BTW, the same caveats apply to the oscilloscopes and current probes we would use to "do it right". Frankly there is some art and science to making good measurements in complex situations, and a huge part of this is really knowing your instruments.

Sorry, I know this isn't that helpful, but it is the way the world really works. Asks us if you want some specific clarification, like what is the difference between an analog meter that say AC vs. one that says RMS on the meter movement. Also see if you can find a datasheet for the meter you have.

 

[anorlunda]

The OP has not yet returned to PF to read any of the replies. So we can only speculate what he means by fluctuations. They may not even be periodic.