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Need ampere meter explained



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An ongoing discussion beginning back in 2007 ...

2007

Q. Please help me deal with Air Quality Control. -- Here is an example.
We have an ampere-hour meter attached to the Chrome Plating Tank
On one particular day we plated for 10 Seconds at 1000 Amps, 15 Seconds at 1300 Amps, and once again for 15 Seconds at 1300 Amps. A total of 30 seconds for the day. The Amp Meter Reading at the beginning of the day was 677696 and 677718 at the end of the day. The surface tension reading was 26-55=31.97. Can Someone tell me what the amp-hour meter is registering? It tabulated 22 Amp Meters. Can you give me a formula or something in layman's terms of how that totals 22 Ampere-Hours. Please help, I do not understand.
Thank you, Sharri.

sharri neel
Sharri Neel
Office Manager - Yuba City, California, USA
^


2007

A. An ampere-second means one ampere of current flowing for one second. If you had ten amperes flowing for one second that would be 10 ampere-seconds. If you had one ampere flowing for ten seconds, that would also be 10 ampere-seconds. And if you had ten amperes flowing for ten seconds, that would be 100 ampere-seconds.

Now, if you had 60 amperes flowing for 60 seconds, that would be 3600 ampere-seconds. Since there are 60 seconds in a minute, you could also call this 60 ampere-minutes. And since there are 60 minutes in an hour, you could call it 1 ampere-hour. "Ampere" is sometimes abbreviated as "amp", so an ampere-hour and an amp-hour are the same thing.

If your numbers are accurate, you used a total of 49,000 amp-seconds that day, or 816.67 amp-minutes, or 13.61 amp-hours -- not 22 amp-hours.

It is possible that the ampere-hour meter is not calibrated quite correctly or not hooked up correctly.

Ted Mooney, finishing.com
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
^


2007

A. Ted is right about the calculations instead of having the power on for 30 seconds, as you stated, it was for 40 seconds and you used 49,000 Ampere-seconds. This works out at 13.611 Ampere-hours, so if your meter is showing you used 22 Ampere-hours, there is something wrong. It could be that the meter is wrongly calibrated, but to be about 50% out is most unusual and very worrying! I would suggest you recheck the days work log and see if anyone put down an incorrect number or check no-one did work that didn't get logged. I reckon you are about 21,600 Ampere seconds adrift, but the accuracy of the meter may be poor because it is measuring Ampere-hours, for which there are 3,600 Ampere seconds in 1 Ampere-hour. Good luck with your detective work.

trevor crichton
Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK
^


2007

A. Hi, Sharri,
Let's compare electricity (electrons passing by) with car driving. Speedometer tells you how fast you go, how many miles would pass by if you drove at that constant speed for exactly an hour. It's an instantaneous measurement. You don't have to drive for an hour or go anywhere. That's current or amperage. An instantaneous measurement of charge passing per second. Then you have your car's odometer. It accumulates total mileage regardless of speed or elapsed time in a ride. The Ampere-hour meter does the same. It accumulates the total charge that passed through the circuit. Since the current is not always steady, taking an average value and multiplying by time may be misleading. Calibrate your Amp-meter and rely on it.

Guillermo Marrufo
Monterrey, NL, Mexico
^


2007

A. Sharri
As so often, a simple query raises more questions.
1000 amps for 10 seconds is a very unusual plating cycle. Are you sure it was not minutes?
Amp second meters are usually found in a lab not a plating shop and amp hour meters are mostly used to control chemical additions. Where the plating is controlled, amp minutes is the normal calibration. The instrument is commonly called an IT meter (I is the symbol for current and T for time)
The meter should be clearly marked with the units, but why not ask the plating staff?
I am sure we would like to help you with air quality, but I cannot see how this reading helps. Surface tension has a tenuous connection with air quality in controlling the spray formation but it is unlikely to be sufficient without an efficient air extract system.

geoff smith
Geoff Smith
Hampshire, England
^


2007

A. Sharri perhaps has to report ampere-hours of chrome plating for her air permit, Geoff. If she is doing decorative chrome plating, 10-15 seconds sounds a bit short, but 10 minutes would be way too long. If she is doing hard chrome plating, though, 10 minutes is certainly possible for a thin coating.

Ted Mooney, finishing.com
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
^


2007

A. Sharri

While you're having the AH counter calibrated, have the amp & volt meters calibrated at the same time. I would hope your technician would require this.

We use AH counters and after installing the last 2, we found one would accumulate AH's with no load on the rectifier. We powered the counter off for a minute, and when restored, it behaved normally. No problems since.

Lastly, however remote, the counters rely on a shunt. Make sure you have the right one.

Willie Alexander
- Colorado Springs, Colorado
^


2007

A. Another possibility: The voltage/amperage is being ramped up/off rather than instant on/off. That will add amps at the high load settings you are using.

James Watts
- Navarre, Florida
^


2007

thumbs up signThe last response seems more likely the answer to our problem. But of course all suggestions will be checked out and are very much appreciated. Yes, California Air Quality Control Management District is something else to contend with. Every half our (or Ampere-hour) Ha Ha They seem to make a new law making it more expensive to stay in business.
But once again I thank everyone for their help.

sharri neel
Sharri Neel [returning]
- Yuba City, California USA
^



Amp hour meter readings wrong for tri-chrome plating tank

September 3, 2015

Q. Hi Everyone,

I have been having some issues with a Process Technology AHM that is to be used to monitor our tri-chrome bath. The unit was purchased new some time before I came on board, but was never installed because there were issues of "incorrect readings" that were never resolved. The unit was shipped back to the manufacturer for calibration at the time, but the folks here were told that everything was fine.

I recently incorporated the unit into a new control that I built for this tank and have been having the same issues of what seems to be incorrect readings. After reading Sharri's post regarding the ampere meter explained, I calculated the following for some cycles.

* 6.5 VDC, 350 A, 4 MIN = 375 A x .0667 = 23.345 AH
* 8 VDC, 750 A, 4 MIN = 750 A x .0667 = 50.0025 AH

I forgot to log the actual clicks on the AHM, but they were not even half of my calculations. Is there something that I am missing?

I am in the process of trying to verify the unit specs (written in ink/marker on the unit and since faded away) and the shunt specs (not very easy to get to where the bus bars are running overhead) to eliminate any problems there. Specs say the max distance between shunt and AHM be 20'. My distance is coming in closer to 30' so I was looking to shorten the run between the two if necessary.

Here are a couple links for the unit:
http://www.processtechnology.com/pdf/ahm.pdf
http://www.process-technology.com/processtechnol/ahm.pdf

Thanks in advance!
Steve

Steve Skibbe
Industrial Engineer - Chicago, IL, USA
^


September 2015

A. Hi Steve,
... in a galaxy far, far away, I was involved in the design and installation of amp-hour meters / brightener feeders.

Although I am not familiar with the particular meter you mention, it gets easier to understand and troubleshoot what may be wrong if you understand that an ammeter is actually just a millivolt meter. You may realize this, but for the benefit of the readers following along ...

What actually happens is you cut a short gap in your bus bar copper, and you insert in its place a block of copper of exactly the right size and composition that, if you run the rectifier at its full nameplate capacity, you will experience a voltage drop of exactly 50 millivolts across it. If you run the rectifier at 50% of its nameplate capacity, you will experience a 25 millivolt drop, etc. This is called a "50 mV shunt". I'm not sure that Process Technology plans for a 50 mV shunt, but that's the most common value.

So one thing you can do to start troubleshooting is to determine the relationship between the millivolts you read across the shunt, and the ammeter reading, etc. It's possible the wrong size shunt is installed for the rectifier, or the ammeter on the rectifier is wrong, etc.

Re. the length of the leads, you'd like them short so you lose no voltage and so you don't pick up any noise. But you can see that if you use larger gauge shielded wire, 30 feet may not be a problem. Good luck.

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
^



Amp-hour Meter Reads Right on the Bench, Wrong in the Field

April 13, 2016

Q. I found some time to revisit this project and now I'm really scratching my head! Here's what I'm working with: Process Technology AHM configured for 3000A and 50mV. Shunt is confirmed 3000A and 50mV as well. Leads from the ± terminals on the shunt are just under 30 ft.

I took the AHM out of the control circuit and did a bench test with a DC power supply. Ran 25 mV thru it for an hour and it was pretty darn close to 1500Ah. Put the unit back into the control circuit. Set control to 750 A and tested 12.5 mV at the shunt leads on the AHM as well as 12.5 mV on the control meter that was at 750 A. I then timed the count clicks on the AHM at just about 10 seconds, but I calculated that it should be 4.8 seconds.

Any ideas about what's going on here?

Thanks in advance!
Steve

Steve Skibbe [returning]
- Chicago, Illinois, USA
^


April 2016

A. Hi again Steve. From your numbers, apparently a "click" is 1/100th of an^One Amp-hour. There would seem to be two possibilities --

1). You are getting noise or voltage drop in the wiring. Although Process Technology says the wire should not exceed 20 feet, I'm sure we occasionally hit 30 foot or more back in the days when I was doing this. Although noise or voltage drop could be the problem, as long as you are using a heavy gauge shielded, grounded wire, I just don't think that's it. But maybe check the resistance of the wire -- after all, if somehow there is a voltage drop in the wiring, you record less voltage. Did you by any chance use that 30 foot wire between the power supply and your meter for the bench test?

2). The meter is somehow out of calibration. My recollection is that Amp-hour meter calibration, like pH meter calibration, takes at least two points rather than one. I think there will be something like "offset" and "gain". If you can get instruction from Process Technology, maybe you can calibrate it with your bench power supply and 30 foot of wire. Good luck.

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
^


April 14, 2016

Q. Hi Ted...

Each click on the AHM should actually indicate 1 Ah...not 1/100th.

1). The 30' leads are standard 14g stranded copper wire that is shielded. When the control is set to 750A I checked 12.5mV at the meter on the control as well as 12.5mV at the end of the leads that are attached to the AHM. There may be a voltage drop difference between the reading at the shunt and at the control, but shouldn't the AHM be calculating from what mV is present at the input? I did not use the 30' leads for the bench test, but I could try that today.

2). The unit was ordered for the following specs: 3000A, 50mV. The issue was present on the initial install and the unit was sent back for re-calibration and it was determined by Process Technology that the unit was OK. We then put it back into the control circuit and experienced the same issues. It does however check out OK when I did the bench test on another DC power supply...very strange.

Steve Skibbe [returning]
Precision Instruments - Chicago, Illinois USA
^


April 15, 2016

Hi Steve
Assuming that your bench instruments are themselves calibrated, I would accept your calibration.
Bench instrumentation can be a far cry from in process conditions where current can be subject to constant minor fluctuations. The obvious extreme case is barrel plating where the effective surface changes as the barrel rotates but poor work connections and agitation can have an effect.
That is why we often use an IT meter instead of relying on amps and a timer.
I would put an oscilloscope across the bath while it is in operation.
Cathode efficiency also has an effect on the weight of metal deposited and this too can change with time so although an IT meter gives improved consistency, settings are not absolute.

geoff smith
Geoff Smith
Hampshire, England
^


April 18, 2016

Q. Thanks for the feedback Geoff.

If I understand correctly ... even though I am reading 12.5mV at the AHM inputs, the current may not be constant and that is why the unit is incrementing at a rate that is less than what it would be if ideal conditions were met?

All of my testing on the control for the bath was done with dummies in the tank, so the barrel plating concerns shouldn't be an issue. What should I be looking for when I have the oscilloscope connected?

Steve Skibbe [returning]
Precision Instruments - Chicago, Illinois, USA
^


April 24, 2016

A. I am guessing that the meter integrates current over a time interval. An oscilloscope could show any fluctuations in current that are not followed by the IT meter.
Just a guess but it could shed some light on the problem.

geoff smith
Geoff Smith
Hampshire, England
^

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