POCO meter accuracy

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Jim W in Tampa

Senior Member
Location
Tampa Florida
Starting seperate post to deal with this issue. When POCO guy was changing out my drop we talked a bit about shop. He told me the new digital meters cost $34 and were the low bid. Then i asked the million dollar question of how accurate they are. His answer was did my bill go up after they changed. Very hard to judge it that way when usage changes.
Are there any easy ways to check this myself. Am sure it's useless to think POCO will give me true answer. Who over sees them ?
 

wptski

Senior Member
Location
Warren, MI
Just seen a short piece on the morning news about people claiming higher electric bills after the so-called Smart meters were installed but no details were given.
 

WorkSafe

Senior Member
Location
Moore, OK
We just got our smart meters, but at the same time, we signed up for the guaranteed amount billing. I'll have to check on actual usage when my statement is ready.
 

Jim W in Tampa

Senior Member
Location
Tampa Florida

Thanks Bob , might need to contact them if i have any more problems with the service drop.
For now i would like to just verify accuracy myself. Calling them might be a mistake if it by chance is reading low.
Am thinking perhaps use something like space heaters or perhaps cook top as a non inductive load and my digital volt meter and amp meter. Not sure how accurate that would be. Any suggestions on how to do it on my own ?
 

mivey

Senior Member
Then i asked the million dollar question of how accurate they are.
A lot more accurate than they are required to be. However, they can fail at times.

Any suggestions on how to do it on my own ?
By installing a sub-meter, of course. The question would be: what kind of sub-metering equipment do you have? A PQ meter would be nice.

At the minimum, you will need some means to measure the voltage, current, phase angle, and a stopwatch. A large, steady load helps a whole lot.

You can get an approximation by using the average of several measurements taken at different times. For each measurement, count the number of dial rotations (simulated by the display of an electronic meter), and the elapsed time in seconds. You usually want a time of at least 30 seconds or more to cut down on stopwatch errors. If a full turn of the dial takes forever, you may want to use a fraction of a turn that equals the amount of patience you have as it may take many minutes if the load is small. You will need to measure each phase. Take the voltage, current, and pf readings at the same time you are counting the dials turns.

The meter secondary constant is labeled on the front of the meter (the Kh constant). The primary constant multiplies the secondary Kh by the CT and PT ratio to get the primary constant.

Then compare these two:
meter kW = 3.6 x Pri Kh x # revolutions / seconds
validation kW = sum(V1 x A1 x pf1 + V2 x A2 x pf2 + V3 x A3 x pf3)

As you can see, it would be much easier with a single PQ meter instead of a voltmeter+ammeter+phase angle meter.
 

mivey

Senior Member
A lot more accurate than they are required to be. However, they can fail at times.

By installing a sub-meter, of course. The question would be: what kind of sub-metering equipment do you have? A PQ meter would be nice.

At the minimum, you will need some means to measure the voltage, current, phase angle, and a stopwatch. A large, steady load helps a whole lot.

You can get an approximation by using the average of several measurements taken at different times. For each measurement, count the number of dial rotations (simulated by the display of an electronic meter), and the elapsed time in seconds. You usually want a time of at least 30 seconds or more to cut down on stopwatch errors. If a full turn of the dial takes forever, you may want to use a fraction of a turn that equals the amount of patience you have as it may take many minutes if the load is small. You will need to measure each phase. Take the voltage, current, and pf readings at the same time you are counting the dials turns.

The meter secondary constant is labeled on the front of the meter (the Kh constant). The primary constant multiplies the secondary Kh by the CT and PT ratio to get the primary constant.

Then compare these two:
meter kW = 3.6 x Pri Kh x # revolutions / seconds
validation kW = sum(V1 x A1 x pf1 + V2 x A2 x pf2 + V3 x A3 x pf3)

As you can see, it would be much easier with a single PQ meter instead of a voltmeter+ammeter+phase angle meter.
For residential you will probably only have 1 & 2 so:
validation kW = sum(V1 x A1 x pf1 + V2 x A2 x pf2)
 

Jim W in Tampa

Senior Member
Location
Tampa Florida
For residential you will probably only have 1 & 2 so:
validation kW = sum(V1 x A1 x pf1 + V2 x A2 x pf2)

I am on digital so that parts bit easier, just start counting when it reaches a hole number.
Thinking of something constant and pure resistive as load. If readings are within 5 % i would be happy. If off by 10 % might question it but only if the 10% is wrong direction.

Being higher or lower than old meter only means 1 of them was wrong.
 

mivey

Senior Member
I am on digital so that parts bit easier, just start counting when it reaches a hole number.
Thinking of something constant and pure resistive as load. If readings are within 5 % i would be happy. If off by 10 % might question it but only if the 10% is wrong direction.

Being higher or lower than old meter only means 1 of them was wrong.
I said dial but I meant disc. You are counting disk rotations, not dial rotations.

add: and I forgot to divide by 1,000
validation W = sum(V1 x A1 x pf1 + V2 x A2 x pf2 + V3 x A3 x pf3)
validation kW = sum(V1 x A1 x pf1 + V2 x A2 x pf2 + V3 x A3 x pf3)/1000
 
Last edited:

mivey

Senior Member
I said dial but I meant disc. You are counting disk rotations, not dial rotations.
This is an example of the difference:

I am pulling 4 kW right now. My Kh is 1.0.

One dial rotation would take 1,000 disk revolutions and I would have to count these over a period of 900 seconds (15 minutes). Also, I would need the average voltage, current, and pf over those 15 minutes and that is just a long time.

For a shorter reading I might have something like 67 disk revolutions in 60 seconds or 4.02 kW. The 60 seconds would give you enough time to record several voltages, currents, and pf readings to use for an average. I would repeat the process a few times and average the results. Way faster than a 15 minute read.

If the disk is really whipping by, you may need someone else to count the disk revolutions while you take the v, i, & pf readings.
 

mxslick

Senior Member
Location
SE Idaho
If your old mechanical meter was several years old, it is possible it was running slow (in your favor) and the new one will result in an increase in your bill. :grin:

We just got our smart meters here in my palatial estate and it will be interesting to see how much if any my bill goes up. I kind of doubt it, as about a year ago they installed new mechanical ones (getting rid of the original "A" Base meters) and there was no noticeable change in my bills then.
 

iwire

Moderator
Staff member
Location
Massachusetts
Jim, if you spring for me and the families trip to FL, maybe some theme park passes and hotel I will set up a recording meter for the entire time I am done there. :cool:
 

cowboyjwc

Moderator
Staff member
Location
Simi Valley, CA
Your bill could go up, depending on how your meter reader read the old one, mine went down and it went down a bunch and is more consistant.

You can call your POCO and you should be able to get a copy of your monthly usage for as long as you've owened the property.

You have to remember that with the old meters is was a judgement call on whether the meter was closer to one number or the other, with the digital the guess work is gone.
 

mivey

Senior Member
Your bill could go up, depending on how your meter reader read the old one, mine went down and it went down a bunch and is more consistant.

You can call your POCO and you should be able to get a copy of your monthly usage for as long as you've owened the property.

You have to remember that with the old meters is was a judgement call on whether the meter was closer to one number or the other, with the digital the guess work is gone.
Kinda-sorta. You only have a 1 kWh resolution on the digital display so you might be off almost 1/2 kWh (the digital would not flip at XXXXX.44 kWh). You can read a dial much closer than 1/2 point so there would be very little difference in the digital rounding and manual guess...maybe a 1/4 or 1/8 of a kWh difference before the rounding decision is made. So after rounding, at most there would be a 1 kWh difference for an individual billing month but very little overall.

The big different comes in with the morons who can't read a dial meter or the occasional error by the genius. :grin:
 

mivey

Senior Member
Your bill could go up, depending on how your meter reader read the old one, mine went down and it went down a bunch and is more consistant.
Most mechanical meters slow down over time but some do speed up. With AMR, they can be more consistent with the number of billing days in the cycle.
 

Jim W in Tampa

Senior Member
Location
Tampa Florida
What i have in mind is lets say my meter reads 80023, I set up load constant resistive load and all others off. Then run till it hits 80024 ,start stop watch and run till i hit 80025.
Then do the math. In all likely hood it is correct. I have no disk to watch turn. Just numbers

Bob , believe it or not i can get in disney free, have friend that works there ,but not taken her up on offer yet. But when i do will send you pictures. LOL
Not really sure i am up to doing that much walking.
 

kwired

Electron manager
Location
NE Nebraska
Starting seperate post to deal with this issue. When POCO guy was changing out my drop we talked a bit about shop. He told me the new digital meters cost $34 and were the low bid. Then i asked the million dollar question of how accurate they are. His answer was did my bill go up after they changed. Very hard to judge it that way when usage changes.
Are there any easy ways to check this myself. Am sure it's useless to think POCO will give me true answer. Who over sees them ?


Most if not all states should have a division of weights and measures or some other agency that basically could have this title.

It should be illegal to use a measuring device for commerce that is not accurate, especially if it is in error against the customer. I don't know how these laws are encfroced for utilities but I have seen state employees that check out scales used for selling goods, as well as checking accuracy of metering devices on fuel pumps at the gas stations. I have heard that fines are pretty high if you are not in compliance, don't know if there is warning then fine or if you get fined hard first time.
 

mivey

Senior Member
What i have in mind is lets say my meter reads 80023, I set up load constant resistive load and all others off. Then run till it hits 80024 ,start stop watch and run till i hit 80025.
Then do the math. In all likely hood it is correct. I have no disk to watch turn. Just numbers.
It may take quite a while. Say your meter is at 80023.1 and then you plug in two 1200 watt space heaters (the residential meter does not follow Blondel's Theorem so you need a balanced load for an accuracy check) to get a total 2400 watt load. that means it takes 25 minutes for each flip of the meter number. To get to the start point of 80024.00 you will have to wait 22.5 minutes. Then you will have to start your watch and wait 25 minutes for the meter to flip another number to reach 80025.00

So for 47.5 minutes you are sitting outside in the heat staring at a meter because the air is off because you want a constant load (unless you cheat a little bit). Even with cheating, the voltage at your home will likely be changing as the utility system is regulated and you won't really have the steady load you wanted.

To me, it makes more sense to use the disk rotations and you will be done in about 5-10 minutes with a more accurate sample. Now if you want to pull the meter and put it on a test stand...
 

mivey

Senior Member
Most if not all states should have a division of weights and measures or some other agency that basically could have this title.

It should be illegal to use a measuring device for commerce that is not accurate, especially if it is in error against the customer. I don't know how these laws are encfroced for utilities but I have seen state employees that check out scales used for selling goods, as well as checking accuracy of metering devices on fuel pumps at the gas stations. I have heard that fines are pretty high if you are not in compliance, don't know if there is warning then fine or if you get fined hard first time.
The meters are certified but that is no perfect guarantee. Errors are usually trued up but there is a limit on how far back the true-up goes. No fine for the bad meters, just replace and true-up. I would think it would have to be a case of willful misconduct for a fine.

We try to stay in a +- 2% window of accuracy. The meters used to be spec'd at 0.5% accuracy but I think most of the new smart meters are spec'd to be 0.2% accurate. Even then, some manufacturers claim they are averaging better than 0.05% accuracy. All well within the 2% goal.
 
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