[NLRS] RF read water meters

[Dr. Gerald N. Johnson]

On 7/21/2012 6:23 PM, Doug Reed wrote:
>
>
> I'm slightly surprised by the internal battery since that will require
> them to perform a service call very 10 years. But that is built into the
> estimated lifetime cost of the new meter.... Once every 10 years to
> replace a battery has to be cheaper than 4 times a year to read the
> meter.....

Probably like electric meters, the meter ought to be calibrated at least 
every 10 years by some state laws and the state of the art of Automatic 
Remote Meter reading changes so much that 10 year old hardware isn't 
worth fixing anyway. The previous meter readout here didn't last 6 years 
anyway. This one may do better. The one at my farm has failed once in 
the past 18 or so years, may have filed again. Consumption there isn't 
high enough now to detect whether its working or not.
>
> I would bet there is a PLL based transmitter in the box and the
> operating frequency is based on a programmed multiplier off the CPU
> crystal. That is pretty common these days. The CPU crystals are not very
> accurate but usually end up being a bit better than SAW-based transmitters.

Could be. With a transmitted bandwidth of 405 kHz, the center frequency 
doesn't have to be held to within 0.1 ppm to be found. A PLL would be 
handier and less costly than a gaggle of SAWs for the three frequency 
version and just wouldn't be practical for the frequency hopping device. 
The FCC filings show a continuous spectrum for the hopping mode, but it 
could be a software accumulated result of testing over a long time and 
that flat top could be from the DUT having used the frequencies all equally.
>
> I would expect when they say hopping they mean each transmission is on a
> different one of those three frequencies and the data collection site
> would simply have three receivers on one antenna. This would improve the
> chances of a transmission being heard in a crowded metro environment or
> apartment scenario. Although I'm surprised they don't have some sort of
> random timing between transmissions, either based on usage or TX serial
> number, or a combination.

Hopping by FCC regulations requires more than three frequencies, the 
test reports say for their bandwidth 25 are required and used.

Since the transmitters don't have receivers to trigger them, in the 
drive by situation they want them to transmit often so the odds of the 
mobile receiver being in range for at least one transmission is high. I 
fully expected the meter units to be transponders and so looked for 
radiation of requests from the monitor and found none. For this system 
the monitor and the mobile receiver are passive waiting for the bursts. 
There's sure to be QRM in an apartment complex with individual water and 
gas meters using this scheme, but the random clocks and short data 
bursts and repeated transmissions should solve most of those. On my 
water system, they gave me the monitor and I read it at bill paying 
time. I can read it at any intervals (with 4 second updates) to check 
for leaks, or the consumption of some water using event, like a shower 
or toilet flush. It has the capability of giving updates of consumption 
over a couple programmable time periods which I've not used. The rural 
water system is planning on going away from customer reading to a 
driving meter reader. I presume that's because they find some customers 
fudge the reading to save on paying bills and when the company makes an 
annual or biannual check reading there are a few wild errors. The 
electric coop I used to buy from made that change also. I know on the 
electric bill I found that based on their rates that if I fudged high 
one month and low the next that the total of the two bills was a few 
cents less than paying a leveled average.

When the meter reading isn't heard, there is plenty of room for an 
estimated bill. Last summer the electric company here estimated my 
August bill as my highest for the year, but they didn't know that I was 
away 17 days that month with minimum power consumption especially no AC 
running. The next month they read the meter and that bill was the lowest 
for the year.

I know from courtroom experience that utilities keep detailed 
consumption records for many years, so they have a history of power 
consumption that they can dig out to show errors in metering or cheats 
at metering but I've also found they didn't do that as much as they 
could until they thought they had a metering error either their fault or 
from customer meter tampering. I cost one company about $40K in alleged 
back bills by showing from the nursing home bills that went back further 
that the meter multiplier error was made earlier than the power company 
thought (and their local meter guy admitted) and that the metered power 
consumption had a very consistent pattern around the year until the 
meter factor was doubled when the power company finally discovered it. 
In their testimony they included data from another nursing home with the 
same number of beds at the same latitude where they moved the meter 
after swapping meters for calibration. The metering transformer was 
inside a transformer case and so could not be inspected by the operator 
or its engineer (me) to check the multiplication factor by the wire routing.

The power company discovered the error and went back and figured up the 
correct bills for 8 or 10 years and put in a demand to the nursing home 
to pay the corrected bill which came to aome $25K, and then whan that 
wasn't paid, added monthly interest. By the time it went to trial the 
bill was about $40K. They based the lawsuit on the state law that says 
they can't give any customer a discount. The same sentence continues to 
say "can't cause a customer hardship." Where the income for the nursing 
home was largely paid by federal funds audited annually and the majority 
of the past clients were dead, there was no way for the nursing home to 
go back and recover the doubled power costs. Worse because of the low 
readings they didn't update lighting or old AC units and in their chain 
they won the annual award for low energy conservation. I told the judge 
I sure was glad I'd not been hired to improve their energy consumption 
because I'd have detected the meter multiplier error which would have 
ruined my energy savings results because all my techniques would not 
have reaped the forecast savings. I said, "I don't like being tarred and 
feathered and don't think riding a rail out of town is comfortable." 
Anyway the trial judge ruled the nursing home didn't have a defense and 
should pay up. The Iowa appeals court ruled we did have a defense and 
there should be a full fledged trial, not just one to present evidence 
for appeal. At that point the power company went silent and ate the loss.

That power company wasn't exactly being reasonable demanding the 
customer pay for all the consumption and bill rates when the error was 
all the utility's. One other power company chief engineer I talked to 
said that they had made such errors and rather than the full bill they 
requested the customer pay the utility's incremental power cost, e.g. 
their cost of coal for the added KWH. But they didn't sue over it.
>
> Ten years ago ITI/GES built an alarm sensor with a rated 10 year battery
> life using a 3.6V 2Amp-hour AA-size lithium battery. The only reason it
> was rated at 10 year battery life is because the battery manufacturer
> wouldn't warranty the batteries for 20 years. We based its battery life
> on having under 10ua standby current. New designs 3 years ago had
> standby current under 1ua. Chip technology had improved a lot...
>
> But I have to say a 4 second update rate is very high and will reduce
> battery life considerably. I don't understand why they want that fast an
> update rate instead of just using a longer counter in the meter. I could
> see having data that fast if they want to graph your water usage every
> second of the day, but that really makes little sense. But maybe they
> have a sliding scale and slow down the TX rate if there is no change in
> the reading?.... But if you have a fixed rate it is easier to know when
> there is a problem....

The short time interval is to allow driving by at 30 mph because the 
meter module is not a transponder, just a blatter, like APRS. The duty 
cycle is short, like 1.76 ms every 3.98 seconds, like .000442 of .0442%. 
In ten years the total transmit time is under 39 hours. FCC tests show 
11.5 mw transmitted power. I expect the controller takes some power to 
run the 3.98 second timer, but modern PIC chips could do all these 
timings, wake up by timer, count meter turns by waking up for each one, 
and idle at microamps. Two weeks ago I bought MCHP stock and its beat 
the market and my other recent investments and pays a 3.5% dividend. So 
I'll probably be more partial to PIC chips since they are making me money.

There are systems using a local fixed receiver that's networked at 220 
or 450 MHz to eliminate the mobile reader. Galaxy by Badger is one.
>
> If you want some major power for long term low current usage, take a
> look at the size DD lithium batteries from SAFT. I think they were
> 14Amp-hours in a double-D size package. They were sounding pretty good
> for an Antarctic data collection project except they were only rated to
> -40 degrees Centigrade rather than -60 C..... :-)

15 20 years ago they were popular for powering ham balloon transmitters 
and telemetry.
>
> 73, Doug Reed, N0NAS.
>
>
73, Jerry, K0CQ