[time-nuts] Watts Up (was Re: Prologix GPIB/USB converter help...)

Neon John jgd at johngsbbq.com
Tue Apr 17 15:51:51 EDT 2007

On Tue, 17 Apr 2007 10:25:35 -0700, "Tom Van Baak"
<tvb at LeapSecond.com> wrote:

>I'll give you a recent example. I have a bunch of AC power
>meters in my lab (model: Watts Up PRO) that have RS232
>output and I wrote software that logs and plots the data. 

Ohhh, you hit on a sore spot, Tom.  That POS Watts Up Pro.  I'm what
you might call a "power nut".  The exact equivalent of a tine nut but
with utility metrology equipment.  I spent much of my career in the
utility biz and have a nicely equipped personal meter shop.  I do
energy and power quality audits as one of my sideline businesses.

Last year I bought a Watts Up Pro to evaluate for use as a cheap power
logging tool.  One of the first things I did when I got it was plug a
400 watt mercury vapor fixture into it, a fixture I knew to have a PF
of about 0.5.  It registered a noisy 0.15 on the WUP!  That really got
my attention since the very inexpensive (~$20) Kill-A-Watt gets it

I put the WUP on my bench and become much more dismayed.  I found that
the measured values (volts and amps) were pretty good but the computed
values (PF, KWH, KW, etc) were pretty much garbage when the PF went
below about 0.8.  I didn't waste a lot of time evaluating this thing
so I don't have a lot of specifics - it just wasn't worth my time.

I tried to have a conversation with the company but it ended up being
pretty 1-way.  I don't think my unit is defective since the volts and
amps indications are within specs.  It looks like whatever he's doing
to compute the other values blows up when the PF deviates much from

The interesting thing is just how accurate the KAW is.  Unfortunately
it doesn't have a data port nor battery backup so line transients tend
to erase its memory.  I've worked out a mod involving installing a Li
battery to maintain memory that I'm going to post to my web site
shortly.  Still no data port but at least it can be used to log
accurate cumulative data.

I recently came across another nice and cheap instrument.  The Itron
(formerly Schlumberger) Centron line of electronic revenue watt-hour
meters.  A client utility that just started using them pays about $40
ea in quantity.  Even this very basic watt-hour-only meter has an
infrared LED that pulses once for every watt-hour, making data logging

If you have the capability of testing your WUPs, I'd certainly be
interested in what you find.  I'd like to think that maybe the problem
is in just this one revision of firmware.  But I suspect not.

John De Armond
See my website for my current email address
Cleveland, Occupied TN
All great things are simple and many can be expressed in single words:
Freedom, Justice, Honor, Duty, Mercy, Hope.  -Churchill

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