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Old 25th May 2015, 5:04 pm   #1
delaitt
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Default Advice for plugging in wattmeter

Hello

I have a Weston S67 wattmeter and i'm looking for some advice for connecting it to the mains and the load. (to make sure i do not create a short)

my assumption is that the mains connects to +VOLT and 2.5A (or 5A) and that the load connects to +/- & AMPS. Not sure what the uncomp is for?

Has anyone got some experience with wattmeter and Weston perhaps?

Thanks

Thierry
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Old 25th May 2015, 5:35 pm   #2
kalee20
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Default Re: Advice for plugging in wattmeter

The wattmeter will have two inputs, one for voltage, one for current. Generally these are isolated from each other, so you can make a common terminal as is convenient for you.

The voltage input goes across the supply - you need to be sure if is rated for mains (or whatever voltage you use), else it might overheat even though the pointer doesn't go off scale.

The current input goes in series with the load (similar caveat applies).

You can connect the voltage input across the supply or across the load. Either will introduce a small error! If you connect across the load, the reading will be in error because the meter will register the power taken by its voltage coils - a steady offset of a couple of watts maybe.

If you connect across the supply, you won't get this error, but the meter will read slightly higher than the true power taken by the load, because the load actually sees marginally less than supply voltage, due to the voltage drop in the current coils.

These meters are generally pretty accurate (allowing for the above!) and of course measure true power, whether on DC, AC, in-phase, out-of-phase, or plain non-sinusoidal currents.
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Old 25th May 2015, 7:56 pm   #3
Ed_Dinning
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Default Re: Advice for plugging in wattmeter

Hi Thierry,. a nice piece of kit you have there.
As it is a dynamometer type it should also work across the AF spectrum as well as at 50Hz and with voltage and current range switches it will make a good AF output meter.

Ed
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Old 25th May 2015, 8:30 pm   #4
Eddy_Stone
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Default Re: Advice for plugging in wattmeter

Are you sure this is not a DC only wattmeter?
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Old 25th May 2015, 8:52 pm   #5
kalee20
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Default Re: Advice for plugging in wattmeter

Right, I've looked at the photos better.

The second photo says AC Wattmeter so no problem there!

You need to configure the voltage windings for 300V, to use on 240V mains, which you do with the selector switch (set to 300).

You need to configure the current windings for whatever current your load is.

I can't help any more because there are 4 terminals on the left and I can't read the markings! Can you post a clearer photo?
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Old 25th May 2015, 9:22 pm   #6
delaitt
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Default Re: Advice for plugging in wattmeter

Hello All,

Yes it is a nice piece of equipment. thanks for your responses.

Please find attached some high res pictures of the terminals.

Thanks

Thierry.
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Old 26th May 2015, 8:45 am   #7
pmmunro
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Default Re: Advice for plugging in wattmeter

Thierry,

You can buy an instruction book here http://www.abebooks.co.uk/servlet/Se...c-_-ats-_-used

Rather than risk any damage to such a beautiful instrument it would be worth it and you will be supporting a good cause at the same time. (If you take a good quality scan of the book, I and probably a few others will share the cost of buying it).

You have to be careful as the current selector sliding links will be live at mains potential. Users were expected to know how to be careful when these were made.

I have seen two mint condition Weston wattmeters destroyed in one morning by a "student" who was either a heinous vandal, very stupid or should never have been let loose without some training, in which case it was the instructor who was the idiot.

PMM
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