Testing Wattmeters

[ion]

I wanted to test the Intertek Wattmeter basically to see how well it behaved with phase fired loads versus loads driven by a small Variac.

As you know, phase fired control devices of the type such as a light dimmer or other thyristor controller produce a chopped sine wave with the phase angle of firing controlled as opposed to a Variac which can generally produce a relatively  clean sine wave of variable amplitude. I used a small 3 amp Variac for these tests. Excitation power was less than a watt.

To test the differences in actual power, as read by the Intertek, I used temperature as the final value in heating the surface of a 150 Watt clear incandescent lamp. I chose values at 25 Watt intervals and recorded temperature after settling, a lengthy procedure.

Ambient and bulb surface temperature were noted using a Fluke 52 dual thermometer and results corrected for ambient.

The test results show that the Intertek displays comparable  (to a Variac) Watts, automatically corrected by power factor for the chopped light dimmer control device. (see attached spreadsheet)

Conclusion: The Intertek power monitor does a satisfactory job in displaying  power in Watts when a light dimmer or other thyristor control device is operating into pure resistive load as compared to a more expensive Variac.

At around 16 USD and free shipping, it is a bargain for every FE researcher.

Note: Control devices, in each case, dimmer or  Variac are placed on the output of the Intertek.

[Peterae]

Now that is very useful information 

Thanks ION

[ion]

Thanks Peter

I will be adding other test results from time to time including absolute accuracy of such devices as compared to external instrumented monitoring of power.

Measurement can get tricky when a large power factor exists in our test circuits or when testing half wave rectified circuitry.

I will also add info on the "Kill A Watt" series of power meters.

Everyone is encouraged to add their comparative testing (of Wattmeters) to this thread. By understanding the use and limits of our equipment we become better scientists.

[poynt99]

ION,

I'll wait for your Killawatt results before I order the Intertek, as I already have one. Do you suspect it will not do as well?

Thanks for taking the time to perform this testing

[Chet K]

ION
A beautiful piece of work!! Not only have you proven the viability of using a nice economical system for experimenting on a budget ,You also give us a ruler to measure output based on temp of bulb! [so many of us love bulbs  ]
this could be expanded a bit for quick seat of the pants measurements that may ultimately be quite accurate?.[especially in those much more complicated settups that seem to be "unmeasurable" with instruments]


Can you share the procedure which was used to acquire that temp data?["settling, leveling" ETC..]
It seems like a nice variation of your "fixed loss to ambient" work from your bench here at OUR.

Thanks for all you do, this will make our community much more productive and effective in our experiments and possibly bring in more experimenters that may not have the "pockets" for more expensive equipment.

Great stuff!!
Chet

[ion]

From Chet:

Can you share the procedure which was used to acquire that temp data?["settling, leveling" ETC..]
It seems like a nice variation of your "fixed loss to ambient" work from your bench here at OUR.

Yes it does represent the fixed loss to ambient. Actually the losses are fixed in that they represent a stable loss at each power level but the amount of loss is different at each power level and increase as power level increases..

Heat source was a clear envelope 150 Watt incandescent lamp. Thermocouple was fastened in such a way to make a pressure contact with the lamp envelope. Over this an inverted coffee tin was placed, bright tin inside and outside, with  3/4 spacers  for some air flow at the bottom of the tin.

Temperature data was recorded when it had settled in that no more increase was seen in the tenths of a degree C.

A Fluke 52 dual thermometer was used for ambient and bulb measurement.