Can't find a high-power accurate power meter.

[alphacat]

I've been searching through several websites for a rental power meter which its accuracy is 0.1% (or at least bellow 1%), and is able to measure up to 3KW-4KW.

Did anyone have go to work with such power meter or does anyone know where i could find one that is for rent?

Thank you in advance.

 

[Sceadwian]

That's pretty high precisions measurement for that much power, why?

 

[RODALCO]

Over the top.

Most power meters in that 3 to 4 kW range are class 2 for electromechanical or class 1 for static solid state meters.

Precision metering at class 0.1 or 0.2 S accuracy is only used at bulk metering points or grid exit points where the loading is in the Megawatt hour range.

 

[kchriste]

What kind of power?
RF?
DC?
AC power line? Number of phases?
Mechanical power?
etc...

 

[alphacat]

Hello and thanks for the help.

I'll explain why i need such accurate power meter and what kind of power it is to measure.

I have a Power Sensor IC which its theoretical accuracy (according to datasheet) is 0.1% (typical).
I want to test its accuracy and to calibrate it if needed, and for that i need a very accurate power meter.

The power meter is to measure AC power line - the power that regular home appliances consume.

Is there any chance of finding one?

 

[Mikebits]

Power is the product of current and voltage. Perhaps you should be searching for an AC current meter and a high voltage probe. I have no idea how accurate AC current meters are.

 

[alphacat]

Hello.

Well, power is a product of current, voltage and power factor.
Having only current and voltage meters isnt enough for measuring power.

 

[alphacat]

How shall I test and calibrate the 0.1% accuracy of the IC i use?

 

[tcmtech]

You will need a referance power meter with a calibrated accuracy greater than your own. Or a full range of meters with known calibrations of greater accuracy than your power meter is rated for.

Do you really need a .1% resolution on your power monitoring ability?

 

[RODALCO]

You can calibrate an error out of a power meter but you need to have the meter on a test bench with an accuracy higher than the meter itself.

It is usually at a particular loading as most meters have an error at the extremes of the measurement range.

Years ago working in the metering section we used a Landis & Gyr TVH reference with a Ferranti test bench to calibrate and check electromechanical and solid state meters.
The standard was accuracy class 0.02 with overall error of 0.1 %.

For your measurement see if you can get a kWh meter from the utility with a pulsing output.

 

[The Electrician]

Hello.

Well, power is a product of current, voltage and power factor.
Having only current and voltage meters isnt enough for measuring power.

If your load is purely resistive the power factor will be 100% and you can then use a good quality DVM to measure the applied voltage to better than <.1%. Use another DVM, or individual digital panel meter to measure the current to <.1%. With these two values you can calculate the power to about .1%. This all depends on knowing that the power factor is 100%, which it will be if your load is purely resistive.

Then you can create a load of known power factor by adding some good quality capacitors of known value in parallel with your resistive load. The actual wattage drawn by the load won't change if you maintain the voltage across the load unchanged, perhaps with a variac (variable transformer). Then you will be able to see how much error is introduced by a power factor of less than 100%.

 

[The Electrician]

This Yokogawa electromechanical meter would meet your requirements except for the accuracy requirement. It is normally a .5% instrument. Perhaps you could get it specially calibrated over the range and temperature where you would use it.

**broken link removed**

 

[tcmtech]

I dont see the practicality side of it justifying the possible costs involved in calibrating it.

Do you really need to know if your 3000 watt heater is using exactly 3000 watts and not 2997 watts or 3003 watts?
With home appliances being accurate to within a few percent is probably more than close enough.
Given your utility power can have a +-10% variance on the supply voltage alone and still be within legal specs.

 

[Sceadwian]

Hello.

Well, power is a product of current, voltage and power factor.
Having only current and voltage meters isnt enough for measuring power.

Power factor is the measure of current and voltage from two separate points... You need multiple synchronized meters at the true electrical input and the load to determine true power factor.

Inductance and capacitance affects power factor, they are not actually power factor though they just adjust the perceived current/voltage levels. True power factor is more complex than all of that, if I'm not mistaken in power circuits phase angle controlled circuits amplify power factor by their degree of phase angle shift. So the later in the AC cycle the phase angle control circuit toggles the worse the actually effciency becomes. It can become a real hole of power loss, none of it real.

 

[alphacat]

Do you really need a .1% resolution on your power monitoring ability?

Yes, I need that for measuring exact standby power consumption of different appliances.
Its also desired to be able to measure accurately the ON-mode power consumption of appliances, but not as desired as accurately measuring their standby power consumption.

This Yokogawa electromechanical meter would meet your requirements except for the accuracy requirement.

I entered to the datasheet of that power meter.
Where do you see there that it can measure power of KW and an indication on its accuracy level?
It says there that for 240V, the rated power is 2.4VA, does it mean that it can measure power of up to 2.4VA @ 240V?

 

[The Electrician]

The datasheet shows that it's a class .5 instrument; that's a 1/2% accuracy according the the JIS standards.

This is an electrodynamic wattmeter: Wattmeter - Wikipedia, the free encyclopedia. The current coils and the voltage coil multiplier resistors dissipate a little power themselves. The small VA ratings you see are the values of power consumed by the instrument itself; that's what the data sheet refers to as "Low self-consuming power". You need to take these into account for extremely accurate measurements.

The meter shown on eBay has voltage ranges of 120/240 volts, and current ranges of 5/25 amps. This means that the instrument can have 4 different full-scale ranges--600 watts, 1200 watts, 3000 watts and 6000 watts.

There is a single scale reading from zero to 120. The indicated number has to be multiplied by an appropriate scale factor to give the actual power reading. The scale factors are shown on a label on the front of the meter. There is a picture of this label on the eBay site for the meter.

Since the meter responds to DC, you can calibrate it yourself. You need a voltmeter that can measure DC voltage accurately, and an ammeter that can measure DC current accurately; you could use 2 DVMs for this. Since the voltage and current coils are electrically isolated, you use two different power supplies and apply accurately measured voltage and current to the meter. Multiply the value of the DC voltage and the DC current and you have the DC power in watts, which the meter should indicate.

You can see from the data sheet that these meters are available with much smaller current ranges, which you might need to use if you want to accurately measure low standby power consumption.

These meters are expensive if you buy them new; around US$600 each. The one on eBay is a good bargain.

 

[alphacat]

Thank you very much Electrician!