electric power measurements

[sezame]

...i have ni pci 6014E, ni pci 6024E and ni usb 6009 DAQ an want to use some of them for measuring electrical power up to 500 W...i want to measure current with the series resistor and redused voltage on resistor divider...but i doubt if it is enaugh to use transformer for galvanic isolation between the measuring system and power grid...or do i have to purchase an another DAQ...for example USB-9215A...got somebody any idea...thanx...

[G_Lo · Accepted solution]

Sezame,

There are a few questions that I have which may clarify the issue. What are the resistance values that you are using for the series and voltage divider circuit? Also, is the current measured from the series resistor and the voltage measured from the voltage divider going to be used to calculate your power? As long as the voltage input to your cards does not exceed the maximum voltage ranges then you should have proper readings.

USB 6009: 14 bit resolution, 48kS/s, +-20V range using differential

PCI-6024E: 12 bit resolution, 200kS/s, +-20V range using differential, DC input coupling

PCI-6014: 16 bit resolution, 200kS/s, +-10V range using differential with a .5 gain setting, DC input coupling

Both voltage measurements can be made on one card but the type of card depends on how accurate your reading must be, how fast you would like to sample, and the overall voltage input range. Please keep in mind that the PCI cards will require a cable and a connector block to properly wire your inputs. The recommended cables and connector blocks can be found on the product pages at ni.com. I have also included a link which explains how differential measurements should be made. This information can be found in Table 1 of this document: https://www.ni.com/en/shop/data-acquisition/measurement-fundamentals/field-wiring-and-noise-consider... 

[sezame]

sheme

[sezame]

i got some problems in submitting repely...so most of my original mesage desappeare...

1. series resistor is 0,5 ohm/5 W

2. dividing ratio is 1:100 (10kohm/1Mohm)

3. yes, the current measured from the series resistor and the voltage measured from the voltage divider is going to be used to calculate your power and power factor aswell...

4.i wil take a sample per secuond, accuracy les better than 5 %

5.i got R6868 is 68-pin flat ribbon cable with appropriate conetor and SC-2075 experimental board aswell...is it enaugh...?...for such a measurement...

6.but i still dough does any dangerous voltages arise during transitions whwn the loda is powered off on which could harm DAQ card or pc itself...

....thanx... 

[G_Lo]

Sezame,

If you would like to use your SC 2075 then your PCI-6042E card would be compatible.  In differential mode, keep in mind that the voltage from a given channel (AI+ or AI-) must be within +/-10V from the ground reference.  As long as the +/-10V from Channel to ground is not exceeded and you stay below the overvoltage protection limit of 42V, then you will not be exceeding the card's specifications.  When the load is powered on or off, does it cause some sort of voltage spike that would exceed these voltage limits?  If so, how high would the voltage be?