I assume you mean a communications card in a PC. Check the power consumed by the PC without the card installed, and again with the card installed. If you use a watt meter, don't forget the PF.
The power consumed by a card in a PC slot will most likely vary as the card functions. The voltage is well regulated by the power supply at either +5V or +12V or -12V so measuring voltage is kind of a waste of time.<br>You need to know the current the card draws from the DC bus. this can be done by using a card extender to raise the card from the bus where you can work with it.<br>The card extender will have a connector for the card to plug into and will itself plug into the mother board.<br>The connector will be an ISA, PCI or VLB type.<br>You need to identify the power connections with a voltmeter. Once identified, cut the traces on the card extender and install a jumper wire across the etch cut.<br>If you have three current meters you could forget about the jumpers. If you have one current meter install the meter across the jumpers one at a time. while the meter is installed remove the jumper and read the current.<br>Note while making these connections the PC should be powered down! While monitoring the current put the card through it's paces recording which modes draw the highest current. Then repeat the procedure for all three voltages.<br>You may find that power consumption on all three lines track each other during some modes of operation but maybe not!
