How We Test Power Consumption
Test Equipment and Test Procedure
Our power consumption test setup was planned in cooperation with HAMEG (Rohde & Schwarz) to yield accurate measurements at small sampling intervals, and we've improved the gear continuously over the past few months.
AMD’s PowerTune and Nvidia’s GPU Boost technologies introduce significant changes to loading, requiring professional measurement and testing technology if you want accurate results. With this in mind, we're complementing our regular numbers with a series of benchmarks using an extraordinarily short range of 100 μs, with a 1 μs sampling rate.
We get this accuracy from a 500 MHz digital storage oscilloscope (HAMEG HMO 3054), while measuring currents and voltages with the convenience of a remote control.
The measurements are captured by three high-resolution current probes (HAMEG HZ050), not only through a riser card for the 3.3 and 12 V rails (which was custom-built to fit our needs, supports PCIe 3.0, and offers short signal paths), but also directly from specially-modified auxiliary power cables.
Voltages are measured from a power supply with a single +12 V rail. We're using a 2 ms resolution for the standard readings, which is granular enough to reflect changes from PowerTune and GPU Boost. Because this yields so much raw data, though, we keep the range limited to two minutes per chart.
|Measurement Procedure||Contact-free DC measurement at PCIe slot (using a riser card)Contact-free DC measurement at external auxiliary power supply cableVoltage measurement at power supply|
|Measurement Equipment||1 x HAMEG HMO 3054, 500 MHz digital multi-channel oscilloscope 3 x HAMEG HZO50 current probes (1 mA - 30 A, 100 kHz, DC) 4 x HAMEG HZ355 (10:1 probes, 500 MHz) 1 x HAMEG HMC 8012 digital multimeter with storage function|
|Power Supply||Corsair AX860i with modified outputs (taps)|
A Lot Can Happen in 100 Milliseconds...
...and we mean a lot! Let’s take a look at an analysis of all three voltage rails using a 2 ms sample across 100 ms (giving us 50 data points). Just looking at those results makes us pity the power supply. Draw over the auxiliary connectors jumps from 94 to 356 W within a few milliseconds. Fortunately, the test points on the PCIe riser don't have to endure the same drastic load changes.
In contrast to most consumer cards, there is no coil chirping. Of course, given the FirePro's price point, there better not be...
We like that neither AMD nor Nvidia top out the PCIe slot's 75 W ceiling. Instead, the auxiliary connectors shoulder most of the load. There aren't any drastic transients on the motherboard connector, which helps ensure system stability and benefits multi-GPU setups.