Graphics cards and power draw have always been quite synonymous with each other in terms of how much performance they put out for the power they take in. Measuring this has not always been the most straightforward when it comes to accuracy and methods for reviewers and end-users. NVIDIA has developed their PCAT system, or Power Capture Analysis Tool in order to be able to capture direct power consumption from ALL graphics cards that plug into the PCIe slot so that you can get a very clear barometer on actual power usage without relying on hacked together methods
The Old Way
The old method, for most anyway, was to simply use something along the lines of a Kill-A-Watt wall meter for power capture. This isn’t the worst way, but as stated in our reviews it doesn’t quite capture the amount of power that the graphics card alone is using. This results in some mental gymnastics figuring out how much the graphics card is using by figuring the system idle, CPU load, and the GPU load and estimating about where the graphics card lands, not very accurate, to say the least.
Another way is to use GPU-z. This is the least reliable method as you have to rely entirely on the software reading from the graphics card. This is a poor method as the graphics cards vary in how they report to software when it comes to power usage. Some will only send out what the GPU core itself is using and not consider what the memory is drawing or any other component.
The last way I’ll mention is the use of a multi-meter amperage clamp across the PCIe slot by way of a riser cable with separate cables then more power clamps on all the PCIe power cables going into the graphics card. This method is very accurate for graphics card power but is also very cumbersome and typically results in you having to watch the numbers and document them as you see them rather than plotting them across a spreadsheet.
The PCAT Way
This is where PCAT (power capture analysis tool) comes into play. NVIDIA has developed quite a robust tool for measuring graphics card power at the hardware level and taking the guesswork out of the equation. The tool is quite simple to set up and get going, as far as components used there are; a riser board for the GPU with a 4-pin Dupont cable, the PCAT module itself that everything plugs into with an OLED screen attached, 3 PCI-e cables for when a card calls for more than 2x 8-pin connectors, and a Micro-USB cable that allows you to capture the data on the system you’re hooked up to or a secondary monitoring system.
Well, that’s what it looks like when all hooked up on a test bench, you’re not going to want to run this one in a case for sure. Before anyone gets worried, performance is not affected at all by this and the riser board is fully compliant with PCIe Gen 4.0. I’m not so certain about those exposed power points however, I will be getting the hot glue gun out soon for that. Now, what does this do at this point? Well, two options: Plug it into the computer that it’s all running on and let FrameView include the metrics, but that’s for NVIDIA cards only so a pass, OR (what we do) plug it into a separate monitoring computer and observe and capture during testing scenarios.
The PCAT Power Profile Analyzer is the software tool provided to use to capture and monitor power readings across the PCI Express Power profile. The breadth of this tool is exceptionally useful for us here on the site to really explore what we can monitor. The most useful metric on here to me is the ability to monitor power across all sources, PCIe power cables (individually), and the PCIe slot itself.
Those who rather pull long-form spreadsheets to make their own charts are fully able to do so and even able to quickly form performance per watt metrics. We’ve found a very fun metric to monitor is actually Watts per frame, how many watts does it take for the graphics card to produce one frame at a locked 60FPS in various games, we’ll get into that next.
Control was the first game that we wanted to take a look at running at 1440p with RT on, and then again with RT off.
These results for Control show that NVIDIAs measurements and claims of improvements were accurate, but it’s not always the case. We tested Forza Horizon 4 in a spot to test the same way again but this time at 1440p and looking at when we target a 1440p60 scene in this game