Wednesday, March 12, 2014

Bryant's network control/measuring PDUs

My good pal Simon Quill at Bryant has been developing this line of intelligent bay mains distribution for the last few years and I bought a couple last year and have (due to the weight of work) only just got around to playing with them. Quite a lot of manufacturers offer remotely controllable power strips with either a bit of client software or a web interface to control the various circuits. Some even offer current monitoring (typically via a shunt-resistor so you get apparent current; the heating effect, in effect!) but Bryant claims to actually measure the current via a clamp-inductor and they calibrate each circuit's 16-bit ADC prior to it leaving the factory. Simon tells me each circuit can measure to 50A to an accuracy of 1mA and they sample at 1Khz so you can see any harmonic content that is being put on by UPSes etc. 

Some of the other features;
  1. Macro start-up, close sequence. You can (for example) get o/p 2 to hold off powering up until o/p 1 has settled.
  2. Control of each circuit via the web interface - re-power that server?
  3. Inspect the current draw (and power factory) on a per circuit basis; worried that an array of disks is starting to show odd consumption; maybe a drive is about to fail?
  4. Look at the quality of the incoming mains - it's rarely a sine wave nowadays!
Simon & I intend to do an episode of The Engineer's Bench on IP controlled PDUs (not just these Bryant ones) but until then here are some screen-grabs.

 This one shows the graph for the third circuit which has an AlicePak audio balancing interface attached and is (we hope!) a linear supply and hence should be an entirely resistive load.
 This is my trusty Tektronix WFM7120 which is clearly using a switch-mode supply; notice how the current draw is when the driver transistor switches as the voltage passes a set value.
 This one shows the earth leakage current against incoming mains; a bit more sine-like but remember the effect is made worse by the presence of the Tek & the AlicePak.
This is a circuit which has no load and so consequently we're seeing the auto-ranged current draw which is just the quantised noise of the ADC.


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