From: SMTP%"BLUSK@acdfq.fnal.gov" 28-JAN-2000 11:17:02.62 To: BLUSK CC: Subj: Pigtail power and mass issues Date: Fri, 28 Jan 2000 11:16:52 -0600 From: "Steven R. Blusk -- University of Rochester" Subject: Pigtail power and mass issues To: blusk@fnal.gov, zimmer@fnal.gov, vince@fnal.gov, gotra@fnal.gov, gold@fnal.gov, herndon@fnal.gov, spalding@fnal.gov, shepard@fnal.gov, cmlei@fnal.gov, brenna@fnal.gov, ely@cdfsga.fnal.gov Message-id: <000128111652.240002b1@acdfq.fnal.gov> X-Vmsmail-To: @PIGTAIL.DIS Hi, Some of you are getting this for the first time. I have been trying to quantify some of the pigtail issues relating to a design which uses discrete wires for power and control. A description of the proposal can be found at http://www-cdf.fnal.gov/upgrades/svxii/barrel_testing/pigtail_description.html The intent of this email is to address some issues regarding mass in the tracking volume and the tradeoff with power consumption. I calculated the mass of the power lines for the 2 oz/ft^2 flex pigtail, and it comes out to =================================== Flex Pigtail Mass/cm = 0.507 g/cm. =================================== This results in a power of 1.4 W per 6' cable I calculated the mass for a couple of configurations of discrete wires which I assumed we could use and came up with about =================================== Discrete wires Mass/cm = 0.7 g/cm. =================================== This gives a power of ~1.1 W/cable. I can reduce the wire gauge on some conductors so that we get 1.4W per cable and see how it compares to the Kapton, but I think it'll be close. My concern is the following: When we first power up the ladders, the digital components are not in any well-defined state until we initialize the system. During this time, the currents could easily be 3X as large, in which case the power drop in the pigtail will be ~2W/cable. This is likely to be too large. If we build into the system that whenever it is powered up, we immediately initialize, we can avoid being in this state for very long. In addition, we can set limits on the DVDD currents so that they do not exceed certain values. However, during readout, the current is high for a small time (~7%), and that might be ~3X the nominal value, and in that case, we can't set the trip limit at 3X. Given the state of these pigtails, I think we should/must bury some RTD's into these cables in a few strategic locations and interlock on that temperature. Your thoughts? Steve