current rating of refmass coil v dattilo n.
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Current rating of RefMass coil ( V.Dattilo )

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Current rating of RefMass coil ( V.Dattilo )

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  1. Current rating of RefMass coil • (V.Dattilo ) • Intro • Max coil temperature • Current rating SAT Control System weekly meeting Cascina, March 6th, 2012

  2. Introduction • Coils operating in vacuum can reach too high temperature also when energized with relatively low power (~ few Watts), because: • No heat convention • Poor heat conduction • Mainly heat radiation • The temperature increase, before being an issue for coil damage (Kapton insulated wire can sustain more than 300C), produces an exponential increase of the outgassing flow of organic compounds.  Risk of mirror contamination! • In this respect, RefMass coils are more critical because: • The kapton insulated wire is wound on macor support (macor thermal conductibility is a factor ~160 lower than that of aluminum) • They are very close to the mirror surface. • Importance of defining max acceptable values of temperature, power and current for the RefMass coils.

  3. Max coil temperature • Since the max temperature value depends also on the duration, the following criterion has been used, based on the fact that the tolerated deposition on the mirror is below one monolayer: • in case of incident in driving a single coil (human error or HW/SW failure), the worst case is when the event happens in a weekend, where the system might be unattended up to 60 hours. In this case, at a T=85C, the outgassing flux is such that a monolayer is deposited on the mirror* • in case of all the 4 coils in operation at T~50C, the time for the deposition of a monolayer is 1 year. • Coil Drivers (or coils) for AdV should be designed in order to avoid reaching a steady T higher than 85C on the coil.

  4. Current rating • Temperature rating has to be translated in current rating, to be part of the requirements on Adv CDs. • Considering that there is no temperature sensor mounted on the coils, a simple way to measure the coil temperature is to use the coil itself as T sensor. • METHOD (applied to the NE RefMass Right): • knowledge of the copper TCR (0.0039-0.0041 [1/K] ) • Knowledge of the coil resistance (6.50 ohm, elog #26630 ) • measurement of resistance seen by the CD vs current • extract the resistance variation • extract the T variation (under the assumption that the heating occurs only at level of the coil and not along the connection cable)

  5. Current rating • Temperature rating has to be translated in current rating, to be part of the requirements on Adv CDs. • Considering that there is no temperature sensor mounted on the coils, a simple way to measure the coil temperature is to use the coil itself as T sensor. • METHOD (applied to the NE RefMass Right): • knowledge of the copper TCR (0.0039-0.0041 [1/K] ) • Knowledge of the coil resistance (6.50 ohm, elog #26630 ) • measurement of resistance seen by the CD vs current • extract the resistance variation • extract the T variation (under the assumption that the heating occurs only at level of the coil and not along the connection cable)

  6. Current rating T=85C with I=0.6 A

  7. Current rating

  8. Current rating