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cso:instruments:fts:bolo-cool [2011-03-28 23:23] (current) sradford |
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+ | ====== Bolometer Cycle ====== | ||
+ | |||
+ | <file> | ||
+ | |||
+ | SUMMARY OF INSTRUCTIONS FOR BOLOMETER INITIAL COOL DOWN | ||
+ | |||
+ | 1)Pump on the bolometer with the turbo pump until a pressure of 10 -5 is | ||
+ | achieved. Secure bolometer from turbo pump. | ||
+ | 2)Open(CCW) green Nupro Valve on the bolometer. Close(CCW) "Pump" and "He3" | ||
+ | switches approximately 30 turns. Retract shafts and secure with vinyl tubing. | ||
+ | Tubing is labeled for each shaft. | ||
+ | 3)Pre-cool with liquid nitrogen for 1-3 hours, longer is better. Fill LN2 | ||
+ | reservoir(outer) first. After it is full, fill the LHe reservoir(inner). | ||
+ | The 3He pressure gauge reads 40 PSI and "Pump Tem" BNC on pre-amp reads | ||
+ | >1.35K ohms when the bolometer is at equilibrium temperature. | ||
+ | 4)Ensure all 3 pre amp power switches are off. Replace all 3 batteries in the | ||
+ | pre-amp. Turn on "Power", "Bias" and "Input" switches on the pre amp. | ||
+ | 5)Invert the bolometer to dump out the LN2. Blow helium gas into the helium | ||
+ | reservoir to make sure it is empty. | ||
+ | 6)Refill the LN2 reservoir(outer) with LN2. Slowly transfer liquid helium into | ||
+ | the helium reservoir(inner). | ||
+ | 7)Allow the bolometer to sit at least 4 hours. The "Pump Temp" BNC on the pre- | ||
+ | amp reads approximately 19K ohms. The "3He Temp" BNC reads about .026V. | ||
+ | Close(CW) the green Nupro valve and open(CW) the "Pump" switch. | ||
+ | |||
+ | START HERE IF THE BOLOMETER IS ALREADY AT LIQUID HELIUM TEMPERATURE. | ||
+ | |||
+ | 8)Check liquid helium level. Retransfer if there is <3 inches left. | ||
+ | 9)Besure the pump is on. Screw the dewar pumping fixture to the liquid helium | ||
+ | fill port. | ||
+ | NOTE: You will be performing steps 10 and 11 simultaneously. During pump down | ||
+ | and heating, the 3He gauge should go up to 5-15 in/Hg then go back down | ||
+ | slowly to about 18 in/Hg. For the initial cycle, it may go slightly | ||
+ | higher, but should not get over 0. If it does, you are out of liquid | ||
+ | helium of the switches are not in the correct positions. | ||
+ | 10)Slightly open the large vacuum valve until you hear a hiss. You are pumping | ||
+ | too fast if it frosts more than a foot beyond the hose coupling. Observe | ||
+ | the vacuum gauge. It should take >20 minutes to reach 100 torr. When it | ||
+ | reaches 100 torr, open the valve slightly more to reach 33 torr in 10-15 | ||
+ | minutes. Open/close valve to maintain this rate. When the gauge reads 33 | ||
+ | torr, open the large valve all the way. | ||
+ | 11)The "Pump Temp" BNC on the pre amp reads 3.83K ohms. Immediately after | ||
+ | startind the pump down, apply 2.5V to the "Heater" BNC on the pre amp. | ||
+ | "Pump Temp" resistance should reach 2.5K ohms at the same time that the | ||
+ | vacuum gauge reaches 3-6 torr. Adjust the heater voltage to regulate this. | ||
+ | Voltages up to 5V are ok. | ||
+ | 12)When the vacuum gauge reaches 3-6 torr and the "Pump Temp" resistance equals | ||
+ | 2.5K ohms, disconnect the heater voltage and closed the large vacuum valve. | ||
+ | 13)Open(CW) the 3He switch and close the Pump switch in that order. | ||
+ | 14)Connect helium gas cylinder to nipple on vacuum system. Open small vacuum | ||
+ | valve and slowly fill vacuum with helium gas until pressure on the large | ||
+ | gauge reaches 450 torr. Close small valve, and put helium gas cylinder away. | ||
+ | 15)Remove the pumping fixture from the liquid helium fill port. Top off both | ||
+ | the LHe and LN2 reservoirs and light stuff kim wipes into the openings. | ||
+ | 16)Mount dewar on telescope. Dewar is at operating temperature when the | ||
+ | following conditions are met: | ||
+ | 3He Temp is approximately .055V | ||
+ | Pump Temp resistance is approximately 17.99K ohms | ||
+ | Vs BNC reads .4-.5V with "Bias" off | ||
+ | .6-.7V with "Bias" on | ||
+ | |||
+ | THE MORNING AFTER OBSERVING | ||
+ | |||
+ | If the bolometer is going to be cycled later in the day by the daycrew or | ||
+ | yourself, top off the LHe reservoir(inner) and LN2 reservoir(outer). Leave | ||
+ | the "Pump" heat switch closed and the "3He" heat switch opened. Proceed to | ||
+ | "CONTINUED 3He OPERATION" when you are ready to cycle the bolometer. | ||
+ | |||
+ | CONTINUED 3He OPERATION | ||
+ | |||
+ | 1)Turn off pre-amp power. Replace 2 batteries on the bottom of the pre-amp. | ||
+ | Turn on the pre-amp power. | ||
+ | 2)Open(CW) the "Pump" heat switch and close(CCW) the "3He" heat switch. | ||
+ | 3)Refill the LN2 reservoir. | ||
+ | 4)Go to step 8 of "SUMMARY OF INSTRUCTIONS FOR BOLOMETER INITAIAL COOL DOWN". | ||
+ | </file> | ||
+ | |||
+ | Summary by Ed Bufil | ||