The setting for the power supply is a combination of the controls on the front and the 0 to -5VDC signal input on the back. However, the controls on the front can be set up to be used as a limit on the current (for safety), this is how we use them.
Before turning on the magnet, make sure function generator (the DS345 from Stanford Research Systems -- located above the target computer) is not connected to the power supply (the BNC cable that normally connects to the "function" output on the front should be disconnected.
Then, go to the hall, and turn on the power supply. Push the button marked "OUTPUT ON/OFF". Now you can turn up the voltage and the current. As you turn up them up, you will see an arrow indicator over either "CC" or "CV". These indicators stand for "constant current" and "constant voltage," respectively. The output will only change when you are turning the knob that corresonponds with the correct control (i.e., when the indicator is "CV", the output will only change when you turn the voltage knob). Turn up the power until you reach 45V (our safety limit).
At this point leave the current knob alone, and slowly turn down the voltage knob. Then slowly turn the voltage knob up to 45V again, then down, then up, then down. Leave the power supply in this state (voltage turned to zero, and the current turned up).
Returning upstairs, you should now reconnect the function generator. The function generator is wired to control the power supply's voltage. When you reconnect it, the voltage (and current) may jump. This is not cause for alarm.
Now, you are ready to load the parameters into the function generator. This is done by opening the folder on the desktop of the target computer labelled "Target Expert". Run the LabView virtual instrument labelled, "NMR Helium Initialization GEn.vi". Please do not change any of the parameters as the field has been mapped out with the parameters set this way. The voltage may change when the program has finished running.
Now, you are ready to set the field. Run the VI, "sweep_no_meter.vi". Run it, wait 2 minutes, run it again, wait two minutes, and run it again. This sends the sweep that will be used for helium NMR to the power supply. The field at the end of the sweep is quite repeatable and will be where we sit for most of the data taking (it will sit there except when we are making an NMR measurement). Each sweep takes a couple of minutes. You can watch the sweeps by looking at the Fluke multimeter that can be seen on the monitor. The field will not be set at all correctly until the first sweep has been run, and a second sweep is sometimes necessary. A third sweep is very cheap insurance.
If this doesn't set the field properly, please page me at 584-5007.
Aidan