Instrument Operation and Commissioning
Mercury iPS
The power supply for e1039 is an Oxford Instruments Mercury iPS (intelligent power supply), the manual for which is available here:
http://mymercurysupport.com/sites/default/files/59_UMC0072_01.pdf
The power supply includes one master unit, and one slave unit, each of which are capable of providing up to 40 A of current, or 80 A in parallel. The master has a touch screen and allows control of the magnet current from this front panel, while the slave listens for commands from the master and has no way to control it directly. On being initially commissioned, the master and slave should be connected by the provided DB-9 female to male cable, which goes from the DB-9 'out' port on the master to the DB-9 'in' port on the slave. The master should then be connected via the DB-27 RS232 cable to the computer which will be running the power supply control.
It is inadvisable to attempt to use the USB-B to USB-A connector to connect the master unit to the computer, as the associated driver seems to cause intermittent blue screen errors. If necessary, the power supply control can support this option, but it is best to use only the RS232 connection if possible.
At this point, you should connect the positive terminal of the master to the positive terminal of the slave by screwing in one of the flat metal busbars, and the negative terminals should be connected together with the other busbar. If it is desired to test the power supply while shorted before connecting it to the magnet, use the large copper braid to connect the two busbars, and the large brown resistor to connect the red and black terminals on the back of the Master unit. These two shorts should be removed before the power supply is connected to a real magnet. To connect to a real magnet, the positive terminal of the magnet cable should be connected to the positive busbar and the negative terminal to the negative busbar. Further, the switch heater in the magnet should be wired to the Red and Black terminals on the back of the master unit. For this configuration, the red and black terminals on the Slave unit are unnecessary.
At this point, a standard instrument power cable may be connected to the back of both power supplies, and the switches on the back of both units set to on. The Master may then be switched on by pressing the button on the front. It takes several minutes for the power supply to initialize at this stage, so please wait until the front panel displays readings for current and voltage and the like before attempting to do anything else.
USB Relay
The other piece of equipment necessary to commission is the USB Relay board which allows the computer to control the switch heaters for the shim coils, which is a small metal box with alligator clips on the top labeled "USB Relay." This box may be connected to the computer via a provided USB-B to USB-A cable. The shim coils should then be connected to the alligator clips at the top of the USB Relay, with both ends of the circuit for the shim 1 switch heater connected to the clips next to the "1" label, and both ends of the circuit for the shim 2 switch heater connected to the clips next to the "2" label.
This board simply provides two circuit switches which may be opened or closed via the controlling computer, while the light next to each label indicates whether that switch is open or closed. If the light is on, the switch is open, and if it is off, the switch is closed. A small clicking noise is also audible when either switch opens or closes.
The USB Relay sometimes has troubles connecting to the computer the first time it is plugged in, so before attempting to ramp the magnet, it is important to verify that the computer can actually control the shim coils by watching the lights on the box. If the computer is unable to initially connect to the relay, simply unplug it and plug it back in after all other instruments have been connected to the computer. A tool for testing just the function of the relay board is available from the manufacturer at:
https://www.sainsmart.com/products/4-channel-5v-usb-relay-module
Integrated Power Supply & Shims Control
The computer control for the power supply and shims is a labview VI that uses the library of functional subVI's provided by Oxford Instruments for use with the Mercury iPS. Once properly commissioned, the control works to prevent dangerous situations from occurring with respect to the power supply. It also contains several controls for the shim coils, and possible use as a level meter, which will be described below.
Initial Connection
When initially loading the control on a new computer, most things should be automatically configured, but it will be necessary to tell the control what ports the Mercury iPS and USB Relay board are connected to, respectively. This can usually by identified on Windows by loading the device manager and looking at the list of COM ports, then looking at which number COM port disappears when you unplug each instrument respectively. Once everything is plugged in, set the Serial Port dropdown box to the COM port address of the power supply, and the Shim Board Serial Port dropdown box to the COM port address of the USB Relay board.
When you hit run on the VI, if everything is connected properly, the Connected? light should light up bright green, and you should see values near to 0.00 appearing for the current to the right. Further, by clicking the "Shim 1 and Shim 2" buttons, you should see a response from the lights on the USB Relay box itself (see Shim Control, below.)
Basic Operation
Once the control is properly connected to both the power supply and the shims, it reads out from the power supply several quantities:
Output Current: This value refers to the current in the leads, and matches the black needle on the left color dial. If the switch heater is on, this should match the value of Persistent Current.
Persistent Current: This value refers to the last current the power supply recorded leaving in the coils. It matches the value of the Output Current while the switch heater is on, but once the magnet is placed in persistent mode by turning off the switch heater, it serves as a reminder of where the current was left last time the power supply was used.
Output Voltage: This designates the voltage presently being provided by the power supply.
The value of Output Current and Persistent Current are recorded on the strip chart in the center of the screen so the behavior of the current can be monitored.
The power supply can be controlled by setting a Ramp Rate, and one of a Target Current, Field, or NMR Frequency. The ramp rate refers to the number of Amps per minute that the power supply attempts to match while ramping. Fast values of the ramp rate are dangerous at higher currents, so the control clamps this value to always be a safe one unless overridden by an expert. (See Safety Features, below.) The Target Current, Field, and Frequency all set the target current in the power supply, or, the current it attempts to reach while in 'To Set' mode. The target Field and Frequency simply change this value indirectly via the best calibration available.
Ramp Rate: The value in A/min that the power supply will ramp at while in To Set or To Zero mode. This may not exceed the following values:
| Allowed Ramp Rate | Output Current |
|---|---|
| 2 A/min | < 40 A |
| 1 A/min | 40-63 A |
| 0.5 A/min | > 63 A |
Target Current: The current the power supply will attempt to provide to the leads while in To Set mode. This may not exceed a value of 76.9 A.
Target Field: The value of the field the user wishes to achieve from the magnet, based on calibrations from the UVA cooldowns in January and June to convert this field into a desired current. To examine the drift of this field calibration, a box is available in the upper right corner which reads "For Drift Calibration." If the user occasionally enters the value of the target signal's frequency displayed from the NMR system, the control will automatically log this information and update the Target Field calibration.
Target Frequency: The frequency which the user wishes to see the target signal at, based on most recent calibrations. The box above all numerical controls allows the user to switch the target species between Proton and Deuteron, which updates what the calibration is that converts target frequency into target field (and subsequently, into target current.)
The power supply can be in one of three modes while it is turned on: Hold, To Set, and To Zero. When the power supply is first turned on, its output will be clamped for safety, which is signified by the 'Hold' light blinking yellow. The lights below each relevant button otherwise indicate what mode the power supply is in.
Hold: The default state of the power supply. In this state the current in the leads will be locked at whatever their current value, the value displayed under 'Output Current', is. In case the user is unsure what they are doing or if an unexpected event occurs, they should always switch the power supply to Hold until it is safe to continue ramping.
To Set: While in this state, the power supply will ramp until it reaches the current value displayed in the "Target Current" field. Once it reaches this value, it will switch to Hold mode automatically. We have observed the behavior of the power supply is such that after switching to hold, it takes a minute or so for the current to stabilize at the set point, as it overshoots and undershoots several times as it nears the set point. If the switch heater is off, the power supply will ramp very fast, if it is on, it will ramp at the rate set in "Ramp Rate."
To Zero: While in To Zero state, the power supply will ramp the leads towards a value of zero current. On reaching an output current of zero, it will switch to Hold mode automatically. If the switch heater is off, the power supply will ramp very fast, if it is on, it will ramp at the rate set in "Ramp Rate."
Finally, the power supply's Switch Heater can be turned on using the square button marked Switch Heater. If the switch heater is off, the power supply will be essentially shorted, and can ramp the leads up or down as it pleases, to actually ramp the magnet, it is necessary for the switch heater to be on. On clicking the square button, the switch heater will be turned on if it is off, or off if it is on. The switch heater takes time to open or close, so on hitting the button, a 30-second timer will be displayed on the screen, locking out other actions until the switch heater has completed changing state. The light next to the button indicates a read back from the power supply as to whether the switch heater has successfully opened or not. If the light is green, the switch heater is on, and if it is red, the switch heater is off.
If the switch heater is on, then ramping the output current by using "To Set" or "To Zero" will ramp the current in the magnet itself. If the switch heater is turned off while the current has been driven to some nonzero current, the magnet will be left in persistent mode. The current value displayed in "Persistent Current" logs the last known value of the current before the switch heater was turned off. Allowing for small field drifts, this should be roughly the current in the coils at any future time. It is unsafe to turn the switch heater on while the current in the leads and the current in the coils differ, so the user is locked out from changing the state of the switch heater unless the current and persistent current match within error bars.
The user is also unable to turn the switch heater on or off unless the power supply is in "Hold" state.
Shim Control
The USB Relay can also be used to control the state of the shim coils, using this same control. Pressing the Shim 1 button will open the switch for Slot 1 on the USB Relay, turning on Shim 1 if everything is connected properly. Pressing it again will turn Shim 1 off. Similarly, the Shim 2 button can be used to turn the second shim coil on or off. Note that in this case, the light next to the buttons only indicates the last command the computer knows it has sent to the shim coils, so it will be on if it last told them to turn on, and off if it last told them to turn off. If there is a cable connection that is lost or damaged, there is presently no way for the computer to determine that the shim is not actually on.
The state of the shim coils is also changed automatically by using the other features of the power supply control. When the Switch Heater is turned on, both Shim 1 and Shim 2 are also turned on, and when the main Switch Heater is turned off, both Shim 1 and Shim 2 are both turned off. Further, to prevent moving the field without both shim coils being on, if the user switches the power supply to "To Set" or "To Zero" while the switch heater is on, Shim 1 and Shim 2 will both be turned on, and locked from being turned off until the power supply is back in Hold mode. This means the shim coils may only be off at any point while the power supply is in Hold mode, and otherwise will be automatically turned on.
Safety Features
