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The MICE target and the ISIS BPS system

By Edward Overton

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Overview• Background• Target Behaviour & BPS Limits• Implementation– FPGA– Software– Hardware

• Calibration & Testing Plans

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BackgroundThe decision to implement a firmware based BPS system was taken based upon

discussions/recommendations from ISIS staff in August last year.

The firmware based BPS system aims to monitor the trajectory of the target on an actuation by actuation basis by comparing key points in the trajectory to similar key points in a pre-computed reference trajectory.

The comparison between the key values and the actual target trajectory is done in firmware to ensure that the system remains reliable even in the event of a disconnection between the computer and controller.

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Set Point 2• Position Set• Flip Acceleration

Begin Actuation

Set Point 1• Flip Acceleration• Record time

Minimum PositionRecord position & time

End actuationRecord actuation timeEnter capture mode

(cm)

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Set Point 2• Position Set• Flip Acceleration

Begin Actuation

Set Point 1• Flip Acceleration• Record time

Minimum PositionRecord position & time

End actuationRecord actuation timeEnter capture mode

Limits on “normal” Actuation, if outside send BPS error

(cm)

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FPGA Implementation• 8 USB registers set by control software

• Provide upper and lower limits for:

• FPGA Firmware monitors above position/times and throws an error if they lie outside the limits set in the registers.

• The start position and final position are implicitly monitored by the target system. Any deviation from a normal range will throw an error, this has been tied into the BPS system.

"USB_SP1_MAX_TIME" "USB_SP1_MIN_TIME" "USB_MIN_POS_MAX_TIME” "USB_MIN_POS_MIN_TIME”

"USB_MIN_POS_MAX_VALUE”"USB_MIN_POS_MIN_VALUE”"USB_ACT_MAX_TIME“"USB_ACT_MIN_TIME“

SP1 TimeActuation Time.

Minimum PositionMinimum Position Time

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Calculation of Trajectory

)/exp()( 0 RCttata

Target acceleration decays exponentially due to decaying power in capacitor bank:

C function calculates trajectory from: a0, tRC, Starting Position, SP1 and SP2.

Fit using C function to analogue data shown as red line =>

Limits can be calculated from the expected trajectory and downloaded to the FPGA registers

(cm)

a0 depends on current and can be calculated for different voltage or temperature coils.

All necessary functions for calculating a0 and trajectory included in c++ class.

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Example from Sheffield target

Target warm up

Coolant Temperature

SP1 time

Minimum Position Minimum Position Time

Coil Temperature

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Hardware

FPGA Relay DriverEach relay driver is connected to separate FPGA logic pin.

50R DriverAdded a third logical output to give a monitoring signal connected to a BNC

We were asked to provide 2 independent sets of relay contacts for the BPS system itself:

RelayRated to 1A 30VDC but PCB tracks limited to about 250mA

BPS LogicRequired to switch 2 relays. 24VDC, 16.8mA total.

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HardwareRow of relays down the RHS of board DC2.

There are 2 spare relays on the circuit board, so if more relays are required then this can be accommodated.

Back panel connectors

Relay Contacts Available here

50R signal for sending to ISIS CR – If required

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Calibration & Testing Plans• Current calibration for outdated test system in Sheffield.

– Single minimum position.– Limited data recorded before controller was moved to R78.

• New calibration required for ISIS, R78 targets.– Multiple minimum positions.– Determination of upper/lower limits to place on actuation.

• Thorough testing in R78 required to ensure system is working reliably prior to installation.

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Conclusion• FPGA code and Electronics implemented, but requires testing.

• Software for estimating parameters is also implemented.– Works well for Sheffield target.– Calibration required for R78 target.– upper/lower limits on actuation need setting.

• Control software upgrade underway to include BPS functionality.

• Thorough testing in R78 required to ensure system is working reliably prior to installation.