1. BCTW calibration status and future
Michal Krupa
10/03/2016

2. M. Krupa BCTW calibration BI/TB
WCT internal PCB
Beam current path: low impedance, precise matched resistors for symmetry, short traces for good RF performance
Calibration path: low DC resistance, high RF impedance to decouple from beam, optimised for calibration with current, symmetry not critical
09/03/2016
M. Krupa BCTW calibration BI/TB

3. Decoupling calibration from beam
Beam signal coupling to the calibration winding introduces an important error to the beam current measurement
Minimising the calibration winding current translates to minimising the beam current measurement error
Decoupling distributed over the PCB with different ferrite beads covering different frequency ranges ( MHz)
09/03/2016
M. Krupa BCTW calibration BI/TB

4. Status - calibration of analogue integrators
Analogue integrators (DABs) are meant be replaced with the VFC digital acquisition as soon as it is ready
Absolute calibration of DABs is very challenging as they measure the bunch integral directly
The same procedure as last year: relative calibration with the least effort and cross- calibration with the DCCTs for absolute scaling
09/03/2016
M. Krupa BCTW calibration BI/TB

5. Status - calibration of analogue integrators
Bench top signal generator installed in UA47 connected to the three installed WCTs in parallel
Calibration signal is a 5 µs square pulse
The generator can be triggered from the DABs
The generator can be controlled remotely over ethernet
09/03/2016
M. Krupa BCTW calibration BI/TB

6. Future - calibration of digital integrators
The digital integrators digitise the signal level and compute the integral
Only the amplitude needs to be calibrated, timing is intrinsic
Precise calibration is possible only with a current source – independence of the cable and load impedances
Precise current sources are typically feedback systems – only slow pulses (tens of µs) possible
Averaging can be used to increase precision and lower the noise influence
09/03/2016
M. Krupa BCTW calibration BI/TB

7. Calibration by current
To maintain a reasonable calibration current dynamic range and to reduce the power dissipated on the WCT PCBs, low load is essential
Signal path is very well defined – a single and separate cable pulled to each of the monitors
Long pulses look like DC – no capacitive current leakage, only well defined galvanic connections
IDEA: use the same current source to calibrate all WCTs
09/03/2016
M. Krupa BCTW calibration BI/TB

8. BCTW calibration circuit
Current source:
~10 ppm shot-to-shot stability
~100 ppm accuracy
~5 µs switch-on time
ICAL limited by VCAL (~1.5 A for RCAL ~ 10 Ω)
RREF: 5 Ω ± 0.01% < 0.2 ppm/oC
09/03/2016
M. Krupa BCTW calibration BI/TB

9. BCTW calibration circuit
Current measurement:
Half-bridge principle
Variable reference voltage source controlled by potentiometer and DAC (coarse / fine)
RREF: 10 Ω ± 0.01% < 0.2 ppm/oC
RHB: 100 kΩ ± 0.01% < 1 ppm/oC
09/03/2016
M. Krupa BCTW calibration BI/TB

10. BCTW calibration circuit
First prototype / proof-of-concept
09/03/2016
M. Krupa BCTW calibration BI/TB

11. BCTW calibration circuit
Trigger options:
Internal (26-pin connector)
External (2x SMA)
Pulse defining the length of the output current pulse
Edge triggering a pulse of one of the predefined lengths
WCT PCBs protected from excessive power dissipation by hardware limiting the duty cycle to 1% at 20 Hz
09/03/2016
M. Krupa BCTW calibration BI/TB

12. BCTW calibration circuit
Other features:
8 selectable outputs with reflection compensation circuitry
Unused WCT calibration inputs terminated
Infinite daisy-chain support, multiple calibration currents possible
Temperature monitoring, outputs for monitoring reference voltages by an ADC etc.
All control through a simple I2C interface
09/03/2016
M. Krupa BCTW calibration BI/TB

13. BCTW calibration circuit
Future:
Measurements and optimisation…
Some changes to the PCB design
Remote control
Internal ADC boards for monitoring the reference voltages and the half-bridge measurements
09/03/2016
M. Krupa BCTW calibration BI/TB

14. M. Krupa BCTW calibration BI/TB
Summary
Calibration of DABs done the same way as last year
Future calibration pulsed current source for the digital acquisition – work in progress
09/03/2016
M. Krupa BCTW calibration BI/TB

15. Thanks for your attention
Questions?