Fk. Bordry AB/PO

Ability of the converters to follow the reference function

(static, dynamics)

I1I2I3

Static part is covered by the static definition :

accuracy, reproducibility(see session 7)

Dynamic part comes from :- timing error- lagging error in the regulation

Tracking errorbetween I1 and I2

Iref

Tracking

11th Chamonix workshop - 18th January 2001

Fk. Bordry AB/PO

IIref

Dynamics :- Measurement and command must be synchronised : timing (1ms)

- Lagging error : # Iref => I : regulation loop are designed with no lagging error independent of the load time constant

Dynamics :- Measurement and command must be synchronised : timing (1ms)

- Lagging error : # Iref => I : regulation loop are designed with no lagging error independent of the load time constant

Power Converter+

CircuitT 1/S

R

Ts

ADCDigital

controller

DAC

Ts

BMagnet

F(s) = 1/(1+Ts)

# I => B : time constant (T : vacuum chamber, beam screen…) must be known (could be corrected by control)

Measurement campaign : test benches and String 2.

Tracking : dynamics

Fk. Bordry AB/PO

The curve marked feed-forward uses the knowledge of the transfer functions as established on the test benches. This correction compensates well the difference in the high field saturation, but leaves a substantial deviation at low and intermediate field. This deviation is mostly due to a systematic measurement artefact. Irrespective of its nature however, and because this is a systematic effect, the deviation is well corrected by iteration on the measured B2/B1 ratio as shown by the curves marked feed-back.

In this case the tracking error on the B2/B1 ratio is definitely inside the range to be achieved for the tune feed-back system to lock, and in fact quite close to the range necessary to maintain the maximum allowed tune variation to within 3 × 10-3 as dictated by the nominal LHC performance.The optimised current ramp was sent unchanged in a second cycle, with the aim to verify the reproducibility of the ramp. The result demonstrates that the reproducibility is excellent.

The ratio B2/B1 for the focussing quadrupole plotted as a function of the dipole field along the reference current ramp.

Tracking at String 2

20 ppm Accuracy after calibration

B/Bultimate = I/Iultimate = 20ppm

B = 9 * 20 10-6 = 1.8 10-4 TB/Bo = 3.3 10-4

Orbit excursion :X = Dx . B/Bo = ~ 0.7 mm

Tracking between the 8 main dipole converters

3

8

7

2

4

5

1

6

Could be corrected with a pilot runand new cycle => reproducibility10 ppm reproducibility Orbit excursion :X = Dx . B/Bo = ~ 0.35 mm

”It would be better with 5 ppm”Oliver Brüning (X < 180 m)

Could be corrected with a pilot runand new cycle => reproducibility10 ppm reproducibility Orbit excursion :X = Dx . B/Bo = ~ 0.35 mm

”It would be better with 5 ppm”Oliver Brüning (X < 180 m)

11th Chamonix workshop - 18th January 2001

Fk. Bordry AB/PO

Power Converter Tolerances for LHCPower Converter Tolerances for LHC

Precision Control

Circuit Nominal Current One Year One day 1/2 hour ResolutionType Current Polarity Accuracy Reproducibility Stability

(A) (ppm of Inominal) (ppm of Inominal) (ppm of Inominal) (ppm of Inominal)

Main Bends, Main Quads13000

Unipolar ± 50 ± 20 with calibration

± 5 ± 3 1

Inner triplet 8000/ 6000

Unipolar ± 100 ± 20 with calibration?

± 20 ± 10 15

Dispersion suppressor6000

Unipolar ± 70 ± 10 ± 5 15

Insertion quadrupoles6000

Unipolar ± 70 ± 10 ± 5 15

Separators (D1,D2,D3,D4)6000

Unipolar ± 70 ± 10 ± 5 15

Trim quadrupoles600

Bipolar ± 200 ± 50 ± 10 30

SSS correctors600

Bipolar ± 200 ± 50 ± 10 30

Spool pieces600

Bipolar ± 200 ± 50 ± 10 30

Orbit correctors 120/60 Bipolar ± 1000 ± 100 ± 50 30

Tracking between the dipole and quadrupole converters

20 ppm AccuracyB/Bultimate = I/Iultimate = 20ppm

B = 9 * 20 10-6 = 1.8 10-4 TB/Bo = 3.3 10-4

Energy error in the machine leads to a tune change :Q = nat . p/po = nat . B/Bo = 100 * 3.3 10-4 = 0.032

Tuning quadrupoles can correct up to Q = 0.3

20 ppm AccuracyB/Bultimate = I/Iultimate = 20ppm

B = 9 * 20 10-6 = 1.8 10-4 TB/Bo = 3.3 10-4

Energy error in the machine leads to a tune change :Q = nat . p/po = nat . B/Bo = 100 * 3.3 10-4 = 0.032

Tuning quadrupoles can correct up to Q = 0.3

Tracking between the main quadrupole converterssmall beating : no problem

Fk. Bordry AB/PO

– Accuracy

Long term setting or measuring uncertainty taking into consideration the full range of permissible changes* of operating and environmental conditions.

* requires definition

– ReproducibilityUncertainty in returning to a set of previous working values from cycle to cycle of the machine.

– StabilityMaximum deviation over a period with no changes in operating conditions.

Accuracy, reproducibility and stability are defined for a given period

– Accuracy

Long term setting or measuring uncertainty taking into consideration the full range of permissible changes* of operating and environmental conditions.

* requires definition

– ReproducibilityUncertainty in returning to a set of previous working values from cycle to cycle of the machine.

– StabilityMaximum deviation over a period with no changes in operating conditions.

Accuracy, reproducibility and stability are defined for a given period

GlossaryP

reci

sion

Precision is qualitative . Accuracy is quantitative.

INominal

IMeas. ± Accuracyppm

* INominal

half an hour

Cycle 1 Cycle 2 Cycle 3

One day max

IB1 IB2 IB3

11th Chamonix workshop - 18th January 2001

Fk. Bordry AB/PO

Accuracy Accuracy Long term setting or measuring uncertainty taking into consideration the

full range of permissible changes* of operating and environmental conditions.

LHC :The accuracy is defined by default for a period of one year .The accuracy is expressed in ppm of INominal .If the one year accuracy is too large, a calibration process should be executed more often (e.g every month)

LHC :The accuracy is defined by default for a period of one year .The accuracy is expressed in ppm of INominal .If the one year accuracy is too large, a calibration process should be executed more often (e.g every month)

* For LHC :Engineering Specifications General parameters for equipment installed in the LHC (e.g. T = ±2 oC in UAs) (LHC-PM-ES-0002.00) Main parameters of the LHC 400/230 V distribution system (LHC-EM-ES-0001) INominal

IMeas. ± Accuracyppm

* INominal

Fk. Bordry AB/PO

Reproducibility Reproducibility

LHC :

The reproducibility is defined by default for a period of one day without any intervention affecting the calibrated parts (e.g. DCCT, ADC)The reproducibility is expressed in ppm of INominal .

Cycle 1 Cycle 2 Cycle 3

One day max

IB1 IB2 IB3

IB2 = IB1 ± (Reproducibility pmm . Inominal )IB3 = IB2 ± (Reproducibility pmm . Inominal )

Uncertainty in returning to a set of previous working values from

cycle to cycle of the machine.

Uncertainty in returning to a set of previous working values from

cycle to cycle of the machine.

Fk. Bordry AB/PO

Stability Stability Maximum deviation over a period with no changes in

operating conditions.

Maximum deviation over a period with no changes in

operating conditions.

LHC :

The stability is defined by default for a period of half an hourThe stability is expressed in ppm of INominal .

± Stabilityppm . INominal

half an hour

Time in Minutes-40-200

2040

0 60 120 180 240-2-1 0 1 2

Cur

rent

offs

et in

Mill

iam

ps

Cur

rent

offs

et in

ppm

of 2

0 kA

I0 = 16000 Amps