THMP Calibration Miriam K ummel Ruhr-Universit at Bochum - - PowerPoint PPT Presentation

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THMP Calibration

Miriam K¨ ummel

Ruhr-Universit¨ at Bochum Institut f¨ ur Experimentalphysik I

PANDA-Collaboration Meeting March 2016

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Why Do We Measure Temperatures?

PWO-II: LY depends on T with d(LY )

dT

= 3 %/❽ at -25 ❽ Goal for PANDA: ∆T < 0.1 ❽ → sensors with σT < 0.02 ❽

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How Do We Measure Temperatures?

The resistance of most materials depends on the temperature Platinum best material for resistance thermometers: R vs T relationship quite linear R(T) ≈ R(0 ❽)(1 + αPt · T), αPt = 3.89 · 10−3K−1 For commercial Pt100 sensors R(0 ❽) = 100 Ω, so that R(−25❽) ≈ 90.23 Ω For our manufactured sensors R(0 ❽) ≈ 105 Ω, so that R(−25❽) ≈ 94.7 Ω The measurement accuracy σT for temperature sensors, translates to a measurement accuracy σR for the THMP: σR ≈ ∂R(T) ∂T · σT ≈ 7.8 mΩ ⇒σR R ≈ 0.08% = 80 ppm

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How Do We Measure Resistances?

4-wire measurement constant current I = UI

RI

gain G = 5 + 200 kΩ

RG

• ffset voltage Uoff

ADC conversion factor C (R · I · G + Uoff) · C = R ·I · G · C

• m

+ Uoff · C

n

= N ⇔ R =

1 m

• p1

N +

−n m

• p0

→ σR corresponds to 3.5 ADC channels for optimized values of UI, RI, RG and Uoff

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How Do We Measure Resistances Accurately?

! Electronic components vary within their production accuracy all readout channel k on a PBB are different! constant current Ik =

UI RI,k

gain Gk = 5 + 200 kΩ

RG,k

• ffset voltage Uoff

ADC conversion factor C Rk · Ik · Gk · C

• mk

+ Uoff · C

n

= Nk ⇔ Rk =

1 mk

• p1,k

Nk +

−n mk

• p0,k

→ Calibrate each channel by fitting a 1st order polynomial to pairs of known resistors and measured ADC conversions!

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How Do We Measure Resistances with Respect to the AT?

! resistances depend on the ambient temperature T for RI,k, RG,k is (∆R/R)/∆T = 10 ppm/K the best available constant current Ik(T) =

UI RI,k(T)

gain Gk(T) = 5 +

200 kΩ RG,k(T)

• ffset voltage Uoff

ADC conversion factor C

10 20 30 40 50 60 t / h 10 20 30 40 50 THMP temperature ∼T / ◦ C

measurement of stable resistors

94.60 94.62 94.64 94.66 94.68 94.70 measured resistance ∼R / Ω

Rk · Ik(T) · Gk(T) · C

• mk(T)

+ Uoff · C

n

= Nk ⇔ Rk =

1 mk(T) p1,k(T)

Nk(T) +

−n mk(T) p0,k(T)

→ Fit a 1st order polynomial at different temperatures, describe dependency on T & monitor THMP temperature!

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How Do We Measure Resistances Reliably?

! There is an additional PBB-wide drift of unknown origin (t)! constant current Ik(T, t) =

UI (t) RI,k(T)

gain Gk(T) = 5 +

200 kΩ RG,k(T)

• ffset voltage Uoff(t)

ADC conversion factor C

2 4 6 8 10 12 14 16 t / d 94.44 94.45 94.46 94.47 94.48 measured resistance ∼R / Ω

measurement of stable resistors k=6 k=4

Rk · Ik(T, t) · Gk(T) · C

• mk(T,t)

+ Uoff(t) · C

• n(t)

= Nk(T, t) ⇔ Rk =

1 mk(T,t) p1,k(T,t)

Nk(T, t) +

−n(t) mk(T,t) p0,k(T,t)

→ Use a reference resistor on each PBB! The 10 THMPs foreseen for the fw. endcap are still sufficient.

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How to Take the Reference Resistor Into Consideration?

Two possible sources have been identified: UI and Uoff → Determine the impact of each source mk(T, t) =

UI (t) RI,k(T) · Gk(T) · C = mk(T)α(t)

⇒Rk · mk(T) · α(t) + n(t) = Nk(T, t) ⇒ Nk(T, t) − Nj(T, t) Rkmk(T) − Rjmj(T) = α(t) → Long-term measurement with known resistors of different resistances for each channel case 1 UI stable: n(t) = Nref(T, t) − Rref · mk(T) case 2 Uoff stable: Rk = Nk(T,t)−n

Nref(T,t)−n mref(T) mk(T) Rref

case 3 Both unstable: Best ansatz with only one reference sensor:

Nk(T,t)−n(0) Nref(T,t)−n(0) mref(T) mk(T) Rref = Rk

• 1 − n(t)−n(0)

Nref

• 1 − Rrefmref(T)

Rkmk(T)

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Summary and Outlook

! The resistance of resistors depends on T. The effect has already been minimized, but still must be compensated. A temperature dependent calibration is ongoing. → The THMP temperature must be monitored. A temperature sensor is included in the final THMP design, but possibly one channel per THMP has to be sacrificed. ! Additionally a slow drift has been observed. It is unknown, how long it continues in the same direction. The source of the drift will be determined by a long-term measurement. → The drift can be compensated by using a reference resistor with different methods, depending on the source of the drift. We can sacrifice one, but not two channels per PBB. The resistance should be as close as possible to R(−25❽)

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