anovel ln ﬁlllevelmeter - agenda (indico) · thecapacitiveln 2-level-monitor...

A novel LN2 fill level meter

D.Lersch, B. Birkenbach, B. Bruyneel, J. Eberth, H. Hess, G. Pascovici,P. Reiter, H.G.Thomas∗, A. Wiens

IKP-Cologne, ∗CTT

January 20th − 2010

Daniel Lersch (IKP-Cologne) AGATA-Week @ Legnaro January 20th − 2010 1 / 13

Motivation

AGATA detectors are operated at90K and p ≈ 10−7 mbar

When detector gets warm:getter starts gasing out andHV-sparks may damageelectronics in the cold part →long downtimesTemperature-monitoring viaPT100-sensor: detector systemreacts slow on changes oftemperature in cold partLeakage current-monitoring:Detector is not operationalanymoreDirect monitoring of theLN2-level


The capacitive LN2-level-monitorEach AGATA-dewar is equipped with a further (inner) cylinder in theinterior → cylindrical capacitorCapacity is measured as function of the LN2-filling-level


The capacitive LN2-level-monitor

!r,g=1

h

h0

2r1

2r2

N2(l)

N2(g)

C1

!r,g

C2

!r,l

C1 " !0A(h0-h)

C2 " !0 ! r,lA(h)

!r,l=1.4

The capacity C as function of the LN2-filling-level h of a cylindricalcapacitor with radius r1 and r2:

C (h) = C1 + C2 = 2πε0 · ln(

r2r1

)−1·(h0 + 0.4h

)Daniel Lersch (IKP-Cologne) AGATA-Week @ Legnaro January 20th − 2010 4 / 13

The capacitive LN2-level-monitor

0 2 4 6 8 10 12

960

980

1000

1020

1040

1060

Measured filling level h @cmD

Mea

sure

dca

paci

tyC

@pFD

0 10 20 30 40 50 60

1000

1020

1040

1060

Time t @hD

Mea

sure

dca

paci

tyC

@pFD

Measurements show lineardependency between capacityand LN2-filling-levelFilling-capacity is also a linearfunction of timeDifference ∆C between emptyand full dewar:∆C = Cmax − Cmin =1054 pF− 924 pF ≈ 12 %

Cmin

Cmax

0 10 20 30 40 50 600.92

0.94

0.96

0.98

1.00

1.02

1.04

1.06

Time t @hD

Cap

acity

C@nF

D


LN2-consumption-Measurements

Another advantage of capacitive LN2-read-out: information aboutLN2-consumptionConsumption influenced by configuration of the cold part (e.g.cabling, electronics, applied low voltage)

bL

LV OFF

LV ON

0 1 2 3 4 5 6 71040

1060

1080

1100

1120

1140

Time t @hD

Cap

acity

C@pF

D

LV ν[

mlh

]τ [h]

ON 419± 19 11± 0.5

OFF 378± 23 12± 0.7


The C/V-transducer

BNC-read-out

SMA-input

Power supply

adjustable offset O adjustable gain G

3.8cm

3.8cm

C/V-transducer: does not measure whole range of 1000 pF, butdifference Cm − Cr → sensitive to ∆C ∼ 12%

The filling capacity Cm is translated into a DC-voltage signalV (G ,O,Cm) = m(G ) · Cm + V0(G ,O) with adjustable gain G andoffset O


The C/V-transducerPrinciple

+Iosc

-Iosc

S1

S2

Cosc

Cm

Cr

+Im

-Im +I

r-Ir

Integrator Integrator

Reference oscillatorCapacitor is charged /discharged by constantcurrent → triangular wavesignalReference oscillator drivesphase-locked andclock-synchronized twoidentical integrators withcapacities Cr and Cm

Difference signal Cm − Cris filtered and amplified →DC-voltage


The C/V-transducerAdjusting and calibrating

Last AGATA-week: prototype of LN2-read-out was successfully testedat ATC(4)4 further devices @ Cologne and tested at ATC(4) (Cmin = 924 pF,Cmax = 1054 pF, ∆C = 130 pF)

black: Box 1blue: Box 2orange: Box 3green: Box 4

900 950 1000 1050 1100

4

6

8

10

Input capacity C @pFD

Cal

ibra

ted

outp

utvo

ltage

Uca

l@V

D Adjustment of output-voltagewith gain- andoffset-potentiometerOutput-voltage of each devicedefined: Vmin(Cmin) = 5V,Vmax(Cmax) = 10V∆C = 130 pF→ ∆U = 5V


Position-dependent measurements

Horizontal axis

Vertical axis

!

Detector axisAGATA-detector-array

!r,g

!r,lS

S0

2r1

2r2

N2(l)

N2(g)

Different detector positions inarrayInfluence of inclination θ onLN2-read-outGeometrical shape of liquidnitrogen inside dewarParameterisation: Surface S(θ)covered with liquid nitrogen isproportional to filling-capacityC : S(θ) ∝ C


Geometrical shapes of LN2 inside the dewar


Position dependent measurementsCalculations and results

red: 90° cL

blue: 0° aL

green: 45° bL

0 5 10 15 20

900

950

1000

1050

Time t @hD

Cal

cula

ted

capa

city

CHtL

@pFD

black: box 1blue: box 2orange: box 3green: box 4

aL

0 5 10 15

5

6

7

8

9

10

Time t @hD

Vol

tage

U@V

D

black: box 1blue: box 2orange: box 3green: box 4

bL

0 5 10 15

5

6

7

8

9

10

Time t @hD

Vol

tage

U@V

D black: box 1blue: box 2orange: box 3green: box 4

cL0 5 10 15

5

6

7

8

9

10

11

Time t @hD

Vol

tage

U@V

D


Summary and outlook

The capacitive LN2-read-out is workingI C is a function of filling height hI Difference between full and empty dewar: ∆C ∼ 12%

Implementation of the C/V-transcenducerPosition dependent measurements of the filling capacity

I Inclination have an influence on the filling capacityI Common operation timeI Define common treshold

Integration of C/V-transducer in AGATA-patchpanel and the cryogenicfilling system


anovel ln ﬁlllevelmeter - agenda (indico) · thecapacitiveln 2-level-monitor...

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