testing thermistors as liquid level sensors

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Testing Thermistors as Liquid Level Sensors

Kristy Lubinski

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Circuit Diagram #1

V

5 V

PT 1000 PT 1000

750 Ω

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Circuit Diagram #2

V

5 V

PT 1000 PT 1000

750 Ω

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Set-Up

PT 1000’s 1 mm space

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Boil Off Test

• Place PT 1000’s just into liquid• Collect data while the liquid boils off• Boil off rate measured separately– Liquid Nitrogen• 0.2 mm/min

– Liquid Argon• 0.2 mm/min

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Circuit #1 – Liquid Nitrogen

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Circuit #2 – Liquid Nitrogen

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Circuit #2 – Liquid Argon Trial 1

Both Out

Both In

One In

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Circuit #2 – Liquid Argon Trial 2

Both Out

Both In

One In

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Time Resolution Test

• Quickly place both PT 1000’s in liquid at 1:30• Quickly pull both PT 1000’s out of liquid at

2:30 • Measure response time

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Circuit #1 – Liquid Nitrogen

Both Out

Both In

Both Out

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Circuit #2 – Liquid Nitrogen

Both Out

Both In

Both Out

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Circuit #2 – Liquid Argon

Both Out

Both In

Both Out

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Two Jump Test

• Lower PT 1000’s into liquid• Using only LabView Interface, stop apparatus

when 1 PT 1000 is in liquid• Repeat lifting out of liquid• Verify location of PT 1000 visually

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Circuit #1 – Liquid Nitrogen

Both Out

Both Out

One In

One In

Both In

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Circuit #2 – Liquid Nitrogen

Both Out

Both Out

One InOne In

Both In

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Circuit #2 Liquid Argon

Both Out

Both Out

One InOne In

Both In

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LN vs LArLiquid Boiling Point

(K)Density at B.P. (g/mL)

Surface Tension at B.P. (mN/m)

Nitrogen 77 0.807 8.94

Argon 87.3 1.40 14.19

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Level Test

• Three sets of PT 1000’s on outside of plexiglass cylinder ring

• Level using three strings that suspend the ring above liquid (like a puppet)

PT 1000’s

Blue string used to hold ring up

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Boil Off Test with Ring (not leveled)

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Attempt to Level Resistors and then Boil off LN2

1. Trying to level ring by pulling on individual strings until one resistor was in the liquid and one was out of the liquid ~3.7 V

2. All three resistors around same level

3. Wiggled all three cords to see if they responded

4. Re-leveled all three and let sit to boil off liquid

5. Boil off points were different for all 3 sets, design set-up was not ideal, resistors were not all exactly 1 mm apart, not exactly on same location around the ring