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Thermometer wires in Fridge4

V.Zavjalov, 2020

wiring DXF(wires)

Replacing thermometer and heater wiring in Fridge4. The plan is to convert 3-wire measurements to 4-wire ones (and use new computer-controlled LakeShore resistance bridge), add low-pass filters.

Following wires are to be done:

• 32 twisted pairs for LakeShore resistance bridge (model 3716 scanner supports sixteen 4-wire channels). Wires should go inside vacuum can. Maximum frequency 15Hz, resistive load - up to 10 kOhm (?)
• 8 twisted pairs for low-power heaters (still, mixer, cell). Wires should go inside vacuum can. Maximum frequency below 1Hz, load resistance 100-1000 Ohm.
• 8 twisted pairs for bath resistors. There are 10 bath resistors with 1+10 wires. the plan is to keep this scheme. Wire resistance should be minimized.
• Extra 8 twisted pairs in the vacuum can feedthrough.

Wires from device rack to the filter box

Six cables LEMO FGG.2B.316 to DSUB 25, with same pinout compatable with LakeShore resistance bridge. Each one contains eight RG174 coaxial lines inside the single copper shield. Four cables have length 150 cm, they should go to the resistance bridge scanner mounted on the cryostat flange. Two has length 300(?) cm, they go directly to the device rack.

Copper shield (12x2.3mm): RSN(365-559), plastic cable wrapping (I.D. 10.3mm): RSN(811-7695)

LEMO FGG.2B.316

DSUB 25

Filter box

A box with vacuum-tight connectors for 6*16 = 96 wires to be put on the cryostat flange.

Filter box, drawing for workshop DXF(conn_box1)

Drilling additional holes, drawing for workshop DXF(conn_box2)

Filter boards was ordered in https://www.multi-circuit-boards.eu (20x130mm, FR4 1.55mm, 76EUR for 12 boards): KiCAD project, Gerber files for ordering.

Screw-in KF16 flange and 50 cm metal hose was ordered in https://en.wissel-vakuum.de/. Flange central hole was drilled to 10mm diameter.

filters

Lemo connector for the filter box

Lemo connectors for the filter box, before filling with stycast

filters

filters

filters

installing filters and Lemo connectors in the box

Wires from filter box to the cryostat

Six cables with 8 twisted pairs in each, Eureka wire, 40swg (0.122mm), length about 200 cm, resistance 86 Ohm/wire. Harwin M80-85016* connectors on both sides (see also here).

constantan twisted pairs

wires

Vacuum can feedthrough

Main feedthrough parts have been done in ULT workshop: 7mm CuNi tube with sharp edge, brass adapter hard-soldered to the tube, small vacuum can for testing. Plastic parts have been done later by me.

Connector boards was ordered in https://www.multi-circuit-boards.eu (56x44mm, FR4 1.55mm, 73EUR for 12 boards): KiCAD project, Gerber files for ordering.

Wires was organized in 6 bundles with 8 twisted pairs each and soldered to the connector boards (Harwin M80-85316 16-pin connectors). Feedthrough was filled with Stycast-1266 and pumped. It would be better to pump Stycast twice: before and after filling.

Parts, 1st drawing for workshop DXF(vc_feedthrough1)

Parts, 2nd drawing for workshop DXF(vc_feedthrough2)

Parts, done by me DXF(vc_feedthrough3)

connecting six cables together

cables with six Harwin connectors

feedthrough parts (see drawings)

after glueing

assembled feedthrough

testing setup

testing the feedthrough in liquid helium

Connector block inside the vacuum can was done using a standard matrix PCB (RSN(391-7232)), soldered to a copper holder.

making windows in the copper holder

old feedthroughs removed from the cryostat

board is temporary fixed to the cryostat for soldering

All wires are soldered

connectors inside the vacuum can

connectors outside the vacuum can

Lines were measured using a decade resistor at room temperature. Resistance bridge excitation 1 $\mu$A, frequency: 9.8, 13.7, 16.2 Hz. Filters works up to resistance 1 k$\Omega$:

measured resistance vs. resistance

error in resistance measurement