pBN VT heater test

Test of VT pBN heater plate

• Remove old sample, re-attach top plate, verify thickness of assembly and heater brushes
• 7.6 mm total, 2.9-3.0 from top of brush to bottom of top plate
• 17 ohm left brush (seen from handle) to ground. Right brush grounded.
• Sample Heating Selector to "Direct Current"
• Initial 1.6 V at 0.16 A (10 ohm), gentle pressure rise, manipulator TC increases linearly with time 22 to 28 C over 6 minutes, 0.25 W
• Next 3.24 V 0.40 A 1.3 W 8.1 Ohm
• 4.49 V 0.65 A 2.96 W 6.7 Ohm, temp rises slowly with time
• 5.73 V, 1.04 A, 5.96 W 5.7 Ohm, current rises to 1.18, pressure low 1e7 outgassing
• More tests
• Set 6.26 V 1.05 A Monday 9:23 am
• by 10:14 current limited at 1.49 A, 5.7s C 8.5 W, stage at 270 C
• pressure rose to 1e-7 then down to 2e-9
• increase current to 2.01 A, initial 7.43 V drops to 7.23 steady state, 14.5 W
• stage steady state 332 C. pBN heater uniform "cherry red" 
• contact bars also hot, darker red
• heat shield, top plate, sample straps do not glow
• pressure has dropped to 1e-9
• Set 1.49 A, 5.55 V increases to 5.70, initially 3.72 Ohm -> 3.83
• heater "incipient red" just at visible glow threshold
• steady state base 280 C
• 8.5 W

Photo of heater at 14.5 Watts, pBN "cherry red"

Approximate sample temp vs power for pBN VT holders