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I am using Labview to control Keithley instruments to function as Hall Measurement System, but I am having some problems as the mobility values I measured are always lower than the values given in wafer datasheet. I think the problem might be inaccurate 2182A measurement values as I always get negative voltage when it is not supposed to be negative. I tried to short the circuit, by connecting ABCD four pins on sample PCD board using wires, and the measurements from 2182A fluctuated from 0.7-2 uV (Current input 10mA) with occasionally negative values, while the 6485 ammeter's values relatively stable. Attached is a screenshot of one result.
The commends for reading from 2182A are "*RST", "voltage:range:auto on",":READ?"
Could anyone give me some suggestions?
- Shorted 10mA4.JPG (140.45 KiB) Viewed 12386 times
- Keithley Applications
- Posts: 2849
- Joined: June 10th, 2010, 6:22 am
- Country: United States
Disconnect the 2182A channel 1 HI and LO from the sample.
Connect the low thermal short to the input of the 2182A channel 1 HI and LO.
Select 10mV range.
Press the REL button on the 2182A.
Should see less than 70nV (0.07uV) of noise after a two hour warm up.
Step two. Check it with the cable.
Place the input cable on the front panel terminals.
Short it at the end of the cable.
Select the 10mV range.
Press the REL button.
Should notice some more noise as the cable it - up noise. Mark this down. as a baseline.
Step three. Check it with the cable connected to the HALL sample. No current source, just the sample.
This is where you should see the noise and offset voltage of the system.
Now press REL and should see almost zero on the display.
Step four. Check it with the current source applied.
Now source the amount of current to produce the HALL voltage.
That should help narrow it down for you.
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