Convertion of a 920 Series Hall system from DC to AC

[suhridkhan]

Hello,
I have an old 920 series Keithley DC Hall measurement system. It is equipped with a 705 series scanner with 7065 Hall card, 220 current source and 196 DMM.
My plan is to measure cadmium telluride samples with resistances upto 100 Mega-ohm.
Could anyone please suggest the possibility of converting the system for AC measurement by adding a AC current source and/or lock-in amplifier?
Thanks.

[Dale C]

Certainly the Model 6221 AC current source from Keithley could be used instead of the Model 220 current source.
I will have to check on it to be sure.
I will post when I have the complete answer.

[suhridkhan]

Thanks for a quick reply. I look forward to hearing from you.
Another thing is that, the magnet is powered by an 'Oxford Instruments magnetic power supply'. Please give me some options to make the magnetic field Alternating.
The magnet coil has a cold resistance of 90 ohm, and maximum current rating of 1.1A per coil (water-cooled). I am thinking that a stepped-down 60Hz line voltage can be used to power the magnet.

[Dale C]

The 6221 has a KI-220 Language mode. I would suggest that you obtain a demo of the 6221, put it in the 220 language mode, and then run the 920 software. The 220 Language mode is in Section 15 of the Model 622X manual.

In order for you to replace the 196 with a lock-in amplifier, you would have to rewrite the code.
It was written in an old programming enviroment called Assyst. Probably very difficult to do as there is no one here that knows that old system.

[suhridkhan]

I am not a programmer myself. In that case, my option is to run the system manually without the 920 system, controlling and reading the data form the modules directly. Then i need to calculate the parameters outside.
Do you anticipate any problem for the 705 scanner (with 7065 Hall card) to pass the AC signal without noise?

[Dale C]

The only bandwidth specs on the Model 7065 are fo voltage noise and it is stated at 0.1Hz to 10Hz.
So you should be good to that. But above that is not specified.

[suhridkhan]

Thanks Mr. Dale for the useful information.
Another suggestion I shall ask from you is - does Keithley have a magnetic field measurement device? I am going to need a way to measure the AC magnetic field, as I power the magnet with AC supply. If not, can you suggest one? Thanks.

[Dale C]

Sorry. Keihtley does not have magnetic field measurement device.

[suhridkhan]

No problem. One more question for you please.
On the 920 series manual, it was mentioned that Keithley could provide calibration sample for hall measurement. I am aware that any information on this very old manual can be long outdated.
Could you please let me know if Keithley have any calibration sample that could be used on the sample stage of our 920 series system?
Thanks.

[Dale C]

Sorry, no calibration sample from Keithley.