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question on 6221 Delta Ohms reading

Posted: October 9th, 2014, 5:54 am
by hachiko
I just found a problem when I measured Hall resistance. With Delta Ohms reading, 6221(together with 2182A) always gives positive values (Ohms). As you know, Hall resistance should be negative on reversing magnetic field.
Does 6221 automatically make the absolute values when Delta measurement unit is Ohm? And Is there the same problem with differential conductance (dV/dI)?

Re: question on 6221 Delta Ohms reading

Posted: October 9th, 2014, 6:09 am
by Dale C
Delta mode will always show a positive reading.
This is because the delta mode uses two voltage readings to calculate the delta mode reading.
The delta mode sources a positive current and takes a voltage reading.
The it sources a negative current of the same magnitude and takes another voltage reading.
Then some algorithm that is described in the 6221 and 2182A manuals is performed.
Then the delta mode reading is displayed.

Re: question on 6221 Delta Ohms reading

Posted: October 9th, 2014, 6:31 am
by hachiko
Do you mean even if the Delta measurement unit is Volt, it gives always positive reading?
If so, that will be a pity. Because, if one has the connection order of I+ V- V+ I-, one would not get the correct signal of this order.

Re: question on 6221 Delta Ohms reading

Posted: October 9th, 2014, 6:47 am
by hachiko
See the attached figure from the manual.
The 2182A A reading could be negative at I-high, and B reading could be positive at I-Low, if you have the 4 contacts on a resistance in the order of I- V+ V- I+. So with this Delta algorithm, the Delta voltage reading could be negative.
Delta.PNG
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Delta.PNG (35.43 KiB) Viewed 19148 times
As for Delta Ohm reading, according to the manual (see the snapshot from the manual), it could be negative too. I don't know whether there is any other details in the manual.
Ohm reading.PNG
Ohm reading.PNG (18.25 KiB) Viewed 19148 times

Re: question on 6221 Delta Ohms reading

Posted: October 9th, 2014, 12:59 pm
by Dale C
:oops:
I guess I have never considered using negative values for the high value.
So you are correct.
I have never run into such an application. Therefore, I have never seen a negative value for delta.
Thanks for pointing it out.
Not sure how that relates to your HALL effect issue.