Tektronix Technical Forums are maintained by community involvement. Feel free to post questions or respond to questions by other members. Should you require a time-sensitive answer, please contact your local Tektronix support center here.

2182A buffer-last reading is duplicate of the 2nd to last

2182 Series Support
Post Reply
jmichel
Posts: 7
Joined: May 2nd, 2012, 9:47 am
Country: United States

2182A buffer-last reading is duplicate of the 2nd to last

Post by jmichel » May 9th, 2012, 10:13 am

I am trying to do simple sweeps using a 2400 and 2182A and a trigger link cable, controlled using Labview 8.0 and GPIB.

When I read the buffer from the 2182A most of the time, but not always, the last two readings in the buffer are the exact same reading, as in they are both positive when one should be negative and not exactly the same magnitude. Somehow the second to last reading is being duplicated in the buffer. For the time being I just tell Labview to remove that point, but I'd like to know why it's happening.

jmichel
Posts: 7
Joined: May 2nd, 2012, 9:47 am
Country: United States

Re: 2182A buffer-last reading is duplicate of the 2nd to las

Post by jmichel » May 9th, 2012, 12:46 pm

It seems that may have "solved" the problem. By doing :TRAC:CLE and then asking :TRAC:FREE? I get the message 18432,0\n meaning that there are 18432 total usable bytes in the buffer. If I ask for exactly that many bytes when asking :TRAC:DATA? I get all points as they should be every time (so far).

jmichel
Posts: 7
Joined: May 2nd, 2012, 9:47 am
Country: United States

Re: 2182A buffer-last reading is duplicate of the 2nd to las

Post by jmichel » May 9th, 2012, 1:13 pm

Nope.

I was wrong. It stopped doing it for a while, but it's right back to doing it again.

So this is still an unsolved issue. :|

jmichel
Posts: 7
Joined: May 2nd, 2012, 9:47 am
Country: United States

Re: 2182A buffer-last reading is duplicate of the 2nd to las

Post by jmichel » May 9th, 2012, 2:03 pm

I think I've finally got it now.

After the buffer is read, if I take it out of trigger mode with :TRIG:SOUR IMM I get all the data points on the next sweep.

If I don't do that, on the next sweep the 2nd to last data point is duplicated. If I do it, the next sweep runs fine. 8-)

jmichel
Posts: 7
Joined: May 2nd, 2012, 9:47 am
Country: United States

Re: 2182A buffer-last reading is duplicate of the 2nd to las

Post by jmichel » May 9th, 2012, 3:02 pm

:x
Ok, that's not it at all either.

What's the deal here?

The only thing that makes the behavior change is if I set NPLC low on both 2400 and 2182A. Or, if I set the trigger delays above a certain time. If I set NPLC levels low and trigger really fast, it won't duplicate the 2nd to last reading. If I set the NPLC of the 2182A anywhere above 2 OR the trigger delay on the 2400 above 0.03 seconds OR the trigger delay on the 2182A above 0.1 second or some combination of any of these, I get the duplicate reading problem.

Can anyone tell me what's going on here?

jmichel
Posts: 7
Joined: May 2nd, 2012, 9:47 am
Country: United States

Re: 2182A buffer-last reading is duplicate of the 2nd to las

Post by jmichel » May 9th, 2012, 3:41 pm

Well, now I feel stupid. :oops:

I believe I finally have the answer. All I had to do was put a really big number for the timeout on the RQS (polling the service request bit) in Labview. What was happening was that sweeps with slow readings were not finished until after the RQS had already timed out. If I just set the timeout to something like 60 seconds (way more than enough time for any sweep to complete) then all the points in the buffer come out fine. Before, I had just set it to something like 10 seconds and forgot about it.

Anyway, hopefully anyone else reading this will learn from my mistakes.

modonnell
Posts: 1
Joined: October 19th, 2012, 2:15 pm
Country: United States

Re: 2182A buffer-last reading is duplicate of the 2nd to las

Post by modonnell » October 19th, 2012, 2:30 pm

I have a related problem with a 2440 SMU: I'm sweeping voltage and reading current, ie, an I-V curve. The last one or two data points in the scan (read from the buffer) are the first few points of the I-V scan!

Post Reply

Return to “Nanovoltmeters”

Who is online

Users browsing this forum: No registered users and 1 guest