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Minimal current pulse during memory sweep & transient effect

Models 2400, 2401, 2410, 2420, 2425, 2430, 2440, 6430
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zsanta
Posts: 4
Joined: May 30th, 2011, 3:47 am
Country: Hungary

Minimal current pulse during memory sweep & transient effect

Post by zsanta » May 30th, 2011, 7:37 am

Hi all,

I need to output a bipolar current waveform with a 2410 Sourcemeter (75Hz frequency, high value: 900mA, low value -900mA, dc offset preferably 0A). I'm doing a memory sweep for these to setpoints with variable source delay settings. I need only source functions, so all sense functions are turned off. (The measurement can tolerate some degree of difference from the ideal square wave...)

Problem1: The minimal pulse width for 0sec source delay setting remains to be 1.3msec. According to the user manual, and an application note the minimal pulse width is defined by a firmware overhead time, and is 640usec. I tried to turn all "auto" function, and measurement off but maybe I'm missing something.

The settings I use for a setpoint are:

:SOUR:VOLT:PROT 20;
:DISP:ENAB OFF;
:SOUR:FUNC CURR;
:SOUR:CURR:RANG 1;
:SOUR:CLE:AUTO ON;
:TRIG:DEL 0;
:SENS:FUNC:OFF 'VOLT','CURR','RES';
:SYST:AZERO:STAT OFF;
:SOUR:CURR -0.9;
:SOUR:DEL 0;
:SOUR:MEM:SAVE 2;

For generating the waveform I use the following instructions:

:SOUR:FUNC MEM;
:SOUR:MEM:POIN 2;
:SOUR:MEM:STAR 1;
:ARM:COUN INF;
:TRIG:COUN 2;

:TRIG:CLE;:INIT;
.
.
.
ABOR;:TRIG:CLE;

Problem2: During output change the resulting current settles to zero for a limited amount of time (1.1msec). I guess this behaviour is defined by the output stage hardware, but is there any way to get rid of it?

Thanks in advance!

zsanta
Posts: 4
Joined: May 30th, 2011, 3:47 am
Country: Hungary

Re: Minimal current pulse during memory sweep & transient ef

Post by zsanta » June 8th, 2011, 7:21 am

Hi,

Could someone answer these questions?

Thanks!

Jeremy G
Keithley Applications
Keithley Applications
Posts: 76
Joined: April 29th, 2010, 7:56 am
Country: United Kingdom

Re: Minimal current pulse during memory sweep & transient ef

Post by Jeremy G » June 10th, 2011, 3:51 am

Hello zsanta,
There is an Application note explaining how to pulse with the 2400 series at the following link:

http://www.keithley.com/support/data?asset=14414

I tried this method for your 75Hz square wave and the SCPI commands are below:

*RST
:SYST:AZER:STAT OFF
SOUR:FUNC:MODE CURR
SENS:VOLT:PROT 10
SENS:VOLT:NPLC 0.01
SOUR:LIST:CURR 0.9, -0.9
TRIG:COUN 20
SOUR:CURR:MODE LIST
TRIG:DEL 0.0024
SOUR:DEL 0.0024
OUTP ON
INIT
*WAI
OUTP OFF

Adjust the delay times to achieve the pulse train you require.

zsanta
Posts: 4
Joined: May 30th, 2011, 3:47 am
Country: Hungary

Re: Minimal current pulse during memory sweep & transient ef

Post by zsanta » June 14th, 2011, 10:03 am

Hi Jeremy,

Thanks for the answer. I still need some clarifications.

1. Actually I am already doing some similar method by programming setpoints to the memory and doing a memory sweep. My problem is: no matter what I do the minimal pulse width remains to be 1.3msec with 0sec delay settings, while the application note you copied says 640usec for minimum. Of course its suitable for generating a 75Hz square wave, I am just concerned about overlooking something, which might affect long term supportability of my application.

2. During value change (from 0.9A to -0.9A and vice versa) the current flowing in my circuit settles to zero for a short amount of time. I guess its caused by hardware layout of the output of the Sourcemeter (bridge connection capable of 4 quadrant operation I guess), but I need confirmation for long term supportability. (It would be fantastic to remove this effect if any way exists.)

I know I'm using this device somewhat outside of its specifications, but even with the uncertainties described above its a really good feature. :)

Thanks in advance!
Zsolt

Andrea C
Keithley Applications
Keithley Applications
Posts: 1389
Joined: October 15th, 2010, 10:35 am
Country: United States
Contact:

Re: Minimal current pulse during memory sweep & transient ef

Post by Andrea C » June 17th, 2011, 4:34 am

Hello,

I think the 1.3 msec timing that you are seeing is due to the additional overhead of the source memory list and the use of multiple arm events. Look at figure 11-3 in the 2400 Manual for a flow chart of the remote trigger model. The app note you reference was staying in the trigger layer for the finite number of pulses while your loop is in the trigger layer for count of 2 and then comes back up to the arm layer.

For the current settling to zero in between, it might have to do with the :SOUR:CLE:AUTO ON; Have you tried explicitly turning the output on at the beginning of your loop and let it remain on during each toggle from 0.9 to -0.9? And then on exit from the loop turn it off?

Andrea

zsanta
Posts: 4
Joined: May 30th, 2011, 3:47 am
Country: Hungary

Re: Minimal current pulse during memory sweep & transient ef

Post by zsanta » June 20th, 2011, 8:59 am

Hi Andrea and Jeremy,

The explanation about the timing overheads makes sense. So far it seems to be more convenient to use both the trigger and the arm layers to do continuous generation so we will
deal with the 1.3msec timing overhead.

About the behavior around zero: I set ":SOUR:CLE:AUTO OFF" instead of ":SOUR:CLE:AUTO ON" and turned the output on\off manually, but the behavior remains to be the same. I tried however to use the programing sample provided by Jeremy and the time which my signal spends around 0A drops to 0.43msec instead of 1.1msec. So maybe this behavior is not defined by hardware, but by the timing overheads present during output value change.

Let me know if there is any way to further decrease the time my signal spends around zero amps, otherwise thank you very much for your help.

Best Regards!
Zsolt

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