How to increase the speed of measurement

[zhaosir]

Hello everyone,

I need to use a Keithley 2450 to apply a DC voltage and an SR 830 Lock-in to measure AC signals. In my case, I need to continuously change the DC voltage and have a real-time measurement of V-I DC from Keithley 2450 and V AC from SR830. The picture below shows Keithley 2450 code. The small while loop on the left gives a series of DC voltage. In the large while loop on the upright, for each iteration, a V DC is applied, a current value is measured and the values of time, V and I are input into a queue for plot a graph and maybe some other process in the downright while loop.

For the upright while loop, every iteration takes 43 millisecond, which is quite long. What can I do to reduce this time? 

Thank you.

Zhu

[GerdW · Accepted solution]

Hi zcchina,

For the upright while loop, every iteration takes 43 millisecond, which is quite long. What can I do to reduce this time?

43ms is rather short I guess: you have an external DAQ device connected by a bus (serial?, GPIB?, LAN?). The communication takes time, the command processing in the device takes time, the measurement itself takes time. Atleast the last usually is mentioned in the Keithley manuals!

To improve measurement time you could decrease measurement resolution of the K2450…

[zhaosir]

Hello GerdW,

Thank you!

In my case, Keithley 2450 is directly connected to the computer by the usb connection. I have also tried with a GPIB connection. Both take 43 millisecond.

I found some guy has got a much higher speed, about 60 points/sec(see http://forum.keithley.com/phpBB3/viewtopic.php?t=78440)

Are there any improvements for the structure or measure scheme of my code?

BTW, how to lower the measurement resolution of K2450? Lower the NLPC?

Zhu

[GerdW]

Hi zhaosir,

are you the same as zcchina? Are you working as tag team?

Both take 43 millisecond.

So time need is driven by execution speed (of Keithley) and measurement time…

I found some guy has got a much higher speed, about 60 points/sec

In the link things like disabling autorange is mentioned. Have you tried that?

how to lower the measurement resolution of K2450? Lower the NLPC?

It's all in the manual of your K2450. Did you read it? Keithley usually supplies very good manuals, explaining all commands with all their options…

[zhaosir]

Hello GerdW,

Same guy. I just changed ID.

The auto range is off. But I dont change the default  NLPC. I think maybe that makes a difference.

The manual is so long, especially the reference manual. I just ctrl+F to go through the ref manual...

Regards

Zhu

[crossrulz · Accepted solution]

Things that typically help acquisition speed (some may not apply to this instrument):

• Turn off the display
• Turn off autozero
• Turn off autorange
• Lower resolution
• Lower NPLC (Number of Power Line Cycles) used to take measurement

[zhaosir]

Hello GerdW,

I have changed the NPLC from 1 to 0.5, one iteration time are reduced to 23 ms. I also tried to turn off the display, which made little difference.

Thank you agian.

Best

Zhu

[zhaosir]

Hello crossrulz,

I changed a lower NPLC (from 1 to 0.5). One iteration time changed from 43 ms to 23 ms.

Thank you.

Zhu

[billko]

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@zhaosir wrote:

Hello GerdW,

Same guy. I just changed ID.

The auto range is off. But I dont change the default  NLPC. I think maybe that makes a difference.

The manual is so long, especially the reference manual. I just ctrl+F to go through the ref manual...

Regards

Zhu

---

Kids and their attention spans these days.  😉

You can't tell me a manual is long unless it's longer than those hairy several-hundred page long HP/Agilent manuals!  I think I read one that weighed in at over 500 pages!!!  (Although i will say that those manuals are worth the read if you can sit through them.) 😄

[zhaosir]

Actually the Keithley 2450 reference manual is over 1000 pages long