Sampling rate, time base for Tektronix DMM 4040 and DMM 4020

[hcastor]

Hello,

I'm using the Tektronix DMM4040 with LabView Signal Express Tektronix Edition. When logging time-dependent data from the DMM4040, the results are displayed as a function of the number of 'iterations'. How can I correlate the number of iterations with the time (e.g. since the beginning of the log) ? When a duration in seconds is defined as a stop condition for the log, the logging terminates at the number of iterations, not the number of seconds. If, for instance, a duration of 30 s is specified and the sampling rate is approximately 2 iterations per second, execution terminates after 15 s, not 30. This is clearly a malfunction of the software.

I would like to able to record my data as a function of time directly, ideally without having to manually convert iterations to seconds. As far as I can see, there is no way how the software could tell me how many iterations correspond to a second.

I hope someone can help ...

With many thanks in advance !

[hcastor]

Hello,

I'm using the Tektronix DMM4040 with LabView Signal Express Tektronix Edition. When logging time-dependent data from the DMM4040, the results are displayed as a function of the number of 'iterations'. How can I correlate the number of iterations with the time (e.g. since the beginning of the log) ? When a duration in seconds is defined as a stop condition for the log, the logging terminates at the number of iterations, not the number of seconds. If, for instance, a duration of 30 s is specified and the sampling rate is approximately 2 iterations per second, execution terminates after 15 s, not 30. This is clearly a malfunction of the software.

I would like to able to record my data as a function of time directly, ideally without having to manually convert iterations to seconds. As far as I can see, there is no way how the software could tell me how many iterations correspond to a second.

I hope someone can help ...

With many thanks in advance !

[chris88]

Hi hcastor

How are you configuring the steps?

Are using continuous samples, number of samples, scales?

All this is to help you further!

[hcastor]

Hi Chris

Thanks for your reply.

There isn't much to configure ... settings for the data transfer(baud rate etc.) as in the manual.

Logging with default settings for continuous acquisition of DC voltage and DC current.

No settings for start/stop conditions,i.e. the logging is triggered manually by clicking 'run' and stopped manually.

The settings for the scales have no effect on the data acquisition rate. And I have checked it hundreds of times - whatever you do to the scales or the time stamp, you don't get seconds out. Actually, setting the time stamp to 'absolute' does ... nothing. If it did work, it would be a simple matter to assign a time in s to each measurement.

There is no possibility to define a sampling rate. With default settings for voltage measurement, I get a sample every 0.64 s (approximately).

When using  'playback', SE treats each measurement cycle as if they were seconds (i.e. it assumes as constant sampling rate of

1 measurement per second). Highly misleading !

Instruments and measuring gear worth thousands of $ and having to determine the duration of a log with a 10$ stopwatch, it's ridiculous. Not to mention that it takes about 10 s between hitting the 'run' button and the moment the logging actually begins. The DMM 4020 is somewhat faster, though. The only option seems to be to start the logger, and once it is running, begin with the measurement and subtract the idle time at the beginning from the time axis.

The simple logging of data as a function of time is the single most fundamental and straightforward functionality that logging software should provide...

[chris88]

Hi hcastor

Using plain SE I wasn't able to reproduce your behavior so could you please attach a screenshot that represents the issue? 

[hcastor]

Hello Chris,

many thanks for getting back to this.

I don't mind sending a screenshot, but I don't know what it should show to illustrate the problem :

All  I need to know is how to get the software to display the time in seconds on the horizontal axis of the graph.

I have gone through all the menus and options and I can't find a possibility to do this. Maybe there isn't one ?

N.B. I don't mean simply changing the axis labels, I need to convert the units of the abscissae from iterations to seconds.

All I can do at the moment is measure the duration of the log using a stopwatch and then perform this conversion, which won't be very precise...

Thanks again,

I'd love to post a screenshot if you tell me what you want to see...

marc

[chris88]

Hey hcastor

Have you tried downloading the step for the dmm 4040 available at this link:

http://www.tek.com/digital-multimeter/dmm4050-4040/dmm4050-software/labview-signalexpress-step-dmm40...

[hcastor]

Thank you.

Yes, I've done that. It makes no difference.

There does'nt seem to be a possibility to display data as a function of time, which I find very diffult to believe, as this is the most important and basic functionality that logging software should have. All the wonderful analysis functions of SE are useless without this.