speed of measurements using LABVIEW, HP34970A, RS-232 cable and a pentium 4 CPU 1.6GHz 512RAM

[Ruudje]

Hi all,

I´m currently doing some measurements with a type T thermocouple. Currently I get 1 value every second and I can´t figure out how to get more measurement samples per second. Is the system the problem or Should I change some settings in LABVIEW?

Regards Ruud Verschaeren

[Ruudje]

This is the file I´m working with. Trough a SISEA board i also collect some voltage signals. This is the signal I want to read in high frequency, can someone please help me?

Regards, Ruud

[BEHajder]

Try reducing the value of the constant you have set to 1000 that is connected to the "Wait Until Next ms Multiple" function in your while loop. This causes the loop to execute once per second. Reducing the constant to 250 will cause the loop to execute 4 times per second. See if that increases your sample rate.

[Joe_H]

Well as it is right now your program has a wait function in it that has a value of 1000 wired into it. This means that the loop that it is in will only run once per second. If you want the loop the run faster then change the time for the wait function. I would set it to about 10mS, this will give you about 100 samples per second.

[johnsold]

Ruud,

One reason you only one reading per second is the Wait until next ms multiple function in the while loop in frame 1. It is set for 1000 ms, so the loop will not run any faster than that.

Another factor may be the time it takes for the instrument to return a reading. I am not familiar with that instrument. Some instruments take tens to hundreds of milliseconds or longer to respond.

Your program can easily be cleaned up by using data flow to eliminate the sequence structures and local variables.

Lynn

[Ruudje]

Thank you for the advice, i set the value to 100 and it worked, however below that value something strange happens:

It returns a value of zero after every measuremant (or after 2 or three depends on the value) 

Regards, Ruud

[johnsold]

If you try to read faster than the instrument can respond, is the Readings string empty? You only report the error from the last iteration of the while loop. Does the HP34970A Read.vi return an error if no data was available? Try replacing the tunnels with a shift register for the error or stop the loop if an error occurs. This may tell you what is happening.

Lynn

[BEHajder]

It looks like if you try to sample too fast you exceed the instrument's ability to provide new data. You will probably have to make the time interval long enough so you don't get any zero data, and that will be as fast as you can sample - unless the instrument has some settings to speed it up.

[LabViewGuruWannabe]

Sounds like you found the solution. In addition, the HP34970's also have a function that reads data into a buffer at a higher rate (that rate depends on the type of channel multiplexer and the number of channels you are scanning). You can then read that buffer at a set time, therefore increasing the number of samples per second, while reducing the number of scans to the device. I don't have the user's guide in front of me, but it explains the commands to do that.

[Ruudje]

Thanks all,

I added some more channels and had to measure even slower. Found in the manual of the HP that if i set the precision 10 times lower (1digit) i can measure 10 times faster. Do I have to do this in the HP itself or is it possible to do it trough Labview?

regards