Tracking time for instruments measurements in a buffer?

[bdonius]

I have a group of four current meters that I'm trying to get high rate of data acquisition out of. I have done this by using the instruments buffer to take a 1000 readings on one command and then import the information back at once rather than taking each reading one  at a time. However by doing this I no longer apear to be able to track the time at each measurement is taken. Is there any way to track the time of data acquisition within a instrument buffer? I am using two Agilent multi meters and two Keithly meters and neither set of drivers appears to have this option. By accessing the drivers sub VI database I was able to find a node marked "time stamp " however if I try to wire this the visa address  wire becomes broken. If I disable the database access the time stamp wire becomes broken. I do not have access to my code to post it here as it is considered private information. Any thoughts would be most welcome.

Thanks     

[Dennis_Knutson]

Getting a timestamp from the instrument is a function of the instrument. Some instruments have an internal clock and some don't. You need to look at the manuals to see if there is such a thing. You haven't provided the model numbers of the4 instruments and I doubt that is proprietary.

Otherwise, use the date/time function in LabVIEW to generate a timestamp and use the scan rate you specify for the instrumets to create your own array of timestamps.

Another option, and one that would give you much faster scan rates (magnitudes higher), would be using a single DAQ card. An NI DAQ card and it's software will generate timestamps.

I have no idea why you would try the 'enable database access' option. Have you read theLabVIEW help to see what this does?

[bdonius]

The instruments are an Agilent 34410A Digital Multimeter and a Keithly Model 6487 Picoammeter/Voltage Source. Neither of the manuels make mention of a time stamp capabilty. The system is going through a single DAQ card but to process a reading from each instrument without using a buffer system takes .5seconds while buffering the data I can get the rate down to .02 seconds. Without having an associated time this data is next to useless. The enable database access was only an option I was considering it seems odd that you can see a node to get time information from the sub VI but not atcually use it and the documentation on this feature is nearly non-existant. I will not be able to try your suggestion until monday I will see how it turns out. 

[Albert.Geven]

If using the internal clock od a keithley multimeter, be sure to use it relative to a starting time in the pc.

I've seen differences of more than 20 seconds over a day between two different multimeters.

[Dennis_Knutson]

Actually, the documentation on the database access is quite extensive and if you would read the on-line help, you would see it has absolutely nothing to do with getting time information from a VI.

A 20 msec scan rate is pretty fast for a GPIB instrument. It is extremely slow for a DAQ card. 

Could you explain what you mean by the system is going through a single DAQ card

[bdonius]

All four instruments GPIB cables are stacked on one national instruments interface card to the PC. Its possible the information regarding the enable database access was limited as my computer at work is a stand alone machine and not internet capable.         

[Dennis_Knutson]

Okay, you don't have a DAQ system available at all. You just have a system that can acquire some data.

[ivkicin]

The 6487 Picoammeter of Keithley have a timestamp with de SCPI command:

:FORM:ELEM READ,TIME;

With this, we have a read of current (I) or resistance (Ohm) and the reading time.

There is somehow to syncronize in time two devices?

[ShishKeBobby]

Hi ivkicin,

Could you be more specific?  I would also recommend posting this question in a new thread as this thread is from 2009.

[ivkicin]

Hi, I want to take measurements of current with two devices Keithley, the 6487 and the 6517B.

The question is: Can i syncronize this devices? i.e. take a measurement at the same time with this devices.