Switching speed slowed down

[ChaeS]

I am using a GPIB card to measure voltage of a set of samples as a function of time by using a switch system. In a normal condition, it reads one voltage per second, roughly speaking. However, the switching speed sometimes slows down terribly so that it reads only one voltage in 10-20 seconds. How can I fix this problem?

[JasonSmith]

Hi ChaeS,

To clarify the configuration of your system, does it consist of two devices (A switch and a data acquisition device), or a single data acquisition device which performs its own switching?  What are the make(s) and model(s) of the device(s) you are using?

Are you using an instrument driver for this device, or are you programming it using direct VISA or GPIB calls?

The following information may also be useful:

1. Which GPIB adapter are you using?

2. Which version of NI-488.2 and NI-VISA are installed (If using a NI GPIB adapter)?

3. Which operating system/development environment are you using? (such as Windows XP with LabVIEW 8.0.1)


Please answer all of the questions above and we will see if we can suggest any possible sources of the problem.

Jason Smith
Applications Engineer
National Instruments

[ChaeS]

Hi JasonS,

Our GPIB card (NI PCI-GPIB IEEE 488.2) is connected to three Keithley switch system (due to the testing capacity), a Keithley multimeter and a HP power suply. We are using LabView 7.1 to control the whole system. A former student in our group programmed it. The driver version of the PCI-GPIB that I read in Control Panel is 2.2.0.3500. The operating system is Windows 2000.

[JasonSmith]

Hi ChaeS,

Although I do not think it is the source of the problem, I would recommend downloading and installing NI-488.2 version 2.4 from our website, along with NI-VISA 3.6 (If you are using NI-VISA).  The next step I would recommend you take is to use the NI-Spy utility to capture the driver calls made when you are experiencing the slowdown.

By looking at the calls captured by NI-Spy, we should be able to tell if your application is introducing the delays between driver calls, or if the driver calls themselves are taking a long time to complete.  You can find instructions for performing a capture using NI-Spy in this KnowledgeBase.

Once you have captured the driver traffic, double clicking on any line will give you the timing details to let you determine how long the call took.  You can also save the .spy file and attach it to a post here and we can help interpret what you have captured, but we may need you to point out lines which correspond to the delays which you are seeing.

Jason Smith
Applications Engineer
National Instruments