watchdog in GPIB

[Blokk]

Hi!

I am looking for the best solution for the following task:

I have a Win7 + LabView 2011, my LAbView program controls several Keithley sourcemeters, and nanovoltmeters. In any windows system failure, the LabView program stops controlling the sourcemeters. It means that, the sourcemeters will continue running with the last power output. This is an undesirable case. What is the common solution for this? Is there a kind of watchdog methode, to reset or shut down keithleys?

Thanks!

[MHoffmann]

Hi,

I am not sure about the state of a keithley device if there is a system problem. The National Instruments DAQ board outputs e.g. will remain unchanged until you reboot your computer. Upon reboot, the DAQ board will return to its default state. So you could ask Keithley if their devices react the same way. 

So the only solution with daq boards is to reboot the computer. 

What Happens to My DAQ Devcie Outputs When My PC Locks Up or Crashes?

http://digital.ni.com/public.nsf/allkb/B88DF3A8EEBD943E8625698400736EE3?OpenDocument

Best regards,

Michael 

NIG

[Blokk]

I think I have found the most simple solution for this:

I will buy an RS-232 watchdog timer relay circuit (approx. 50 dollars with cables), and from my LabView program I will send periodical RS-232 signal via the serial cable from the PC to this watchdog circuit board. If this continous signal stops, then the relay will break the connection at the output from the Keithley source meters. (I think better to cut the Keithley's output, instead of its power supply).

In this way, my system is safe in any Windows/LabView hang-up/crash.

[MHoffmann]

Hi, 

sounds good, I think this might work!

Regards,

Michael

NIG

[johnsold]

Blokk,

A hardware watchdog is usually the best when dealing with non-deterministic OSes.

Do you mind telling us the brand and model of the RS-232 watchdog device you found?  Questions about watchdogs and similar safety issues come up on the Forum quite often.  It would be nice to be able to refer others who are intersted to this thread.

Thanks,

Lynn

[Blokk]

Hello,

Actually I did not order anything yet, I am still searching the net for a EU located company, who sells a usable watchdog device.

I am looking for a ready to use "out of the box" device, it means, it has the RS-232 interface, the watchdog timer logic, and also 1 ore more relays with two modes (normally close, or normally open).

So far I have found a device what is relatively cheap, and looks like okey for the task I want to use it for:

http://www.industrologic.com/uwdtdesc.htm

This company is located in USA, so it is not suitable for me (the postage would cost more then the product), since I recently work in Germany.

If anyone can give me a link for a product or company, I would be happy 🙂 So I really look for something ready to use, I do not want to bother with relay attaching, microcontroller programming, and so on...The only work I would like to do with such a device, is to connect to my PC with RS-232, hook its relay to my Keithley's current output line, and I can start to send the TTL watchdog signals from my LabView program...

By the way, I wonder why the Keithley source devices do not include a GPIB watchdog option? I guess there must be smart engineers at Keithley, and they just do not think about such a simple but very useful feature in their products??? 😞

It would be VERY simple to use such a sourcemeter: there could be a menu settings, lets say: "Max allowed GPIB dead time in seconds" for example. If this menu activated, then the Keithley device would shut down its output after the given dead time, so if the PC or the software hangs-up, or locks-up...

[Blokk]

Okey, I am just asked for a quotation from a company who can make the desired watchdog electronics for my project.

Actually the system will be more sophisticated: we will not put the relay on the output of the Keithley, but there is a digital I/O port on the rear of the Keithley 2400, and the watchdog relay will control the "Output enable" digital input. I have to watchdog control also a Sorensen current generator (15 amperes output), and in this case also a digital port on the device will be used to disable the output (a relay on the output could kill the device electronics) ...

[johnsold]

Thank you for the link.

I am glad that you are finding some options which may work for you.

I have no connection with Keithley, although I heard Joe Keithley speak once.  My guess is that Keithley engineers tend to think about measurements in a laboratory environment with the scientist or engineer supervising the experiment.  Watchdogs are much more common in industrial and process control applications.  What you request would not be difficult for Keithley to implement.  Perhaps you should suggest it to your Keithley representative.

If you have a PLC or other industrial controller availabel, check to see if if has a watchdog timer.  Many do.

Lynn