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vrf Precision Timing

Question asked by rsb on Jan 26, 2005

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"Pickles, Warren" <Warren.Pickles@tycoelectronics.com> wrote:
> I need to send a particular command to an instrument, wait for a precise
> period of time, then send another command. Problem is, this period of time
> needs to be accurate to the microsecond.

That's not going to happen inside any common desktop OS
using any software solution. That includes Linux, Windows, HPUX,
openBSD, whatever. None of these desktop OS's are capable of
realtime control like you are referring to. Consequently no
software of any flavor running inside them will do the job.

If you really need miscrosecond timing you have two basic choices:
(1) use a realtime OS ( there are quite a few ), in which case
    you won't be using VEE ( or labview or VB, etc).
or
(2) implement a hardware solution controlled by your application
    in a desktop OS. In this case, the realtime control would
    be implemented in hardware that is connected to your computer.
    The VEE program would read/write data to this controller.
    There's many options for buying a realtime controller
    or you could build something yourself.

Desktop OS's are great for lots of things- realtime control is not
one of them.

regards

Stan

--------------------------------------------------------------------------
Stan Bischof Agilent Technologies 707-577-3994 stan_bischof@agilent.com
--------------------------------------------------------------------------

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8 Replies

alex.barrett Jan 24, 2005 10:51 PM
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Warren - just to clarify, what sort of length of time do you need to delay
by, and is the second command a copy of the first, just delayed?

Al.

|---------+-----------------------------------------------------+---------|
|"Beliveau|           Document Marked as Unclassified           |         |
|, Bruno" |                                                     |         |
|<BrunoBel|                                                     |         |
|iveau@sol|                                                     |         |
|ectron.co|                                                     |         |
|   m>    |                                                     |         |
|---------+-----------------------------------------------------+---------|



                    "Beliveau, Bruno"       To: VRF <vrf@agilent.com>
                    <BrunoBeliveau@solect   cc: VRF <vrf@agilent.com>
                    ron.com>                Subject: [vrf] Re: Precision Timing
                              25/01/05
          14:45

          Please respond to "Beliveau,
          Bruno"

          Stationery name:-Untitled-






I guess that even the IO itself is not done within a time period that
accurate. Is there a way to use some external timing to trigger your
instrument?

-----Message d'origine-----
De: Pickles, Warren [mailto:Warren.Pickles@tycoelectronics.com]
Date: 25 janvier 2005 09:37

I need to send a particular command to an instrument, wait for a precise
period of time, then send another command. Problem is, this period of time

needs to be accurate to the microsecond. I imagine this is beyond the
limitations of the delay object. The delay object resolution must be a
function of the resolution of the computer's internal clock (mustn't it?).

This problem is further compounded: I am assuming that the delay between
execution of the commands is exactly the same as the delay between sending
the commands from VEE - a reasonable assumption but probably not true.

What about the "WAIT" transaction in the Direct IO object - is that any
better?

If I can't time that precisely within VEE, what options have I got? Some
external hardware perhaps?

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phakluytt Jan 24, 2005 10:59 PM
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I don't know if this is any help but here it is anyway.

For an application of monitoring a Signal generator's Frequency Drift (over
a 24(25) Hour period), I have required an exact ( i.e. every two seconds,
Rubidium locked) sequence of logging of the phase (in voltage, via a phase
comparator) on a DVM.

I have done this using the SRQ Method ( I/O ... Advanced I/O ... Interface
Event ). The DVM is Externally triggered by the Rubidium (RAPCO GPS
Frequency Standard) 1Hz (1 second) output.

All commands are then sequenced from this event occurring.

The only draw back to this method is that you need to set up the SRQ /
(Staus Byte) unique to the instrument. But with Vee this is relatively
easy.

Hope this helps.

Best Regards,

Phil

-----Original Message-----
From: Pickles, Warren [mailto:Warren.Pickles@tycoelectronics.com]
Sent: 25 January 2005 14:37
To: VRF
Subject: [vrf] Precision Timing

I need to send a particular command to an instrument, wait for a precise
period of time, then send another command. Problem is, this period of time
needs to be accurate to the microsecond. I imagine this is beyond the
limitations of the delay object. The delay object resolution must be a
function of the resolution of the computer's internal clock (mustn't it?).

This problem is further compounded: I am assuming that the delay between
execution of the commands is exactly the same as the delay between sending
the commands from VEE - a reasonable assumption but probably not true.

What about the "WAIT" transaction in the Direct IO object - is that any
better?

If I can't time that precisely within VEE, what options have I got? Some
external hardware perhaps?

Thanks and regards,
Warren Pickles

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alex.barrett Jan 24, 2005 11:27 PM
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>>Problem is, this period of time needs to be accurate to the microsecond.

There is another option which I always favour in these cases.

1. Find a suitable heavy object.
2. Throw it at the person who gave you the impossible requirement.

Not that it always works, but it will make you feel better...

(note: I am not condoning violence)

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warren.pickles Jan 24, 2005 11:37 PM
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I need to send a particular command to an instrument, wait for a precise
period of time, then send another command. Problem is, this period of time
needs to be accurate to the microsecond. I imagine this is beyond the
limitations of the delay object. The delay object resolution must be a
function of the resolution of the computer's internal clock (mustn't it?).

This problem is further compounded: I am assuming that the delay between
execution of the commands is exactly the same as the delay between sending
the commands from VEE - a reasonable assumption but probably not true.

What about the "WAIT" transaction in the Direct IO object - is that any
better?

If I can't time that precisely within VEE, what options have I got? Some
external hardware perhaps?

Thanks and regards,
Warren Pickles

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VRFuser Jan 24, 2005 11:51 PM
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Hi Warren,
I am intrigued. What instrument requires this? What is the nature of the
measurement? Can it be done using a hardware trigger instead - provided
perhaps by a pulse generator?

Regards

David Watling


             "Pickles, Warren"
             <Warren.Pickles@t
             ycoelectronics.co                                          To
             m>                        VRF <vrf@agilent.com>
                                                                        cc
             25/01/2005 14:37
                                                                   Subject
                                       [vrf] Precision Timing
             Please respond to
             "Pickles, Warren"
             <Warren.Pickles@t
             ycoelectronics.co
                    m>



I need to send a particular command to an instrument, wait for a precise
period of time, then send another command. Problem is, this period of time
needs to be accurate to the microsecond. I imagine this is beyond the
limitations of the delay object. The delay object resolution must be a
function of the resolution of the computer's internal clock (mustn't it?).

This problem is further compounded: I am assuming that the delay between
execution of the commands is exactly the same as the delay between sending
the commands from VEE - a reasonable assumption but probably not true.

What about the "WAIT" transaction in the Direct IO object - is that any
better?

If I can't time that precisely within VEE, what options have I got? Some
external hardware perhaps?

Thanks and regards,
Warren Pickles

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warren.pickles Jan 25, 2005 12:54 AM
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Thanks for all the responses, especially this last from Alex. To summarise
your various inputs, this requirement cannot be fulfilled within the VEE /
Windows platform, and it would probably be difficult and expensive anyway.
That should be enough to persuade my client to relax the requirement or even
better abandon it altogether.
Warren

> -----Original Message-----
> From: Alex.Barrett@raytheon.co.uk [mailto:Alex.Barrett@raytheon.co.uk]
> Sent: 25 January 2005 15:28
> To: VRF
> Subject: [vrf] RE: Precision Timing
>
>
>
>
> >>Problem is, this period of time needs to be accurate to the
> microsecond.
>
> There is another option which I always favour in these cases.
>
> 1. Find a suitable heavy object.
> 2. Throw it at the person who gave you the impossible requirement.
>
> Not that it always works, but it will make you feel better...
>
> (note: I am not condoning violence)
>
>
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> Warren.Pickles@tycoelectronics.com
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VRFuser Jan 25, 2005 5:35 PM
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Beginning with the Pentium IV(?) all processsors have an build-in precision
clock with ms-accuracy (means independend from Windows).
You can very fast read out this clock with assembler instructions.
BUT Windows won't let you do it at the moment you wish.

>> external hardware !

Detlef

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VRFuser Jan 25, 2005 8:47 PM
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Warren,

I think you need a programmable timer with a set of output triggers, else
you'll have to assemble one. To trigger on events, you'll need something to
capture events, a real time spectrum analyzer, a very good scope, or some
other digitizer. Once this is set, you should be able to define the series
of events very well. So look at what you need, where you want to trigger
and tell your boss you'll need a few more dollars for test equipment in
order to get the job done, and you're still waiting.

I know, I know, the timing joke is too corny. "still waiting"

Rufus Warren

-----Original Message-----
From: Pickles, Warren [mailto:Warren.Pickles@tycoelectronics.com]
Sent: Tuesday, January 25, 2005 9:37 AM
To: VRF
Subject: [vrf] Precision Timing

I need to send a particular command to an instrument, wait for a precise
period of time, then send another command. Problem is, this period of time
needs to be accurate to the microsecond. I imagine this is beyond the
limitations of the delay object. The delay object resolution must be a
function of the resolution of the computer's internal clock (mustn't it?).

This problem is further compounded: I am assuming that the delay between
execution of the commands is exactly the same as the delay between sending
the commands from VEE - a reasonable assumption but probably not true.

What about the "WAIT" transaction in the Direct IO object - is that any
better?

If I can't time that precisely within VEE, what options have I got? Some
external hardware perhaps?

Thanks and regards,
Warren Pickles

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