GPIB

[DanielJackMorley]

This design requires a GPIB interface with an operating temp from -20 to 120 C. The issue is the current available GPIB do not meet this spec. Is there a way of designing one of these through VHDL on a FPGA? Does some one know any literature that can help me with this task.

 

[VEBill]

The -20°C makes sense.

The +120°C smells like a typo in the requirements.

 

[DanielJackMorley]

It might be 100 C. But these values are from some test that some one did on it. Rather than some military standard. Fitting the requirements for either one would be an improvement from my current options.

 

[VEBill]

Most GPIB interfaces would be found between a typically-delicate computer and a typically-delicate instrument. You're unlikely to run across many of those that would function in an environment of +120°C.

Are you sure these requirements (or measurements) aren't in °F ? +120°F is just about +50°C, and that's a lot more reasonable.

 

[DanielJackMorley]

Spartan FPGA's are well within those specs on their industrial package. So it sounds like the only way one can get this system up and running is to develop the VHDL code. Is their a source for this GIPB stuff that can help in the design of this device.

 

[IRstuff]

Seems like a lot of work to create and validate a GPIB interface. Have you talked to someone like National Instruments?

http://sine.ni.com/nips/cds/view/p/lang/en/nid/209211

http://sine.ni.com/nips/cds/view/p/lang/en/nid/201586

Both will run up to 55°C, and while they're not rated for -20°F, you might be able to demonstrate that they'll still work, provided the moisture environment is controlled.

TTFN

FAQ731-376

 

[VEBill]

But he's looking for a +120°C capable solution.

 

[MikeHalloran]

A friend of mine went into 'downhole' instruments.
According to him, TTL works just fine when it's glowing red.
I see 120C as a problem only for thermoplastic insulation and connectors.

Mike Halloran
Pembroke Pines, FL, USA

 

[IRstuff]

"works" but for how long? And TTL is by far more robust than most CMOS devices, particularly when it comes to junction spikethrough.

Additionally TTL's [Δ]T_jc is relatively small. A 20°C or 30°C junction temperature rise in a CMOS part would severely degrade the MTBF.

TTFN

FAQ731-376

 

[MikeHalloran]

Yes, I recognize that TTL is not CMOS.
My friend used TTL _because_ it survived _long_enough_ while operating _far_ outside its normal temperature range. There is no 'book' data from which to evaluate an application like that, and no warranties are offered or expected.

But 120C is not _that_ hot. Certainly MTBF, not specified here, will be shortened, so defensive measures like derating and disclaimers are advised.

I too think the OP spec may be a typo, but I can conjecture applications where it would be appropriate. I think that actually achieving it is more of a packaging materials selection challenge than an electronic design challenge.

No, let me rephrase that. I don't mean to minimize the challenge of actually meeting such a spec on the electronic side, but I do mean to suggest that it will be equally challenging and expensive to get the electronics into a package that will help it survive for a reasonable time, and to deal with the interconnect problems that appear.











Mike Halloran
Pembroke Pines, FL, USA

 

[DanielJackMorley]

Yes I have looked at National Instruments. The problem is the specifications are under what I require. I am currently using a specialty chip they made for this company but it is not supported and will run out at sometime. All the chips they have are rated far below the operating conditions. My feeling is that the chips will work but the problem is any one can pull up the data sheet and see that part is not with operating parameters. Totally independent of the physics involved. I have search the internet for another chip with no luck.

I agree this might be more work than it is worth but if it is an option I need to explore it. FPGA development. Is there a place where you can get a tutorial or state diagram for GPIB development.

 

[IRstuff]

Why can't you do a "last time buy?"

Even if you have a 120°C rated FPGA, it's quite likely that none of your other peripheral components will be rated for 120°C.

The Arrhenius rate equation applies to expected MTBF. Assuming a 1 eV activation energy for a typical failure, a 100°C rise in ambient temperature will degrade the MTBF by a factor 5*10^-5, i.e., a 100,000 hr MTBF at RT will be about 4 hrs at a 120°. That's assuming there aren't physical-architectural limitations on either MTBF or performance.

One option is to find surplus MIL-STD-883 qualified components. They were all supposed to be fully functional at 125°C ambient temperatures.

TTFN

FAQ731-376

 

[IRstuff]

typo 1/23800 ~ 4.2*10^-5

TTFN

FAQ731-376

 

[IRstuff]

GPIB is often known under its IEEE specification: IEEE-488

http://en.wikipedia.org/wiki/IEEE-488

TTFN

FAQ731-376