USA calibration club

[Ash]

Do you mean some devices load the bus more than allowed by IEEE 488.1, or that they load it more than a wimpy micro that does not conform to IEEE 488 can drive? GPIB drivers are supposed to be pretty beefy and able to drive up to 20m of cable and up to fifteen devices at the same time.

By the way, you could skip X on all but the last command, or even write it as a single string (K0F0R3Z0...X).

It is hear-say from Prologix when I asked them about drive capabilities. Sorry I should have been clearer. The told me that some older devices load the bus more than the spec allows.

Basically they have an Atmel device directly driving the bus, but claim it should be able to drive lots of devices. I currently have 4 older Keithley devices (K705 matrix switch, K740 temperature logger, K196) and a newer K2015 in my bus, but all short 1m cables, in a daisy chain.

I was worried about cable drive capabilities, but is seems to be working ok for me. (I've had my system logging for days at a time without incident), however I'd be wary about driving the cables directly from microcontroller I/O if I was building an interface. Not just for drive capability, but also for protection.

And yes, thanks, I could combine all the commands together in a line as you suggest, but I'd rather have the comments on each line so I can remember what I'm doing later.. only get executed once so I'm not worried about speed

Ash.

[nisma]

The 244 octal 3state bus driver  is able to drive 8 gpib units.  AVR cpu can drive  not more as 4 units directly.
Pic cpu is superior to 244 driver.
What fool AVR:
GPIB high is stated at 2V min and low at 0.8V max.
AVR cpu have 3V min for high and 1.5V max for low at 5V and when driving -20ma the voltage is 0.9V max from Datasheet.
If instead the AVR cpu is running at 3V, things changes, 2V min for high and 1V max for low. Driving -10ma the voltage is then 0,6V
and the limit of 10mA instead of 20mA reduced the number of devices to max 4.

If you use AVR without drivers, then (avr)  Arduino must be 3.3V powered for driving it directly, otherwise 74..244 drivers are needed for 5V operation.

[Ash]

The 244 octal 3state bus driver  is able to drive 8 gpib units.  AVR cpu can drive  not more as 4 units directly.
Pic cpu is superior to 244 driver.
What fool AVR:
GPIB high is stated at 2V min and low at 0.8V max.
AVR cpu have 3V min for high and 1.5V max for low at 5V and when driving -20ma the voltage is 0.9V max from Datasheet.
If instead the AVR cpu is running at 3V, things changes, 2V min for high and 1V max for low. Driving -10ma the voltage is then 0,6V
and the limit of 10mA instead of 20mA reduced the number of devices to max 4.

If you use AVR without drivers, then (avr)  Arduino must be 3.3V powered for driving it directly, otherwise 74..244 drivers are needed for 5V operation.

Thanks Nisma, exactly what I was concerned about. I didn't get far enough to check the logic level voltages though. good info.

If I was going to design an interface, I'd spend the extra on proper GPIB drivers - for instance there are a pair of devices specifically designed for it from TI:

http://www.ti.com/product/SN75160B - data lines
http://www.ti.com/product/sn75161b - control signals

there are 2 variants of the control signals chip - 161 and 162, the 162 will deal with multi controller busses as you can control the REN and IFC lines independently of the others to assert certain states.

These are only a few dollars each on DigiKey. I'm sure there are other options as well. Just the first ones I came across.

I'm probably pushing the limits on the capabilities of the non-buffered interfaces. Seems like most of these are just for one or two instruments. Also longer cable lengths are going to make this worse..

Ash.

[nisma]

The open source gpib interface from University of Ljubljana use that driver.
Hovewer this drivers are slow if you want use the hs mode.

The special feature of this drivers is the defined impedance at power off and the missing glitch during power on/off,
when GPIB devices are switched on and off during measurement in order to prepare next measurement
setup where the specification allows 30 devices on one bus, but only 2/3 can be powered at the same time.

[alm]

I would not worry about about high-speed mode. For starters, there is no way that something like an Arduino or 8-bit AVR would be able to keep up with it. I believe the Prologix devices are limited to 500 kB/s (at least they were when I acquired about them a couple of years ago). Even the old IEEE 488.1 supports up to 1.8 MB/s. I also doubt most voltnut equipment would be able to ever exceed 1.8 MB/s. Maybe if you are into RF. And then only if the equipment is modern enough to support HS488.

where the specification allows 30 devices on one bus, but only 2/3 can be powered at the same time.

I thought the specification allowed only fifteen. And at least two-thirds have to be powered on.

[nisma]

Initially the specs was 30 max and max 2/3 powered on (21 total) because the used driver was MC3441A and that had a better fanout.
Then the specs was  reduced to 20 max on and max 2/3 powered on at same time because the  75160/1 drivers that hp and other have created for gpib had
a fanout of 14, this is then 15 devices max including controller and the max speed was specified 250Kbyte/sec .
For 1Mbyte/sec and more, the specs say, that all device must be powered on.

hs488 is not difficult to implement into arduino or any other cpu.

After setting up the data transmitters (addressing the sender, addressing the receivers), the controller enters the system into the data transmission mode (ATN = "0"). Recipients are ready to receive the RFD message by setting the NRFD line to high (NRFD = "0"). The sender then sets the NRFD line low (NRFD = "1") for a moment, informing the recipients of the possibility of an accelerated data transmission, and then sends the DIO message (DAV = "1") after setting the first data byte on the DIO bus. If all data recipients have the ability to receive data expeditiously, they inform the sender by leaving the NRFD line high, and then leaving the first byte (NDAC = "0") to leave the NDAC line high. The second data byte and the next are already sent in an accelerated manner without the participation of NRFD and NDAC lines. The sender sets the byte on the DIO bus and then after the programmable delay time (T 11 ) sends a DAV message (ie set low line DAV) to the programmable reception time (T 12 ) during which all receivers must receive a byte from the DIO bus. Data transmission is therefore without acknowledgment of receipt. The recipient may set the NDAC line low to pause the transmission of further bytes. It can also set the NRFD line low, thereby forcing the sender to cancel the accelerated transmission cycle. Both of these mechanisms allow the recipient to adjust the average bit rate to its receiving capacity. It is, however, necessary for the device to have the appropriate input buffer to which data byte groups can be sent at the maximum rate at the time necessary to reach the NRFD or NDAC signal to the sender. Delay times (T 11 ) and reception (T 12 ) can be set by the user. These depend on the total length of the cables and the number of devices in the system. The data transfer rate between two devices connected by a 2 m cable during an accelerated transmission cycle can reach 8 MB / s. For a full system consisting of 15 devices connected by 15 m total cables, the baud rate can reach 1.5 MB / s.
It have to be noticed that some device support only speeds up to 7.2mb/s.

The increased data rate requires several additional conditions:

The power supply of all devices connected to the bus must be switched on,
I / O buffers of all devices must be three-state,
The signal line capacity of each device must be less than 50 pF.
The HS488 procedure only concerns data transmission (ie programming texts, measurement results, STBs). IEEE-488 instructions and instructions are always transmitted using the full transmission cycle.
Interesting mostly on RF setups, that is correct.

[cellularmitosis]

CatalinaWoW reminded me that I hadn't yet set up a github repo where we can post CSV data and such.

I've just created a github organization: https://github.com/USACalClub

and a first repository: https://github.com/USACalClub/data

Send me a PM and I'll add you to the org!

[cellularmitosis]

Github Update: TiN just informed me about datashort!  https://xdevs.com/datashort/ 

He has graciously offered to host CSV data for all of us.  I can see how this might be a better option than github -- not everyone is familiar with how to use git.  Perhaps we should all use that instead?  PM him (or me) for details on how to access his ftp upload.

[TiN]

No need PM, uploads are free for all, over FTP with login and password datashort. All data automatically mirrored with https URL. Make sure to use passive mode for ftp. Welcome to create specific folders, for example USACalClub/Round1_Nut1 etc.
Meaningful file naming also helpful.

[bitseeker]

I've only used command-line git, so I don't know if Github has a friendlier way of managing files and revisions. Basic operations in git are OK, but the concept of working with decentralized revision tracking can take some getting used to.

Thank you, TiN, for the FTP space.

[CatalinaWOW]

I'll add my thanks to TiN for the space.  I have logged in and browsed, but was unsuccessful in creating a USA_Cal_Club directory and adding my data.  I am not an FTP maven so am sure I am doing something wrong.  Will look into it.  I have added my data to the Github so some progress has been made.

[alm]

Were you using an FTP client (I use lftp on Linux)? Web browsers will usually only be able to download from FTP, not upload.

[drtaylor]

Getting back to metrology and actual calibration, I'd propose that if there are enough individuals that would like to be able to calibrate their high end DMMs and other precision equipment, why not share the price of a high end calibrator. Either a new one from Fluke (>>$30000) or a working used one from eBay. I've seen decent calibrators in the $15000 range. I guess the logistics of shipping a large calibrator around the nation is the problem, but perhaps someone could host it regionally and club members could make the trip to use it. Working out share prices would also be a problem, but considering how much Cal labs charge, it could still be worth it. I know I'd be willing to fork up $500~1000. I could host in the Northwest region (Seattle area).

If there are 50 people all willing to pay $500 the budget would be $25000. Leaving it in 12 regions (TBD) for a month at a time should give every member a chance to use it. It would also be a chance to get together with like minded engineers and Volt-nut enthusiasts.

There would also have to be a maintenance fee for shipping costs, and eventual recertification.

Ah well, the more I write, the more I realize that this would never work. Sure wish I could get my hands on a really great multifunction calibrator just once in a while without going to the poor farm. Still posting this just for the heck of it.

[bitseeker]

No worries, Dr. T. It's a good thought experiment and probably still worthwhile with enough participants in a metro region (i.e., no need to ship the calibrator around).

[Echo88]

Sharing the calibrator would be pretty much out of the question and voltnuts would simply send their stuff to the calibrator-location. Aside from that this lab would also need a few Voltage standards and at least a 3458A and a KVD to be really useful. So we need more TiNs around the world. 

[bitseeker]

I have logged in and browsed, but was unsuccessful in creating a USA_Cal_Club directory and adding my data.  I am not an FTP maven so am sure I am doing something wrong.  Will look into it.

I logged in, found that someone already created a USA_Cal_Club directory, added a test file to it, and subsequently removed said test file.

CatalinaWOW, be sure to use an FTP client in order to have full functionality. On Mac and Linux, I use the command-line ftp client. On Windows, I use WinSCP, which supports FTP, SFTP, SCP, and WebDAV.

[CatalinaWOW]

I was using the command line FTP client from Windows.  It has been 25 years since my last use of FTP so lots of rust.  I will try WinSCP to see if it makes it easier.

[ManateeMafia]

I use FileZilla on the Mac but it is also available for other platforms. It is constantly updated and it is what I use to upload everything to xDevs and KO4BB.

[TiN]

Group funded calibrator (if we talking real calibrator, like 5440/57xx/480x) is really worst idea possible . Even w/o shipping (somebody drops it and bye-bye for those ppm's), just usage scenario does not work well. To reach proper stability and uncertainty most of these must be ran 24/7 at stable controlled environment, and supported by set of high-performance standards. It's a full-time job on it's own to maintain lab with calibration capability even just for basic DCV/Ohm/ACV stuff calibrator provide. Leave alone learning and tweaking procedures and measurements for every obscure DUT abovementioned voltnuts have. Also maintenance of calibrator is not an easy task, even if you send it to Fluke for their standard 3K$ cal. Just open service manual for 5700A and check what are the performance test and calibration procedures? Has no 5790A, 792A, stash of expensive transfer standards? No performance tests for you .

What works though is local voltnut gatherings (2-4 people) for extended time (at least a week, best if 2-3 weeks) around a crazy voltnut which has calibrator, supporting gear and history in calibrated gear. That justify for visitors to bring their stuff and run it for days/week to get it all nice and stable.

[drtaylor]

Group funded calibrator (if we talking real calibrator, like 5440/57xx/480x) is really worst idea possible .

What works though is local voltnut gatherings (2-4 people) for extended time (at least a week, best if 2-3 weeks) around a crazy voltnut which has calibrator, supporting gear and history in calibrated gear. That justify for visitors to bring their stuff and run it for days/week to get it all nice and stable.

TiN - I already acknowledged this was a bad idea at the end of my post. However, I deal mostly with 3.5 - 5.5 digit DMMs, not in the Volt-Nut realm. Weeks of stable operation in a controlled environment is not really needed at the 4.5 digit level. I was just frustrated that I have no low cost way to fully calibrate many of my low end DMMs. I'm not paying a cal service for old multimeters for hobbyist use.

Now in regards to gatherings of Volt-Nuts with all this cal gear, who are you, where are you, who would organize these voltnut gatherings? Is there really an EEVblog forum member willing to share his high end equipment? I would if I had it, but then I'm retired now and have time. I'm talking about a true multifunction Calibrator.

[orin]

Group funded calibrator (if we talking real calibrator, like 5440/57xx/480x) is really worst idea possible .

What works though is local voltnut gatherings (2-4 people) for extended time (at least a week, best if 2-3 weeks) around a crazy voltnut which has calibrator, supporting gear and history in calibrated gear. That justify for visitors to bring their stuff and run it for days/week to get it all nice and stable.

TiN - I already acknowledged this was a bad idea at the end of my post. However, I deal mostly with 3.5 - 5.5 digit DMMs, not in the Volt-Nut realm. Weeks of stable operation in a controlled environment is not really needed at the 4.5 digit level. I was just frustrated that I have no low cost way to fully calibrate many of my low end DMMs. I'm not paying a cal service for old multimeters for hobbyist use.

Now in regards to gatherings of Volt-Nuts with all this cal gear, who are you, where are you, who would organize these voltnut gatherings? Is there really an EEVblog forum member willing to share his high end equipment? I would if I had it, but then I'm retired now and have time. I'm talking about a true multifunction Calibrator.

There are quite a few of us in the Seattle area...  I have a Fluke 731B for example.  No 3458A yet unfortunately, just a 34461A.

[TiN]

I'm not paying a cal service for old multimeters for hobbyist use.

Well, than why would you pay for somebody's calibrator just to check stash of your 4.5d meters
Heck, it's cheaper just to buy new meter of that level, than get setup for a calibration .

Who would organize these voltnut gatherings?

Interested parties organize themselves. At least I want to believe that, as I know that happened before, being on such calibration "party" last year, when I calibrated both of my K2002's and stash of references. Even though cost of such (due to airplane fares from TW to USA) was close to sending meters to Keithley/Fluke for calibration, it was manyfold much more fun to play with gear, instead of getting just expensive piece of paper with numbers. Would I do it again? Heck yes, TBD next year!

Is there really an EEVblog forum member willing to share his high end equipment?

That depends too. Usually hardcore voltnuts are fond of their gear, and are happy to show off a bit. 

I'd be happy to accept visitor for few days to hangout, calibrate some meter, play with the references and chat about ppm-hunts over the cup of tea/beer/something else.  . But that's unlikely to happen in my current geo.

But I'd expect the owner of expensive set/MFC would expect guest party to be at same level , so both sides can benefit. Meaning that meetup with everyone bringing 8.5d meter to verify with one member's MFC is likely possible, unlike having guests with ten 4.5 handhelds, which just mean work for calibrator owner   After all cross-comparisons are key aspect in metrology. No matter how great and stable is the equipment, there are always statistic laws at play. And all of this is not cheap, so resulting cal club member list will be rather short anyway.

[dr.diesel]

Now in regards to gatherings of Volt-Nuts with all this cal gear, who are you, where are you, who would organize these voltnut gatherings? Is there really an EEVblog forum member willing to share his high end equipment? I would if I had it, but then I'm retired now and have time. I'm talking about a true multifunction Calibrator.

I'd gladly take the time to share my equipment, including travel and hotel expenses. 

The Volt-Nut community here is growing stronger, lots of good equipment is being restored, stable homebrew stuff being born, looking forward to the future.   

[CalMachine]

Now in regards to gatherings of Volt-Nuts with all this cal gear, who are you, where are you, who would organize these voltnut gatherings? Is there really an EEVblog forum member willing to share his high end equipment? I would if I had it, but then I'm retired now and have time. I'm talking about a true multifunction Calibrator.

I'd gladly take the time to share my equipment, including travel and hotel expenses. 

The Volt-Nut community here is growing stronger, lots of good equipment is being restored, stable homebrew stuff being born, looking forward to the future.   

Dr!  Perhaps we should think about hosting a midwest cal get together 

[Conrad Hoffman]

My door is always open to volt-nutters and audio people, but nobody wants to come to Rochester even in good weather and I've taken a vow of poverty, so don't get out much.