topic Re: Intermittent Read of Instrument using Library LabVIEW VI's in LabVIEW

Intermittent Read of Instrument using Library LabVIEW VI's

biernaskieb — Tue, 15 Dec 2009 14:04:43 GMT

Problem - I am currently having an ongoing problem where I can only sometimes read (~2/10 attempts) the ID of an instrument. The instrument is an EG&G M0del 279A Digital Coulometer and I connect to it via RS232 Cable. I beleive the instrument is working properly because I can consistently read the ID, VERSION etc from the instrument using a HYPER Terminal session. The ID is immediately returned on the same line with no space after the last command character because the instrument does not use a line terminator or carriage return.

Instrument Documentation - The Commands are ASCII Commands with no line terminator so the instrument looks for the end of each command string based on the number and type of ASCII Characters. An invalid character or string is rejected and a ? is sent back by the instrument.

Troubleshooting - I tried using the "Basic Serial Write and Read.vi and the drop-in replacement serial-write-and-read-1-byte.vi" but I still can only read the ID intermittently (~2/10 reads). 8/10 reads return a ? or * (Instrument Prompt) which indicates an error based on the instrument documentation. I tried increasing/decreasing the delay of the read as well as the delay between characters but still reads intermittently.

Attached are some additional docs to describe the Hyper Terminal Settings used as well as the Data Interface used by the Instrument.

Any help in solving this problem would be greatly appreciated !

Barry

Re: Intermittent Read of Instrument using Library LabVIEW VI's

Smootastic — Wed, 16 Dec 2009 23:42:26 GMT

Hi biernaskieb,

The first thing I would check is whether or not your strings have '\' codes display enabled. This can be checked by right-clicking your control/constant/indicator.

Secondly, I would verify that LabVIEW is sending the correct commands with a loopback test.

The PDF you attached seems to suggest that if you don't set up handshaking, then only commands will work and you won't be able to get data. While I don't see what the correct setup should be, you can play with the VISA property node to set that for the instrument.

Re: Intermittent Read of Instrument using Library LabVIEW VI's

biernaskieb — Thu, 17 Dec 2009 16:15:30 GMT

Hello Kyle,

Thanks for your reply and helpful suggestions !

I had a look at my command strings and I indeed have '\' codes display enabled.

I do beleive that LabVIEW is sending the correct commands because I am also communicating successfully and consistently with another instrument using the other COM Port. The only difference is that I receive a different ID and this instrument accepts carriage returns after the command is typed in. Attached are string snapshots with "\" codes display enabled of both instrument ID returns from within Hyper Terminal. You will see there are spaces and carriage returns embedded in the first (working) instrument and nothing embedded in the second (intermittent) instrument as this one does not accept carriage returns, strings or invalid characters.

As suggested, if I don't set up handshaking, then only commands will work and I won't be able to get data. Can you give me an example how to properly setup the VISA property node for the intermittent read instrument ?

Thanks !

Barry

Re: Intermittent Read of Instrument using Library LabVIEW VI's

Dennis_Knutson — Thu, 17 Dec 2009 17:15:28 GMT

Either attach the actual VI or the images. Do not place them inside some proprietary file.

Re: Intermittent Read of Instrument using Library LabVIEW VI's

biernaskieb — Thu, 17 Dec 2009 17:32:35 GMT

Okay, attached is the actual VI that I am currently working on.

Thanks !

Barry

Re: Intermittent Read of Instrument using Library LabVIEW VI's

JÞB — Thu, 17 Dec 2009 18:50:20 GMT

biernaskieb wrote:
Hello Kyle,

Thanks for your reply and helpful suggestions !

I had a look at my command strings and I indeed have '\' codes display enabled.

I do beleive that LabVIEW is sending the correct commands because I am also communicating successfully and consistently with another instrument using the other COM Port. The only difference is that I receive a different ID and this instrument accepts carriage returns after the command is typed in. Attached are string snapshots with "\" codes display enabled of both instrument ID returns from within Hyper Terminal. You will see there are spaces and carriage returns embedded in the first (working) instrument and nothing embedded in the second (intermittent) instrument as this one does not accept carriage returns, strings or invalid characters.

As suggested, if I don't set up handshaking, then only commands will work and I won't be able to get data. Can you give me an example how to properly setup the VISA property node for the intermittent read instrument ?

Thanks !

Barry

Taking a look in you code I noticed that you are using the Basic Serialxxx.vi from the examples. This VI uses a constant F for termination character enableing. The Advanced Serial example give youa control for termination char and term char enable. Optionally you can set these through a VISA property node when you initialize the com port

Re: Intermittent Read of Instrument using Library LabVIEW VI's

biernaskieb — Fri, 18 Dec 2009 16:04:44 GMT

Hi Jeff,

I downloaded and tried out the Advanced Serial Option you mentioned but I didn't have much luck. I can see there is much more control over things like termination char and term char enable in the code. I tried different combinations when comparing the working instrument read to the intermittent instrument read with/without char enable and termination char but it still failed same as before. I tried the "ASRL End Out" options as well but no change. I also tried different probes in different locations and highlighted execution but I could not isolate the fault.

I am unsure what I can try next but I am open to any suggestions at this point ! :>)

Thanks !

Barry

Re: Intermittent Read of Instrument using Library LabVIEW VI's

Dennis_Knutson — Fri, 18 Dec 2009 16:34:02 GMT

You did not attach the subVI "serial-write-and-read-1-byte". It would seem that this initializes the port each time since you are passing the com settings to it. this is almost always a bad idea. It would be very nice to see what else this subVI is doing and how it is actually reading the results from the instrument since there is no termination character.

Re: Intermittent Read of Instrument using Library LabVIEW VI's

biernaskieb — Fri, 18 Dec 2009 18:05:14 GMT

Hi Dennis,

Attached is the subVI "serial-write-and-read-1-byte" that I downloaded some time ago from the NI WebSite. I have tried comparing results and debugging directly using various subVI's such as this one as well as others.

What gets me is the fact the proper ID is indeed read back from the instrument but only sometimes (~2/10) reads. Since it is very intermittent, this would indicate to me some sort of timing issue but I have already experimented with this by increasing/decreasing the delay of the reads. Possibly there needs to be another delay injected into the code somewhere ??? The Tech Docs for the instrument that I have uploaded already, indicate the instrument looks for the end of each command string based on the number and type of ASCII Characters, would it be possible to create a custom loop that takes care of this ???

Thanks !

Barry

Re: Intermittent Read of Instrument using Library LabVIEW VI's

biernaskieb — Fri, 18 Dec 2009 18:07:00 GMT

Re: Intermittent Read of Instrument using Library LabVIEW VI's

Dennis_Knutson — Fri, 18 Dec 2009 19:09:28 GMT

Okay, that has some of the same problems as the regular basic serial example. This and the basic example should not be used in a loop. Do not configure and close the port in a loop.

Instead of a fixed delay and the Bytes at Serial Port, a bit more sophisticated approach would be to first use VISA Bytes at Serial Port in a loop. Exit the loop when the available bytes are greater than 0. Go to another loop with a VISA Bytes at Serial Port and exit this loop when the number of available bytes is 0.

Only use this when the command is supposed to return data.

Re: Intermittent Read of Instrument using Library LabVIEW VI's

biernaskieb — Thu, 07 Jan 2010 13:39:31 GMT

NI Support,

Based on the combined effort from myself and NI Support thus far to perform various debug attempts and gather findings with respect to the intermittent problem at hand, perhaps this problem should be reported and documented as a Specific Bug for this type of instrument communication protocol (ie - command sensing with no line terminator).

That beig said, I understand there most likely is not much demand for instrument drivers for old equipment such as this, but where I am from there has been some recent demand from various Chemist's to have me develop some process automation for this equipment to make there experiments less cumbersome and easier to run and manage.

If someone from NI Support can reply and provide me some feedback on this matter it would be greatly appreciated !

Thanks !

Barry

Re: Intermittent Read of Instrument using Library LabVIEW VI's

Dennis_Knutson — Thu, 07 Jan 2010 18:41:37 GMT

I'm not sure what kind of bug that you think exists. I have successfully communicated to instruments that do not require a termination character on the write and do not send one with a read. There is no bug in the low level VISA functions. I have no idea what code you are running now or what kind of modifications you have made as a result of your contact with NI Support. I would suggest you post your existing code.

As I already mentioned, you probably need to do more than what is provided by the basic and advanced examples. If you are well and truly stuck, you can find an experienced LabVIEW programmer and hire him/her for a period of time. There comes a point where on line support is of limited value since you are the only one with the actual hardware.

Re: Intermittent Read of Instrument using Library LabVIEW VI's

biernaskieb — Thu, 07 Jan 2010 20:34:23 GMT

Dennis,

Okay, using the term "bug" is the wrong choice of words..... I agree, there is no bug in the low level VISA functions as I use them all the time in other LabVIEW Projects I am actively working on. What I am trying to say is possibly have another very simple and basic example VI written to specifically handle instruments that do not require a termination character on the write and do not send one with a read.

You stated that you have successfully communicated with instruments that do not require a termination character on the write and do not send one with a read, would it be possible for you to post this code example for me ? If so, then I can try it out standalone with the instrument. If you don't have any example code written, possiblly your more sophisticated approach where VISA Bytes at Serial Port in a loop. If time permitted, would it be possible for you or someone else to create very basic code based on this premise for me to try ?

Thanks !

Barry

Re: Intermittent Read of Instrument using Library LabVIEW VI's

Dennis_Knutson — Thu, 07 Jan 2010 21:43:31 GMT

Here's the basic idea of the read. The write is simple - just don't append a termination character.

Message Edited by Dennis Knutson on 01-07-2010 02:43 PM