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GraemeJ

Autosampler Serial Communication

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An autosampler is being considered for future connection to a purpose built chemical analyser. The preferred autosampler uses a standard RS232 port. The autosampler manufacturer is mainly selling the RS232 version although also supplies USB, but in far fewer numbers. The analyser software is written in LV 8.6. No drivers exist for the autosampler.

The intention was to use NI VISA and direct i/o to communicate with the autosampler, which will be located close to the computer. Data transfer rate will be low.

Any advice or comments concerning reliability or any other issues on the following alternates would be appreciated.

  • Output to computer COM port with direct cable connection to autosampler.
  • Output to computer USB port and connect using NI Serial Hardware USB-232 1 port cable. Is this likely to give more reliable communication that 1. above? It would seem to have the advantage of using current technology, and also to use NI-Serial software to configure and monitor communication.
  • Purchase a USB version autosampler. The sales history of mainly selling RS232 machines to OEM instrument manufactures left a small question mark.

Not having a driver is unfortunate. The autosampler drivers on ni.com/idnet are not able to be modified since the details are not disclosed. I would be grateful if anyone knows of an open source version which I could use as a starting point.

Regards,

GraemeJ.

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Sounds like you need a Hardware Abstraction Layer (HAL). See the white paper or the webcast for more details. Searching for "hal" on the NI website will get you tons more info.

As for the method your describing you could simply use the build in visa commands and then you can easily accomodate either or both solutions (USB or traditional Serial) from a programming standpoint. As for USB being more reliable, I don't really think the USB would affect the reliability as much as the autosampler itself would.

Two things you might want to consider.....Why are people not buying the USB version? The underlying reason may help your decision.

and two.....................................................I don't know about you but at my company we have to go through extra effort to get a computer with a serial port. They are all coming with USB's instead now.

Jason

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Does the USB version of the autosampler actually connect as a USB device, or does it show up as a virtual COM port? The latter is what I would expect, and if that's the case then the point about "newer hardware" is moot. From the way you phrase option 2, I think this is the case.

Is the autosampler well documented with regard to its protocol? If it is, writing a driver using VISA would be relatively trivial.

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To echo what has been said a bit, using serially directly or through a USB converter shouldn't really impact much other than USB is more widely available. There are hundreds of converters out there, functionally I am not sure if there would be a key advantage to using NIs but it is going to be a higher quality than a cheap converter off eBay!

The USB instrument is an interesting point. My experience when you have this choice is that the manufacturer has simply built the converter in. This is the case where it gives you a virtual COM port in which case there is no reason not to go with that. What I wanted to add is that if it is not a virtual COM port, I would avoid at all cost! VISA USB programming is more difficult than serial.

EDIT: Unless it conforms to USB test and measurement class

Cheers,

James

(null)

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To echo what has been said a bit, using serially directly or through a USB converter shouldn't really impact much other than USB is more widely available. There are hundreds of converters out there, functionally I am not sure if there would be a key advantage to using NIs but it is going to be a higher quality than a cheap converter off eBay!

The USB instrument is an interesting point. My experience when you have this choice is that the manufacturer has simply built the converter in. This is the case where it gives you a virtual COM port in which case there is no reason not to go with that. What I wanted to add is that if it is not a virtual COM port, I would avoid at all cost! VISA USB programming is more difficult than serial.

EDIT: Unless it conforms to USB test and measurement class

Cheers,

James

(null)

NIs USB to COM adapters are well worth the price, the quality is excellent. Never had any problems with them.

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Hello GraemeJ,

A couple of years ago I wrote some control software for a Gilson 215 mulitprobe autosampler. Documentation was diffucult to come by for this hardware but there was an existing piece of setup software. I used this software in combination with a serial port sniffer and trial and errror to determine the commands required to control the autosampler.

My first choice for communication would be direct to a COM port on the PC. Unfortunately many PCs no longer have this as an option, in which case I would go with the NI Serial to USB converter simply to have the support should you run into trouble. However, that hardware should make no difference to your code other than perhaps the COM port you are communicating on.

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@Pallen,

I'm hoping you are still active here....

I have a Gilson 215 with no documentation or setup software. Gilson say this is obsolete, but they would try to help. However I've heard nothing back from them for quite a while now. Do you know where I can download the setup software? I'm getting a homing phasing error (due to having had a loose pulley on the X drive). I can't even start to use this until that is sorted. I'm told there is a procedure in the setup software which will reset the encoder home phasing.

Thanks for any help.

Joe

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