Do I need a NI serial device?

[Gurdas]

I am working on an application which involves reading pressure data from two pressure gauges (differential and vacuum).
My PC has two free serial ports. My questions:

1) Can I use the PC serial ports or is it advisable to opt for a NI 2-port serial device? Reason?

2) If you suggest that I go ahead with existing PC serial ports, then, can I still use the power of LabVIEW and VISA to read and display data from these ports?

I have LabVIEW 6.1 professional.

Thanks!

- Gurdas
gurdas@qagetech.com

[Chris_Rake]

LabVIEW and VISA work with both built-in serial ports and NI's serial intreface cards. However, there are several things to consider:

- Are your devices RS-485/422 or RS-232? If they are RS-485/422 you will need to add a RS-485 interface (either card or adapter - NI offers several types).
- Are your devices communicating at baud rates faster than 115.2k? Enet-232 and USB-232 devices run up to 230.4k and most of NI's 485 interfaces run up to 460.8k.
- Do you need deep FIFOs? PC COM ports generally have 16 byte FIFOs. Most of NI's interfaces have at least 64 byte FIFOs. FIFOs are important for reducing the chances of data overrun.
- Do you need electrical isolation? NI offers 2-port isolated RS-232 interfaces. Built-in COM ports are not isolated.


Hope this helps!

[Gurdas]

Thanks Chris. That helped!

Find below replies to your inputs. Feel free to provide any further inputs and suggestions.

- All devices are RS-232
- No. All devices are slower than 115.2K
- No, we do not need deep FIFOs. The application is simple and involves acquiring data from two pressure gauges at slow intervals of say once every 5 minutes.
- I am not sure. What do you advise?

Do you think I need to invest in NI hardware?
Can I save money by using built-in COM ports and still leverage the power of NI LabVIEW?

- Gurdas
gurdas@qagetech.com

[DiegoF]

Hi Gurdas,

From what you describe, the built-in serial ports should be fine. You can use LabVIEW and VISA with this ports. in fact, from the software point of view, there is no difference between the built-in ports and the ports provided by the NI serial interfaces.

DiegoF
National Instruments.

[Chris_Rake]

Regarding isolation (which you don't get with the built-in board) - if you are running in an electrically noisy environment (lots of motors and other interference for example) or are communicating with a device that has a different ground, then you should take a good look at getting an isolated board.