ni 4350 daq

[scott 133]

I have a few questions concerning the ni4350 usb daq device.

1. Can thermocouples be directly connected to the 68 pin connector on the ni 4350 using a custom cable or is some type of signal conditioning required? Can the digital i/o also be directly connected to relays in the same fashion?

2. What is the maximum length usb cable that can be used from a computer to the ni 4350?

Thanks,
Scott

[Adam_U]

You can connect directly to the 68-pin connector on the 4350. No signal conditioning (attenuation/etc.) is required. This will degrade your signals however if the cable is not shielded well (twisted pair). In addition, you will not have the CJC compensation built into the TBX68T (on channel 0) nor the auto-zeroing circuitry on channel 1 (also built-in).

The Digital I/O can be connected directly. Do ensure that your relays don't exceed the DIO specs on page A-8 of the user manual at www.ni.com/manuals.

The maximum cable length for the USB 1.1 spec is 5m. NI sells a 2m cable. These specs assume that your environment is within CE specifications. If you are working in a noisy environment, I recommend using a well-shielded cable (USB 2.0) and providing additional
shielding if a USB solution is necessary. Working with an internal (PCI) solution would reduce your susceptibility to noise and is recommended. You can use a repeater to extend the cable but be aware that this will increase your susceptibility to noise.
http://digital.ni.com/public.nsf/websearch/0D4951EAEE72CC0586256B8B0052C6ED?OpenDocument

Hope this helps,
-Adam

[scott 133]

Thanks, this helps quite a bit.

I believe I would be require up to a 3m usb cable so it sounds like this would work if proper shielding is employed.

Since you recommended the internal pci solution as an alternative, I am wondering whether there would be any definitive advantages between a 3m usb or a 3m shielded 68 pin cable going to the internal pci device?

[sergesl]

Given the length of the cable, I would recommend using USB which is serial and less subject to error due to cable length.
Thanks

Serges