Why SCXI is required?

[ITA]

Hi All,

Why one should use SCXI module? When is it required?

I know the Ideal answer are 

1. If you need signal conditioning....you will need it....
2. If you want to multiplex input channels...

But actually when I'll need signal conditioning? If all of my input signals are in the range of 4-20mA, then will I need to consider SCXI?

For reason 2 mentioned above: Is R series / higher density I/O cards......is noat a cost effective solution?

Need guidance.....

Thanks!

[Paul M.]

ITA,

Signal Conditioning a broad term that covers everything from simple current to voltage conversion up to complex filtering and scaling.  The SCXI platform is NI's "high end" signal conditioning platform and is best used for high channel count applications and/or more stringent signal conditioning requirements. 

SCXI has been around for a while, and NI is rapidly adding more signal conditioning options to other products which may make them more attractive for your application.  

With 4-20mA signals, you still need a calibrated resistor of an exact known value to get a good reading as all ADCs operate by voltage, not current.  This is signal conditioning.  The questions to ask whether you need SCXI or a newer platform like CompactDAQ or CompactRIO incldue: how many channels are you trying to acquire, what PC bus you prefer (PCI, PXI, USB, Ethernet, wireless 802.11, wireless sensor nodes, etc), whether you require isolation (4-20 signals are often associated with industrial equipment that runs over long distances and requires isolation to prevent ground loops and the like), and what operating system you want to work with. 

With these questions in mind, you can then narrow down the correct NI platform that will best suit your needs. 

[ITA]

Hi Paul!

Thanks for the information.

Does SCXI provides Isolation?

[Paul M.]

Hi ITA,

Absolutely. It varies by module, of course.   Many NI platforms do. In fact, there's a great guide here: 

http://zone.ni.com/devzone/cda/tut/p/id/3546