USB-6221 SCB-68

[LV_Pro]

Is the USB-6221 DAQ unit compatible with the SCB-68? I'm trying to make a number of analog measurements in <10V range with two of them being J type thermocouples and would like to have CJC capabilities.  In my quick glance at the SCB-68 page, and at the one for the 6221 it isn't clear.

Thanks!

[LV_Pro]

OK, it shows it being used with the M series "68 pin" devices, but not with the USB-6221, so I'm still unclear on using the 6221 to make reasonably accurate T-couple measurements.

Message Edited by LV_Pro on 04-01-2009 09:01 AM

[stilly32]

Hi Putnam,

The USB-6221 does not have a mass termination (68 pin connector for a cable) option so it can't be cabled to an SCB-68. The current versions have their own built in screw terminal connections or BNC connectivity. The USB-6251 does come in a mass termination option (part number 779694-01) which you could use with the SCB-68. You could also provide your own CJC source for the USB-6221 and use the screw terminals for a single box solution. 

Hope this helps, 

Andrew S

Message Edited by stilly32 on 04-01-2009 09:23 AM

[LV_Pro]

When you refer to supplying my own CJC are you meaning another J TC connected at the USB-6221? I had thought of doing that, puts my AI count at the current number of needed inputs. Of course I could get a 6008/6009 if my count goes up, the TC's are the only inputs needing the resolution of the 6221. I haven't broken the news, cost wise, to my customer, their conversation with the local NI rep resulted in them asking about the 6008/6009, hope that the sticker shock isn't too bad. The $400 difference between the 6221 and the 6251 will be "offputting" to my customer.

Thanks,

Message Edited by LV_Pro on 04-01-2009 10:29 AM

[stilly32]

Actually I was thinking of using a temperature sensor like the one on the SCB-68. It uses an LM35 (if you own one you can read the exact part number off,) and gives it 5V from the +5V pin then scale the output voltage to a temperature. They run a couple dollars, but with a USB-6221 with this you would still have the screw terminal connectivity, but wouldn't have to pay for the cable or the SCB-68 so a dollor or two won't hurt 🙂

This would also scale to the USB-6229 or USB-6225if you needed more channels... actually the 6225 does come in mass term, but you could only use the cjc from the scb-68 on connector 0. Connector 1 doesn't have the +5V power needed to power the cjc circuitry. 

Another option to look at would be the USB-6212 or 6216 (isolated version of 6212). They're bus powered, come in mass term versions and have the same channel count as the 6221 (no correlated DIO and the drive strength is less, though they do have a max rate of 400kHz vs 250). 

Please post back if you have any questions about these options, 

Andrew S

Message Edited by stilly32 on 04-01-2009 09:44 AM

[LV_Pro]

Thanks!

    One more (hopefully the last) question, do all AI channels have to be configured the same i.e. Single ended or differential?

Message Edited by LV_Pro on 04-01-2009 01:05 PM

[stilly32 · Accepted solution]

Nope - you can scan through channels as either RSE or differential or NRSE... all in the same task (ie AI 0-3 differential, AI 4-6 RSE). The M-series user manual (/book) shows how in the "Configuring AI Ground-Reference Settings in Software" section.

cheers, 

Andrew