Reading discrete input with SCXI-1303

[Savitr]

Hello,

     I want to be able to tell when a heating element in a water tank is on or off.  I have an SCXI-1303 and SCXI-1302.  I figured it would be a discrete input but am not sure how it would be read in LabVIEW.  Any help would be appreciated.

Thank you.

[David S.]

Hi Savitr -

Can you be more explicit in describing "on" and "off"?  Do you mean to look for disconnected thermocouples, or do you want to use the measurement from a thermocouple to determine some logic?  The input from a thermocouple measurement is always time-referenced analog data, but you can use the analog values in LabVIEW to trigger boolean logic.

On a side note, the SCXI-1303 is only a connector block.  Behind it lies an SCXI module (either the 1102/B/C or the 1100), and attached to that module is your DAQ card (E-series or M-series).  Can you give us the model numbers of those devices too, so we know what you're working with?

[Savitr]

Hello, David,

     Thanks for your reply.  Basically, I will be putting in a relay to detect when there is power to the heating element.  A question about the relay is will I need to supply additional power or can the connection to the DAQ system supply the voltage?

     As for the DAQ hardware, I am using the NI SCXI-1000 module and the card on the back is the SCXI-1349.

Cheers.

[David S.]

Hi Savitr -

The SCXI-1000 is a chassis that holds SCXI modules, and the SCXI-1349 is a connector block from the back of a module to a DAQ device. Unfortunately, neither of these model numbers gives me any more information.  You can find out all of your system hardware in MAX (Measurement and Automation Explorer). Here's a screenshot of the kind of info you'll probably see:

As for the relay, you probably won't be able to source enough current to operate it.  Voltages provided from most of our hardware are derived from the PCI/PXI bus rails, and those are designed to give very little current.

Message Edited by David S. on 07-27-2007 10:10 AM

[Savitr]

Hello, David,

     Sorry for any technical goofs - I'm not an electrical engineer.    Below are the values I got from MAX:

1.  SCXI chassis:  SCXI-1000: SC1
2.  SCXI module:  SCXI-1102: "32Thermocouple"
3.  SCXI connector block:  SCXI-1303
4.  DAQ device:  PCI-6250: "Dev1"

     Does that information help?

Thank you.

[David S.]

Hi Savitr -

Yes, it does.

The SCXI-1102 is designed solely for analog voltage inputs.  As such, you won't be able to source a voltage to your relay or read from the relay with a digital input.  You could, however, set up and Analog Input task to read the voltage across the relay, then interpret that value as "high" or "low" in your software.  Simply configure one of the unused input lines on your 1102 to read the voltage.

Your DAQ device also has some available DIO lines, but they're covered up by the connector from your SCXI chassis.  You can access them using the SCXI-1180, which breaks these lines out for use on the front panel of the chassis.  You will have to refer to the 1102's User Manual to find out which DIO lines it reserves for communication with the DAQ device, then choose one of the unused ones.  You can then assign this line to a DAQmx Digital Input task to read the relay's value as a discrete input.