LED Output

[Shay]

Hi there all,
I have a thermocoupe connected to a NI USB-6009 DAQ.

I want to switch 2 external (on the digital I/O side of the DAQ 0-5V)
LEDS on/off dependant on the voltage level of the thermocouole input.
How do I do this... I have a little tester running but I'm not to sure
how to assositae a switch for example to one of the external LED's.
Thanks loads,
Shay

[Dennis_Knutson]

What do you mean by "assositae a switch"? By your description, you would have some comparison done on the analog input and based on that, set a Boolean value that you would pass to a DAQmx Write set to digital output. The setting of the digital output could be done in something as a case statement. What are the conditions that you want to test for and the corresponding digital outputs?

[Otis]

Hi Shay,

First off, I wanted to let you know that trying to read a thermocouple with a USB-6009 is not the most accurate system in the world.

The USB-6009 has 14-bit resolution with a minimum range of +/- 1 volt. This gives a voltage resolution of 122 microvolts. The estimate of the response of different thermocouple types can be seen below.

Common thermocouple types have the following response:
K type: 41 microVolts per degree Celsius
J type: 56 microVolts per degree Celsius
T type: 52 microVolts per degree Celsius

Essentially that means that if you are using a K Type thermocouple then you are only going to notice a change of temperature for every 3 Degrees C (~5.5 Degrees F).  This might work for your application, but just keep in mind that you have pretty poor resolution when trying to read a thermocouple with a USB-6009.

Other than that, for the switch you can't source much amperage from the USB device, but other than that, just do a digital output and it should work fine.