How to generate current signal using DAQ 6009... And i also want to know how to calculate sampling time for any process loop???
You will find some examples in LabVIEW (Menu Help > Search examples...) showing how to generate current with DAQ boards.
But as far as I know, you cannot use a USB-6009 for generating currents. So you will need to generate analog voltage and use some resistors.
You will probably need an amplifier. The analog outputs can only source a few mA and the valve likely requires much more than that. If you have a controller with a 4-20 mA input, you will also need external active circuitry because the 6009 cannot produce that much current.
You could use an industrial signal converter similar to this:
or you could get adventurous and use one of these:
I have used the latter before with a 6009 (I used digital lines to do SPI) and it was a successful project, I think it is still in use 5 years on. You can easily fit one of these in the prototyping accessory NI sell for the 6009.
I tried with 250 ohm resistor but i got 18.73mA for 5V.......
I require 20mA for 5V.....
did you read my last post...
if you could do it with a resistor i would have suggested a resistor...
search op-amp current source on google...
and read the specs of your device especially analogue output...
The analog outputs of the USB-6009 are rated for 5 mA, maximum. So the fact that you got 18 mA is an indication of how conservatively NI rates their devices.
You need an external circuit to drive a 4-20 mA device. There are ICs made specifically for such purposes or you can build your own with an op amp and a transistor.
Check some of the threads in the Breakpoint Forum. A few laughs can help.
Sometimes it seems that the same advice is accepted when the second or third person proposes it, usually in slightly different terms. When I get to the point of annoyance, I usually just drop out of that thread. Sometimes I jump in (as here) when it seems like the OP is not paying attention or several responses have made varying guesses about what the OP wanted. Unfortunately, there does not seem to be any universal technique for staying calm. Remember you are not obligated to continue to post in any thread.