Change Excitation Value after DAQmx Start

[Peter_S]

Hi,

I have a remote  NI 9234 with LAN carrier cDAQ 9181 and need 3 measurement channel (ai0..ai2). And I also need a digital output to switch a SMD relalais, connected to ai3. The digital output is the excitation current for ai3 (0/2 mA with resistor or 0/21 V without resisitor) . This worked  fine in an earlier project with switching relay  outside of the measurement loop.

Now I need continuous data.

But the daqmx property node give the error:

Error -200557 occurred at Property Node DAQmx Channel (arg 2) in setswitch.vi
Possible reason(s):
Specified property cannot be set while the task is running.
Set the property prior to starting the task, or stop the task prior to setting the property.
Property: AI.Excit.Val
Channel Name: Dev1/ai3
Task Name: _unnamedTask<15>

How can I switch the excitation current for ai3 without DAQmx Stop / DAQmx Stop  and loosing some samples for ai0:2?

Peter

[jSturm]

Hi Peter_S,

I think switching the excitation current for ai3 without DAQmx Stop isn´t possible in my eyes.
Specified property cannot be set while task is running. You can read that here:

Error -200557 Occurs When Using Property Node After Calling Abort on a task (via the DAQmx Control Task.vi) - National Instruments
http://digital.ni.com/public.nsf/allkb/B84FB2E8915E601086256D1D00646B1B?OpenDocument

Maybe it´s possible for you to use only current or voltage inputs for AI3?
Otherwise you can use two sepperated channels for AI, if you have more or other hardware?

Maybe someone else here have a good idea, but changing property of one task without using DAQmx Stop seems

not to be possible in my eyes.

[Peter_S]

The same error come in the Measurement Studio DAQmx examples. I assume that is an restriction of the DAQmx Driver.

I will use an other network device to switch the relay.