446x power up state

[TLA]

Hi all,

I'm using 4461 for some audio testing that involves a sequence of measurements.

In the first step, test signal is output through AO0 to an amplifier and speaker (Artificial mouth, non-referenced) and the response is acquired on AI1 (from a single-ended source).
In the second step the test signal is output through AO1 to single-ended input and the response is acquired on AI0 (from a non-referenced ICP microphone).
The step may be repeated in any order.

Both steps use the same tasks - one task for input and one for output. When a step executes the input task is created at the beginnig and cleared at the end. For the output task, any old task  is cleard before creating a new at the beginning and left at the end.

The problem is that when the second step is executed, the AO0 is in an unconfigured state and the hum can be heard from the atificial mouth. The DAC is appearantly returned to that power-on state, where the output impedance is high AND the 50 Ohm resistance is disconnected from the BNC outer shell to leave the output floating.

A similar situation arise on the input. After second step executes, the input task is cleared leaving AI0 unconfigured and the ICP current turned off. When the step is executed again, the ICP power is turned on, causing a long settling time for the microphone.

Question: is there a way to program the power-on / reset state of 446x to set grounding and IEPE paramters that will take effect when a channel is not part of a task?

[Morini]

Hi, here is a link that maybe can help you:

http://forums.ni.com/ni/board/message?board.id=100&message.id=585&requireLogin=False

Also you can use a "Channel Property Node" to changing the output idle state in Labview. There is an example program that does analog input and analog output called "Multi-Function-Synch AI-AO.vi". you may want to check that out.

Regrads

[TLA]

Hi Dennis

thank for your reply. I did read that thread about DC output and the issue is similar, but the solution a bit different.

I have also tried the channel property AO.IdleOutputBehavior, but it seems to work only when the channel is assigned to a task?!

I even found a 'DAQmx Set Power Up States.vi', but it does not provide settings for grounding and channel configuration.

When the task is cleared it apears that the output goes high impedance and disconnect the 50 Ohm resistor to chassis ground
The challenge is to find a way to prevent that.

One option might be to add the idle channel to the task and feed zeros. The down side to this solution is a more advanced task handling and some 100 - 2000 kByte memory overhead.

If any better ideas pop up, please let me know.

Best regards
Torben

[Morini]

Hi Torben,

I found some links for you:

http://digital.ni.com/public.nsf/websearch/3AD6CCE935192B4086256F6B0079CB1F?OpenDocument

http://digital.ni.com/public.nsf/websearch/862567530005F09C86256736004FCAF1?OpenDocument

And you can use a property node to set the input terminal configuration:

Place a property node on the block diagram, and right click it to change the classe to DAQmx channel. Then change the property to Analog input->General properties->Input configuration->terminal configuration.

Regards

[TLA]

Hi Dennis

just to focus my last reply - the issue is how to control what happens to channel when their task is stopped and cleared!

I have observed that when the task cleared the channel return to the power on state: No IEPE, differential mode, high-impedance.

This is a resonable power on state, but I kind of miss an option to keep my ground reference and IEPE power as long as the system is up and running. On 4451 you would often connect through BNC-2140, where grounding and power supply was set manually using switches on a per channel basis. On 4461 you connect directly to BNC on the board itself so now we must rely on the board configuration.

I think an option to specify a 'Default' or 'Hot reset' state for a device could be a good solution. When ever the task of a channel is cleared the channels return to the programmed 'Hot reset' state. By default this state would be identical to power on state of the device. The would be effective until the device is reset or powered off.

What does the DAQmx developers think of such an idea for a future release?

On the short term I will try to improve the task handling in my application.

Best regards

Torben

[Morini]

Hi Torben,

If you are able to use property nodes to set the grounding and IEPE paramters, then you can just use sequence structure in labview to set those paramters right after clear task.

You can use our Product Suggestion center to propose new fetures of our products: http://digital.ni.com/public.nsf/allkb/EDA7C01C684ACB6286256FF0000238D5

Regards