Design practice nor 6008 USB DAQ

Hello

I have a few question, I'd like to introduce. I need some sort of indication on how to better perform a timed cycle of acquisition driven by WSF.
I'll send my VI (conceptual, not one currently working one) and ask for explanations.
The goal

I need to acquire a battery voltage. Load current consumption is driven by a couple of transistor. I drive the hollow transistors two digital i/o for USB data acquisition.

Because I need to have a power for a given time cycle, I need to have some sort of time control on the output.
So I wrote a simple state machine whose States are updated when a timer reaches zero. Each State has its own queue time.
Moreover, I differentiate between acquisition and control operations using two all in cycles.
First question: is this a correct way to a timed WSF of construction?

and now:

The problem (s):

I need to connect and establish a correlation between the input line for the internal of the fsm States. So I madesome digital indicator on the face before of the VI and created a local variable (I know that local variables are BAD, but I had no other idea everything) to pass values for some time to the other.

I also want to select State sequent of the FMS based on the input value, I get a channel. I can stil use a local variable?

Are the two related tasks?

Second question: are local variables, something that I can use for this task?

Last but not least: I need to filter on the values.
In this vi I perform a filtering operation and then I get the I use for control of local variables.

will be this filtering desync the two cycles while? will I run out of control before running the filtering?

The same question is valid for the purposes of registration: the unfiltered data record, I guess is unnecessary. But based on this 'architecture' I know the country reports and the recorded signals are out of sync (as happens in many game data acquired with this vi).
Is this a problem of logging (perhaps given by different buffers for data acquisition and internal State or something similar) or the whole WSF will be out of sync, then all acquired data is more useful because it is out of sync?

Any advice would be much appreciated.

Best regards

Luca.

Luca,

Question 1: This is a reasonable start but need some things to make it a good WSF. There is no waiting or delay in the loop so it will run as fast as possible. U.S.-6008 outputs digital software timed so that the DAQ Assistant can take a long time, but the amount of time is unknown and not necessarily consistent from iteration to iteration. Since the DAQ Assistant Analog Input in the other races of loop to<= 10="" iterations="" per="" second,="" a="" wait="" of="" 100="" ms="" in="" the="" fsm="" loop="" seems="" like="" a="" good="" starting="" point.="" waiting="" 3000="" ms="" is="" not="" a="" good="" idea="" because="" the="" loop="" becomes="" unresponsive="" to="" the="" stop="" button="" for="" long="">

Do you need to write on the lines on each iteration, even when the data has not changed? Add a write state that is called only when the data changes.

The DAQ Assistant has a Stop input and an output of Stopped. When you are ready to stop the loop, the stop signal must be wired to these inputs so that the DAQ Assistant can delete tasks. The output of the order can be connected to a Terminal to stop the loop.

Problem (s):

It seems that you want to link the two loops. Local variables are usually a bad way to do it. The best way is to use queues. A queue can send the current state of the file loop. (More comments later if that's really what you need). Another line can send data, or better, the commands, the loop of the file to the loop.

I think you want digital output values rather than the State. Especially if you add a State writing as I suggested above, the current state will not always represent the condition of the power of your test. To make this work with the additional state Boolean matrix must be moved from one iteration to another via a shift register.

It seems that you have at least two controls to be sent from the loop of the file to the loop. One is the stop command. The other went to the higher power level control. You should probably have a command to set off power level which can be used if the battery voltage becomes too low and before stopping. How your program is currently configured, the last level of power will continue as long as the power of the computer is on and the USB-6008 is always plugged. The cessation program does NOT reset the lines.

When you use anti-parallel to the queues, you must be careful on the definition of wait times and the timed out case management.

The benefits of the queues are that it is easy to ensure synchronization at the level you need, the data can be stored according to the needs, and there are good examples. It also avoids the possibilities of race conditions, often introduced by local variables. This program could be based on a variation of the design producer/consumer model.

Filter questions: any filter introduces a time delay. In your case when you filter 100 samples 10 times per second, it is likely that the filter will do well until the next data set has arrived. The delay of the filter is not affecting your synchronization. The above lines will solve problems. Since you are looking at time of cycle seconds and the minimum interval on the order of 100 ms, the exact chronology (to tens of milliseconds level) is probably not too important.

The real question about filtering boils down to this: does the control work better if the signal is filtered?

- - - - -

I'd probably all this a little differently. Given the slow speeds and the small amount of data, a simple loop with an improved state machine is all that is needed. Get rid of the DAQ Assistant and learn how to use DAQmx screws. States could include: Init THE Init, Init File, Idle, read, write, DO, Analyze, filter, adjust the power, wait, Save, close file, DO, AI Shutdown Shutdown, error and exit. No variables. No indicator fake just to allow the creation of local variables. Very little code outside the structure State case. None of the queues.

Lynn

Tags: NI Hardware

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