Delay between input and output

[JDonne]

Hello,

The VI I have attached is not behaving correctly, What I am trying to do is the following

1. Inform the op with some instructions .

2. Compare two analogue voltages,

3. If the difference between these two voltages is greater than 2 volts, then output a freq (sine wave) of 30 Hz's

4. If the difference is less than 2 volts then output a freq of 10 Hz's.

5. Once both inputs are equal then it will jump out of the loop informing the operator

The VI I have attached is not doing this exactly and I cannot see the reason for it.

The VI will do the following:

#1 (if the 2nd DAQ assistant (outputting a sinewave), has its in it properties section "signal output range" set for Max = +10 and min =-1) the following occurs:

Adjusting one of the voltage inputs, will update the front panel immediately, however there is no signal on the output of the NI 9263

#2 (if the 2nd DAQ assistant for outputting a sinewave, has its signal output range set for Max = +10 and min =-10) the following occurs:

Adjusting one of the voltage inputs, results in there being a huge delay (1-3 min) before the indicator on the front panel updates, however there is a signal on the output of the NI9263

The equipment i am using is the follwoing:

Reading analogue inputs NI 9205

Generating output NI 9263

Any guidance is much appreciated

[vt92]

Based on the configuration of the DAQ assistance, it looks like you are only reading one sample per channel.  I would convert from DDT to a scalar.  I'm not sure what behavior you will get wiring a dynamic data type to the case structure.

Your comparison function is configured for "one result per data point".  Try changing that to one result per channel. 

You don't need the inplace structure for single data points. 

[vt92]

Does this help?

 

[JDonne]

Thanks very much for the info.

Just one issue remaining:

When i adjust the voltage, in the labview osciloscope the freq changes from 10 to 30 Hz or vice versa immediately. However it takes about 12 seconds for the freq from the output of the NI 9263 to change. Is there a way the waiting time can be reduced.

Thanks

John 

[massic76]

Hello, my name is Massimo and I am trying to implement an input output application. I am sending an output that is known a priori and therefore it is not dependent on the input voltages in the NI card. I am using a USB Daq USB-6112. To test the synch between input and output I am reading the voltage that comes out from the output directly from one of the AI in the card. I am finding delays between input and output of about 13-15 ms. Is that normal? I am attaching the code in case you see something I am doing wrong with it. This is just my test code to evaluate the delay. I have followed examples from the NI site. I also spoke to an NI technical assistant but no luck. The person that tried to help, I did not feel very knowledgable regarding this issue.

Can any one help me to see if this delay is normal and whether I should just measure it and just move on or there is a way to reduce it.

Thank you in advance and look forward to hearing back from one of you.

Best, Massimo.