Control analog output based on analog input

Dear forumers,
I am pretty new to the labview programming so excuse me if this was posted before.
I use: Labview 8.5 + PCI 6229
I want to create a real time feedback: to control analog output based on analog input. The task is very simple - if the ai1 (analog input 1) voltage is larger than a constant, then decrease the voltage of the ao1 (analog output 1) by a constant. Otherwise increase the voltage of ao1 by the same constant.
All should work for 10 seconds.
I have tried to implement this using 2 daq asistants and various methods. The problem is that I get the whole signal recorded from the ai1 ( 10 seconds) and then modified and released to the output (another 10 seconds). The execution takes 20 seconds instead of 10 and it is not realtime at all.
Is it a must to make vi in "run continuous" mode to make it work ?
Please help :}.
I am attaching 2 examples.
1. Main idea what I am trying to accomplish
2. Very simple example that still does not work in real time simultaneously.
Attachments:
example-main.vi ‏180 KB
example-simple.vi ‏147 KB

nooto wrote:
Thank you for your suggestion.
I understand the simple arithmetic you are talking about. However I do not understand why it takes 20 seconds instead of 10 to complete the task. In other way to say - why it reads the whole input first (10 seconds) then write the output ( 10 seconds).
Why doesn't ir read and write simultaneously?
If I use Elapsed Time function - what feedback response time can I expect ? Is it good to use Elapsed Time if i need fast response time? In my application i would I need about 1 milisecond response time. Currently in the example the rate is 50 Hz, later I would like to change the rate to 1000.
You simply don't understand the underlying paradigm of LabVIEW -
dataflow. You have a dependency between the first DAQ Assistant and the
second. The second simply will not start until the first finishes. There
is no way around that given your condition that the output depends on
what you read.
If you want 1 millisecond response time then you will have to swithc to a real-time OS. Windows does not have that kind of resolution and there is way to much jitter.

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Analog output digital start trigger c api

Hi, I am attempting to start analog output based off a digital trigger (either PFIO, or a PXI line) I can do this easy in LabVIEW. However with the C API (through Python wrappers), the problem isthat when I call DAQmxBaseWriteAnalogF64, the write will always timeout as the acquisition has not been triggered. However, I cannot call this after the trigger occurs, as obviously that will be too late.
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Hi PatrickR,
You can review some of the text based NI DAQmx (ANSI C) code examples on generating an analog output using a digital start trigger. If you included/checked text-based support dusing your NI DAQmx driver installation, you can navigate to Windows Start>All Programs>National Instruments>NI DAQ>Teaxt-Based Code Support>ANSI C Examples>Analog Out>Generate Voltage>Mult Volt Updates-Int Clk-Dig Start. If you have any questions/concerns regarding the NI hardware.

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I am programinning in labview and I would like to generate from my DaqPad 6020E sawtooth signal. I have a problem becouse I can generate virtually but not in Analog Output. Please verify my program which is attached to the mail. If you can please write your simple program which generate sawtooth signal in analog Output. I was checked programs (examles) in ni.com but i can generate one. I know that AO works becouse i checked it sending sin (as trigonomethry sig) and there was no problem.
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output_pulses_on_sine_wave.vi ‏27 KB

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Go to Solution.

This is my code in C++, you can optimize it if it looks too messy. This code reads signal from analog input and outputs it through analog output.
To make this code work additional include directories and library directories must be added from NI.
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#include <stdio.h>
#include <conio.h>
#include "NIDAQmx.h"
#include <math.h>
#define DAQmxErrChk(functionCall) { if( DAQmxFailed(error=(functionCall)) ) { goto Error; } }
int main(int argc, char *argv[])
int32 error=0;
TaskHandle taskHandleRead=0,taskHandleWrite=0;
int32 read=0;
float64 dataRead[1000];
char errBuffRead[2048]={'\0'};
char errBuffWrite[2048]={'\0'};
bool32 done=0;
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Hi!
I'm really new to LabView. Pls help!
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e.g.
t=0, stimulus sample 1, response sample 1
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Thanks.
Regards,
Student
Attachments:
Acquiring Linear Encoder Samples.vi ‏44 KB

Hello Htp,
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Hi, iam facing proble in synchronizing 4 ni 4472 cards input with pxi -6052e analog output. please help me out to sort out this problem

hi, iam facing problem in synchronizing 4 ni 4472 cards input with pxi -6052e analog output. please help me out to sort out this problem

Hi achyuth,
Thank you for posting on the National Instruments forum.
I am not sure what you are trying to do. Are you trying to input and output at the
same time? Are you just trying to
synchronize all of your inputs? Do you
want them to run off the same clock? If
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better.
In the meantime, this might help you:
PXI Timing,
Triggering, and Synchronization Capabilities of E-Series Multifunction Data
Acquisition ...
PXI Timing and Synchronization
Thank You,
Nick F.
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Attachments:
dac_good.vi ‏77 KB
adc_good_fw.vi ‏124 KB

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how can i synchronize analog output and analog input timings to generate and measure voltage at the same time.

Read this Tutorial
http://zone.ni.com/devzone/cda/tut/p/id/3615#toc3
And also refer to this link where You have repeated this question.
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Greetings to all --
I've set up a PCI6070E card to do digital input through its "counter 0" channel and output through its "AO 0" channel.
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[email protected]

Chad,
The only way you can perform this type of operation with your device is in software. See the knowledge base entries below for more details.
HW resetting Counter on an STC Device:
http://digital.ni.com/public.nsf/websearch/55AF6CADD87F6F7786256B89005B8AFD?OpenDocument
How To Reset in Software:
http://ae.natinst.com/operations/ae/public.nsf/web/searchinternal/65e3dbc715998c3286256e900075b7f8?O...
Regards,
L. Allen

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Hi there,
I'm guessing the VI you are using is the one from this KB:
http://digital.ni.com/public.nsf/allkb/6F2C2B49A89D685C8625711D007BDD64
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I'm using DAQmx and LV 8.2
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Questions regarding analog output

I want to build a LabVIEW file to generate analog output signal. Basically, if a variable (say, temperature) is between 250 and 500, voltage will be applied to a valve and open the valve. The attached is my first try using LabVIEW. But there is an error:
Error -200077 occurred at Property Node DAQmx Timing (arg 1) in DAQmx Timing (Sample Clock).vi:1->pulse based valve control.vi
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Property: SampTimingType
You Have Requested: Sample Clock
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Task Name: _unnamedTask<2>
The DAQ device I used is USB-6009. I tried different sample modes, but nothing worked. How can I fix this problem?
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1. Is it necessary to set sample rates for the AI and AO channels?
2. Is it necessary to synchronize the sample clocks for AI and AO channels?
Thanks,
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Hi Qifu,
If you are new to LabVIEW and DAQmx, I would suggest reading
this tutorial. The shipping examples are also a wealth of knowledge. (Help >> Find Examples >>
Hardware Input and Output >> DAQmx >> Synchronization >>
Multi-
Function)
You did not specify how fast you will be acquiring
data. I will assume that you will be
acquiring and generating at a slow rate since you are measuring
temperature. Yes, you should set the
sampling rate and sample clocks the same for both the AI and AO. I would refer to the example (Multi-Function-Synch
AI-AO) in the example finder on how to accomplish this.
Respectfully,
Rob F
Test Engineer
Condition Measurements
National Instruments

Control analog output based on analog input

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