PID Control - analog input, digital outputs

Hello everyone,
I am trying to use the PID toolkit to convert my existing feedback control system to one using PID or just PI whatever works best. Problem is that the tutorials out there discuss in detail about obtaining Analog inputs and using the PID output to control an analog output. Are there any tutorials that show how I can control my process variable which is an analog input by using the PID output to generate digital outputs?
Basically, what I am doing is controlling the incline of my device with two digital outputs that control two solenoid valves. The angle is calculated from a calibration curve that plots distance sensor voltage with Angle. Any help would be immensely apprecitated. I want to try this out on my own before I post some vi's. Thanks!
V
I may not be perfect, but I'm all I got!

That is exactly what I am doing currently. I have error bands specified around the target to make sure that it doesn't oscillate. But, under load conditions such as pulsed load conditions, the device goes out of bounds and the values trigger to correct for it. But, what I need is seemless or atleast seemless correction. Currently what I see is sudden adjustments to the incline. Please find attached what I am currently using. I am trying to get a more finer solution if at all possible.
Note: Within 5% of the target = NO action
Between 5% and 15% = Pulsed ACtion ( DO On for Pulse width time)
Greater than 15% = continuous action until it reaches Pulse band
I may not be perfect, but I'm all I got!
Attachments:
TDML_subElevationControl.vi ‏41 KB
TDML_subPulsedValveFuntion.vi ‏16 KB

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I need help in setting both analog input and output in one single VI. How do I assign channels to be either input or output? How do I simultaneously uses both in one single VI with a while loop structure?? Which AO am I suppose to use to obtain signal from the function generator I have built to feed into the DAQCard-1200?? Help!!
Attachments:
Test1.vi ‏48 KB

One thing you'll need to be aware of is that you will need to DMA lines: one for AI and one for AO. If you don't, then you can configure the DAQCard to do without DMA using the Config VI. But you certainly can do this.
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Synchronizing analog input and output

I am in the middle of converting some Traditional NI-DAQ code to the
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6221).

Don't use Connect Terminals. Use the technique shown in this example program
C:\Program Files\National Instruments\NI-DAQ\Examples\DAQmx ANSI C\Synchronization\Multi-Function\ContAI-Read Dig Chan
which is the sharing of sample clocks via the DAQmxCfqSampClkTiming function where the sample clock source of one task is set to the clock of the other task. This example slaves a digital input task to an analog input task but the idea is the same for your application.

How to synchronize analog input and output from two different USB daq boards

Hi all,
I have two very differnt USB boards the NI USB 6008, which I am using to acquire the data (Analog Input) and a NI USB 9263, it is an Analog Output only board that I am using to deliver a signal (in this case a square pulse). The reason why I am not using the 6008 Analog Ouputs is because I need to deliver negative voltages and need the full +/-10V range.
Looking at similar posts I am pretty sure that I can't use an external trigger or a shared clock, I also tried to use the synchronization of timed structures but no cigar.
I am including a quick vi that I whipped out showing how the signal jitters due to the lack of synchronization. The AO from the 9263 connects to the AI in the 6008 in this example.
Solved!
Go to Solution.
Attachments:
Test Pulse.vi ‏117 KB

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Creating a control sequence of digital outputs with timing

I'm trying to create a controls system for a cleaning process. I am controlling a pump, heater, and several solenoid valves using relays that I am opening and closing with the +5V from my USB 6008 and each relay goes to one of the digital I/O lines, where I provide a sink to switch the relay.
I am using the front panel as the user interface for the machine, so the user can specify three different processes, so I'm using an event structure to call each process. An example of the steps in the process are as follows:
1. Open relay #1 (solenoid valve)
2. Open relay #4 (heater)
3. Wait 30 seconds (while relays #1 and #4 are still open)
4. Close relay #4
5. Close relay #1
6. Open relay #2 (solenoid valve)
7. Wait 5 seconds (while relay #2 is still open)
8. Close relay #2
I am trying to use a framed sequence structure within the event cases, with the DAQ Assistant saying which lines are sinks and which are also outputting +5V (no delta, keeps relays closed), but I don't think this is working and will bog down the system if it did. I think inverting the lines will make it so the lines nominally output the +5V so I just need to send it a sink when I want to close the relays, and make sure it keeps doing that while it waits so the process can be completed.
What is the best way to do this? I've used Labview before, but I'm hardly a pro, so any help would be greatly appreciated.

As nijams mentioned a state machine architecture is a good place to start. In case you are unfamiliar in how to implement this in LabVIEW there is a blank state machine template available in LabVIEW. When you create a new VI select From Template->Frameworks->state machine. In addition I've included a link to a simple example posted on our NI Community.
State Machine Example.zip: https://decibel.ni.com/content/docs/DOC-15515
Regards
Regards,
Isaac S.
Applications Engineer
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Multithreaded analog input and output and serial communication during the AIAO

I need to read in analog data on 4 channels (4000 scans/s on each channel for a total of 250ms) and while this is happening send out two signals: A trigger pulse (which I currently send on an analog channel, using channel DAC0OUT) and two ascii commands using the serial port. My problem is that the data acquisition VI I am using is a blocking VI, it runs to completion before allowing the two signals to be sent. I am using the VI titled, "AI Acquire Waveforms (scaled array).vi" I don't need to look at the acquired data until after the whole operation is complete. Any help anyone can offer would be much appreciated.

Hello Mark,
The AI Read VI will block other operations when waiting for data. I would suggest to reduce the number of scans to read (this is an input for the AI Read VI) to help with handling multiple operations simultaneously. By reducing the number of scans to read by the AI Read VI, it won't have to wait for the whole buffer to be read in before "unlocking" the CPU for other operations. You could place the AI Read in a loop and acquire smaller chunks of the data at a time. For instance, your buffer size is probably 1000. Instead of calling the AI Read VI once and waiting for all 1000 scans, you could place the AI Read in a for loop and acquire 200 scans at a time (have the for loop run 5 times).
Or you could set up the AI Read VI to read 0 scans the fir
st time and then just read whatever is in the backlog on subsequent calls. There is a backlog output to AI Read; you could use this with a shift register within a loop to read only the data that is already in the buffer. For both of these cases, I would place a wait in the loop (25-100 ms) to give the CPU time to do other things.
Another method is to use an occurrence. Place the Functions >> DAQ >> Misc >> Set DAQ Occurrence.vi on your block diagram and set the "DAQ Event" input to "Fire every n scans" (the actual string is a little different). Then put in a Wait on Occurrence function (Functions >> Advanced >> Synchronization >> Occurrence) When you use an occurrence, you are waiting for the driver to tell you when the data is acquired, rather than constantly querying the driver, so it is much faster.
One of these suggestions should help.
Let me know if you have any additional questions.
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Todd D.
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PID with digital output

Hi,
I have the application.
I do not clear about PID function but, I would like to ask you about my application.
I have a sensor water level and a few motors to control gates
I measure water level and control motor via digital output(using the fieldpoint system)
I would like to hold water level at level, so I use PV indicator and SV control. when I change SV then will control Motor (RW or FW motor).
Can we use how technology to hold water level PV=SV ?.
Please let me know your comments.
Thanks
Nguyen Van Hung

Hi Nguyen,
There are several examples in CVI under Help » Find Examples that may be able to help speed up the development of your PID program (assuming you have purchased the CVI PID Toolkit). These examples can be found by going to Toolkits and Modules » PID and Fuzzy Logic Control » PID. Depending on how familiar you are with PID algorithms, I might suggest that you look at the GeneralPid example first. Additionally, the PID Control Toolkit User Manual t is also a great place to look at the algorithms and the library functions. Finally, in case you aren't aware, you can double click on any function that you find in the Libraries folder located in the bottom left of CVI to open a functions panel which will show all inputs and outputs of a given function. Then, you can right click on any parameter to view details about that or on the function panel (outside an input box) for more information about the function in general.
I hope these resources help you design an algorithm that works well for your situation!
Regards,
Trey C.
Applications Engineer
National Instruments

How to get signal from analog input and send it to analog output (real-time)

Hi everyone,
I am doing simple task in Visual C++ and I am using PCI-6221(37 pin).
Basically, I want to send same signal from 'analog input' to 'analog output'
at the same time (almost), to make it real-time application.
Can someone please provide me sample program.
I would appreciate if you could provide me with the good tutorial which explains
step by step everything about programing NI-DAQmx for C/C++.
Best Regards,
Khassan
Solved!
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.
I hope it helps someone.
#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;
int32 written;
DAQmxErrChk (DAQmxCreateTask("",&taskHandleRead));
DAQmxErrChk (DAQmxCreateAIVoltageChan(taskHandleRead,"Dev1/ai0","",DAQmx_Val_Cfg_Default,-10.0,10.0,DAQmx_Val_Volts,NULL));
DAQmxErrChk (DAQmxCfgSampClkTiming(taskHandleRead,"",100.0,DAQmx_Val_Rising,DAQmx_Val_ContSamps,0));
DAQmxErrChk (DAQmxCreateTask("",&taskHandleWrite));
DAQmxErrChk (DAQmxCreateAOVoltageChan(taskHandleWrite,"Dev1/ao0","",-10.0,10.0,DAQmx_Val_Volts,NULL));
DAQmxErrChk (DAQmxCfgSampClkTiming(taskHandleWrite,"ai/SampleClock",100.0,DAQmx_Val_Rising,DAQmx_Val_ContSamps,1000));
DAQmxErrChk (DAQmxStartTask(taskHandleRead));
DAQmxErrChk (DAQmxStartTask(taskHandleWrite));
while( !done && !_kbhit() )
DAQmxErrChk (DAQmxReadAnalogF64(taskHandleRead,1,10,DAQmx_Val_GroupByScanNumber,dataRead,1000,&read,NULL));
DAQmxErrChk (DAQmxWriteAnalogF64(taskHandleWrite,read,0,10.0,DAQmx_Val_GroupByChannel,dataRead,&written,NULL));
_getch();
Error:
if( DAQmxFailed(error) )
DAQmxGetExtendedErrorInfo(errBuffRead,2048);
DAQmxGetExtendedErrorInfo(errBuffWrite,2048);
if( taskHandleRead!=0 )
DAQmxStopTask(taskHandleRead);
DAQmxClearTask(taskHandleRead);
if( taskHandleWrite!=0 )
DAQmxStopTask(taskHandleWrite);
DAQmxClearTask(taskHandleWrite);
if( DAQmxFailed(error) ){
printf("DAQmx Error: %s\n",errBuffRead);
printf("DAQmx Error: %s\n",errBuffWrite);
printf("End of program, press Enter key to quit\n");
getchar();
return 0;

How to temporally match/save Input and Output Channels's data?

Hello, I have a voltage-input, voltage-output SISO system, and need to indentify its dynamic response (or transfer function) as a reference to a PID control. Without using the system identification toolbox, my goal is to generate/provide a sine sweep input (ranging 1Hz-5kHz for 10sec) to the system and to save the corresponding output response signal as well as the sweep input signal simultaneously.
I got a sample program online and am trying to modify it as attached, but I really need your advices/comments concerning several problems I am facing with:
1) With the below setting, the number of the acquired Input channel samples obtained is 5461, which is smaller than expected (i.e., 10000). What would I be missing in setting parameters?
- H/W: NI-USB-6341 DAQ
- AO: continuous samples with the waveform timing (1k sampling, 10000 samples => 10 sec, slower sampling just for testing purpose)
- AI: continuous samples, samples to read: 30k, rate: 1k
2) I am using flat sequence structure as a way to making the start point of saving AI and AO data same, but wonders if this is a right method or if there is other better approaches. (I had an idea of using an internal clock with "1-sample mode" for sync, but this may not work at the high speed sine sweep like 5kHz, right?)
3) I just want to provide the sine sweep just once to the system and do not require the "reset" functionality implemented in the original sample program. I failed to remove this "reset" part as I did not fully understand the sample code. If I run the attahed, the generated AO signal is periodically provided to the system. Please give me any advice to modify the program as I want.
Thanks for your help and valualble time.
Attachments:
siso.vi ‏230 KB

Hi J. Kim,
To begin, you say you want to synchronize your analog input and output so that they start at the exact same time, yes? To achieve tight synchronization, you need to use DAQmx VIs instead of the DAQ Assistant. There's a good overview of DAQmx VIs here. There's also a document that deals specifically with synchronization in DAQmx here. Additionally, if you go to Help>>Find Examples in the LabVIEW example finder, you can see many other examples of acquiring data using DAQmx.
As for your configuration, you have your analog input DAQ assistant wired far before your analog output DAQ assistant in your sequence strucutre, so the dataflow of the program will cause the analog input DAQ Assistant to execute before the output. They cannot be in different sequences if they are executing simoultaneously, and I would not use flat sequences here except to start the two tasks in DAQmx. Where did you find this example?
Best,
Dan N
Applications Engineer
National Instruments

Macbook Pro 4,1 (early 2008) is the DVI port analog or digital?

I have been tasked with a slide show presentation on a family member's HD TV using my MacBook Pro 4,1. The TV is a slightly older big screen TV without HDMI inputs. I would lke to use the component (YPbPr) inputs on the TV rather than VGA. VGA degrades the image appearance too much.
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Synchronize input and output tasks to start at the same sample point [C++ NI_DAQmx Base]

I'm trying to initiate the analog input and output streams to start reliably at the same sample. I've tried triggering the output from the start of the input using the following code [NI-DAQmx Base 2.1 under Mac OS X with an M-Series multifunction board]. It compiles and runs, but gives an error message at the call to "DAQmxBaseCfgDigEdgeStartTrig". Any suggestions about synchronized I/O on this platform?
#include "NIDAQmxBase.h"
#include
#include
#include
#define DAQmxErrorCheck( functionCall ) { if ( DAQmxFailed( error=( functionCall ) ) ) { goto Error; } }
int main( int argc, char *argv[] )
// Task parameters
int32 error = 0;
TaskHandle inputTaskHandle = 0;
TaskHandle outputTaskHandle = 0;
char errorString[ 2048 ] = {'\0'};
int32 i;
time_t startTime;
// input channel parameters
char inputChannelList[] = "Dev1/ai0, Dev1/ai1";
float64 inputVoltageRangeMinimum = -10.0;
float64 inputVoltageRangeMaximum = 10.0;
// output channel parameters
char outputChannelList[] = "Dev1/ao0, Dev1/ao1";
char outputTrigger[] = "Dev1/ai/StartTrigger";
float64 outputVoltageRangeMinimum = -10.0;
float64 outputVoltageRangeMaximum = 10.0;
// Timing parameters
char clockSource[] = "OnboardClock";
uInt64 samplesPerChannel = 100000;
float64 sampleRate = 10000.0;
// Input data parameters
static const uInt32 inputBufferSize = 100;
int16 inputData[ inputBufferSize * 2 ];
int32 pointsToRead = inputBufferSize;
int32 pointsRead;
float64 timeout = 10.0;
int32 totalRead = 0;
// Output data parameters
static const uInt32 outputBufferSize = 1000;
float64 outputData[ outputBufferSize * 2 ];
int32 pointsToWrite = outputBufferSize;
int32 pointsWritten;
for( int i = 0; i < outputBufferSize; i++ )
outputData[ 2 * i ] = 9.95 * sin( 2.0 * 3.14159 * i / outputBufferSize );
outputData[ 2 * i + 1 ] = -9.95 * sin( 2.0 * 3.14159 * i / outputBufferSize );
// ------------------- configure input task -----------------------
DAQmxErrorCheck ( DAQmxBaseCreateTask( "", &inputTaskHandle ) );
printf( "Created input task\n" );
DAQmxErrorCheck ( DAQmxBaseCreateAIVoltageChan( inputTaskHandle, inputChannelList, "", DAQmx_Val_RSE, inputVoltageRangeMinimum, inputVoltageRangeMaximum, DAQmx_Val_Volts, NULL ) );
printf( "Created AI Voltage Chan\n" );
DAQmxErrorCheck ( DAQmxBaseCfgSampClkTiming( inputTaskHandle, clockSource, sampleRate, DAQmx_Val_Rising, DAQmx_Val_ContSamps, samplesPerChannel ) );
printf( "Set sample rate\n" );
// ------------------- configure output task -----------------------
DAQmxErrorCheck ( DAQmxBaseCreateTask( "", &outputTaskHandle ) );
printf( "Created output task\n" );
DAQmxErrorCheck ( DAQmxBaseCreateAOVoltageChan( outputTaskHandle, outputChannelList, "", outputVoltageRangeMinimum, outputVoltageRangeMaximum, DAQmx_Val_Volts, NULL ) );
printf( "Created AO Voltage Chan OK\n" );
DAQmxErrorCheck ( DAQmxBaseCfgSampClkTiming( outputTaskHandle, clockSource, sampleRate, DAQmx_Val_Rising, DAQmx_Val_ContSamps, samplesPerChannel ) );
printf( "Set sample rate\n" );
// trigger output when input starts
DAQmxErrorCheck ( DAQmxBaseCfgDigEdgeStartTrig( outputTaskHandle, outputTrigger, DAQmx_Val_Rising ) );
printf( "Set output trigger\n" );
// ------------------- configuration -----------------------
// write output signal
DAQmxErrorCheck ( DAQmxBaseWriteAnalogF64( outputTaskHandle, pointsToWrite, 0, timeout, DAQmx_Val_GroupByScanNumber, outputData, &pointsWritten, NULL ) );
printf( "Write output signal\n" );
// set up input buffer
DAQmxErrorCheck ( DAQmxBaseCfgInputBuffer( inputTaskHandle, 200000 ) ); // use a 100,000 sample DMA buffer
// initiate acquisition - must start output task first
DAQmxErrorCheck ( DAQmxBaseStartTask( outputTaskHandle ) );
DAQmxErrorCheck ( DAQmxBaseStartTask( inputTaskHandle ) );
// The loop will quit after 10 seconds
Dr John Clements
Lead Programmer
AxoGraph Scientific

Hi Michael,
First of all, thanks very much for taking the time to investigate this problem! Much appreciated.
You asked for "an actual error code you got and any description that is given". The full output from the program that I posted earlier in this thread is appended to the end of this message. In summary, following the call to...
DAQmxErrorCheck ( DAQmxBaseCfgDigEdgeStartTrig( outputTaskHandle, outputTrigger, DAQmx_Val_Rising ) );
... with ...
char outputTrigger[] = "Dev1/ai/StartTrigger";
...the error message is ...
DAQmxBase Error: Specified route cannot be satisfied, because the hardware does not support it.
You asked "specifically which M series device you are using"? It is the PCIe 6251 (with BNC 2111 connector block). I'm testing and developing on an Intel Mac Pro (dual boot OS X and Windows XP).
You asked for "the location you pulled the code from". Here it is...
http://zone.ni.com/devzone/cda/epd/p/id/879
...specifically from the file "Multi-Function-Synch AI-AO_Fn.c".
I adapted the NI-DAQmx calls to their NI-DAQmx Base equivalents.
Finally, you asked "Is the trigger necessary, or do you just need to know that the measurements are running on the same clock?". I believe that some kind of sychronized trigger is necessary in my situation (correct me if I'm wrong). Timing is crucial. Say I initiate an analog output stream that delivers a voltage command step 5 ms from the onset. I need to record the response (analog input stream) so that its onset is accurately aligned (synchronized) at 5 ms. A typical recording situation would stimulate and record a short data 'sweep', then wait for the (biological) system to recover, then stimulate and record another short sweep, and repeat. I need all the recorded sweeps to align accurately so that they can be averaged and analyzed conveniently.
I definitely do not want my customers to rely on an expensive external TTL pulse generator to initiate and synchronize each 'sweep'. That would effectively eliminate the cost advantage of an NI board, as well as adding unnecessary complexity in setup and use. It would be a show-stopper for me.
It seems perverse, but would it be possible to use a digital output channel connected directly to a digital input chanel to trigger the input and output streams?
Regards,
John.
Full output from test program. Compiled with gcc 4 under OS X...
[Session started at 2007-05-23 14:17:01 +1000.]
LoadRuntime: MainBundle
CFBundle 0x303cc0 (executable, loaded)
_CompatibleWithLabVIEWVersion: linkedAgainst: 08208002
_CompatibleWithLabVIEWVersion: result= false, mgErr= 1, theActualVersion= 00000000
_CompatibleWithLabVIEWVersion: linkedAgainst: deadbeef
_CompatibleWithLabVIEWVersion: Reseting Linked Against
_CompatibleWithLabVIEWVersion: linkedAgainst: 08208002
_CompatibleWithLabVIEWVersion: result= true, mgErr= 0, theActualVersion= 00000000
_CompatibleWithLabVIEWVersion: linkedAgainst: 08208002
_CompatibleWithLabVIEWVersion: result= true, mgErr= 0, theActualVersion= 00000000
com.ni.LabVIEW.dll.nidaqmxbaselv
CFBundle 0x313760 (framework, loaded)
{type = 15, string = file://localhost/Library/Frameworks/nidaqmxbaselv.framework/, base = (null)}
Amethyst:Library:Frameworks:nidaqmxbaselv.framework
2007-05-23 14:17:02.248 test-ni[4445] CFLog (21): Error loading /Library/Frameworks/LabVIEW 8.2 Runtime.framework/resource/nitaglv.framework/nitaglv: error code 4, error number 0 (no suitable image found. Did find:
/Library/Frameworks/LabVIEW 8.2 Runtime.framework/resource/nitaglv.framework/nitaglv: mach-o, but wrong architecture)
CFBundle 0x1751fdc0 (framework, not loaded)
Created input task
Created AI Voltage Chan
Set sample rate
Created output task
Created AO Voltage Chan OK
Set sample rate
DAQmxBase Error: Specified route cannot be satisfied, because the hardware does not support it.
test-ni has exited with status 0.
Dr John Clements
Lead Programmer
AxoGraph Scientific

PXI-6230 analog input trigger setup

Hi,
Can anyone point me in the right direction of how to configure the PXI-6230 card to implement 3 of the analog input channels as a digital input trigger? The input to each channel is TTL pulses. I want to have a trigger event on every pulse from any of the three inputs. I'm using LabVIEW 8.5. Any help is appreciated. Thanks.

Hey HarveryL,
I'm not sure it is possible to do this. Can you give me some more details on your application, and why you want to use the analog inputs as a digital trigger? Here is an article on how to use PXI triggers with the analog input and output, perhaps you can adapt that code to your purposes. I'll continue to look into this for you, but any more information you can provide would be appreciated. Have a great week!
John B.
Embedded Networks R&D
National Instruments
Certified LabVIEW Developer

PID Control - analog input, digital outputs

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