State Machine Programming books

I just finished the LabVIEW basics I & II.Are there any third party books available that can help explain and expand on building State machines and event driven programming. Or at least cover this material in detail. Thanks in advance.
SS

I definitely agree on the Labview Style book. best LV book i read (and reread).
my experience with the other book was not enlightning, but definitely worth a look.
allow me to propose :
"A Software Engineering Approach to Labview", by Jon Conway and Steve Watts.
the book is really good, and expand on programming techniques and architecture in general. i think it is well written.
The print version has a quality problem of the figures tough (at least some editions), so i suggest you contact the authors directly or purchase the online version.
... And here's where I keep assorted lengths of wires...

Similar Messages

LabVIEW Queued State Machine as Parellel Process Enabler

Hi
LabVIEWs Queued State Machine Architecture is a detailed article on its application for parallel process programming geared to take advantage of LabVIEWs hyperthreading capabilities and multi-core processor PCs of today.
I am writing future book chapters as blog articles so your critique/comments are appreciated.
Anthony L.

I have really enjoyed the articles on ExpressionFlow. I also like this one, but I think it could use just a little work. I think that the content is good. However, about 1/4 of the way down, you have:
A general layout of QSM-PC architecture comprises of the four objects annotated by the encircled numerals 1 to 4 shown in Figure 1.
These objects are namely: (1) Queue reference object; (2) User events
object (optional for head-less embedded applications that require no
user interaction); (3) Main state machine object; (4) One or more
parallel processes subVI objects.
You then go on to have
Item (1) The Queue Reference
Item (2) Consumer Object State Machine
Item (4) Parallel Process SubVIs
You need to reconcile the two. I think that a separate (probably earlier??) chapter/article on event structures including dynamic (user) events could be referenced as item 2.
Thanks for the articles and I hope that this helps!
Bob Young
Bob Young - Test Engineer - Lapsed Certified LabVIEW Developer
DISTek Integration, Inc. - NI Alliance Member
mailto:[email protected]

Data acquisition in a state machine

I've recently learned how to implement state machines, but I have a question that I haven't been able to find an aswer to.
Question:
How do I record uninterupted data (presently i'm using the DAQ assistant to record a single channel at 10kS/s at 1kS intervals) without interfering with my state machine?
Background:
I have a time sensitive test setup (measuring pressure in a rocket chamber), and I'm using labview to both record a single pressure transducer as well as operate the valves (O2, N2, igniter, etc). I'm using a state machine Labview architecture (just learned how). Presently, the DAQ assistant sits in the "Idle" state, and timers (valves need to be turned on at specific times) and manual buttons control when the other states are activated. I have a 10ms timer controlling how often each state is run, and this is the root of my concern.
Main concerns:
I'm worried that:
1) I'm forced to change my data recording to 10ms intervals to match the 10ms timer, and
2) The 10ms timer will interrupt my data recording when it's in another state.
It's very important that the pressure data is recorded without interruption but that I have high time resolution in controlling my valves as well.
Thoughts:
1) Maybe I put the 10ms timer in the "Idle" state only, and this way the other states won't interrupt the data acqusition
2) Maybe there is a way to completely isolate the state machine for controlling the valves and the data acqusition. I'm not sure how to do this.
3) People on the forums have been talking about Queuing their data acqusition, but I'm not sure how this would benefit my situation.
Thanks to everyone for their feedback!

The data acquisition and state machine timer do not have to be equal, you should however have the same data write rate as you have data read rate, otherwise over the course of long running programs you can build up a large buffer of data to be written using a lot of memory, or lose data.
Your data acquisition should be continuous, the most common way of doing this is every time you receive data write it to a queue, then when you are in other states except your data write stage you simply build up data in the queue that is to be written when you enter the write state again.
Think of it as traffic reaching a set of lights:
The traffic represents the data acquisition, there is a constant flow of it always coming through, the state of your state machine is the lights, green is the data write state clearing the queue, red is when in any other state, letting the traffic build up behind the lights.
It is just important that the light is green long enough to let the traffic not build up too much, otherwise you have a jam.
EDIT: For the basics of how queues work, look at the Queue basics example from the example finder.

Data acquisition & state machine

Hi all,
I am working on a project that is capable of data acquisition, analyse, and record processes. I have to acquire data of temperature from 8-32 channels and that of pressure from 7 channels. After analysis, I have 48 outputs. I want to record raw data (acquired) and analysis data at the same time.
1) Is it possible to record two text files (raw data and analysis data records) at the same time?
I also want to adjust acquired sample rate but I have doubts about utilizing it in a state machine. For now, I have just used time elapsed function to acquire data once in 60 seconds.
2) How could I set sample rate of acquisition except using time elapsed function?
I also have one more doubt about timing. If I needed to acquire sample once in 60 seconds, but the analysis took more than 60 secs, what would happen?
3) How can I prevent data loss in this case?
I have not prepared a user interface yet.
4) How can I utilize it? Do I put graphs and indicaters in the same VI or is it better to prepare another vi just for user interface?
Thanks in advance
Egemen
Attachments:
Program.llb ‏433 KB

Hi Egemen
-          If we need to acquire data and analyze it at the same time we recommend the architecture producer-consumer to prevent data loss, and yes you can record two text files at the same time. Please take a look to this architecture.
-          http://www.ni.com/white-paper/3023/en
-          Basically you use the first loop to acquire data and the second one to analyze and record data (using queues).
-          https://decibel.ni.com/content/docs/DOC-2431
-          You can also find examples about this architecture at the developer zone.
Regards

Relay Testing with State Machine

Hi,
Yesterday I very kindly had some help from "crossrulz" in setting out the following procedure. Today, the National Instruments representative called and said I should implement my programme as a "State Machine", which I have attempted in the programme attached. I was wondering how I might now implement the procedures 3 to 5 in this State Machine format as it seemed very complecated in the brief time we had.
What I am trying to do is test relays, using an automated test procedure.
The procedure takes the following steps:
1. A NI9472 DO card and transistor drive turns the relay on/off via energising the coil (needs the time period to be variable).
2. Counts how may cycles the relay contacts have operated, this will easily be in excess of 100,000 cycles.
3. Every 100 cycles (again variable), the contacts are held closed, the load circuit (the current the relay is switching, which will be 15A at 30V) is disconnected, via another relay and a measurement is taken via a separate four wire method. This consists of a 6V supply being placed across the contacts (switched in again via a relay) with a 1A current flowing through the contacts, the voltage drop across the contacts is then inputted into the NI AI NI9219 card (this is in the region of 10’s of mA) and is directly proportional to the contact resistance, which is what I want to measure.
4. The measurement is taken and stored and the measurement circuit disengaged, the load circuit re-engaged, and another 100 cycles is counted before the process goes back to stage 3.
5. This process goes on until the relay fails and hopefully a large set of contact resistance data is gathered.
I have no real experience with NI Labview.
I have looked at the basic academic tutorials and have come up with the following programme for stage 1, however I can't get the DAQ Assistant to output every cycle
Would this be a very difficult programme to implement for the novice? The academic tutorials seem straight forward but when I try to do someting it seems very difficult.
Hoping someone may be able to help, thanks
Andy
Solved!
Go to Solution.
Attachments:
Relay Test State Machine.vi ‏207 KB
Relay Test State Machine.vi ‏207 KB

Hi James,
I've tried to implement some logic as suggested. I can now get the 1A coil to engauge after the nth cycle and I think it's taking a measurement, but can't seem to get the 15 A coil to disengauge at the same moment, which is crucial else the measurement will be across 16 A rather than just the 1 A. Any ideas? I just want to get it working so we can get started with testing.
I'm going to get my supervisor to book me on a course at Newbury for future projects, it's very difficult to pick up of your own back.
Kind regards,
Andy
(Helps if I attach it)
Attachments:
Relay Test State Machine.vi ‏209 KB

How do you create array of enums for transitions in a state machine?

Hello,
I am trying to build a state machine, but, I am struggling with understanding the methods for determining which state to transition to next. In other words, I have several states, but, I don't want to go in any particular sequence. If I have states numbered 1 through 10, I want to be able to go 1-4-2-5-6-2-6-1-10 etc. in no particular order. I want the transition to the next state (and actions) to be determined by the streaming data, which can be random and require access to any of my 10 states at any time and in any sequence.
I saw this picture on the "Application Design Patterns: State Machines" white paper, but, it leaves out some important details. How does one create the structure in BLUE shown in 3C? When I try to create this array of enums, all of them are the same. I am not able to make a list of different enum values. In other words, when I type in "2", then, all the values in the array display as "2."
There is a nice, simple video example of a state machine for dispensing soda for $0.15, however, this state machine moves in a single sequence, from 5 cents, to 10 cents to dispense; it does NOT illustrate how to select a state "out of order." I need to understand how a state machine can move from "5 cents" state to dispense directly, with the addition of 10 cents to the "5 cents" state.
Can anyone suggest a really good tutorial on how to make the selector work in a state machine? I have been reading some of the available material on ni.com, but, I can't find a good detailed explanation of how to do it. I remain confused.
Or, can you just explain how they created the BLUE array in the attached picture? Maybe I can figure it out from there.
Thanks,
Dave
Solved!
Go to Solution.
Attachments:
next state.jpg ‏75 KB

Hi Kathryn,
Yes, this is EXACTLY what I want to accomplish...
So it would basically run:
State 1
Read input
Determine next state (say 3)
State 3
Read input
Determine next state
State
Read input
Determine next state
And so on...
But, I am quite new to programming Labview state machines, and can't figure out how to even start when the sequence of states is random instead of fixed!!! I can do 1,2,3,4, like the vending machine VI example, but, not 1,3,2,2,2,5,2,1 etc. based on external input. Is there some simple example case I can study? I can't believe I am inventing this for the first time.
"select the state to run"
But, HOW do I do this??????? This is exactly the question I am asking...how is this done? Please see the attached 3-state system....how do I hook this up???? I am totally lost here...can you help me understand how to wire this thing?? In this simpe RED/GREEN/BLUE case, my input is just the number a user would input on the front panel.... Apparently, there are two files necessary... a vi and .ctl??? What is .ctl?
Thanks,
Dave
Attachments:
forum nov 12 red green blue.vi ‏7 KB
forum nov 12 red green blue.ctl ‏5 KB

New LabHSM Toolkit - Agile development of complex event-driven maintainable LabVIEW applications with active objects / actors based on a universal Hierarchical State Machine / statechart template.

Dear Fellow LabVIEW programmers:
Most of the systems you deal with are reactive. It means that their
primary function is constant interaction with their environment by
sending and receiving events. But most likely, they can have something
happening inside them too, even when they are not processing messages
received from outside. So, such systems have to continuosly react to
external and internal stimuli. Right? Moreover, most likely, they
consist of subsystems that are reactive too and, in turn, can have
their own "life", to an extent independent from other parts (with
which they still communicate, of course). Reactive (event-driven)
systems are more naturally modeled with active objects. So, why then
should we try to model and code them with GOOP and its passive
("dead"!) objects?
"Flat" State Machines have been known for decades to have severe
limitations. It's been more than 20 years since Dr. Harel invented
Hierarchical State Machines (statecharts) to fight those limitations.
Then why does NI still tout the same old good Moore FSM as the
ultimate tool for event-driven programming in LabVIEW in its $995
State Diagram KIt?
The LabHSM toolkit we are happy to present, makes it possible to
easily create and then maintain complex event-driven applications in
LabVIEW as a collection of HSM-driven active object VIs using a higher
level of abstraction and agile software development methodologies.
These active object VIs are created based on a universal Hierarchical
State Machine ( HSM or statechart ) template. So. all your code looks
similar regardless of its functionality!
We all love just jump to code, right? However, to be good boys, we
need to do design first. Then implement it in code. If the logic is
modified we need to redo the design first and then redo the code. When
using LabHSM where behavior information is abstracted into a separate
HSM data file editable with a supplied editor, there is no need for
coding separate from design any more. The modified behavior becomes
code automatically as soon as the HSM file is saved. Design is code!
The implementation basically follows Dr. Samek's Quantum Programming
paradigm. (see http://www.quantum-leaps.com). However, as already
mentioned, LabHSM stores the behavior information in a file separate
from the code itself. It also adds state dependent priorities to
events, a separate queue for public events/messages, and, of course,
some LabVIEW specific code like capturing front panel user events and
putting them into the private Events queue. Communication and
instantiation functions are also rather specific for LabVIEW.
It is available for UNLIMITED PERIOD trial. Please visit
http://www.labhsm.com for details and download. The site also contains
references which you may want to check to learn more about
hierarchical state machines and active object computing.
Since this is our debut we will appreciate any comments and
suggestions. Our contact information is available on our site, of
course.
Have a G'day!

Symtx is currently hiring the following position. Please contact me if interested.
Amy Cable
Symtx, HR
[email protected]
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Producer consumer vs state machine

Hi there,
I have been on and around for quite a while to understand how can I re-design an application, which was originally built using a mix of sequence structure, while loops and event structures. And now I am making a newer version of the same application, for research purposes, while learning the LabVIEW techniques. Earlier I used LabVIEW versions 5 and 6 to make simple programs for fuzzy logic and neural networks. And that's not a good reference.
Ok, after learning that Producer Consumer (PC) and Standard State Machines (SSM or SM) are two new approaches for a better (scalable, flexible and efficient) coding as suggest by veterans, in one thread where I asked about another issue, I have started digging into this topic and now I am on a point where I have to implement it finally (spent pretty much time in the learning phase).
I have several questions.
To start the discussion, I would give a brief description of my application.
It's a networked application, where the network communication happens using DataSocket (one reason to use LabVIEW as the environment).
We are talking about the client application, which communicates with other applications on remote computer, via Internet.
User interface involves a tab control, with several pages-
On startup, the controls/indicators (now onwards referred as controls only), are initialized, datasocket connection is checked (rather internet is checked, and a connection established with the remote datasocket server) (page 1)
If connected to the datasocket server, the user selects Login/Registration (page 2)
Login and/or Registration happen on page 3/4
Then the user sees a table of remote users to connect to (page 5)
Upon selection of a remote user, and after clicking on "connect", the user will see a video indicator, with a lot of other controls. (page 6)
On this page with video indicator and controls, the user has a lot of activities, in which many messages are sent and received to/from the remote machine.
the user may disconnect and go back to page 5, and log out and go back to page 2 and so on.
I hope this is clear.
I have thought about two different ways to do this application. Using PS or by SSM.
In the attachments, I have given a diagram (with errors, of course, because of unlinked controls), for each of the approach, plus the original application's diagram.
I hope this is sufficient for anybody to understand my case and give suggestions.
I am looking for suggestions about which is a better model for my type of case. I have been to discussions like this one and saw that there are many issues regarding dequeue in PC model. So I am curious to know if SSM is a better and latest model or it's more primitive? Which looks better for my application's performance?
Thanks ahead!
Vaibhav
Attachments:
OldDesign.vi ‏41 KB
PCDesign.vi ‏42 KB
SSMDesign.vi ‏46 KB

Vaibhav wrote:
@ Harold
Thanks. Any suggestion how can I start and stop that loop in parallel with other loops? Like, if some event occurs, the loop should start execution, and keep on moving, while other events are being traced and executed.
In those examples where you had a while loop inside a case structure, that bit of code will only execute one time. It will immediately read the boolean at the start of the program, if the value was true before the porgram started, then the while loop will run. Once that while loop stops, the case structure will end. It will never execute again unless you completely stop and restart your program. If the boolean is false before the program starts, the false case will execute immediately. Nothing happens since it is empty and it is done, never to run again (unless you stop and restart your VI) You should turn the structure around. Put the case structure in the while loop. Make sure you put a small wait statement in the loop so that it doesn't run full speed eating up CPU cycles just polling the status of the boolean.
@ Ravens
Thanks for the detailed comment.
One thing I would clarify. The user will not be able to switch between the pages using the tab control. The program will direct appropriate page to the user. I kept the tabs visible just for your idea of the pages. Sorry, I didn't mention that.
Do you think it's still a bad design?
If the tabs will be hidden or disabled, you will probably be okay. I wouldn't call it a bad design. I wouldn't do it that way. But as long as you understand the possibility of problems and prevent that. Especially some time down the road when you modify the program in some other way that could lead to a problem because you forgot about the dependencies of the event structures on the state of the state machine.
Yes, I agree about only one event structure to handle all the events. But since the user will not be able to click somewhere else, other than those possible controls, I thought to keep it like this.
I thought the events are captured only if we are in that case. I think I am wrong, right? Events are captured at any time, even if the case has never executed before, or will never execute. Ok, The events will be captured, but will not be executed until in that case.
And that's the reason why I have two separate event structures, in two separate phases of the program.
Because, prior to page 6, the events will occur sequencially. The user will click somewhere, then some message will be transmitted over DataSocket, then some message may come , then again some user action and so on. But, when the user starts using page 6, there will be parallel process of user controls events and actions, and incoming messages and corresponding actions. For this, in the page 6, I need a different kind of execution. So I separated the two event structures.
At first I thought to have SSM, and then I thought to PC, just because I can have two separate parallel processes - one for user events, and another for messages (because that way I can take maximum advantage of message tracking). But looking at other complexities, I find SSM more appropriate. Can you please tell me how can I have my message loop and events loop parallel to each other and just one event structure?
You can have a dequeue function in your state machine loop and have it be a consumer loop. Use a timeout on the Dequeue. If there is a timeout, have the statemachine execute normally after that perhaps just passing the enum wire straight into the case structure of the state machine. If it doesn't timeout meaning you got a message, then look at the message that is dequeued and act on it. Perhaps it means ignoring the enum coming in from the shift register and changing the enum to something else to feed into the case structure of the state machine. Attached is an example
Attachments:
PCDesign[1]_BD.png ‏6 KB

State machine VS producer consumer architecture - Time Analysis

After learning various methods to program efficiently and learn how to use SM and Producer consumer. I built a program to control stepper motor in both these techniques.
Here is the RESULT. As we can see a simple state machine without any complicated producer consumer technique performs faster than the second one.
I am not sure which is still the best based on performance and optimization. Please advise which one should I keep and why.
Abhilash S Nair
Research Assistant @ Photonic Devices and Systems lab
[ LabView professional Development System - Version 11.0 - 32-bit ]
LabView Gear:
1. NI PXI-7951R & NI 5761
2. The Imaging Source USB 3.0 monochrome camera with trigger : DMK 23UM021
OPERATING SYSTEM - [ MS windows 7 Home Premium 64-bit SP-1 ]
CPU - [Intel Core i7-2600 CPU @ 3.40Ghz ]
MEMORY - [ 16.0 GB RAM ]
GPU - [ NVIDIA GeForce GT 530 ]

This is with state machine alone
Abhilash S Nair
Research Assistant @ Photonic Devices and Systems lab
[ LabView professional Development System - Version 11.0 - 32-bit ]
LabView Gear:
1. NI PXI-7951R & NI 5761
2. The Imaging Source USB 3.0 monochrome camera with trigger : DMK 23UM021
OPERATING SYSTEM - [ MS windows 7 Home Premium 64-bit SP-1 ]
CPU - [Intel Core i7-2600 CPU @ 3.40Ghz ]
MEMORY - [ 16.0 GB RAM ]
GPU - [ NVIDIA GeForce GT 530 ]
Attachments:
Control 1.ctl ‏6 KB
Control 2.ctl ‏6 KB
Motor-UNI_Directiona Dev 3-TIME_ANALYSIS-2.vi ‏54 KB

Adding customer field to selection screen of RFKORD11 - Customer Statement Printing Program:

Hello,
We are required to add an important customer field to selection screen of customer
statement printing program: RFKORD11 for our South African branch.
Please advise us regarding this matter,
is there a proper user-exit or a repair is needed?
Kind Regards.

Enhancement
text
F050S001
FIDCMT, FIDCC1,
FIDCC2: Edit user-defined IDoc segment
F050S002
FIDCC1: Change
IDoc/do not send
F050S003
FIDCC2: Change
IDoc/do not send
F050S004
FIDCMT, FIDCC1,
FIDCC2: Change outbound IDoc/do not send
F050S005
FIDCMT, FIDCC1,
FIDCC2 Inbound IDoc: Change FI document
F050S006
FI Outgoing IDoc:
Reset Clearing in FI Document
F050S007
FIDCCH Outbound:
Influence on IDoc for Document Change
F180A001
Balance Sheet
Adjustment
FARC0001
Enhancements within
archiving (FI)
FARC0002
Additional Checks for
Archiving MM Vendor Master Data
FEDI0001
Function exits for
EDI in FI
FICT0001
Exits for
inter-company transactions
RFAVIS01
Customer Exit for
Changing Payment Advice Segment Text
RFBVX001
Enhancement for bank
directory transfer (Austria)
RFEPOS00
Line item display:
Checking of selection conditions
SAPLBANK
User exit: Bank data
SAPLF040
WF: Preliminary
posting (authorized for release)
SAPLF051
Workflow for FI
(pre-capture, release for payment)
SAPLFCPD
One-time account data
or different payee in booking
SAPLSSRV
User exit: Bank
account numbers
RFKORIEX
Automatic
correspondence
please check which one is better .

Subtle bug in Deitel & Deitel "Java How to Program" book

Merry x mas and happy new year, guys.
I have this applet (which is at the same time runnable and listener) its printed in Deitel & Deitel "Java How to Program" book 3rd ed.
The program works but as you turn on and off the "suspend" checkboxes some of the threads are not notified, so they go to infinite wait state, deadlock. I couldn't figure out what is wrong or how to fix the problem.. please read the code below, or copy and paste this code to your eclipse, its just one file, then play with the check boxes, some of the threads don't wake up after wait... technically they don't shift from WAITING to TIMED_WAITING state.
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
* @author
// Fig. 15.7: RandomCharacters.java
// Demonstrating the Runnableinterface
public class RandomCharacters extends JApplet implements Runnable, ActionListener {
    private String alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
    private JLabel outputs[];
    private JCheckBox checkboxes[];
    private final static int SIZE = 3;
    private Thread threads[];
    private boolean suspended[];
    public void init() {
        outputs = new JLabel[SIZE];
        checkboxes = new JCheckBox[SIZE];
        threads = new Thread[SIZE];
        suspended = new boolean[SIZE];
        Container c = getContentPane();
        c.setLayout(new GridLayout(SIZE, 2, 5, 5));
        for (int i = 0; i < SIZE; i++) {
            outputs[i] = new JLabel();
            outputs.setBackground(Color.green);
outputs[i].setOpaque(true);
c.add(outputs[i]);
checkboxes[i] = new JCheckBox("Suspended");
checkboxes[i].addActionListener(this);
c.add(checkboxes[i]);
public void start() {
// create threads and start every time start is called
for (int i = 0; i < threads.length; i++) {
threads[i] = new Thread(this, "Thread " + (i + 1));
threads[i].start();
public void run() {
Thread currentThread = Thread.currentThread();
int index = getIndex(currentThread);
char displayChar;
while (threads[index] == currentThread) {
// sleep from 0 to 1 second
try {
Thread.sleep((int) (Math.random() * 1000));
synchronized (this) {
while (suspended[index]
&& threads[index] == currentThread) {
wait();
} catch (InterruptedException e) {
System.err.println("sleep interrupted");
displayChar = alphabet.charAt(
(int) (Math.random() * 26));
outputs[index].setText(currentThread.getName() + ": " + displayChar);
System.err.println(currentThread.getName() + " terminating");
private int getIndex(Thread current) {
for (int i = 0; i < threads.length; i++) {
if (current == threads[i]) {
return i;
return -1;
public synchronized void stop() {
// stop threads every time stop is called
// as the user browses another Web page
for (int i = 0; i < threads.length; i++) {
threads[i] = null;
notifyAll();
public synchronized void actionPerformed(ActionEvent e) {
for (int i = 0; i < checkboxes.length; i++) {
if (e.getSource() == checkboxes[i]) {
suspended[i] = !suspended[i];
outputs[i].setBackground(
!suspended[i] ? Color.green : Color.red);
if (!suspended[i]) {
notify();
return;
Thanks in advance.

Abiel wrote:
No, notifyAll() is used to tell the threads that we're stopping.... see that it's written in the stop() method of the applet. Eg if the user browses away from our applet we set the array of threads to null and notify them all. So notifyAll() makes sense.Yes, it does make sense there too (!!!!!!!).
However, I gave it a try with what u suggested, and it didn't work (as expected) .... Apparently you did not really read my suggestion or my explanation. If you had, you'd have expected it to work and it would have worked.
the problems still remains, some threads are getting in wait state even if their check box is not suspended.Maybe you should add the following code to understand the root cause and solution.
    System.out.println("Thread " + index + " will wait to be notified.");
    wait();
    System.out.println("Thread " + index + " was notified.");
what could the problem be?Improper use of notify()
With kind regards
Ben

How to start and stop video acquisition in a state machine

hello,
I'm a neuroscience student and here's what I'm trying to do: 1) trigger a GigE camera (200fps), 2) start video acquisition, 3) trigger a light that will stay on for x miliseconds, 4) trigger a valve that will blow an air puff, 5) stop the tone and the valve simultaneously and 5) stop the video acquisition 1second after 4). For that, my VI is a state machine, with a state for each trigger (ex, 1 state for trigger camera, 1 state for trigger light, ect) plus a state to "stop" and a state "time to wait". Everything was working except the video acquisition - the program would trigger the camera but only acquire one frame, because it wasn't running in a while loop and this is my first question: for a video acquisition is it always necessary to have a while loop?
I assumed the answer was yes, so I built a "consumer" loop for the camera. Putting a queue in the state "trigger camera" in the producer loop, I was then able to start the video acquisition but now the problem is to stop it in the right time. I have another queue in the "stop" state in the producer loop, but it isn't able to start the "stop" state in the consumer loop, I think that may be because the consumer loop gets "stuck" in the while loop.
I hope you can help me, the VI is attached. Thanks!
Solved!
Go to Solution.
Attachments:
trigger_cam.jpg ‏345 KB
trigger_stop.jpg ‏354 KB
Conditioning MS vi 2010.zip ‏68 KB

Hi Gak,
Thanks for the suggestions. I still didn't got it to work though. I moved the stop command to inside the while loop like you said but it didn't work. The problem seems to be in the communication between the producer/consumer loops. When I run the VI in highlight, the queue message "trigger camera" leaves the producer and arrives at the consumer loop in the appropriate time, starting the "trigger camera" state of the case structure. However, the message "stop" doesn't seem to be sent by the producer loop, so the consumer doesn't receive a signal to start the "stop" state of the case structure. Can you think of anything I should change in the producer loop so that the second state (stop) is added to the queue?
About the functional global, I read about it, it seems that either that or a local variable could work, but I don't quite know how to implement it in my state machine, since the stop of the first while loop isn't activated in the "stop" state but in the "shutdown" state. It works more or less like this: after 10 loops of triggering and stopping the camera, light and valve (so after acquiring 10 movies), it goes for shutdown. Can you show me what you had in mind with the functional variable?
Attachments:
Untitled.jpg ‏286 KB

Saving string array in Standard State Machine.

I use a Standard State Machine to control a laser unit with multiple lasers. When I give the unit a command, it gives me much information back. When LabVIEW is reading this information, it is putting it in a string array.
But the program shows only the information in the array when I enable 'Highlight Execution'. What do I have to do to solve this problem?
Thanks for all commands,
Bjorn
Attachments:
StandardStateMachine 1.vi ‏26 KB
statemachine.ctl ‏5 KB

Does your device use a termination charcter at the end of each transmission? You are already set up to use 0xA as a termination character (default on the Configure Serial Port). If so, do not do the big mess with the checking of bytes at port and what not. Just use a VISA Read with a very large number for the bytes to read. The read will complete when that termination character is reached.
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Best way to update indicators in state machine ?

What is the best method to update indicators constantly in a SM ? ...
MY INDICATORS: I want to update the cluster of OUTPUT INDICATORS for ever new update that is happening inside the FOR LOOP (see next image). How could I achieve that ?
Abhilash S Nair
Research Assistant @ Photonic Devices and Systems lab
[ LabView professional Development System - Version 11.0 - 32-bit ]
LabView Gear:
1. NI PXI-7951R & NI 5761
2. The Imaging Source USB 3.0 monochrome camera with trigger : DMK 23UM021
OPERATING SYSTEM - [ MS windows 7 Home Premium 64-bit SP-1 ]
CPU - [Intel Core i7-2600 CPU @ 3.40Ghz ]
MEMORY - [ 16.0 GB RAM ]
GPU - [ NVIDIA GeForce GT 530 ]

Since on my machine, the second screenshot is cropped, i cannot see the complete FOR loop. You do refer to the loop writing to VISA, correct?
If so:
- Is this loop timed? If so, what is the average iteration time? Note: if this is faster than about 50ms, you should not update the indicator in every iteration as the human simply cannot see changes that fast. An average user would only see some flickering and from time to time something "readable".
- Do you update the indicators elsewhere as well?
Possible solution:
- As Yamaeda suggests: Put the indicator in the FOR loop. Works well if only this loop updates these indicators.
- Local variable: As dataflow serializes access to the indicator (variable in loop, terminal outside the state case), you wont have race conditions. On the other hand bears risks if someone introduces concurrent loops using the same indicators (variables).
- Property node "value": Same as local variable, but is bound to UI thread. Therefore, it takes more time which induces performance drawbacks. On the other hand, a property node has error in/out and is better suited to be placed in well designed dataflow programming.
- Extract UI updates from the state machine and introduce a parallel running "UI Update" loop. Refer to the Producer/Consumer template for an initial start point.
hope this helps,
Norbert
CEO: What exactly is stopping us from doing this?
Expert: Geometry
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Simple State Machine Vs Queued State Machine

Using LV2009 + WIN7+Pentium 4 @ 2.5Ghz with 3 GB RAM.
I have a machine control code inside a 10mS main loop that has 7 ( yes seven ) Queued State Machines ( QSM) and I find the Finished Late boolen keeeps poppping often. Not a very good sign if you ask me.
And the code itself does not have too much of computation or FP activity. But it has four Graphs with one plot on each of them. These are updated once every 10ms. Can slowing this update ( say once every 250ms ? ) help ?
A simple query : In terms of performance overhead, does a QSM demand more than a Simple State Machine ( SSM ) ? Can I avoid the Finished Late warning by switching over to SSM at least in three of the cases out of the seven ?
Thanks
Raghunathan
LV2012 to Automate Hydraulic Test rigs.

I think your question demonstrates my point. Unfortunately, I don't have a good example to point you to and don't have the time to write one. I will try to explain better. Let's take a simple example - a landscape watering controller (sprinkler controller). This controller will have several states (e.g. initializing, waiting, watering, closing). Each of these states will accept several commands, but not all commands are accepted in all states. For example, if the system is watering, a command to start watering could be ignored.
In most programs, at least some states should be interruptible. For example, if it starts to rain, the watering system should stop watering immediately instead of watering for a set length of time. However, if the system is in the initialization state, this will probably not be interruptible (but also short).
As you said, the classic LabVIEW way to implement such a thing is to have a case statement to represent the state, and a case statement (usually queue driven) in each state frame to handle the commands. You thus have a loop with a double case structure. This can get somewhat unwieldy for large programs. Note that which case structure represents what will be determined by the relative number of each item. For example, if you have fifty commands and three states, the state should go into the command case.
So how do LabVIEW classes help? They can eliminate one or both levels of these case structures through the use of dynamic dispatch. This is done as follows. A parent class is created that is a generic command. It has commands for each state. For each actual command, a class is derived from the parent class. There are VIs in the specific command class for each state. A command is generated by creating the correct object for the current state, then calling the parent class command. Dynamic dispatch will execute the code for the correct command. The command execution loop is then reduced to a single command VI which dynamically dispatches based on the actual command and the current state.
In practice, things as usually not quite this simple, and you may want different cases for either different commands or different states so that you can change the connector pane of the dynamically dispatched VI as needed. Look up the LabVIEW examples on dynamic dispatch to see this in action.
I am afraid I have still not made myself clear. Keep asking questions and I will try to keep answering.
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