ned

DO NOT click on the links to the screenshots; they point at a website in a foreign language, and not at full-size images. Reported to the moderator.

QUOTE(ned @ Nov 13 2007, 09:31 AM)

See attached example. I think you'll see it's easier to set up, read, expand and debug.

Someone asked me by personal message for this file saved as 8.0, so I'm adding it here.

http://lavag.org/old_files/post-3989-1196442371.vi'>Download File:post-3989-1196442371.vi

QUOTE(MeltingPlastic @ Nov 29 2007, 11:47 PM)

Thanks ned,

What i've realized the graph is doing is outputing the difference between the two signals instead of displaying two different plots for some reason. I can't seem to get the graph to not do that. any help would be great

Right - which is why I suggested unchecking "Transpose Array." A chart can take a lot of different types of data as input. One data type is a two-dimensional array, where one axis is points in time, and the other is plots. You can add multiple points to a chart at the same time. What's happening here is that your axis are being interpreted backwards. Each time through your loop, instead of adding one point to each of two plots, you're adding two points to the same plot. Then it draws a line between them, which is what you're seeing.

Try replacing your combination of decimate array and build array with the following (index array and bundle), so that you're passing a cluster to the chart:

http://lavag.org/old_files/monthly_11_2007/post-3989-1196441775.gif' target="_blank">

QUOTE(MeltingPlastic @ Nov 29 2007, 03:18 PM)

I have my inputs hooked up to a 7.6V battery and a 20k pot to vary the inputs to confirm my input channels are working. If i hook up only 1 channel it displays that signal as one channel. When i hook up both channels thats when things get weird and don't act the way they should. What am i don' wrong here? I'm using labview 8.0 and plan on upgrading to 8.2 tonight if that will help me but i highly doubt that.

This is just a guess, but try right-clicking on your graph and uncheck "Transpose Array." See if that fixes your problem.

QUOTE(Tomi Maila @ Nov 20 2007, 03:21 PM)

Because if for loop is never executed (N=0), the reference is not passed trough the loop, but a default NULL reference is returned at the other end of the loop instead.

Tomi

Ah, right. I've been bitten by that one before, and now my solution is usually to fork the wire outside the for loop.

QUOTE(Tomi Maila @ Nov 20 2007, 03:21 PM)

Because if for loop is never executed (N=0), the reference is not passed trough the loop, but a default NULL reference is returned at the other end of the loop instead.

Tomi

Ah, right. I've been bitten by that one before, and now my solution is usually to fork the wire outside the for loop.

QUOTE(Jim Kring @ Nov 20 2007, 03:00 PM)

And refnums, too

Why would you need refnums to be shift registers? Unless you're closing the reference within the loop and replacing it with a not-a-refnum constant, I'd expect they would pass through a loop unmodified, and I don't think there would be a benefit to using a shift register over a tunnel (although I don't think there would be a disadvantage, either, which might be enough to make your point).

QUOTE(Jim Kring @ Nov 20 2007, 03:00 PM)

And refnums, too

Why would you need refnums to be shift registers? Unless you're closing the reference within the loop and replacing it with a not-a-refnum constant, I'd expect they would pass through a loop unmodified, and I don't think there would be a benefit to using a shift register over a tunnel (although I don't think there would be a disadvantage, either, which might be enough to make your point).

QUOTE(Nero @ Nov 19 2007, 11:11 AM)

n cRIO system, can the RT controller access the I/O module not through FPGA layer ?

In other words, do I have to code the FPGA vi if I want to use the I/O module ?

Yes, you need to go through the FPGA in order to access cRIO I/O modules.

QUOTE(vito @ Nov 15 2007, 12:09 AM)

ned,

Thanks for your insightful and detailed reply. There's one thign I didn't understand. You mentioned "(... as an aside, in your template code, you could simplify by using the reference provided in the event data node to clear your boolean, rather than using an explicit property node ...)". Which Event Data Node reference do I use and where is it wired?

Regards,

tcplomp understood pretty much what I meant, but I should have looked closer at your code and been clearer in my comment. I had thought that you were clearing the boolean indicators using property nodes rather than writing to them directly, for two reasons: many of your event cases have a property node in the last frame of the sequence, and as a rule I only trigger events on controls so I missed that you are using indicators. However, if you're already doing what you're doing, you can at least avoid accidentally clearing the wrong indicator by using something like this:

http://lavag.org/old_files/monthly_11_2007/post-3989-1195136758.gif' target="_blank">

QUOTE(vito @ Nov 13 2007, 07:20 PM)

ned,

I see that you are not impressed with the new proposed Event Structure As State Machine (ESSM) architecture. Firstly, thanks for taking the time to show me the equivalent functionality using a conventional Event Loop And Consumer Loop (ELCL) architecture.

Sorry if I was a bit harsh in my initial reply; let me see if I can explain myself by responding to your points below. I also realize that there is no one ideal architecture for every program, and that your approach may be a good fit for your applications.

QUOTE(vito @ Nov 13 2007, 07:20 PM)

While using a queue does break strict dataflow, I find it easier to follow what is happening because there is a clear connection (a wire) between the two loops, between the enqueue element and dequeue element. There's no guesswork as to what happens when a value goes into the queue. Also, if you look at the example code I wrote, you'll see that chaining multiple actions together does happen in a strict dataflow way, through the use of shift registers.

QUOTE(vito @ Nov 13 2007, 07:20 PM)

I disagree about this, but perhaps it is a matter of preference. A single string takes up much less space, and if you want to have booleans you still have that option although it requires more coding. A definite advantage of the text string is that it is unique. Let's say one of your event cases hangs up somewhere, but several of your booleans are true (either because you've caused a value change event on one in your event case, or you've forgotten to clear a boolean in a previous state, or you accidentally selected a property node for the wrong boolean). How do you know which case you're in? With an enumeration this is never an issue.

(... as an aside, in your template code, you could simplify by using the reference provided in the event data node to clear your boolean, rather than using an explicit property node ...)

QUOTE(vito @ Nov 13 2007, 07:20 PM)

Please take a look at the example code I posted and note that this is not the case: only in the Idle state do I dequeue actions, so if several states all chain together they are guaranteed to execute uninterrupted in that order. However, I could also chain events together by enqueuing them, and still guarantee execution order by inserting them at the beginning of the queue (as opposed to the event structure which would insert them at the end), something that is not possible in your model. At any time I can examine the entire contents of the queue using the "Get Queue Status" primitive in a separate loop for debugging purposes; in fact, if I use a named queue, I can create a new VI that obtains a reference to that named queue and view its contents without interrupting running code. Furthermore it becomes possible to modify the contents of the queue and discard them if necessary. For example, if someone clicks a STOP button, you can flush the entire queue, forcing a return to the Idle state as soon as the action in progress completes. When you use LabVIEW's internal event queue you give up this control and flexibility.

QUOTE(vito @ Nov 13 2007, 07:20 PM)

I hope you don't find yourself in that situation. I've converted several applications to RT which depended heavily on passing a cluster of references to every front panel object through to every subVI, and because of this, separating the logic from the user interface was not simple. I think you'd find that replacing all your events would be similarly difficult.

QUOTE(vito @ Nov 13 2007, 07:20 PM)

I hope my comments explain why I do not think this would be a good choice for a standard architecture, and I welcome more discussion and opinions from others.

QUOTE(vito @ Nov 12 2007, 11:04 PM)

I hope I've presented a simple, elegant and efficient architecture. It could certainly do with some refining and I look to the community to find holes in the architecture and give me the opportunity to address them.

The benefits I see are:

1) Quick and simple to set up

2) Very legible as all actions are an Event Case that is readily listed and jumped to

3) Easy to expand.

4) Can be used for small or large projects

5) If you're willing to use Value (Signaling), great visibility on where you're code is at without any extra programming.

See attachment for a template.

I have to admit that after an initial reading of this my first reaction was pure horror, and that hasn't changed after reading it again. My primary criticism is that this isn't LabVIEW - you have broken any sense of dataflow. It is impossible to probe a wire to see the sequence in which your states execute. If a user event occurs in the middle of one of your event sequence chains (one case triggering another) you'll lose the ordering and will have trouble following what happened. If you ever need to split your logic from your user interface - say, you decide to move to an RT target with a remote display - you'll have to rewrite all your code. Events are wonderful things but they're designed to respond to occasional, unpredictable actions. They're not intended to control the normal flow of your program; if they were, we wouldn't need wires and dataflow.

The standard approach here would be to create an enumeration with all your states, with one value for each of your current boolean. That value is stored in a shift register around a while loop. An event structure resides in a separate while loop, and a queue communicates between them. When an event occurs, the corresponding enumeration value is placed in the queue to be processed by the case structure. This structure has all the advantages you listed and it follows traditional data flow. If you want to know where you are you just put a probe on the input to the case structure (or wire an indicator to it). Much easier than a page of booleans. If you ever need to separate your logic from your user interface, you just move the case structure to the new target and replace the queue with some sort of network communication. As an added benefit, other LabVIEW programmers will quickly understand what you're doing, because it's a standard pattern.

See attached example. I think you'll see it's easier to set up, read, expand and debug.

QUOTE(Neville D @ Nov 9 2007, 01:24 PM)

Any other pointers on speeding up TCP reads? It currently takes about 50-100ms to read about 500k of data over Gig-E.

Do you have the option of using UDP instead of TCP? UDP should be faster and the dedicated link between the machines should prevent data loss and mis-ordering.

QUOTE(BrokenArrow @ Oct 26 2007, 04:08 PM)

Is it really necessary to release Notifiers and Queues when you're exiting a program? By habit, I do it, but I'm thinking if LabVIEW is quiting, or the EXE is closing, what's the point?

It helps ensure that your application exits, rather than waiting on a notifier or queue in some other loop. I usually release all my queues and notifiers when my main loop finishes, and that forces my other loops, which use those queues and notifiers, to terminate.

QUOTE(yanouk @ Oct 11 2007, 08:44 AM)

I am looking for a way to update only one cell and/or one line in a multicolumn listbox. It is quite easy to use the property "Item names" to update the entire array of string but I didn't find a solution to update a particular cell.

I'm pretty sure you can only update all cells at once, but you can do this by replacing only the single array element you want to modify:

http://lavag.org/old_files/monthly_10_2007/post-3989-1192117042.gif' target="_blank">

QUOTE(zero-tolerance @ Oct 11 2007, 10:25 AM)

I allready did that but the sort array function only works by looking at the first "character" where in my case would be a number i.e. 123 "CD Name". So it sorts it out based on the numbers that are at the beginning of each element of the array. But in my case I want to sort them based on the "CD Name" but when sorted I still want to keep the ascociated number that goes with it.

I have somehow managed to do this but I'm not too happy with the way I have done it. I'm thinking that there must be a much better way of achieving the same results.

The attached program is an example of what I'm woring on and its on two versions of LabView (8.5 and 8.2). Please ask if you need for version 8.0.

Any help appriciated.

Thanks

Bundle the CD Name and the number into a cluster, with the CD Name as the first element. Build an array of those clusters, one for each disc. Sort the array of clusters using Sort Array. Unbundle the cluster and write out your file.

QUOTE(Jon Sweeney @ Oct 2 2007, 03:31 PM)

Does anyone have a DAQmx example or description for setting DIO lines (eg, NI6225M) at runtime - some lines to outputs and some to inputs.

Here's one way to do it. If you need to change the direction of lines as your code is running, you can clear the existing tasks and create new ones with the lines set as necessary. The VI on the left is "DAQmx Flatten Channel String" from DAQmx - Data Acquisition -> DAQmx Advanced -> DAQmx Utilities; the one on the right is "DAQmx Create Virtual Channel".

http://lavag.org/old_files/monthly_10_2007/post-3989-1191415376.gif' target="_blank">

QUOTE(alukindo @ Sep 30 2007, 09:47 PM)

Can you shine some light on search terms or a link related to this question. I have been unable to get info from LabVIEW online help. E.g: LabVIEW notes on the ring control should probably have a note on this behavior but nothing there.

Here's a good explanation from the Info-LabVIEW mailing list archives: http://sthmac.magnet.fsu.edu/infolabview/ILVDigests/2005/10/26/Info-LabVIEW_Digest_2005-10-26_015.html' target="_blank">"type-def constant problem".

QUOTE(george seifert @ Sep 25 2007, 08:53 AM)

I need to shut down a while loop that contains an event structure in a subVI that runs parallel to my main VI.

I know I've seen this somewhere, but am not quite sure what to search for. Just a quick refresher of my options would be most appreciated. I've done it with a named timed loop that I can stop from the main VI, but somehow that seems clumsy.

George

A good option here is to create a user event, register for it in your event structure, and trigger it in your main VI. It would look like this (simplified to one VI with two loops):

http://lavag.org/old_files/monthly_09_2007/post-3989-1190733584.gif' target="_blank">

Alternatively, if you already have a timeout case in your event structure, you could check the state of a notifier in that timeout case to see if the notifier has fired.

QUOTE(Thang Nguyen @ Sep 19 2007, 10:41 AM)

Could you tell me more detail about this? I am not clear about why there is the different between the address of the shared variable in modbus slave 4000001 and shared variable in master 400001.

What I have tried to do is in the target I create the Modbus Slave Server and 1 variable bind to it. In the host PC, I create the Modbus Master Server and 1 variable bind to it. All of the variable have the same address. I cannot read anything form the variable on the Modbus master.

Thanks,

Thang Nguyen

Different Modbus implementations may use slightly different forms for addresses; that's why in my case the master and slave addresses did not match. You may not have a similar problem if your master and slave agree on the number of digits in the address.

Other than that, I'm not sure why you're having problems. Are you certain you're specifying the remote address (for Modbus over TCP, the IP address of the remote machine) properly? Are you communicating over ethernet or a serial connection? Have you tried connecting a null-modem cable between the Fieldpoint module and your host PC, and running Modbus over the serial port?

QUOTE(Louis Manfredi @ Sep 19 2007, 09:51 AM)

But this N terminal thing does seem basic enough that it ought to show up when you call for detailed help from the <ctrl-H> window.

I'm going to be a voice of dissent here and suggest that this is sufficiently basic that it doesn't need to be documented. You run a wire to the N terminal and you don't get a broken wire, so it must be valid LabVIEW code. What other value, other than the actual value of N, could possibly be a reasonable value on that wire?

QUOTE(Gabi1 @ Sep 19 2007, 09:44 AM)

Lets say i have a situation with both a notifier and an occurence wait (or for that matter, two unrelated occurence wait).

I want my piece of software to perform if either one of them has returned a value. the only way i found to do it is to use the "wait on notification from multiple", but it doesnt always fits my needs (mainly because some software i have already has occurences...)

any idea?

Is there any reason you must use an occurrence rather than a notifier? If not, then I'd suggest you use a single notifier, to which you can send a notification from multiple places. If the notifier might need to contain different data depending on the source of the notification, use a cluster, or use a variant with an attribute that indicates how the variant should be converted to to usable data.

QUOTE(Thang Nguyen @ Sep 17 2007, 05:04 PM)

+By the way, could you tell me how can I change the address of the register in the modbus I want to use ?

If you're asking how to change the address of the register using the Modbus I/O Server, you need to type in the number yourself after you select the address range, in the shared variable properties. This wasn't obvious to me at first but you've probably already figured it out. I also found that the IO Server allows one digit more of the address than the Modbus master I used, and to fix this I removed the second digit (starting from the left - highest order) from the address. That is, I assigned 4000001 to a shared variable, and I set the master to read from 400001.

QUOTE(Thang Nguyen @ Sep 17 2007, 05:57 PM)

I'm not familiar with the PI Server, nor unfortunately can I suggest any simulators other than to suggest that if you have a second Fieldpoint module available you could make one of them a master and the other a slave. If you're using Modbus over TCP/IP, is it possible that you have a firewall or other network permissions set in a way that limits access to your Fieldpoint module? As a very basic check, try opening a Windows command window and run "telnet <fieldpoint.ip.address> 502" to see if you can connect.

QUOTE(Thang Nguyen @ Sep 17 2007, 05:04 PM)

+The first thing I know is I cannot use the shared variable bind to modbus because this device does not support modbus (only cFP 18xx). This is confirmed by application engineer of NI.

I feel fairly confident in saying that your NI engineer is mistaken, since I've done exactly this using an FP-2010. I suspect that the NI engineer thought you were asking about direct Modbus access to the modules (or using OPC) which I believe is possible with the 18xx. It is worth using the Modbus I/O server on the Fieldpoint module as it is much easier to use than the Modbus library.

You asked about a similar situation in another thread; did you ever resolve whether your shared variables were working properly, independent of the Modbus binding?

I've just started a new job that is asking me to use LabVIEW in a different application than I've programmed in the past, and I'm looking for suggestions. I'm working on a system that has several stations around an index wheel. At one station a vial is filled, then rotated to the next station where the contents are verified, then the vial is capped, etc. I'm trying to decide what software architecture to use for this.

My original thought was that each station would act as its own subsystem, and communication would occur using two notifiers: the index wheel system would send one notification when it is in position, and each other subsystem would send a notification back when it completed (indicating success or an error). However, there is an existing system here already that uses PLCs and a sequencer (perhaps I have the term wrong) that rotates through a circle each cycle and triggers outputs across all subsystems along the way (one output might turn on at 5 degrees, another at 30 degrees, etc), which makes it easy to see when something goes wrong because it is possible to step through it by advancing the sequencer more slowly. I'm considering using a similar technique in my LabVIEW code.

Does anyone have experience with a similar system, and if so, can you comment on your experience? Did you use one of these two approaches or something else entirely?