Dividing source signal with 2 counters

I have a C/T 6602.
I want to divide by n(>=2) one external signal with my two counters at the same time. But the problem is that I cannot make the two Counter outputs in-phase whenever I set the counters up. Whenever the order is made, the two output phases are random. I think that there is way to do what I want.
Thanks, GraceSun

Hello GraceSun,
Have you tried any example programs? You have not said what programming language you are using, but if you are using LabVIEW 7.x you can go to help >> find examples >> hardware input and output >> DAQmx >> Generating Digital Pulses and find a VI called Gen Dig Pulse Train (either continuous or finite). You can simply put in for your counter channel "Dev1/ctr0:1" to have multiple counters in the task. Your outputs will then be synchronized.
Thanks,
Laura

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No Source Signal, intermittently when using Graphics Cars

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Better estimation of phase difference between two signals with variable frequency!

Hello LabView Gurus,
Being a power engineer and having just a little knowledge of signal processing and labview, I have been pulling my hair out for the last couple of days to get a better estimation of phase difference between two signals.
We have two analog voltage signals; 1. sine wave (50Hz ± 1Hz) and 2. a square wave with exactly half of sine wave frequency at any time.
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As this part is just a small block of a big project, I can only allow 5000Hz sampling rate each for both signals. I read 500 samples (which means I read data from 5 cycles of sine wave and 2.5 cycles of square wave).
Now the problem is, as long as the frequency of sine wave stays constant at exactly 50Hz, I get a good estimation of the phase difference but when the frequency changes even a little (and it will happen in the real scenario i.e 50Hz ± 1Hz and the square wave's frequency is dependent of sine wave's frequency), the estimation error increases.
I have attached my labview program. From front panel, you can set the phase of square wave (between -180 and 0) and you should see the labview's calculated phase in the indicator box named 'Phase'. Then you can press 'Real Frequency' switch that would cause the frequency to change like it would in real operation.
You can observe that the estimation error increases after you push the button.
All I need to do is to reduce this estimation error and make it as close to the actual phase difference as possible. Any help would be greatly appreciated.
I am using LabView 2009 for this task.
The application is for electric machines and the stability/performance of machines under different faults.
Thank you for reading this far!
Regards,
Awais
Attachments:
v603.png ‏320 KB
v603.vi ‏186 KB

Jeff Bohrer wrote:
Basic math gives me a bit of pause on this approach. You are sampling at 50 times the frequency of interest so you get 50 samples per cycle. your phase resolution is 1/50th cycle or 7.2 degrees +/- noise. You will need to samlpe faster to reduce phase resolution or average multiple readings (at a time cost that is signifigant)
Jeff- (Hardly Working)
I am sampling at 100 times the sine wave's frequency and 200 times the square wave's frequency. Increasing the sampling rate completely solves my problem. But since I am acquiring several other inputs, I cannot afford a sampling rate higher than 5kHz.
F. Schubert wrote:
I'm not a signal processing expert, but here my basic understanding.
If you simulate sampling with 5kHz and a frequency of 50 Hz (and both are 'sync' by design), you always get an exact 5 periods. Any variation of your signals frequency gives you a propability to get 4 or 6 'trigger' events. That's an up or down of 20%!
The one measure to reduce such problems is using 'window functions'. They don't fit your current approach (counting instead of a DSP algorithm), so this needs to be reworked as well.
My approach would be to use the concept of a Locki-In amplifier. You need to phaseshift your ref-signal by 90°. Then multiply your measurement signal with the ref signal and the phase shifted ref signal. The obtained values for x/y coordinates of a complex number. Calculate the theta of the complex number (with the LV prim). Feed this in a low pass filter.
The trick on this is, that the square wave has harmonics in it, in this you are interested in the second harmonic which is the sine wave.
To get rid of the effect that the sync between sampling rate and ref signal frequency gives an error, you then can use the window I mentioned above (place it before the lock-in).
For a design that really plays well, use a producer-consumer design pattern to get the calculations done in parallel with the DAQ.
I suggest you to check on wikipedia for some of the keywords I mentioned. Go also for the external links which lead to great tutorials and AppNotes on the signal processing basics.
Sorry, it's not a simple solution I offer and we will have quite some conversation on this forum if you follow this path. Maybe someone else knows a simpler way.
Felix
www.aescusoft.de
My latest community nugget on producer/consumer design
My current blog: A journey through uml
An interesting view. the sine wave can indeed be looked as a second harmonic of the square wave. I will implement your idea and get back to you as soon as I get some results. But since I have very limited knowledge of signal processing, it might take me a while to get my hear around the solution you mentioned.

How to measure different signals with PXI-2501

Hello everybody,
i have a an understanding problem.
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I did some voltage- measurements and everything worked fine. Then i disconnected the power source and measured the temperature with a PT1000 in four-wire-mode ... also worked fine.
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The VI consists of a state machine, the measurements are done in different states, of course with the correct scan list for each measurement.
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Thanks
(and excuse for my english )

Hi Roman,
id I understand you right:
The temperature measurement works fine, if the sensor is directly connected to the 4071, but if connected via the 2501 you see the big deviations?
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kind regards
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Problem Counting A and B Encoder Signals on Two Counters.

Hi All,
I have an existing LabVIEW program that uses three counters to measure A, B and Z signals of the encoder. I can read these signals separately if I hook only one of them to the PCI 6602. If I hook up A and B, I will get intermitten correct reading for signal A. I will always get the correct reading for signal B. Is there a problem of trying to measure these signals using separate counters? This program basically tries to measure the time between the different edges. There isn't any documentation, so I am not even sure which board this application was written for. Although, there is an analog input section of this code. I even tried the counter for the 6502E board. I get the same problem. I am not sure if the physical channels constants in the program is correct. Has anyone run into this problem before?
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Attachments:
Main Encoder Tester.vi ‏883 KB

Hello Van626,
After looking over your code for measuring a encoder, I would suggest performing this acquistion in a different way. The reason why is that it is not advisable to create and clear or start and stop in a while loop. In order to get around this, here are some ideas I had:
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2.) If you want to record each signal, you have enough counters to do this. There is a VI called DAQmx Connect Terminals that will connect PFI lines together. In doing this, you can connect your three signals to three PFI lines but have them go to multiple counters. I have current tested this with an Angular Encoder task with a Two edge Separation and it works perfectly
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Jim St
National Instruments
RF Product Support Engineer

How can I count events during a given time with 2 counters (6025 E)

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what is the best way?
how should i configurate both counter?
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Greetings,
When you perform event counting a gate signal can be added such that if a low signal occurs on the gate, then the counter will pause. When a high signal is seen, the counter will continue counting edges. When you install the NI-DAQ driver you should have installed the examples for Visual C++. The counter examples are found in \Program Files\National Instruments\NI-DAQ\Examples\VisualC\Ctr. Take a look at STCeventCount.C. Be sure to only use STC examples with your hardware. The E-series boards contain the DAQ-STC chip.
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National Instruments

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Hello,
I'm measuring a digital frequency signal using a PXI-6602 module using the 'high frequency with 2 counters' method. From the examples I have found, it seems that you specify only the counter which is doing the measuring and the measurement time. How does LabVIEW know which counter is used to generate the HF pulse reference train, for example:
ctr 0 - measuring 200kHz signal
ctr 1 - generating 50kHz signal
Do I independently set up and start the ctr1 generation, and as log as it starts before the measurement commences, does LV then sort it all out without any other input?
Thanks
Dave

You should connect the signal (whose frequency needs to be measured) to Ctr-1, and there gonna be an internal connection between the output of the first counter and the gate of the second counter (as described here).
You may want to check this link as well.
I am not allergic to Kudos, in fact I love Kudos.
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Hi,
I'm using PXI4461 for audio measurement and there is a question about analog output. I'm using the Basic Multitone vi for generating multitone signal. The sampling rate is 200k and my question is how to determine the number of samples. I used an audio analyzer to measure the distortion of the output signal with 200k and 1k points and there are no different except the update rate. What number of samples is suitable for 200k sampling rate?
Thanks,
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The Sampling Rate determines the maximum frequency that you can see (the rate/2 according to Nyquist).
The number of samples divided by the rate determines how long you will sample. This sample time can only be determined by you. Do you need .1 seconds worth of data, or 1 second? But note that the MINIMUM frequency that you can detect is 1/(Sample Time) or the Sampling Rate/Number of Samples. So if your system has a minimum and maximum frequency specification use that as your guild.
[email protected]

Does the PXI447X and PXI3060E divide the signal by two when connected differentially?

I would like to measure vibration motion with sensors which measure ground velocity.
I would like also to work in a differential way to eliminate the noise. We have bought the acquisition device NI PXI1042Q that contains two acquisition cards : NI PXI4472B and NI PXI6030E.
For the NI PXI4472B, we have connected the positive signal and the negative signal of one sensor to one (of the eight) channel of the DAQ (See the outline on the attached file). So, we are in a differential way.
For the NI PXI6030E, we have put the switch to "diff" to be configurated as differential. For one sensor, we have so connected the positive signal to the channel 0 and the negative signal to the channel 8 for example (See the outline on the attached file).
I would like to know if my two acquisition cards, after having substracted positive from negative signals of my sensors, make themselves the division by two of the resulting signal, or if I have to the division by my own. In fact, substracting positive and negative signals make the amplitude to be multiplied by two. So, the amplitude have to be divided by two.
Attachments:
outline.doc ‏38 KB

Hello Sannaa,
Thank you for your reply. So, you said that I don't have to divide my acquisition result by two. But is it because the division is done by the DAQ, or is it because the signal result of a sensor is ‘(positive signal – negative signal)’ and not ‘(positive signal – negative signal)/2?
Also, for the NI PXI4472B, I said that I had connected the positive signal and the negative signal of one sensor to one (of the eight) channel of the DAQ to be differential (pseudo) But I don’t know if that solution was good because the documentation say that we can't make a non-ground connection to the shield.
So the other possibility was to use 2 channels, one for the positive signal with its ground and the other one for the negative signal with its ground (see the outline in the attached file). Here, I do the subtraction between the two channels by my own thanks to a software (‘Matlab’). So, I don’t know if the positive signal is divided by two (and the same thing for the negative signal), or if I have to do it by my own thanks to a software (in the case that the signal result of a sensor is ‘(positive signal – negative signal)/2)
Thanks a lot,
benMessage Edited by benbol on 05-24-2005 07:01 AM
Attachments:
schema_forum_sanaa.doc ‏28 KB

No Source Signal

This has been popping up on screen for days. When I click for sleep mode, it does not sleep until I press Keyboard button. The monitor switch stays on, the modem goes to sleep. The box with No Source Signal flies around on the dark screen during the entire sleep mode, like a screensaver. Any help or advice would be appreciated. Thanks.

Seems like it is not a monitor problem.
Disconnect hard disk and disassemble the memory RAM.
Switch on the pc, then switch it off again.
Re-connect hard disk and ONE RAM stick only.
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Which pc do you have?
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I have an HP S2031 monitor and I am getting a No Source Signal message after I ran an upgrade from Vista to Win7 operating system.
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Retry boot with one stick after the other.
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Do you have an additional graphics card?
Which output port do you use for the graphics.
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*** Say 'Thanks' with Kudos ***

27Xi stays on displaying "no source signal" after I turn off my PC or PS4, doesn't enter sleep mode.

I started having this issue a few weeks ago. The monitor no longer enters sleep mode for whatever reason after I turn off my devices connected to it (currently my PC via DVI and my PS4 via HDMI), it turns on and displays a box with "no source signal" and never goes to sleep. Before it displayed a box with "monitor going to sleep" for a few seconds and the panel turned off as the montor entered sleep mode. This is extremely annoying. How do I fix it? What's wrong with it? I already tried a factory reset.

Hello, try this...
"Try Disk Utility
1. Insert the Mac OS X Install disc, then restart the computer while holding the C key.
2. When your computer finishes starting up from the disc, choose Disk Utility from the Installer menu at top of the screen. (In Mac OS X 10.4 or later, you must select your language first.)
*Important: Do not click Continue in the first screen of the Installer. If you do, you must restart from the disc again to access Disk Utility.*
3. Click the First Aid tab.
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5. Click Repair Disk, (not Repair Permissions). Disk Utility checks and repairs the disk."
http://docs.info.apple.com/article.html?artnum=106214
Then try a Safe Boot, (holding Shift key down at bootup), run Disk Utility in Applications>Utilities, then highlight your drive, click on Repair Permissions, reboot when it completes.
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If perchance you can't find your install Disc, at least try it from the Safe Boot part onward.
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Capture digital signal with DAQ 6015

I am wondering what is the best way I can capture a digital event accurately using my DAQ 6015 Pad. It seems as though I can only capture it using (on demand) timing which I'm assuming means it will only capture it as fast as the loop iteration. I'm looking to monitor this signal with accuracy down to about 10 ms. Are there any good digital examples i can goto that you can vary how fast you can capture an event using the 6015?

Hi caunchman,
In this card, the digital lines are static so you will have to provide the timing through software, which might not be too accurate. I would suggest using one of the counters of this card to count the digital event. I don’t know what programming language you are using, but if you are using LabVIEW you can find good examples in the NI Example Finder. You can go to Help > Find Example > Hardware Input and Output > DAQmx > Counter Measurements > Count Digital Events. If you are using Visual Studio, C or DotNet you can find the Counter examples here: \All Users\Documents\National Instruments\NI-DAQ\Examples. I hope this is helpful,
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Limitation on source group with services using ip address range

Hello,
I have an interface on CSS which I regard as public and another interface I regard as private. On the private interface is a server farm with private ip addresses. Since the server admin guys insisted the servers need to access internet just for Windows Update, I made a source group to NAT the private addresses to public addresses to allow the servers to access internet.
I defined services for use by the source group. Since keepalive is not important in this case, I set keepalive none to ,I hope so, save system resources.
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I can also get it work if I include 192.168.11.15 and define two services both with a range of 5 ip addresses. But 192.168.11.15 is not actually there.
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CT Yau
Hong Kong

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You mentioned that you can use single ip adress instead of range for the services...but it is not true as you will be stuck when you add them into source groups.
I can think of these following options in your case.
Option 1
Change the ip range on the servers. Use 2 different IP ranges one for those 5 servers and another for those 4 servers.
Create 2 services for each range.
Create 2 groups and add the services.
service server-out-192.168.1.1-5
ip address 192.168.1.1 range 5
active
service server-out-172.168.1.11-14
ip address 192.168.1.11 range 4
active
group server-out-192.168.1.11-14
vip address x.x.x.1
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active
group server-out-172.168.1.11-14
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add server-out-172.168.1.11-14
active
Option 2
Create a service that includes all the ip addresses starting from 192.168.1.1 through .14 using the range keyword.
Now you need to create one source group with a VIP. Add the service to the source group.
If you do not want to cover the unassigned ip addresses just move them up and use consecutive ones.
service server-out-192.168.1.1-14
ip address 192.168.1.1 range 14
active
group server-out-192.168.1.11-14
vip address x.x.x.x
add service server-out-192.168.1.1-14
active
thanks

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Dividing source signal with 2 counters

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