Measuring floating signals

I am using a PCI-6024E DAQ board and I would like to measure a floating signal. I tried to measure the signal by connecting the two leads each to an analog input (like I believe you are supposed to) but damaged the board I was using. The two leads are always within 5 V of each other which should be fine. However, the leads can have a voltage with respect to ground of something more like 120 V at times. It would be disastrous if this signal was connected to ground (which is probably what caused my board to be damaged). Any thoughts on whether or not I can safely measure this signal with my DAQ board? Thanks.

Hello,
Thank you for contacting National Instruments.
The PCI-6024E data acquisition board has a working voltage specification of 11V that means that the board will continue to measure correctly till the input voltage on either of the analog input channels is not greater than 11V. The board also has a power on over voltage protection of 40V which implies that the board will not get damaged for voltages up to 40V while the board is powered on.
To measure a signal that has a common mode voltage of 120V you will need to use signal conditioning with isolated analog inputs. Two simple solutions are:
1. Use an SCXI-1120, 8-Channel Isolated Analog Input Module with an SCXI-1327 terminal block. This configuration will let you measure voltages in the range of +
/-250V.
SCXI-1120/D User Manual
2. Or you can use an SCC-AI04 module in a SC-2345 chassis which has an input voltage range of +/-5V and provides an isolation of 300Vrms.
SCC-Ai series User Manual
If you are interested in purchasing these solutions you can contact a sales representative at NI by calling (888) 280-7645.
Regards,
Nipun M
Applications Engineer
National Instruments

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How can I measure 2 floating signals with a DAQ?

Hello, I have a DAQcard AI-16XE-50 with a BNC2110 adapter to connect signals.
I need to read 2 analog floating signals (less then 1 V, DC).
The configuration of the DAQcard si DIFF Input mode.
I tried to read the first signal and everythings was OK, then I tried to read the second and everything was Ok, but when I tried to read them togheter the values were modified from original values, even measuring them with an external voltimeter.
How I have to connect signals to my BNC-2110? I need some Bias resistor? or what?
Thanks
Lorenzo

Hi lcaggio,
You're BNC-2210 is designed to work in differential mode with your DAQ board. It sounds like this is how you have things configured though. Here are my main suggestions for resolving this.
1) Make sure that the channel switch is set to "FS".
2) Make sure that your DAQ board has the BNC-2110 configured as an accessory. (accessed through board Properties in Measurement & Automation Explorer)
3) Make sure that your DAQ board is configured for the correct voltage range and that your inputs are configured for Differential.
Now, by default, the NI-DAQ driver will sample channels as quickly as it can between channels. Since your channels are floating, it is possible that there is channel cross-talk between your two channels and that is why it l
ooks good when you sample the channel individually but looks bad when you sample both channels together. This is corrected by increasing the period of time between sampling each channel. This is called the "Interchannel Delay".
4) The following Knowledge Base describes and links to documents that mention the importance of the interchannel delay.
What Are the Minimum and Maximum Values for the Interchannel Delay Setting on my DAQ Board?
http://digital.ni.com/public.nsf/websearch/9AE87416C8792FC286256D190058C7D3?OpenDocument
5) Connect an analog channel, both CH+ and CH-, to AIGND. This will ground the channel. Then sammple your first analog channel, followed by the grounded channel and then your second analog channel. The ground channel helps with channel cross-talk (channel ghosting).
Anyway, hope these suggestions help your project. Have a good day.
Ron
Applications Engineering
National Instruments

Sequence 1create output digtal signal- 2 make microseconds delay or less- 3 measure digital signal with board 6023e

hello
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thanks

...My problem is how i can make this delay betwen create and measure a signal.
...how many time the labview get to end one task and start another one.
What I tried to say is, that even if you use the counter of the 6023e-Board
to create the delay and trigger the measure via LabView under Windows,
you leave the realtime-path. Executiontime of LabView-code is then not
determinated.
One way to solve this, is triggering measurement via hardware and use LabView to read Data from the Buffer of the DAQ-card.
You can find more info about DAQ in the "measurements manuall" of NI, delivered with your LabView Software.
Lorand

Measuring 100K signal from piezo electric sensor

Hi programmers,
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Thank you
Labview lovers.

Hi!
   I'm worried about the fact that 10 kHz signal isn't seen, that cRIO module is rated for 100 kS/s per channel, so, with 1 channel, you should theoretically be able to sample as high as 50 kHz, or, with common approximation, say 20 kHz.
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Connecting USB6343 onboard 5v to AI 4 5 6 7 through 4 switches and AI GND results in floating signals and noise

Hey,
I am connecting USB6343's onboard 5v source to AI 4 5 6 7 through 4 switches (and AI GND). This results in floating signals and sinusoidal noise when i close the switches and not the expected 0v / 5v.
I merely want to report on or off for each switch connected to the AI terminals, what very obvious step am I missing?

I'd like to ask further questions, but being new to the forum, I'm not fully familiar with the customs, so please tell me if I should open a new topic or if it's okay, to bundle questions (if related).
The question are: how to extend the described wiring to multiple switches (I need 10)? I attached my assumption as "Wiring 1.png".
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Attachments:
Wiring 1.png ‏9 KB
Wiring 2.png ‏11 KB

Measuring DC signal with ac coupling

I'm TOTALLY new to Labview. I was trying to use NI DAQ 4472 for measuring DC signal with large DC offset. I would like to see an example that sets AC coupling for filtering the unwanted DC offset. I found an example with "DAQmx Channel Property", but I need help in connecting it with the block diagram. I have attached my block diag. and and help in connecting the DAQmx Channel Property Node is highly appreciated.
Thanks.
Attachments:
Sensor_Configuration_Test.vi ‏60 KB

Good afternoon MiamiVipul,
Thanks for contacting National Instruments with your issue, we'll try and get you up and running as quickly and efficiently as possible.
Look like you've got the right approach to your problem.
In order to integrate a property node into your code, you simply have to wire the task reference and error cluster in line with the rest of your code. I.e. after you create the task, you will have the purple task reference out as well as the pink error cluster out, wire those to the corresponding intputs on the property channel node and then wire the task and error out of the property node into the DAQmx Create Channel vi.
Have a look at the examples by going to Help > Find Examples (Browse Tab) > Hardware Input/Output > DAQmx > Analog Measurements. There are a variety of different measurement types which you can start from to give you a strong idea of the general DAQmx coding principles. Several of these also use Property Nodes. For example Acq&Graph Voltage - Int Clk-Analog Start w Hyst.vi
You mentioned you want to measure "DC signal with large DC offset", which I'm assuming is a typo, as AC coupling is of course designed to remove the DC offset so you can measure the AC signal.
Best of luck with your project.
Sincerely,
Minh Tran
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National Instruments

Problems to measure a signal with 10kHz frequenz

Hello,
i want to measure a signal at 10khz frequenz.
My problem is that from 100Hz above i dont get a clear Signal.

Daniel,
Could you provide more information about your task.
- What type of signal is it (sine, square wave, etc.)?
- What hardware are you using to measure the signal?
- What type of input are you using (analog in, digital in, counter)?
- How are you performing the measurement? What functions are you using? What development environment (LabVIEW, C, etc.) are you using? Can you attach an example of your code?
Christian L
NI Consulting Services
Christian Loew, CLA
Principal Systems Engineer, National Instruments
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Floating signal with a time depend thresholding

hello all,
i have a floating signal that need a time depend thresholding. For example if the signal shift more than 0.2 V in less than 1 second then an alarm is set otherwise the baseline and if the signal shift 0.2V in more than a second then alarm stays off and baseline shift. I've tried different techniques such as averaging the signal and deducting its original but nothing seems to work i also tried to put a time delay but all the instrument channel are then delayed even if created in a subvi. could someone help me please?
thank you in advance
Frederic.
Solved!
Go to Solution.

Hi Fred,
As promised i have attached a circular buffer vi. All this does is store your data in a circular buffer. You can specify the size of the buffer. Upon initialisation (will automatically do the first time you write to it) a buffer of your specified size is created with the buffer initialised, filled, with the first value you enter. I did it this way so if you are inputting a voltage, the whole buffer will be filled with that voltage which will immediately allow you to add your peak sensing algorithm after it. (Rather then the buffer be full of 0's and then adding your first input voltage).
Upon entering a new value to the buffer the buffer deletes the oldest value, shifts the buffer and then inserts the new value on top. If for example you configure the buffer to have 100 values, the output of this vi will always be the last 100 values entered. If you store 50 values per second then a 100 values will represent the last 2 seconds worth of data continuously. It does not take 2 seconds of data, stop and then take another 2 seconds worth. The data is a constant rolling representation of the last 2 seconds of data.
You can then do any filtering of high and low values on this set of data output from the vi. I will attach both the circular buffer vi and a demo vi to visually show you how it works. On the demo version i have coded the buffer to a size of 5 just to show you. On the front panel extend the buffer to show 5 values. You will see as it runs how it shows the last 5 values entered into the buffer vi.
Hope this helps you out. If you are still having problems filtering this data to achieve what you want let me know.
I will send you this in LV 2009 and LV 8.6 as not sure what you are using.
Rgs,
Lucither
Message Edited by Lucither on 03-23-2010 07:29 AM
"Everything should be made as simple as possible but no simpler"
Attachments:
Circular buffer.zip ‏27 KB

I can't measure many signals at the same time using the DAQCard-AI-16XE-50.

I'm using a Compaq Presario 1655 laptop with a DAQCard-AI-16XE-50 on the PCMCIA slot, and LabVIEW 6i and MAX 2.0.
I have a SCXI-1001 Chassis with SCXI-1122 and its terminal block SCXI-1322 installed (I have others too).
I'm trying to measure some signals at the same time, for instance, measuring 2 load cells signals, and a frequency of an indutive sensor (using the analog way with the "Extract Single Tone Information.vi").
I realized that I can't measure at the same time my signals, neither the load cells - a 10608 error occurrs "NI-DAQ LV: No transfer in progress for the specified resource".
What's the problem?
Some DAQCard limitation? Configuration?
Thanks!

Hello;
By your description I'm assuming you are trying to read those analog inputs in parallel. The SCXI-1122 doesn't have that feature. All the analog inputs will be multiplexed to one single Analog Input channel on your DAQ board. If you need to make measurements in parallel, you need to use one of the SCXI modules that allows that operation. For more information on what modules support that operation, you can always refer to our home page at www.ni.com.
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National Instruments

How do I measure a signal source that is floating?

I've been trying to measure a source signal that is floating (a voltage around 1V). I'm using the Sc 2345 and I've got the signal coming through a low pass filter module (scc-LP02). I've set up the DAQ board to read in NRSE. When my data aquisition board and laptop are plugged into a battery power supply I have no problem reading the signal correctly. The problem arises when I connect my laptop OR data aquisition board to the AC outlet. When I do this I get a reading of -5V. I believe this is because I'm actually grounding everything to building ground when I use the AC outlet. I've tried plugging my DAQ board into the AC outlet without grounding it, and I get a signal close to what I'm looking for but with a lot
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First of all, what type of power supply are you using for the SC-2345 (e.g. PW01)? When you say "data acquisition board" what exactly are you referring to? The SC-2345? Or do you have an external data acquisition board (e.g. DAQPad 60xx)? It sounds like if nothing is plugged into an AC outlet, then you are getting correct readings. However if one or both of your components are plugged in, then you get bad readings. You mentioned plugging your DAQ board into an AC outlet without grounding it. What exactly are you doing here? How are you accomplishing this? Below is a extensive tutorial on wiring up different types of signals in the field. Take a look at that and see if that helps explain what may be going on here. Another suggestion would be to tie the -
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Field Wiring

Can you tell me how to measure audio signal frequency in measurement studio with visual basic 6.0?

I'd like to measure two differential input signal(I.e. A+ and A-),below is two test projects,
1.connect A+/A- to PCI 6052E card's ACH0/ACH8 ,and refer to GND for testing
2.connect respectively A+/A- to PCI 6052E card's ACH0/ACH8 for testing
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In addition,I would like to measure the audio signal frequency,could you give me a illustration in measurement studio with visual basic 6.0?
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Dear kelven,
Thank you for contacting National Instruments.
To address your question, there are Analog Input shipping examples that demonstrate how to measure an analog input differentially, as you specify in (2).
As for measuring the audio signal frequency, you may want to check out the following KnowledgeBase. The link is:
http://digital.ni.com/public.nsf/websearch/4b08380530d72d3b86256340004c3005
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Thanks again and have a great day!
Chad AE
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Measuring cell signal strength

iOS4 displays fewer signal strength bars than iOS3 did. It is clear that many people are interpreting this as less signal strength.
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How to measure different signals with PXI-2501

Hello everybody,
i have a an understanding problem.
I have a PXI-2501 switch and i want to measuere signals with the pxi-4071, so far so good.
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.
Any suggestions? Am I doing something completely wrong?
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?
Have you measured the the resistance of the Switch-Matrix yet?
kind regards
Heinz

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Hello, Friends
I am interested in developing a data acquisition program from a sensor that gives a pulse signal. I would like that send me please some information about what VI’s I have to use inorder to began the acquisition and How I can measure the pulse frecuency. Some examples will be very excellent.
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Measuring digital signals coming from the HSDIO (PXI-6542) with the DMM (PXI-4070)

Hello,
in attachment you can find the program I'm using for my measurement: I'm generating and acquiring digital signals with the PXI-6542 and at some trigger point of one of those digital signals I'd like to capture the measured values on a plot with the Digital MultiMeter (PXI-4070).
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Hey Jürgen. I apologize that you haven't gotten an answer yet to your post. I looked at your code and had some questions. What is the source of your trigger to your DMM? I see that you're exporting the data active event to PFI1, and your comments indicate that PFI1 and PFI2 are connected to give you a start trigger for your digital acquisition. Exporting the data active event with a finite or continuous pulse should only give you a single edge per run, though - you wouldn't get a pulse each time. Is your trigger coming from a data line? I didn't see any line in your included data that would indicate a single pulse.
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