Signal Conditioning topics

eeg filter design

rashidahmad484 — Sat, 18 May 2013 15:46:19 GMT

AOA;

Hi friends i m doing project on eeg signal acquisition in order to detect drowsy state of driver in order to prevent road accidents....for this i am using amplifier circuit and dsp kit speedy33...in order to filter eeg signal i need to design bandpass filter of 4-7Hz....but when i am design the response of filter is wrong because os sampling frequency ...that is 8000hz...i want to downsample the real time data of speedy33 kit.....how i downsample the 8000hz to 1000hz.............can anybody help me

IIR Filter - Someone please help me!

rwong7757 — Thu, 16 May 2013 09:28:55 GMT

Hi all,

I thought this was a simple problem to do, but for some reason it's not working for me.

I'm taking in some data from an IR sensor and I'm trying to do some filtering on the signal. I want to highpass the signal so that the DC offset of the signal and any low frequency will be attenuated. I've implemented a digital IIR butterworth filter in MATLAB to first verified that it worked and then tried to implement the same thing in LabVIEW. The problem is that the results were not the same. I implemented the IIR filter two ways in LabVIEW with both differing results from MATLAB.

Here's what I did in MATLAB:

I generated the IIR coefficients for a butterworth highpass filter that's 7th order with a digital cutoff frequency of .1. Then I got the filtered results and plotted it. I've attached the MATLAB figure images.

[b a] = butter(7, .1, 'high')

b =

Columns 1 through 4

0.4918 -3.4426 10.3279 -17.2132

Columns 5 through 8

17.2132 -10.3279 3.4426 -0.4918

a =

Columns 1 through 4

1.0000 -5.5890 13.5047 -18.2709

Columns 5 through 8

14.9365 -7.3738 2.0344 -0.2419

PS1filtered = filtfilt(b,a,PS1);

plot(PS1)

figure(2)

plot(PS1filtered)

So in LabVIEW, I thought it would be simple to implement as well. I've attached my VI that I made. In the VI, I used the Butterworth Filter VI and I also used the IIR Filter VI with manually entered forward and reverse coefficient values that I calculated in MATLAB. Please note that I'm only processing the second column of data in my data file. At least one of the graphs in LabVIEW should resemble the result that I got in MATLAB.

Can anyone help explain this?

Transducer techniques MDB-10 load cell. Best NI HW?

MarcoMauri — Tue, 14 May 2013 07:15:50 GMT

Hi!

I need to interface with a Transducer techniques load cell and I'm trying to find the best NI product to do it.

The datasheet states the excitation voltage is 10 VDC, so I'm afraid I can't use a NI 9219 (I've also a thermocouple).

Any suggestion would be appreciated,

regards,

Marco

How scaling a voltage signal (como escalar una señal analógica de voltaje)

ingeniero-LJ — Mon, 13 May 2013 21:48:51 GMT

my problem lies in the scaling of a signal as it is not referred to in the custom reverse scaling of assistaint daq, anyone can help me?

español

mi problem radica en el escalamiento de una señal ya que no se a que se refiere reversa en el custom scaling del daq assistaint, ¿alguien me puede ayudar?

2.5MHz oscillations on scxi-1127 AI channels

E_Coleman — Fri, 10 May 2013 20:14:04 GMT

I'm trying to measure the circuit below through a SCXI-1127 multiplexer and I'm seeing a 2.5MHZ sinusoid when I connect my circuit output to the multiplexer. Alone, I don't see this signal, but as soon as I connect to the mux input, it pops up and it is very large. I can see this signal not only in my software but with an O'scope probe across the circuit's output. The circuit is a simple Inverting amp and I'm using LT1212 op amp. I'm also using a virtual ground between the rails since I'm running on battery. When connected to other DAQ's or Oscilloscope, I get a clean signal, but when connected to SCXI-1127, it shows up - even when the switch isn't on. Any suggestions or ideas of what the cause might be?

rt

+918142355510 — Wed, 08 May 2013 07:41:21 GMT

Hi Everyone,

I am trying to read 4-20ma signal frpm a Rockwin flowmeter using scxi1102b and scxi 1308 connector, when i read 4ma signal I am not getting a constant dc 4ma signal instead its fluctuating with a constant period as shown in image below, but when i read it using a multimeter there is no fluctuation and the reading is constant, how do I read a constant dc 4-20ma signal

Thanks and Regards,

Vishwas

signal output

derkuli — Sun, 28 Apr 2013 14:13:38 GMT

hi, i just done wheatstone bridge with quarter strain gage and I'm using NI-USB 6008 to acquire the signal in labview.

however, the signal is different to what display in oscilloscope. how can this happen? anyoone can help me? oscilloscope shows damping oscillation.

How can I filter thermocouple noise using a TC-2095 and SCXI-1102c?

RALu — Wed, 24 Apr 2013 20:33:39 GMT

Hello all,

I currently have four TC-2095s connected to SCXI-1102c cards inside a SCXI-1001 chassis. These thermocouples are floating and I have been getting a fair amount of noise (3-phase 400 Hz and even 60 Hz noise) when we power on some equipment such as blowers and fans. Using this current set up, how can I filter the noise? Or do would I need to set up a new hardware configuration (i.e. SCXI-1102 cards)?

Quick question regarding the use of external Excitation source for multiple sensors

OKors — Tue, 16 Apr 2013 16:54:49 GMT

I'm currently using a cDaq and NI9263 to provide 10v excitation to some sensors and an NI9215 to read the signal.
Problem I'm having is when all the sensors go full scale it pushes the current output limitations of the AO module.

My solution is to purchase a standalone excitation-grade power supply (PST-10). My question/concern is: will I run into any issues when using a single source to supply constant 10Vex to multiple sensors? Noise, cross-talk, voltage drop on certain channels as other channels increase in scale, etc. My understanding is as long as the mA output of the power supply is not exceeded (which it never will with this PS) I should be fine.

Thoughts? Feedback?

system identification

saifizi — Wed, 10 Apr 2013 06:49:11 GMT

Dear All,

I have problem when handling my system identification toolkit. When I running my system in real time, i get this error;

The model orders are inconsistent with the dimensions of the model coefficients.

How can i settle this problem. I don't know what is happening actually. I hope some can give some suggestion, why this situation occur. Thanks all.

time averaging of blocks of data per turbinenrevolution

sm81 — Sat, 06 Apr 2013 23:59:41 GMT

Hello,

I have been thinking very hard without getting anywhere about a signal processing aspect of a DAQ measurement. I will describe the problem first as below.

Measurement system: a small DC motor driven turbine (24 blades) running up to speeds of several tens of thousands of RPM.

DAQ device: PXI6251 through BNC2120 connector block.

Problem decription: I am acquiring data for passage of each turbine blade past a sensor. I am able to collect a periodic waveform suggesting the rotation of the turbine. This is a noisy signal. I want to perform rotational averaging so that noise can be reduced. There are plenty of exmaples available discussing synchronous averaging which makes sense (recovering noise buried periodic waves such as a sine wave). However, in may case, I must average so that each cycle of averaging line up with the same blade.

[I can do this by collecting a stream of data. slice it into blocks of consecutive 24 peaks corresponding to each blade, and line the sets up to do the averaging. I am struggling to do this in LabVIEW, elegantly. Mind you, if the speed is varied this will be more complex, so I think it will be best to start by considering the turbine is running at constant speed and then think about variable speed situation. ]

Can anyone get me started on this, please? I can try to be more clear if anything requires further clarification.

[I am not familiar with producer-collector loop in LabVIEW, in case this is a standard approach for this type of signal processing task]

integrate pulses from oscilloscope

Arev — Fri, 05 Apr 2013 10:50:56 GMT

Hello!

I get signal pulses from oscilloscope. Could you please help me to integrate each pulse separately. I've found simple examples and tryed to create loops as in the C++, but it doesn't seem to work properly. Thank you very much!

Arev

Time-frequency analysis of vibrational signals

c.fish — Thu, 04 Apr 2013 22:22:45 GMT

Hello to everyone,

first of all I'm a beginner of the signal's analysis and I hope someone can help me.

I'm trying to perform the time-frequency analysis of some vibration signals, acquired on a internal combustion engine. In particular I must do the tfa of a vibrational signal corresponding to one thermodynamic cycle of the engine; my Lb version is 2012.

In order to do this I'm using the advanced signal processing toolkit, in particular the "tfa stft spectogram" and I have attached in this message the simple VI I created. My issue is that in the intensity chart I should see frequencies about kHz, instead in my VI i see at max 25Hz.

Can someone help me in telling me in what I'm wrong?

bandpass filter problem

idt13 — Thu, 04 Apr 2013 08:09:50 GMT

I originally posted this problem as a reply HERE but haven't recieved any responses so I'm trying a standalone thread. Anyway here's a repeat of my problem...

I had an offset in the raw voltage data from the accelerometer that was causing the plots to fly off to extremely large values after two integrations (conversion from m/s^2 to m). I solved this by subtracting the Offset output from Normalize Waveform VI from the original data stream. This worked really well and I can now get a displacement signal that doesn't fly off sharply away from 0. I do now have one further problem with this signal, though. In each of the attached files are two data sets, one exported from the FFT and the other from the displacement plot. In the 3Hz file the displacement plot shows a large peak just short of 0.1s - corresponding to ~2.5Hz. It turns out this is related to the bandpass filter, which passes frequencies between 3 and 500Hz in my VI. The filter worked really well to attenuate a large peak below 2.5Hz that was originally in the FFT but it introduces another large peak that corresponds with the low frequency cut off for the bandpass filter, ~3Hz in this case.

As expected, this feature moves when the cut off is changed so is directly related to it. The further away from 0 the cut off is the smaller and broader the feature is in the FFT but I want the low freq cut off to be as low as possible. Changing the filter settings - order, type, etc, do nothing. I've attached a second data file with the cut off at 10Hz. The frequency of the main feature in the displacement plot is now 4*1/0.0257 = ~10Hz and the FFT shows a feature around 10Hz. I don't understand what's happening, any suggestions?

This happens only after the double integration to get the displacement from the acceleration signal. Keeping the units in 'g' gives the expected response.

As an aside, I assumed the bandpass filter was a low-pass then a high-pass filter in series, but I get very different results when I use this combination. Any ideas why they could be different, even though the settings are the same?

Thanks!

display sample values on a graph

Aleph.ka — Wed, 03 Apr 2013 13:01:53 GMT

Hallo!

I`ve got a problem with a graph, the thing is I really need to have displayed Y values of the samples on a graph. There is a possibility to make a comments (as on a pic attached) but I need the vals instead. Any ideas? Thanks for the trouble,

greetings!

Need help: Best field wiring configuration using NI 9215, 9263 and Celesco string Pot

OKors — Wed, 27 Mar 2013 18:00:28 GMT

I'm using a cDAQ-9172, NI 9215 and NI 9263 to acquire displacement data from a Celesco SP2 potentiometer-based cable extension transducer i.e. String Pot (following this wiring guide).

The 9263 is providing 10Vdc to the string pot and the signal out is being read by the 9215.
I have the generated DC signal and input scaled using Signal Express. So far the scaling is accurate and displacement measurements are spot on using a custom scale (linear slope) generated from our Metrology lab.
My problem is, with the transducer at rest I'm seeing quite a bit of noise.

I realize there's some field wiring considerations and through trial and error I've been able to get the "cleanest" signal by jumpering the COM terminals of the two modules. The other issue is; for terminal configuration options, the 9263 only allows RSE, while the 9215 only allows Differential. This just compounds my confusion on how these two devices need to be coupled to the sensor.

Based on the attached image I've created of my system wiring diagram can someone with a little more understanding of potential ground issues give me some advice?

If it helps, I also have NI 9201 and 9205 modules available to use. I just thought the 9215 was the most universal.

Thank you

And yes, I've read the white paper on field wiring but I'm still unsure of how to get the cleanest signal.

displacement signal from accelerometer

idt13 — Fri, 15 Mar 2013 12:02:51 GMT

Hi all,

I'm new to labview (about 3.5 wks experience) so please excuse any silly questions and/or ignorance.

I'm putting together a VI to take x, y and z vibration data from a peizotronics accelerometer through a USB-6008 and having some problems converting acceleration to displacement. Attached is a modified snippet of the whole vi (small portion of x) and the output from the acceleration, velocity and displacement plots. Assuming the units are consistent, m.s^-2, m.s^-1 and m, something is clearly wrong with the data in that the values are far too high. The displacement will exceed 10m regularly when it should be a fraction of a mm, oscillating about zero. When I shake the accelerometer I get more defined responses that look right, i.e.. peaking velocity at zero acceleration so I'm sure the VI is right. The gradient of the displacement plot can be reversed when I change the offset in the raw voltage data so the average crosses zero - for some reason there is an intrinsic offset in the data of about 36-39mV. I'd like to automatically remove this offset from the data as it's being collected but can't find a way to use the output from the Averaged DC RMS VI that doesn't cause this error: LabVIEW: (Hex 0xFFFFF8F6) Waveforms have different dt values. I've tried conversions to different formats (to DDT etc), pulling the data from an array. Does anybody have any ideas?

I have a couple of other niggling things, although this may be the wrong section for them:

1. When I do a PSD FFT on the acceleration data (unit g) I always get a very high signal at low frequency (<2.5Hz). Attached is a closeup of the FFT. This is mitigated somewhat by averaging but is still often greater in magnitude than the peaks I really want to see. Where does it come from?

2. The maximum frequency I am measuring is 500Hz, why? I'm pretty sure I've had higher from it while I've been building the VI but all the FFTs are limited to this value now.

Thanks in advance!

How to measure more than 10V DC voltage using NI 9205

LuizFelipe — Mon, 11 Mar 2013 15:16:49 GMT

Hello everyone,

I have a solar panel, controller, battery and load. I need to measure their voltages and currents.
The tensions are higher than 10V DC.
I need to use the NI 9205 to measure them? I do not know if a resistive divider will work?
Anyone have any suggestions?

thank you

how to connect labview with microcontroller 89c51

Kongurajesh — Mon, 11 Mar 2013 14:25:14 GMT

Dear all,

I am a beginner in LabVIEW. I want to connect my microcontroller 89c51 project which is the motor driver circuit with labVIEW through RS 232 cable. Please give some ideas.

Acquiring many signals with multi devices (NI 9229 and NI 9205) trough a cDAQ chassis 9188

phidu — Mon, 11 Mar 2013 11:39:05 GMT

I use a cDAQ chassis NI 9188 equiped with 6x NI 9229 (6x 4 AI chnls simultaneous sampled with aliasing filter) and one NI 9205 (32/16 AI chnls single/differential multiplexecd chnls). I have created a simple task wit the DAQ Assistent to acquire 12 chnls with the NI 9229 modues and 4 with the NI 9205 module. A generator is used to produce a sine wave with a frequency of 10 Hz and an amplitude of 500 mVpp as input to all channels. The same generator produce also a square wave (synchron to the sine) which is used as trigger input (PFI 0 - BNC connector on the chassis). The acquisiton is set to take finite samples by a data rate of 2 kHz and a datalength of 4000 samples (it means a acquisition time of 2 secondes) controlled by a digital reference triggered with the cADQn/PFI0 as trigger source.

My problem is the time difference between the signals acquired with the NI 9229 and those acquired with the NI 9205 (show the attachment). These time difference is not constant and change when the frequency of the input signal varies. I suppose that these difference is due to the aliasing filters used in the NI 9229 and I am searching how to resolve the situation. Any help will be appreciated...

Philippe