SCXI 1125 lowpass filter

Hello I am using a SCXI 1000 chase with two SCXI 1125 cards. My question is how can I configure a software filter that works like the one implemented in the SCXI 1125 card. More exactly i what to build a 4 Hz cuttoff lowpass filter. Thank you.
Attachments:
filter.jpg ‏139 KB

Which module are you using?
I suppose you could always just run your signal through the Filter express VI (in the Express » Signal Analysis palette) or one of the VIs on the Signal Processing » Filters palette.
Kyle B | Product Support Engineer | ni.com/support

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NI SCXI 1104 Lowpass filter

I have a NI SCXI-1104 and in its datasheet says that it has on each channel a three-pole lowpass filter with a 2 Hz cutoff frequency to reject 60 Hz noise. I need to know: What kind of filter this device uses? What happen with the data over the cutoff frequency? In my case I need to analyze the frequency between 1 to 8 Hz and reject the others.

This board is for the Excel add-0n called Measure.
Well it's three-pole low pass filter and frequencies above 2 hz are going to be greatly attenuated. This module is intended for thermoucouple (dc) inputs and would not be suitable for any sort of frequency analysis, in my opinion

Noisy thermocouple signal with SCXI-1125

Hi all
Am using SCXI -1125, with 1328 terminal blocks, I have set the filter to 4hz in the signal conditioner. Am using 256 T type thermocouple, with 1 sample per channel at a very low sampling rate "1Hz".
Am receiving lot of noise in the signal, aprox +/- 1deg. But there are other channels which are very stable with hardly 0.2deg variation. I have tried connecting the negative of the noisy signal to ground, but with no results. Can anyone give some input on this?
Thanx a lot
Arun

Arun,
Are you sure you are setting these properties correctly? Before
modifying any of these properties, you must specify the active
channels. Please take a look at the attached example program. It sets
the active channels to all channels in the task and then sets the
auto-zero mode. A similiar process should work for enabling the filter
and setting the cutoff frequency.
Hope this helps!
Ryan Verret
Product Marketing Engineer
Signal Generators
National Instruments
Attachments:
Cont Acq Thermocouple Samples-Int Clk.vi ‏98 KB

Need to be Able to use a TB-1328 with an SCXI-1125

I need some labview code to show me how to read temp from a SCXI-1125 with a TB-1328 thermocouple on it. I have a K type thermocouple wire, I have to stick with Labview V7.0, NI-DAQ 6.9.3f5, and this is running on an RT machine using a PXI-1010 split PXI/SCXI chassis, with a PXI-6040E running the SCXI bus. Please if you could, tell me how to remote DAQ configure this. Thank you.

Hello,
If you have NI-DAQ 6.9.3 support installed for LabVIEW 7.0, then you should have an example which will show you how to acquire a thermocouple reading from a SCXI-1125. The example which I am referring to is called "SCXI-1125 Thermocouple.vi". Regardless of what terminal block you are using with the SCXI-1125, you need to make sure that you configure it accordingly in Measurement and Automation Explorer.
For assistance with Remote DAQ configurations, please refer to the following knoweldgebase: What Do I Need to Know to Set Up My Remote SCXI System?
Regards,
Jared A

How to configure the lowpass filter integrated to the serie M DAQ (6280)

It's written that for the NI 62xx serie M DAQs, a lowpass filter can be programated (to prevent noise or aliasing), but I can't find where I can configure it ...
I use LV 7.1, DaqMX 7.3 and MAX 3.1.1.3003.
Thanks for your help !
Mathieu

Bonjour,
Effectivement, la valeur du filtre de la carte NI-6280 est 40kHz.
En simulant la carte, j'ai pu faire le test avec le VI joint.
Si ce VI ne fonctionne pas, quelle est le code d'erreur obtenu et à quelle fonction apparaît-il ?
Salutations,
Isabelle
Ingénieur d'applications
National Instruments France
Attachments:
filtre 6280.vi ‏73 KB

Lowpass filter help for thermocouple reading

Hello
I have an old legacy E-Series AI-16SE 12bit 500KHz PCI card.
I am attempting to setup a temperature reading test program. I will have the E-Series connected to a SCB-68, which will have five T type thermocouples connected. I realize this is not the best test setup but it is an attempt at a quick setup on a bench so hopefully any noise interferance will be minimal.
I will be using LV 8.2 professional development.
I was wondering if I setup a software based lowpass filter if that would be helpful in this situation?
If so can someone show an example the has a cutoff freq for 2Hz? I am unfamilular with all the settings of the lowpass filter VI and some guidance would be much appreciated.
Thanks in advance
Tim C.
1:30 Seconds ARRRGHHH!!!! I want my popcorn NOW! Isn't there anything faster than a microwave!

Tim,
Rob's idea is probably what you should try first. It is in effect a low pass filter with about a 10 Hz corner frequency.
If you find that you have strong power line frequency interference, you may need to do more aggressive signal conditioning. Especially watch out for ground loops.
Lynn

Noisy Analogue Signal and Lowpass Filter Questions

Hi everyone,
I am getting analogue signals from a strain gauge that are a bit more noisy than I would like... Normally, I jump right in an smooth the signal using a lowpass filter of whatever order gave me the result that was acceptable, without overkill and smootig the signal to nothing... However, I am settingup a new DAQ device and would like to a little more informed about what and how am doing this...
So, here are my questions:
1. How do I determine the filter order? I usually use a 2nd order filter for smoothing.. I understand the comncepts of roll-offs and phase delay as they relate to the order numbers... On what basis should I decide which order filter to use for this specific signal?
2. I am still thinking that using a lowpass filter is the best approach... I assume the lower cutoff freq is in Hz (i.e. 10Hz) and is NOT a normalised freq [i.e. cutoff freq / (sample rate/2)]?.. The default value is 0.125, which seems too low for a Hz value? Also, on what basis should I decide what cutoff freq to use for this specific signal?
3. I need to synch the filtered strain gauge signal with other, unfiltered signals... But as the filter will add a phase delay it will affect signal synchronisation... I heard somewhere that a 4th order filter is zero-phase, but I can't see how that could be right as the filter only operates in one direction... Any suggestions for what I could do to maximise the timing alignment between the filtered and unfiltered signals?
All comments welcome!
Regards,
Jack

Jack,
I was the Instrumentation Engineer at a university for 24 years and worked with several execise physiologists, biologists, and neuroscientists on similar projects. My group was the "lab/tech staff" you have little of. There were 3.5 (engineer, 1.5 electronics technicians, and machinist) of us for the entire university.
OK. The strain gauge signals probably have no information above a few tens of Hz (hummingbirds) or a few Hz for most larger species. EMG is usually filtered in the amplifiers to slightly larger bandwidths (few hundred Hz) unless you are trying to see the individual action potentials. Does the dynamometer have specifications on the bandwidth or sampling rates used?
Since your bandwidths are realtively low, I suggest that you sample all the analog inputs (and the trigger outputs, if the boards have the capability) from the same clock. You can later decimate or average data on channels where less data is needed. Record the trigger signals on an unused analog input if you have one available. It can be very handy to have the information about when the triggers actually occurred in the same dataset as the response data.
Delay equalization is a complex topic. Suppose that you are sampling all your channels at 1 kS/s. Suppose you have a 10 Hz low pass filter, 2 pole Butterworth, on a strain gauge channel and a 50 Hz filter, 4 pole, elliptical, on an EMG channel and you want to synchronize the filtered data with some unfiltered channels. The two filters have very different phase and delay responses over the 0-500 Hz frequency range. To equalize you would need to determine the maximum delay at any frequency in the range for both filters. Then you would need to design THREE all-pass filters. One would have a phase response which compensates the 10 Hz filter. Another would compensate the 50 Hz filter. These would need to be designed so that the total delays through the low pass plus all-pass filters is the same. Then you need a third all pass filter with that same total delay to compensate the unfiltered data. This is may be a non-trivial job for an expert, depending on the low pass filters.
What kind of noise are you seeing and how is it affecting your measurements? Can you post some data?
Lynn

SCXI 1125 self calibration

Hi,
Does SCXI 1125 support self calibration? If yes, can I do it using the DAQmx Self Calibrate.vi?
"A VI inside a Class is worth hundreds in the bush"
യവന്‍ പുലിയാണു കേട്ടാ!!!

Thank you Vishal.
SCXI 1125 user manual says that internal calibration is possible (for offset) and that we should use the SCXI calibration VI (not the DAQmx Self calibration VI). I am not able to find this VI in the DAQmx Calibration palette. The only SCXI calibration VI present is for external calibration.
"A VI inside a Class is worth hundreds in the bush"
യവന്‍ പുലിയാണു കേട്ടാ!!!

Need continuous acquisition of 16 channels through SCXI-1125 to PCMCIA DA board + FFT on all channels. Can it be done?

Where's the limit? Assume a new Dell Latitude running NT with 128 MB RAM and a fast P3. Equip it with the DAQCard-AI-16E-4 connected to an SCXI chassis with 2 SCXI-1125 modules.
How fast can I run the sample rate (per channel) if I want to do continuous DAQ on all 16 channels while computing the power spectrum of all channels once per second (using one second's worth of samples)?
The DAQCard has a tiny FIFO, and I'm hoping to use pretriggered scans so I don't have to wait for data. Is that an option without the DMA functionality of the PCI E-Series boards? Without it I will have to constantly empty the FIFO into a "software" b
uffer which will cost boku (many) processor cycles, correct?
So what say the experts... how fast can this thing run? How about if I ditch the laptop and go PXI with the whole deal? Lets make the case!
Thank you!

I believe the PCMCIA interface is going to be the limiting factor in this case. The maximum continuous rate for a DAQCard will vary from computer to computer, but it isn't extremely fast.
Being optimistic, let's estimate 64 K samples/second. I don't know if this is high or low nowadays, but it is higher than I could ever achieve a couple of years ago. Divide that by your 16 channels, and you have 4K blocks. I think you could process this in 1 second easily. This gives you 1 Hz resolution up to 2 Khz.
Now, if you ditch the laptop and go to PXI, it is a whole different story. DAQ rates will not be the limiting factor. You just need to find out how large of a block you can process and keep up.
My approach to this problem would be to figure out what analysi
s you need, then figure out what hardware can accomplish it. Do you really need 1 Hz resolution? Do you need to process every bit of data that comes in? Are you going to store the results, or just display them on the screen? Can you do post-processing of the data if necessary?
Bruce
Bruce Ammons
Ammons Engineering

SCXI-1125 スケーリング

ご教授下さい。
SCXI-1125にSCXI-1320を接続してあります。
MAX5.0で電圧入力、GAIN=1に設定したチャンネルで、
スケールなしのテスト表示では問題なく４V程度を計測できているのですが、
スケールで５V未満までの表を設定すると、入力範囲上限が2.5Vになり、
それ以上は2.5Vのスケール値でクランプされてしまいます。
何が問題で上記のようになってしまうのでしょうか？
解決済！
解決策の投稿を見る。

TAKINAMI様
ご返信頂きましてありがとうございます。
こちらでは、NI DAQｍｘが提供する「表スケール」の動作を確認致しました。
指定された値がきちんと反映され、特に問題なかったです。
「表スケール」にて信号の入力範囲は、0V-5Vに設定できないでしょうか。
カスタムスケールを「線形」にして頂いた場合の測定結果はどうなりますでしょう。
表スケールの詳細は下記の通りになります。ご確認ください。
表スケール
表スケールを使用して、プリスケール値の配列を対応するスケール後の値の配列に割り当てます。これ以外の値はすべて比例的にスケールします。
たとえば、以下の表スケールを構成するとします。
プリスケール値: 0, 5, 10
スケール後の値: 0, 10, 20
入力操作の場合、デバイスが2というプリスケール値を集録した場合、読み取られるスケール後の値は4になります。出力操作の場合、2というスケール後の値を書き込むと、デバイスは値1を生成します。

SCXI-1125: what kind of A/D Converter structure?

Hello,
Im a student and actually Im writing my diploma thesis.
For this I need some information about the SCXI-1125.
What kind of structure does the A/D Converter have?
What is the resolution of the 1125?
How many Bits does it have?
What ist the accuracy of the CJC sensor?
All other additional information about tht 1125 could be helpfully, so kindly help.
Best regards
Christian

Hello Christain,
The SCXI 11125 user manual that you shall find here should help you
Mind you, SCXI 1125 is only a signal conditioning module
You need to interface it to a suitable DAQ card for any A/D conversion and that DAQ card's A/D architecture, resolution etc shall be your determining factors
Regards,
Dev

Scxi 1125 R202 getting burned

Wondering if anyone else has seen this issue.
I have about 200 of these cards (SCXI-1125) in service in production test machines. Quite a few of the failed units have R202 burned on the SCXI-1125 card. Sometimes replacing R202 fixes the issue, but more often it does not. Since i do not have a schematic of the 1125, it is hard for me to tell if this is a design flaw, or if it is something that we are doing. Luckily, I also have a stack of 32 of these cards that were purchased for a project that was cancelled, so spares is not an issue thankfully.

We are testing power supplies, specifically DC to DC converters. So yes, static DC voltages. We are also reading static DC voltages from the analog controls of some of the other instruments in the rack (power supplies and loads). At no time is there more than +10V present on any channel. These being 8 channel devices, I would find it strange that we are only seeing damage to one component. As far as I know, the way we have it cabled, we are using all 8 channels separately and using the mux in the 6031e card to channel the readings to the AtoD.
So I would like to know the purpose of R202 in the circuit of the SCXI1125?

SCXI-1125 overvoltage criterion

Hello all,
I am going to use a SCXI-1125 module with SCXI-1327 terminal block to condition thermocouple signal. Estimated signal range is about 0-50mV.
The problem is, since the thermocouple bead must be attached directly to a resistance heater, on which current flows at 100Hz with certain duty cycle, it is expected that part of the heating voltage(no more than 1V) will be imposed on the thermocouple bead. We can manage in LabVIEW so that no overlap exists between data acquisition and heating.
I use an oscilloscope to measure the voltage from the thermocouple wires. Surprisingly, at the end of each current pulse, there seems to be a negative peak voltage. The duration of the peak is about 0.02ms out of every period, which is 10ms. Magnitude of the peak varies between 1V to 20V.
I look into the manual of SCXI-1125, which says when measuring voltage larger than 5V the 100:1 attenuator on the terminal block (for example, SCXI-1327) should be applied. But when I tried this way, the temperature signal suffered from large noise, maybe due to its very low nature.
If I bypass the 100:1 attenuator, is there possibility to damage SCXI-1125? I wonder whether the peak voltage or the continuous voltage should be avoided. The manual doesn’t provide parameters such as “input current during overvoltage condition”.
Any suggestion would be greatly appreciated.
Su

Lynn,
Thank you for your very fast reply. In fact our heater was fed by two 12V lead-acid batteries in series and the averaged power input is ragulated by an IGBT module, and the two electrodes which stretches the heater are floating-connected rather than grounded. The thermocouple wires are also ungrounded.
During the run, I think there is no large external interference(such as a welding machine or other on/off operated device) nearby. Once I recharged the batteries beside the apparatus and interference as large as 1 V appeared. In other case no descernable random interference seems to exist.So maybe the problem is from the inner of our device?
The png file named "nonoverlap" shows the voltage signals every 50 samples for a period, during sampling no current flows. The png file named "temp" is the temperature signals corresponding to the previous voltage signals, every data is the result of the average value of the 50 samples mentioned above. The last file named "interactive" is the voltage signals every 150 samples in a period, with each last 100 samples overlapping with the heating pulse. You can see two peak signals in the beginning (the data before the first negtive peak come from a previous run).
Best regards,
Su
Attachments:
Nonoverlap.PNG ‏50 KB
Temp.PNG ‏31 KB
Interactive.PNG ‏35 KB

SCXI-1125 scan rate controlling

SCXI-1125 scan rate is 333kHz in the multiplexed mode. Does anyone knows how to slow the scan rate?.
regards.
naushica

According to the web page "http://digital.ni.com/public.nsf/allkb/410A70C25A4D12B486256A1E0070BDAE"
You will lose resoltuion for increasing the scan rate. Isn't it?
If the scan rate is 100kS/s and the input range is +-5V with the
14bit resolution, does that mean that I have a
noisefloor of 600uV for that range?
If I want to measure a signal in +-1V range does that means the noise floor is around 120uV?
The absolute accuracy table on the other hand states about an accuracy full scale range but
doesn't state about scanning speed.
For example, 18-bit ADC module PXI-6289 data sheet states that +-5V range has a full scale
accuracy of 510uV.If converted to bits, it will be less than 15bits.
So even though I reduced the scanning speed to abt 50kS/s will I get an accuracy of 16bits?
I have a SCXI-1125 + PXI-6289 installed in a PXI-1052 combo chassis.
Please help on this matter.

Does Strain task in DAQmx include lowpass filter?

I am using a load cell with a 2.232 mv/V with an excitation voltage of 10V. When I put a scope to the output, there is a lot of high frequency noise which causes me to have to use an amplifier with a lowpass filter built in.
I would like to be able to accomplish this same task without having to purchase the amplifier (I have 3 load cells per machine, 6 machines so cost does add up). I am currently using a PCIe-6320 for some encoder measurements on this same application and did find where I can use the analog inputs to measure Strain using DAQmx.
My question is does the Strain measurement in DAQmx have a built in lowpass filter to clean up the signal? If not, is there a solution to this that does not require a Toolkit or additional module for signal processing? We have the basic LabView 2009 SP1.

aeastet wrote:
I would also look at why you are getting so much noise. How do you have your channels hooked up to the system?
Yes.
Using a strain guage module the bridge is built into the terminal block and the hardware does the mv/V thing so there must be some place the noise is entering the system, long, non-shielded, non-twisted pairs, bad ground...
Ben
Ben Rayner
I am currently active on.. MainStream Preppers
Rayner's Ridge is under construction

SCXI 1125 lowpass filter

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