SCXI 1520 Simultaneously sampling

Hi there,
for my application i need to read simultaneously all the channels from 2 SCXI 1520 modules. (2 x 8 = 16 channels)
The control module will be SXCI 1600 and the software - Signal Express. Is this possible ?

Hello metrisys,
I believe that it is possible to simultaneously sample from analog input channels on two SCXI-1520 modules that are controlled with the SCXI-1600. PFI 0 of the SCXI-1600 is used to transmit the signal that triggers an acquisition for the SCXI-1520s. You would need to configure the acquisition to recognize the signal from PFI 0 of the SCXI-1600 as the start trigger, and add all of the channels on the two SCXI-1520s to the scan list of your analog input task. For your convenience I've posted a link to a knowledge base article titled 'Synchronizing Multiple SCXI Simultaneous Sample-and-Hold (SSH) Modules.'
http://digital.ni.com/public.nsf/allkb/A01F8168AFCFE9DC86256B3300758CD0?OpenDocument
Best wishes,
Wallace F.
National Instruments
Applications Engineer

Similar Messages

Can you simultaneous sample multiple SCXI-1520 cards in multiplexed mode?

Can you simultaneous sample multiple SCXI-1520 cards in multiplexed mode?
In parallel mode, you can have all channels sampled and held, and then have each
of your E or M series cards multiplex through each of the 8 channels of each card.
This yields simultaneous sampling on all channels at a faster rate in this "SCXI-1520
Parallel Mode" than you can derive from the "SCXI-1520 Multiplexed Mode."
Does the "SCXI-1520 Multiplexed Mode" also provide the capability to Simultaneous
Sample and Hold, all be it at a slower net throughput yield then the "SCXI-1520 Multiplexed Mode?"

Hello,
Thank you for posting to the NI Forums! The SCXI-1520 User Manual does indicate the Simultaneous Sample and Hold can be used with Multiplexed Mode. Please refer to the last two paragraphs of page 69 and the first paragraph of page 70 for a better explanation. Hope this helps! Let me know if you have further questions!
Message Edited by Margaret F. on 04-21-2009 05:25 PM
Regards,
Margaret Barrett
National Instruments
Applications Engineer
Digital Multimeters and LCR Meters

I Am Getting Inaccurate Readings When Some Channels of the SCXI-1520/SCXI-1314 Are Open Circuits

Am Getting Inaccurate Readings When Some Channels of the SCXI-1520/SCXI-1314 Are Open Circuits
My hardware is :-
PCI MIO 16E-1 - 1 no.
SCXI-1000 chassis - 1 no.
SCXI-1520 - 4 nos.
SCXI-1314 - 4 nos.
MAX is showing all hardware ( DAQ card + Chassis + SCXIs), set in Multiplexer mode.
I am using MAX task to configure channels ( as per requirement ) and then use the same task in Labview 7.1
When I am trying to generate task only for connected channels then reading are coming some times....... but when i generate task for all channels including (not connected channels) then the reading are either on - side or on + side (max or min).
I have tried to ground the +S but not work
tell me some solution
Thanks
Surender Kumar

No, DAQmx is superior and I strongly recommend you used DAQmx
Elijah, I guess I understood the problem that Sunder is facing, coz even I had experienced it 2 years back
What happens is if you scan only the channels to which sensors/strain gauges are connected, all is fine and you get good strain readings.
But if you happen to include an unconnected channel into the scan list, all the subsequent channels after the open channel will show saturated readings.
Right, Surender??
The problem we found, lies in the settling time of the E series DAQ card's ADC. Even we were using PXI 6071 E
Once the ADC saturates on reading an open channel, it cannot settle fast enough to read the next channel.Hence, the next channel also reads saturated value, instead of the correct value.
This is irrespective of the sampling rate because, this happened even when we did continuous sampling at low scan rates of 10 to 100 samples /sec
We found 2 solutions to this problem
Disable Simultaneous sampling and hold for the SCXI 1520 module ( using a DAQmx property node)
Use a M series DAQcard, which did not have this settling time problem
Hope this helps,
Regards,
Dev

SCXI-1520 Zero Offset Changes with Variable Loads

We are using the SCXI-1520 to calibrate sensors based on strain gauge bridges. The problem I'm having is that the offset changes when changing the bridge resistance. For example, the output reads 0.0000 mV/V for 350 ohm bridges. It reads 0.0112 mV/V for 700 ohm bridges. It reads 0.0135 mV/V for 1000 ohm bridges. The signal input is a constant zero for all three of these examples. The span (gain) is very consistent. In other words, changing the bridge resistance does not affect the gain. I know the excitation sense lines are working and they are applied very near the bridge. Enabling or disabling the autozero mode makes no difference. What can be done to eliminate the variable offset when changing the bridge resistance?

Dear Dj143,
Are you calibrating your strain gauge lines in the Measurement and Automation Explorer (MAX) or in your LabVIEW program?
In MAX you can create a task and use the calibrate tab in the task to calibrate your line. You would then call the task in LabVIEW. If you are using this method, make sure that you are specifying the correct Gage Resistance (gauges in an unstrained position). The default is 350 so it would make sense that you are getting 0 V with this resistance.
In LabVIEW you can use DAQmx Perform Bridge Offset Nulling Calibration.vi to calibrate your lines. There is an example in the Example Finder that shows how to use this VI. (LabVIEW Help menu>>Find Examples. Search calibration. Cont Acq Strain Samples (with Calibration).vi). In this case make sure that you are specifying the correct Nominal Gage Resistance (gauges in an unstrained position). Once again the default is 350.
If you still get incorrect voltages when specifying the correct resistance, let me know how you are calibrating your lines and I will see what I can think of. Have a great day!
Sincerely,
Marni S.

SCXI 1520 measurement in microstrain

I am trying to acquire samples from several SCXI-1520 channels and save / display them as microstrain instead of strain (calibration factor of 1,000,000) while at the same time applying a different calibration factor to two other channels acquired using an SCXI-1141. I basically want to know how to apply different calibration factors to several different channels using DaqMX. I have been chasing my tail with this for several days and I think I have just about exhausted all of my options...any suggestions would be greatly appreciated.

Hi Dave,
It sounds like what you're looking for is applying custom scaling to different channels. There are a couple of ways you can do this. The easiest would be to use the DAQ assistant and apply a different scale for each channel. You would just need to set up a custom scale for each type of scaling you want. You can set up the scales from here:
This would be quick and easy, but if you don't want to use the DAQ assistant, you can set this up in DAQmx directly. Probably the quickest way is to configure a task in Measurement and Automation Explorer (MAX) with the channels and scales (similar to the DAQ assistant setup). You can then drag that task over to LabVIEW, right click on it and select Generate Code>> Configuration and Example. This will generate the code for you, and give you a good example to work off of later. You could also just build the code yourself by setting up scales in MAX, and configuring your code like so:
Hope this helps,
Andrew S.
National Instruments
Message Edited by stilly32 on 11-03-2006 10:49 AM
Getting Started with NI-DAQmx
Measurement Fundamentals
Attachments:
multipleScales.JPG ‏65 KB
DAQ_asst_Scale.JPG ‏107 KB

Need help to choose a DAQ for simultaneous sampling

We need to choose a DAQ for simultaneous sampling. The restrictions are:
a) 2 channels
b) The signals on both channels are not continuous. A valid input on the channels is signaled by a falling edge in a third line that can be used as a trigger.
c) The rate of these signals can be up to 50000 per second but they do not arrive in a periodic way.
d) The timing:
The trigger is a pulse of 600 ns
The signals on the channels are stable 200ns before the leading edge of the trigger pulse and remain stable for 900ns.
We have seen the PCI-6143 but we are not sure if it is the best choice.
We have some questions:
1) Does the 6143 fulfill the timing requirements ?
2) Is it posible and easy to set the board to take one sample after the trigger ?
3) Is there a better choice than the 6143 to solve the problem ?
4) Can we solve this problem programming in VB or VC++ and using the software that comes with the board or do we need to buy extra libraries ?

1) Does the 6143 fulfill the timing requirements ?
Yes, the 6143 should fulfill these requirements. It has a 250 KS/s sampling rate per channel which should give you 5x oversampling at the 50 kHz maximum bandwidth you indicated. The minimum delay from the recognition of the trigger to the first sample on this board is 100 ns which falls within the 900 ns window.
2) Is it posible and easy to set the board to take one sample after the trigger ?
It's not clear to me whether you want to take a single sample after a trigger and stop or use the trigger as an external sample clock to acquire several samples at the rate of the trigger. In either case, it's possible and relatively easy to do so. The only quirk is that the minimum number of samples to acquire for a hardware timed acquisition is two samples. This means if you really only want one point after the trigger, you'll have to setup the hardware to acquire two samples and then throw the second one away in software.
3) Is there a better choice than the 6143 to solve the problem ?
This seems like a pretty solid choice for the application you described. However, you didn't mention what the amplitude of your input signals are. The 6143 has a fixed +/- 5 volt range. If this isn't sufficient, you'll have to provide signal conditioning or choose a board with a wider input range. Also, I'm assuming your trigger signal is a TTL signal. If it's an analog signal, you'll want to choose a board with an analog trigger circuit (the 6143 doesn't have an analog trigger). The PCI-6111 is a 2 channel board with a +/- 42 volt input range, an analog trigger, a 5 MS/s sampling rate, and will also meet all of your requirements. The only down side of the 6111 is that it is more expensive and is a 12 bit converter instead of 16 bit. The PCI-6120 has even more functionality than the 6111 and has a 16 bit converter at 800 KS/s. PXI has some more simultaneous offerings, but I'm assuming you want to stick with PCI. You can also check out some of our modular instrument offerings such as the PCI-5102. I'm not as familiar with the modular instruments, so you'll have to check out the specs for yourself. Whether there is a better choice or not is pretty subjective. That will depend on how much you're willing to spend for the features and specs you really care about. From the information you provided, the 6143 will be the lowest cost solution that meets the requirements you specified.
4) Can we solve this problem programming in VB or VC++ and using the software that comes with the board or do we need to buy extra libraries ?
The DAQmx driver provides interfaces to both of these programming environments at no extra cost.

How can I use LabVIEW to ground floating SCXI-1520 channels (in order not to lose scanning capabilities from the multiplexer)?

Currently I am reading quarter bridge strain with several SCXI-1520s. When in MAX I noticed my values were no longer reading after a certain gage and as I attempted to troubleshoot, found out that the multiplexer in this module will not scan past any open channel (or if it does, channel results are not consistent) for a very logical reason. If I lose a gage, I usually lose any data from any subsequent gages which we really cannot afford.
Are there any suggestions programming in LabVIEW (right now i'm using NI-DAQmx with an analog task set up)so that each time my loop executes, the program will check for any open channels and either not collect that data or change the order of acquisition (i.e. place the open channels last on the scan list?
I'm open to anything that might be of help

Yes, by "open channel" i mean that there is no signal returning from the gage because it has broken off the structure or the signal to the terminal block has been disconnected somehow.
When I lose data, I'm referring to the data that is acquired on following channels. The behavior appears to be fairly random (which was a troubleshooting nightmare ) but usually if a channel is open, then that and those behind it in the scan order do not return any data. It returns a number like 10.357E-6 and I do not pick up any noise or fluctuations. As far as I understand, the multiplexer stops scanning at this point (open channel) because it has nothing to ground to and subsequently "hangs" - not (or randomly) scanning the following channels. I have gone through the bridge configuration and as of yet, have not figured out how to fix this using any hard-wiring techniques. I emailed NI, and was sent a library file to "ground the channels" but it actually resets the Analog input Task I have defined each loop.
I am new to NI-DAQmx so I do not know if this will alter any configurations I already have in MAX for NI-DAQmx. Will it override? I am concerned it will slow my loop time, and also I cannot see the code for this sub.vi so am a little skiddish about using it if i do not know if it can be tailored to my app.
What do you think? Am I on the right path?

How do I deal with a cascaded system, First Stage SCXI-1520's and Second Stage SCXI-1143's?

I am aware of the following link:
http://digital.ni.com/public.nsf/allkb/653505DF63AD04E686256DD7005D42F6
I'm kind of stuck here. The system is already in place. 1520's in first stage and 1143's in second. I am supposed to configure the 1520's and scan the 1143's.
What problems do you see with this?
How do I go about doing an end to end calibration?
Should I just rip out the 1143's and hope nobody notices?

Hello Frank,
Let's start from the beginning. I understand that you have some SCXI-1520s and 1143s that you are using in your measurement system. What type of sensors are you acquiring data from? It seems that you intend to use the 1143s to filter the data between the 1520s and the software. Is this correct? Another question that I have is what do you mean by "end to end calibration?" The more specific that you are about the application you are developing, the easier it will be for others to help you with any questions that you might have.
Looking at the knowledge base article that you linked in your original post, it seems that the point was to filter the data from the SCXI-1520 in software, using the LabVIEW Filter Express VI. Would this be a viable option for you? If so, then you could just rip out the 1143s.
Regards,
Wallace F.
National Instruments
Applications Engineer

Scxi 1520 excitation current specs?

In p. A-3 of the scxi 1520 manual, for the excitation specs there, it says:
"Max. operating current in all ranges - 29 mA"
Is this for the whole SCXI 1520 or just for each channel? Because I need for each channel 5V with 1.6 mA supply. That means for all channels, about 12.8 mA.
Can the SCXI 1520 support this?
Please help me on this. Thanks!

Dear cb34,
Thank you for choosing National Instruments Support!
The SCXI 1520 Module has the operating current range of 29 mA per CHANNEL and not for the whole board. So, You are in good shape to use the system that you have because 1.6 mA per channel is well below the limits that you would need.
Thanks and Regards
Shekhar S
National Instruments

What is the combined effect of the SCXI-1520 Gain and NI-Max Gain?

LabVIEW 6.1
SCXI-1000
SCXI-1520
SCXI-1314
PCI-6031E
Windows 2000
Greetings-
I'm trying to determine how the gain that is settable on a given channel of an SCXI-1520 module is combined with the gain that NI Max assigns to a Virtual Channel.
For example, if you set a gain of 100 on ch0 of an SCXI-1520, and you then create a Virtual Channel to read the mV output of the Ch0 sensor, (in this case a full bridge load cell), should the AI limits (range) that you specify in the Virtual Channel creation reflect the gain of 100 that the 1520 module is already applying to the signal? And after the 1520 module applies it's gain, does NI Max attempt to apply another gain if there is still capacity to amplify the signal within the AI range of the daq device?
Also, when measuring a full bridge sensor as an analog input voltage signal, and after performing a Null on the sensor, there is usually some residual offset. Does one then programmatically (in LabVIEW) tare, or zero this residual offset by subtracting its value from all subsequent measurements?
Thanks for your help.

Hello Steve,
How are you applying gain if not through a virtual channel?
When you set the input signal ranges in MAX for your virtual channel, SCXI and DAQ board gains are applied. For example, if you create a voltage channel to read the mV output of a sensor, and set the range to +/- 10mV, the SCXI Module would apply a gain of 1000 to the signal and send the resulting +/-10V to the MIO DAQ device. The DAQ device will then attenuate this signal to +/-5V (the range of the ADC) by applying a gain of 0.5. Now, if you set the input signal range to +/-1mV, the SCXI Module will apply its maximum gain of 1000 and send the resulting +/-1V to the MIO device. The DAQ device will then amplify this signal to +/-5V by applying a gain of 5.
If you are still seeing a residual offset after null calibration, you should use the Auto Zero property. This property measures ground before an acquisition and then subtracts that value from every subsequent measurement. You can set this in a strain task, or with a Channel Property Node in LabVIEW.
Let me know if you have any further questions.
Sean C.

Intermittent channel in SCXI-1520

I have been using an SCXI-1520 and recently channel 0 has become intermittent in operation. It drifts off to either the plus or negative rail and stays there. This problem is noted with and without connections made to it, including the use of the Test Panel function in MAX. Resetting the module sometimes helps, but not for long. It appears to me there is a malfunction in the module, but I wanted to get an additional opinion before I send it in. (An additional uncertainty is that the SCXI-1520 seems a little touchy, or unstable in it's setup. It's just an impression I have.)
Also, is it possible to programmatically reset the module in LabVIEW?

Part of the reason I don't want to send it in for evaluation is we are using it in production. (We make strain gauge based load cells.) We are expanding operations and so I've ordered an additional module and chassis. However, I will not be able to get to it till January.
I reassigned channels to keep production going until I can sort things out.
Thanks for your response. It gives confidence that I'm not missing something in the programming.

SCXI 1520 quarter bridge setup will not output excitation voltage, but full bridge will

My SCXI system will not output an excitation voltage to the quarter bridge(verified with voltmeter). It works for a full bridge setup. When connected to a 'quarter bridge I' configuration, I can use MAX to null and shunt calibrate. The quarter bridge circuit appears to be balanced after the calibration, but the calibration results post a software gain factor close to zero, as well as a close to zero excitation voltage (eventhough I have the voltage configured for 5 volts). I have the SCXI 1520 module, the virtual channels, and the wiring properly configured (several years experience with this device). I'm using an old E series DAQ card AI-16XE-50, with the 50 pin cable that plugs in the back of the SCXI chassis. I noticed I had two bent pins with the cable connector module that plugs into the SCXI backplane. I was able to straighten them, so the cable connects properly, but I suspect the bent pin incident caused electrical circuit damage. Any suggestions on trouble shooting? None of the three 1520 modules I have will output an excitation voltage for a quarter bridge.

Sorry that I don't have an answer for you tyea, but I'm interested in your thread because I have a similar issue with a 1520. My excitation votltage, as measured with a DVM, is always 1V. I've tried 0V, 1V, 5V --- it's always 1V, on Full or Quarter bridge. I'm using a similar DAQ to yours - a PCI 16XE-10 (and a PCI-6030E on antother system).
I don't have a lot of experience with these modules. This could be a wiring or programmatic thing I'm doing wrong.
Richard

Using SCXI-1520 in Parallel Mode.

Hi all,
I am using SCXI-1000 chassis and PCI-1024E DAQ card.
I want to use my SCXI-1520 in Parallel mode.
Is there any other way to configure my 1520 in parallel mode other than directly connecting to DAQ board using SCXI-1180 feed through panel and SCXi-1302?
Some of my friends are telling that there are some Patch files, through which we can use the scxi-1520 in parallel mode. Is it true? If it is true please give me how use the Patch files( or alternative solutions).
Thanq
Regards
Preetam

Preetam,
As explained in the SCXI-1520 user manual, Traditional NI-DAQ does not support true parallel mode operation of the SCXI-1520. However, NI-DAQmx does. I would recommend installing NI-DAQ 7.2, which includes the latest version of both Traditional NI-DAQ and NI-DAQmx. Then you can use the NI-DAQmx driver to control your SCXI-1520 in parallel mode. To configure the SCXI-1520 in parallel mode with NI-DAQmx, simply select the Parallel Mode check box when setting up your chassis and modules in MAX. I hope this information helps.
SCXI-1520 User Manual
NI-DAQ 7.2 Download

Reading a thermocouple with the SCXI 1520

Does the SCXI 1520 have something to account for the interface connection heat, and is it needed? I've heard this is what the thermocouple modules do, and it is necessary.

The SCXI-1520 uses the SCXI-1314 Module which does not have cold-junction(CJ)compensation capability - meaning it can not compensate for either the temperature of the connection to the DAQ system, nor, the additional voltage effect due to the dis-similar metal contacts of the DAQ system. This correction is absolutly necessary for accurate temperature measurement. I suggest you use a "third-party" cold junction module from a vendor such as OMEGA Engineering (www.omega.com). The CJ sensors are battery powered and reference the signal to 32 Deg F while at the same time providing standard copper leads for the DAQ system.

How do I wire my SCXI-1520 quarter bridge completion in parallel?

I have a quarter bridge set-up using the qtr completion in the system. In parallel with my strain gauge I'd like to have another resistor. I'm using the strain gauge as a dummy, and am interested in the current traveling in a parallel path through a film resistor as I change the film thickness. However, I'm not convinced that what I've wired has the strain gauge and other resistor in parallel. I have the strain gauge wired to: P+, QTR, S+ and the other gauge wired to QTR, S+.
Thanks!

Greetings,
You will want to wire the other gauge between P+ and QTR or between P+ and S+. To make this decision, you will need to determine how the lead resistances will affect your measurement. Page 2-4 of the SCXI-1520 User Manual (link available below) contains the wiring diagram for Quarter-Bridge Configuration I.
SCXI-1520 User Manual
Good luck with your application.
Spencer S.

SCXI 1520 Simultaneously sampling

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