SCXI-1520 AND 700 OHM LOAD CELL?

Will the SCXI-1520 work with a 700 ohm full bridge load cell? I'm a load cell mfg proposing a 700 ohm load cell solution to a customer. He says he doesn't think the 700 ohm cell will work with his 1520. The load cell will can take a maximum 20 VDC excitation and outputs 2 mV/V.

Hi,
Can you verify that the voltage coming out of the thermocouple is correct? You can do this by measuring across the thermocouple using a hand held multimeter. You may also want to input a known voltage into the module (a simple battery would suffice) and see if this produces the correct voltage in Measurement and Automation Explorer.
Abhinav T.
Abhinav T.
Applications Engineering
National Instruments India
LabVIEW Introduction Course - Six Hours
Getting Started with NI-DAQmx
Measurement Fundamentals

Similar Messages

Connecting Half Bridge I Config with SCXI 1520 and 1314

Hi! I'm using Half Bridge -I Configuration with SCXI 1520 and 1314, but the diagrams in the SCXI-1520 manual are not very comprehensible to me. Three questions:
1) Is it "necessary" to connect SCx terminals?
2) If yes, why is there no lead resistance "RL" shown?
3) Are one end each of two strain gauges to be shorted externally, or wired all the way upto SCXI-1340?
If u can also post a drawing with actual leads and gauges shown, it will be great.
These questions may seem trivial, but I'm just starting with strain measurement so...
Thanks
Rajat

Rajat,
If you are wanting to perform a shunt calibration on your strain gauges then the SCA terminals will need to be connected. The reason that no lead resistance (RL) is shown is that the resistance of those leads will not be affecting the reading you are taking. Lead resistances only need to be considered when they are part of the wheatstone bridge.
The strain gauges are R3 and R4 in figure 2-3 on page 2-7 of the SCXI-1520 User Manual (linked below). One side of the strain gauges should be connected to each other, then the other side of the strain gauges need to be connected to P+ and P-. Only connections to the right of the 1314 terminal block (in figure 2-3) are connections you will need to make. I hope this helps.
SCXI-1520 User Manual
http://digital.
ni.com/manuals.nsf/webAdvsearch/ED087ED0FDB34CF5862569DC0068992B?OpenDocument
Regards,
Todd D.
Applications Engineer
National Instruments

Is it possible to condition a load cell signal with a 1520 SCXI and then use it as the primary analog feedback for a 735X motion control board?

My system
PXI 1052 chassis
PXI 8196 RT controller
Flexmotion 7356 motion controller
Flexmotion 7354 motion controller
6259 M series DAQ
1520 SCXI
1520 SCXI
1314 SCXI frount mounting terminal block
DSM strain gage load cells
Exlar SR Brushless PM motors
Kollmorgen servo star CD series 5 drives
My objective:
I want to measure the force on the load cells with the 1520 SCXI (i.e. excite the load cell then amplify and condition its output) then I want to use this analog (force) signal as the primary feedback for my motion control system (7356 and 7354 motion controller connected to my drives and motors).
The problem:
The motion controller boards (7356 and 7354) can be configured for force feedback control via analog feedback from a load cell. However the boards implicitly expect the load cell signal to be amplified and conditioned with and external signal conditioner rather then using an NI SCXI module. Currently I’m am reading the SCXI signals via the 6259 M seriers DAQ and consequentially have no way to route the signal into the 735X boards for force feedback control. I can use softmotion to control the motors but then I loose the fast PID update rates possible with the 735X boards.
The question:
Is it possible to condition a load cell signal with a 1520 SCXI and then use it as the primary analog feedback for a 735X motion control board?
Thanks
Patrick Aubin
Ph.D Candidate
University of Washington &
VA MedicalCenter of Excellence for
Limb Loss Prevention and Prosthetic Engineering

Hi GG,
Thank you for your feedback.
>create your own external circuitry to amplify the signal.>
True a few op-amps could amplify and filter the signal externally but the performance of such an amateur built system will never match the accuracy and functionality of the 1520 SCXI. That’s why we spent the $2500 for the professional version.
>One thing that you could do is to use a UMI with your motion controller and then wire your signal from your SCXI to the UMI.>
As I understand it the UMI is basically a break out connectivity interface for third party drives. After conditioning and amplifying the analog force signal with the SCXI module the analog signal isn’t available to wire into a UMI. To my knowledge the conditioned signal of the SCXI resides only in the PXI backplane (i.e. there is no physical access to the conditioned analog signal). Can you explain how the UMI could be help here.
Again thanks for your input GG.
Patrick

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.

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

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.

Absolute Accuracy of a Load Cell measurement.

I see how to calculate absolute accuracy for the SCXI-1520 and SCXI-1600 combination. To call out the accuracy of a load cell measurement, do I have to add the load cell specification numbers for non-linearity, non-repeatability, and hysteresis to the absolute accuracy calculations?

Hi KPR,
If you want the entire system accuracy, including the load
cell, we definitely need to include the load cell accuracy in our calculations.
I am not sure which document you were looking at to get the accuracy thus far,
but KB 2X4HGEBG
gives a great explanation about accuracies. In order to include the load cell accuracy, first
get the absolute accuracy of the load cell, and then put this in the equation ‘System
Accuracy = ( (Absolute Accuracy 1)^2 + (Absolute Accuracy 2)^2 + (Absolute
Accuracy 3)^2 + ...) )^(1/2)’ as ‘Absolute
Accuracy 4’.
David L.
Systems Engineering
National Instruments

Data acquisition from switching 500lbs load cell to 100lbs load cell

I am using 500lbs load cell, and acquiring data by inputing 2volts from 2345 signal conditioning board, and sensor output is connected to SCC-AI03 pin 3 and 4 , and configure this load cell to a channel using NI MAX, data neighborhood, traditional NI-DAQ virtual channel, the physical quantity is voltage set at range -10 to 10, and sensor also set at voltage with no scaling, but, I couldn't get any signal when 100lbs load cell is use, the difference of this 100 lbs load cell is the rated output is at 2.958mV/V, while the 500lbs rated at 1.8295mV/V , how should I do this?
Thanks.

Hi,
At this point, it is difficult to determine exactly what is happening to your acquisition. Could you please provide some additional information by answering the following questions:
What voltage are you reading with the 500 lb load cell?
Would it be possible to connect your load cells to a DMM and see what voltage reading you receive? If so, what do you see?
What is specifically happening when you connect the 100 lb load cell?
I also noticed that you are using the Traditional NI-DAQ (Legacy) driver. I recommend upgrading to the NI-DAQmx driver. Here are a couple of links with more information about DAQmx:
Advantages of NI-DAQmx:
Transition from Traditional NI-DAQ to NI-DAQmx:
Learn 10 Functions in NI-DAQmx and Solve 80% of Data Acquisition Applications:
Regards,
Hal L.

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.

Applying Excitation Load to the SCXI-1520

We use the SCXI-1520 signal conditioner to test and calibrate bridge sensors that we manufacture and it works great. While the system is not used (i.e. when the operator connectes a sensor to the system) the SCXI-1520 is automatically isolated by using relays in a switching system. The primary intent for this is to avoid possibly damaging the signal conditioner. (Operators do regretful things.) This means that the excitation power is floating with no load while the signal conditioner is disconnected,. I was wondering if it would be appropriate to have the system automatically apply a load resistor to the excitation source to keep it "warmed up" so to speak. Most sensors are a 350 ohm bridge and may be as high as 5000 ohms. I was thinking of applying a common 330 ohm 1/2 watt resistor as a load. (We are currently only using two channels at a time.) Although I'm sure it would not make things worse, I just wonder if it's worth the bother. Please advise...

In my opinion, I don't think it is worth the trouble. The temperature
of the SCXI-1520 probably won't change much from connecting a load to
the exictation since there is plenty of heat generated from the
SCXI-1520 to keep it at a stable temperature with or without the
excitation source being connected. A bigger concern would be that
strain gages can have self-heating errors when current is applied,
which is usually accounted for by using a Quarter Bridge Type II
configuration with a dummy strain gage next to the active gage. These
self-heating errors occur when the strain gage is connected to the
excitation source - so if you wanted to keep anything "warmed up" it
should actually be the strain gage that you are disconnecting; not the
SCXI-1520.
-Logan K

SCXI 1520 for load measurement cable lengths of 500 meters

HI ,
I ned to measure lod from a 1000 ohm full bridge circuit. The distance between the sensor & my SCXI 1520 is 500 meters. Please let me know how can I compensate for the lead resistances both in Excitation & while reading back the actual sensor value.

grte,
For extremely long cable runs resulting in much higher than normal lead resistance to bridge resistance ratios, you must use remote sense, which is a six wire connection (four wires for excitation and two for signal). Refer to your SCXI-1520 manual for more information: http://www.ni.com/pdf/manuals/372583d.pdf, specifically page 2-9 and Chapter 4, Theory of Operation.

I loaded ios7.1 to my Ipad2 and my wife's cell phone came up. I can't change it and now I get her text messages on my iphone4S and she is getting apps I download on her iphone 4S. How do we fix it?

I recently downloaded ios7.1 to my ipad and my wife's cell phone # appeared on my ipad. It would not let us change it. Now I am getting her text messages and she is getting the apps I load on her iphone4S. We both have iphone 4S, but she has version 7.1 and I still have 6.0 because I didn't like the changes in v.7.0. We share an Apple ID and password which was not a problem before. My daughter says this is our problem, as she had her husband had this issue. She doesn't know how he fixed it. Has anyone else had this issue and can you tell us how to separate our Apple ID/passwords if this is, indeed, the problem?

If you share an Apple ID, both of your phone numbers should be linked to that ID. You should be able to use your phone number as well. My wife, my daughter and I all share an Apple ID for purchases, and we each text from our iOS devices using our own iPhone numbers.
When iOS 6 came out, you were able to link the phone number with your Apple ID to use for Messages and FaceTime. You will need to sign out of messages on all devices and then start the process all over again.
Take a look at this.
iOS and OS X: Link your phone number and Apple ID for use - Support

How do I physically connect the SCXI 1180 when using a 1520 and 1346 adapter?

Here's my current configuration:
SCXI 1000 chassis
x2 SCXI 1520 Bridge Modules (Slot 1, and Slot 2)
1180 Feedthrough panel.
I recently purchased a 1346 adapter so I can use the feedthrough to access AI channels on the DAQ card.
My question is, how do I physically connect the ribbon cable of the 1180? Does it plug into the BACK of the last module in the chassis (ie. bridge module2 in slot 2) or does it plug into the other 49pin connector on the 1346 adapter?
If you read the installation manual for the 1180 http://www.ni.com/pdf/manuals/371062a.pdf (Page 2-3)
And the installation manual for the 1346 http://www.ni.com/pdf/manuals/320722b.pdf (page 2)
it seems the instruction contradict eachother. The 1180 manual says connect it to the back of the module
the note under Fig.2 on page 2 of the 1346 says you cannot have anything plugged into the module next to the one that has the 1346 plugged into it; in my case that's module 2...
SCXI- 1000 Chassis w/ 1346 adapter
PCI 6281 DAQ card
SCXI- 1520 Bridge Board w/ 1314 Terminal Block (x2)
SCXI- 1180 Feedthrough Panel w/ 1302 Block
Signal Express 2014.
Win7 Enterprise

I have the 1346 plugged into the first module in slot 1.
But let me try and clairfy what you're saying...
"Then the cable from the 1346 kind of loops back into the chassis and through the 1180". So this is my answer? But I'm actually taking the cable from the 1180 and plugging it into the other 49-pin connector on the 1346. Sorry, symantics...
"...it must be on the first card when using a 1520". By "it" are you referring to the 1346 (which is how it's currently configured) or the 1180 cable?
and lastly; why does the 1180 need to go into slot 2? I can currently fill both slots (1&2) with the 1520's and with the 1346 plugged into module1/slot1, I can pass the ribbon cable around back of module2 and into the 1346.
Is there some other reason beside potential space limitations that you'd use the feedthrough in slot2?
Thanks for your info and patience!
Message Edited by OKors on 03-31-2010 12:50 PM
SCXI- 1000 Chassis w/ 1346 adapter
PCI 6281 DAQ card
SCXI- 1520 Bridge Board w/ 1314 Terminal Block (x2)
SCXI- 1180 Feedthrough Panel w/ 1302 Block
Signal Express 2014.
Win7 Enterprise

PASCO Load Cell and NI DAQ Interfacing

Hi everyone,
I have a PASCO Load Cell PS-2200 and I am trying to interface it with an NI-9201 AI (in conjunction with a NI-cDAQ 9172). Instead of attaching wires to the cell's pinout, I stripped a PS2 connector and rearranged the wires to match the pinout of the sensor (which are the strain gauge input, strain gauge output, the excitation voltage of 4.2 and the ground). I connected the strain gauge signal to a channel of the NI 9201 and I am using an external power source to provide voltage to the cell. My VI is trivial and consists of an input DAQ and Lowpass filter.
The problem is that the input signal is obviously not right, it looks periodic for one. The filtered signal appears stable at first but slowly increases over time. And the signal does not respond to applied stresses.
I would really appreciate any help on this. I am a ME sophomore and have little experience with LabVIEW.
Thank you.

Thank you Jignesh and Dave,
Jignesh, I do not have a scope I can measure the ouput with. And no, the cell does not respond to variable loads. Also, please find attached the snapshots you had asked for. The front panel snapshot shows the cell's reponse when under no load
Dave, the module I am using has a 16 bit resolution and within a +/- 10 full inut range, don't we have enough resolution to acquire the smallest change?
Also, from the pinout of the load sensor, the pin for the excitation terminal and the positive strain gaugw output are adjacent. They are not the same terminal. We took every possible precaution to make sure that the terminals of the PS2 connector did not touch during soldering.
Thank you for your help again.
Attachments:
block diagram.jpg ‏159 KB
front panel.jpg ‏390 KB

Read from both load cell and accelerometer

Hi,
I'm trying to collect data from both load cell (which doesn't need excitation) and accelerometer (which needs 4 mA excitation). As you can see below, I wrote a simple program to collect data from both devices. However, my program provides 4 mA of excitation to all channels, one of which shouldn't receive any current. How can I selectively provide the excitation to specific channels?
Any suggestions?
Solved!
Go to Solution.
Attachments:
readfromtwodevices.vi ‏47 KB

Good morning jeongho20000,
Both aeastat and falkpl have provided excellent solutions for this. I also wanted to mention a good KnowledgeBase article found at ni.com by searching for "daqmx channel same task" in the internal search bar. This helps to outline both solutions. After searching, you can then select multiple entries, but the best that I found was the 3rd choice, titled: Using Different Types of DAQmx Global Channels in the Same Task.
You can download from the article the attached example VI titled Multiple Channels Created.vi, and modify the block diagram to fit your needs. Wiring the Task Out to the Task In of two DAQmxCreateChannel VIs is the programmatic equivalent of adding multiple Global Virtual Channels created in Measurement and Automation Explorer (MAX) to a common Task in MAX. Either method works, it is only a user preference. Feel free to reply if you need further clarification/explanation.
Best,
Message Edited by cyclone2k9 on 04-06-2010 11:08 AM
Message Edited by cyclone2k9 on 04-06-2010 11:09 AM
Adam
Academic Product Manager
National Intruments

SCXI-1520 AND 700 OHM LOAD CELL?

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