My strain gauges (full Wheatstone bridge) give me a constant negative voltage

Hi, I'm currently trying to calibrate strain gauges to work with a one-axis tribometer...I'm using XP, LabVIEW 8.5.1, have the latest version of NIDAQmx and SignalExpress 2.5.1. Right now the strain gauges are hooked up to a SC-2043-SG signal conditioning board, which in turn is hooked up to a PCI 6251.
The problem right now is that while the computer recognizes the device and is getting output from it, I'm getting a constant negative voltage (-10.2 V or something like that). My configuration for the SC-2043-SG is as follows:
Custom voltage w/ excitation
-External excitation (can't switch to internal excitation source- apparently it doesn't exist even though I've set the switch on the board to INT)
-Full Wheatstone bridge
-Differential terminal configuration
-Not using ex for scaling
-Ex value is 1m
-Channel is ai0
I've currently got this set up in SignalExpress 2.5.1 and have been generating VIs from the task that I've made there.
Another odd thing is that the gauges don't seem to respond to when I put pressure on them.
So what I mainly need to know is
1) Do I have bad gauges?
2) Do I have an incorrect configuration?
I guess on a side note I've noticed that when I set the terminal configuration to RSE, the values oscillate around 0.08V. Should I use that instead and calibrate it from there, so that at least the configuration reads 0 by default?

Hi balaclava,
Since the SC-2043-SG is an older signal conditioning board
is does not support programmatic control of its excitation or settings. This is
why there is no internal excitation available to select in your DAQmx task. These
setting must be configured on the SC-2043-SG using the on-board jumpers.
You will want to set the jumpers for internal power and
excitation and set for full bridge gauges. More information on all of the
jumper settings can be found in the SC-2043-SG User Manual. Also page 30 of the
manual shows how to connect a full bridge sensor.
Once you have the SC-2043-SG configured correctly it then
does the bridge signal conditioning and provides the DAQ card with a voltage signal
referenced to AI Sense. You can measure this signal using a normal analog input
voltage task with the terminal configuration set to NRSE or RSE. It does not
provide the DAQ card with a differential signal.
Please let me know if you have any questions and take care.
Thanks,
Nathan
National Instruments
Digital Hardware Engineer

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I am experiencing a problem perfomring my shunt calibration using a 350ohm(GF 2) strain gauge connected with NI9949 and NI9237 in a NI cDAQ-9178 Hardware.
When i click on strain callibration under configuration-Device: R3 being my shunt of 100k ohm, i can measure the errors and calibration but when i hit the calibration tab, it gives me an error 200077 occured at Strain Gauge Calibration (see aatached jpeg file for the error type).
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error 200077.jpg ‏73 KB

Hi
This error code may be occurring due to the specified signal input range in max (-1m to 1m), being set to a value outside of the expected readings from your strain gauge.
Also the Gage Factor, Gage Resistance, Initial Voltage, Vex Source, Vex Value (V), Lead Resistance and Strain Configuration need to be configured based on your sensor specification.
This link gives more details on connecting strain gages to a DAQ device:
http://www.ni.com/gettingstarted/setuphardware/dataacquisition/straingages.htm#StrainGageCalibration
Hope this helps.
Andrew.N
Applications Engineer
National Instruments

Is there a strain gauge bridge on the 6025E?

Is there a strain gauge bridge on the 6025E?

No, however, there are several ways in which you can perform a strain gage measurements with NI products, you can buy SCCs, which are small signal conditioning modules. There is a set of strain gauge modules that can serve that purpose. Depending on the number of channels you need to measure strain in you might want to go for SCXI, which will give you a much higher channel count and configuration options. There is an E-Series board with signal conditioning that will take care of that too. You can find plenty of additional information in this tutorial: Strain Measurement with a Strain Gauge. And of course, you can always just build a small Wheatstone Bridge
yourself.

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Hi Coffeyfj,
Did you ever had this set up working? The first thing that I would do as I mentioned in the previous comment would be to use one of the LabVIEW examples. I recommended to you using the (strain - Continuous Input.vi). If you can read any voltage changes with the example vi, then we will know the problem we are having is in your code. If you cannot read any voltage changes using the example I mentioned, we can start trouble shooting the hardware connections. Are you connecting the excitation voltage? If yes, Are you making the right connections. Please refer to page 19 of the following document (half and full bridge modes)
NI 9219 Operating Instructions and Specifications - February 2009
http://digital.ni.com/manuals.nsf/websearch/4197ED4BD126E0B486257546005851CA
Regards,
William Fernandez
Applications Engineer
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Setting up DAQ system for testing (using pressure transducer, linear position sensor and strain gauges)

Hello,
I like to get your suggestion in setting up the DAQ system. I am very beginner in this issue.
These SCXI listed below are what we have in the laboratory. I will use DAQ card 6062E.
SCXI 1000
SCXI 1520
SCXI 1140
SCXI 1142
SCXI 1305 , 1302 , 1300
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I will use linear position sensor in my experiment. But I'm not sure which SCXI shoud I connect to this sensor.
This sensor gives 4-20mA output. it requires +13 to +28Vdc excitation.
I will use pressure transducer (strain gauge type) which gives 100mV output and requires 10Vdc supply.
I will use strain gauges 350 ohm.
Regarding to the number of channels used in my experiment, I will use 1 channel of pressure transducer, 1 channel of linear position sensor and 3 or 4 strain gauges.
Could you please suggest me which SCXI should be used with pressure transducer, linear position sensor and strain gauges.
Now I'm thinking to use SCXI 1520 with strain gauges and pressure transducer. Is that ok?
But I'm not so sure on the linear position sensor which gives current output.
And regarding to sampling rate, I like to get minimum of 60-70 KS/s for pressure transducer. And around 1KS/s for linear position sensor and 1KS/s for each channel of strain gauge are enough. Can I archieve these sampling rate from the available SCXI modules mentioned before? I attached the datasheet of pressure transducer and linear position sensor for you. Please see attached files.
I'm reallly look forward for your suggestion.
Thank you in advance,
Ganchai.
Attachments:
XPM6_mini. pr. transducer.pdf ‏115 KB
linear-position-sensor.pdf ‏1683 KB

Hi Ganchai,
I would recommend the 1520 with a 1314 terminal block for connecting your pressure transducer and strain gauge. It is designed for excitation, bridge completion and has many other features to fit these applications. For your linear position sensor, try using the 1100 module with an additional precision shunt resistor. For example, our 1308 terminal block has built in 249Ohm shunt resistors for taking current inputs for your 1100. These connections should give you the readings you would like.
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PBear
NI RF

Constant current excitation for strain gauges

Ideally I would like to log 46 strain gauges using a scxi-1000. At the moment we have two 1102B modules, one 1100 module, and a 1122 module.
The 1122 module supports quarter bridge strain gauges but is very limited in scan rates when logging 16 strain gauges all at once.
Stuart from ni gave me an idea of constant current excitation for the strain gauges. The 1581 would be very suitable seem it delivers 32 channels of costant current and would suit the 32 channels of the 1102B we already have. Only problem is whether the 100 micro amps will be sufficient current to excite the strain gauges with reasonable accuracy.
The remaining strain gauges that wouldn't fit into the 1581 would run on a 6 channel strain gauge amplifier and then run through the other 1102 module we have and use a datataker for any left overs.
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Message Edited by Peter W Brown on 01-11-2006 09:55 PM

The full range of a strain gage in most applications is going to be
less than 1 ohm, which means that a typically strain application needs
to be able to measure the output on the order of fractions of an ohm to
be even remotely close to accurate.
The reason strain gages are typically put in a bridge configuration is
so that their output can be centered around 0V which enables the signal
conditioning module to apply very large amounts of gain to the
measurement (up to 2000 on the SCXI-1520). Without this gain, the
sensitivity of the strain gage is so small that you will be very
hard-pressed to get remotely accurate readings.
For this reason alone, I don't think there is a current-excitation
solution available that will enable you to get sufficient resolution
from the strain gage reading.
The SCXI-1521 is probably your best solution for measuring a large
number of quarter bridge strain gages. If you also need to measure
other bridge configurations (i.e. half or full) then the SCXI-1520 is
your other option.
-Logan K

I can not measure strain gauge

I'm trying to work for strain gauge measurement with scc-sg04, sc2345 signal conditioner and ni-6223 DAQ card. Internal +2.5V supply I have used as excitation voltage. I want to get the data via Measurement & Automation explorer and I have created a task for strain measurement. I have selected the SCC1Mod1/ai0 channel for this purpose and adjusted task timing to Continuous mode. When I have pushed the Test button, Analog Input Test Panel is shown and observed strain value is -0.0021. This value do not changes while I pushing my finger to the load cell.
With +2.5V excitation voltage can I see the any changes for output (note that manufacturer recommends 10V excitation voltage).
Message Edited by immortal on 11-12-2007 02:11 AM
Message Edited by immortal on 11-12-2007 02:12 AM
Attachments:
fig.JPG ‏89 KB

Dear Hani,
Thank you for your reply firstly.
I connect external power as you give but there is some problems I have encountered. I connect cables of DC voltage supply to input of the load cell (DC supply is not running) but acquired data (there should be only noise ideally in this state) is fluctuating (See q3_1.jpg). After, I run DC supply and there is a sinusoidal wave in this phase (See q3_2.jpg). If I push my finger to load cell, DC value of this sinusoid changes only. So, I have a big problem with my external excitation supply .
The other problem I've encountered is Vex value of external excitation. I change Vex source to external and Vex=10V and my task is not working and gives an error as "requested value is not supported value for this property" (See q3_3.jpg). I couldn't understand why this error occurs.
Waiting your reply...
Attachments:
q3_3.JPG ‏76 KB
q3_1.JPG ‏31 KB
q3_2.JPG ‏30 KB

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i hope that i will find someone who can help me at this point.
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Connecting Strain Gages to a DAQ Device - National Instruments.pdf ‏707 KB
AD624.pdf ‏599 KB

In the future, you should post this to multifunction DAQ. The 6251 is not an academic product and you'll get a different set of eyes as a result.
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Carried out first test for my data acquisition project for uni today. The general basic operation is I am carrying out a test on a super duplex steel tube. A new load is applied every 30 seconds and the program should record when the change in strain occurs which is then plotted on a table in an excell file. Some slight issues that I was hoping someone could maybe explain to me...
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Hi there,
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I've commented the changes I've made, but in summary:
1) Removed sequence structure and enforced dataflow with error line
2) Modified the DAQ section to just a random number generator for the sake of testing.
3) Set data feed into excel section to indexing output rather than last value
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5) Changed text file logging to "open or create" to avoid errors which might occur if the file already exists during multiple runs - but this would depend on you wanting to write to the same file each time
Note: In your for loop, if your attempting to relate the loads in the first column to your last 10 strain measurements, then this would be an incorrect way to go about interacting with the listbox. Please see this example which demonstrates how to address items in a listbox: https://decibel.ni.com/content/docs/DOC-5808
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Strain Gauge Edit.vi ‏124 KB

Can anybody recommend me on the strain gauges which are attached along a steel bar, say, 3 mm in diameter, and can respond at a sampling rate of 100 kHz?

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Me and my college class have been having trouble with filtered full-wave bridge rectifiers in Multisim 11.0. I have not seen a post about this topic, if i am mistaken then please direct me to said post.
When i try to simulate a full-wave bridge rectifier with a filtering capacitor, Multi sim immediately throws me a convergence error. I have tried letting multi sim resolve the error, to no avail. I have tried using many different componoents and even pre-made parts from the FWB category. It has worked for me a few times but i have no idea what the differences were.
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Attachments:
Bridge_schematic.png ‏16 KB

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Bridge.ms11 ‏70 KB

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My strain gauges (full Wheatstone bridge) give me a constant negative voltage

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