Tags: block, conditioner, connector, experiment, gage, gages, labview, measurement, programming, scxi-1000, scxi-1317, signal, strain, working
strain gage experiment
I am working on strain measurement experiment using strain gages. I am using
SCXI-1000 signal conditioner, SCXI-1317 connector block. I have a plate sup
ported on 4 sleeves. 2 strain gages are attached to each sleeve. When I conn
ect 4 strain gages one from
each sleeve to the connector block and apply a force of 200lbs on the
plate and do a test run in labview, the strain values I am getting are way o
ff. Here the details of inputs
Lead Resistance: 0Gage Resistance: 120Gage factor: 2Strain range max = 1M&nb
sp; min = -1MV(initial) : 0V(exe) : 5VV(exe) Source:
ExternalSrian gage config: Quarter Bridge 1
The Strain values I expected to be around 50 microstrain.The vlaues I am get
ting are 180, 520, 370 microsrtain, fluctuating +/- 50 microstrain to the ab
ove vlaues. The fourth strain gage is reading -75microstrain and is stable.
I tried changing V(exe) but
nothing really chaged in readings except the fourth strain gage but it alway
s was a negative valve.
I could not figure what am I doing wrong. If anyone in the group has any exp
erience with this please help me out.
Leave a comment...
- 8 Comments
- Hi Mekdeng,
I will attempt to answer your question, but i also advise that your queries
on SCXI in the Signal conditioning Discussion forum board.
Here it looks like you are using External Excitation instead of internal exc
itation that your SCXI 1521 module is capable of sourcing.
so, check how you have wired on your sensor to the SCXI 1317 Terminal block.
plus your max min range settings 1M ( is it 1000000 micro strain?) seems to
be too high, so check it.
Dev#1; Wed, 07 May 2008 00:08:00 GMT
- Thank you Dev,
Yes, I also have SCXI-1521 module along with SCXI-1317 and SCXI-1000. When I
select internal source I get a error message that source is not connected s
o I selected external source and did a trial run.
My strain gages have 3 lead wires and I connected then to the connector bloc
k as per the manual. 2 wires coming out of one leg of the strain gage were c
onnected to the AI and QTR, and one wire coming out of the other leg to the
Ex+ just as per the SCXI-13
I'll decrease the max and min range of the input and try the experiment.
Thanks once again.
Hari#2; Wed, 07 May 2008 00:09:00 GMT
Are you using a LabVIEW example for reading SCXI-1521 strain gages?
What are the details of the error that you get when you try to use the
internal excitation? This module is designed to use internal
excitation, so your strain measurements won't work unless you select
the internal option.
Are you or the exmple that you are using perform an Offset Null and
Shunt Calibration? These are important for making sure that your strain
measurements are accurate. When you perform these calibrations you must
ensure that your strain gage is in it's resting state.
I hope this helps.
-Logan#3; Wed, 07 May 2008 00:10:00 GMT
- Hari,Are you using a LabVIEW example for reading SCXI-1521 strain gages? Wha
t are the details of the error that you get when you try to use the internal
excitation? This module is designed to use internal excitation, so your str
ain measurements won't work
unless you select the internal option.Are you or the exmple that you are usi
ng perform an Offset Null and Shunt Calibration? These are important for mak
ing sure that your strain measurements are accurate. When you perform these
calibrations you must ensu
re that your strain gage is in it's resting state.I hope this helps.-Logan
Thank you Logan,
Iam using LabVIEW for reading strain. I could not read anything of my
strain gages when I select internal excitation. But when I select external I
could read some values though they are not what I am expectiing.
I tried to calibrate my strain gages using Measurement and Automation Explor
er, but when I go to step where I have to select DAQ hardware , the program
not detecting SCXI-1521. So unable to calibrate my strain gages.
If you know how to make Measurement and Automation Explorer detect SCXI-1521
please help me out
Mekdeng#4; Wed, 07 May 2008 00:11:00 GMT
- Hi Mekdeng,
Try configuring/adding the SCXI chassis to the DAQ card Properly.
These links should tell you how.
<a href="/app/links/?link=http://digital.ni.com/public.nsf/websearch/5902345227DFCA1286256EDA0063F50C" t
<a href="/app/links/?link=http://www.ni.com/support/scxi/scxidaq/soft.htm" target="_blank">http://w
Then, see if your SCXI 1521 and its terminal block SCXI 1317 are detect
ed by your MAX
Then do a self test for chassis on max itself.
If all this goes fine, you should solve the problem you mentioned.
Hope this Helps
Dev#5; Wed, 07 May 2008 00:12:00 GMT
Those documents that Dev pointed you to are good, but in your situation
I personally think the best place to get started with configuring your
SCXI system in MAX is the SCXI Quick Start Guide, which should have
come in the box that your SCXI module and chassis were shipped in. Here
is the online link to that document if you need it:<a href="/app/links/?link=http://digital.n
If you follow the steps in the quick start guide and still are having
problems detecting your SCXI-1521 in MAX, then let us know the specific
details of the problems.
Message Edited by Logan K on 12-02-2005 08:55 AM#6; Wed, 07 May 2008 00:13:00 GMT
- Thank you Logan,
I followed the steps in SCXI Quick start Guide and configured my hardware im
MAX and worked fine. Now that I configured my harware I tried to calibrate
my strain gages and the error I got is attached with this reply. I figured o
ut that I got this error ma
y be bacause I am trying to use 120 ohm strain gages with SCXI-1521 which wo
rks only with 350ohm resistors as per NI application engineers. Do I really
have to get a SCXI-1521B module which works 120ohm resistors to do my experi
ment or get new set of 350o
hm strain gages?
One thing I am amazed of is why does NI makes different modules to go with d
ifferent capacity resistors. I only know about 1521 and 1521B modules and wh
at if anybody uses 240ohm or 1000ohm resistors.. which module should they us
I am wondering if anyone know of any work around for me with out changing my
module or strain gages.
calibration-error.doc:#7; Wed, 07 May 2008 00:14:00 GMT
- The short answer is that you are correct. The SCXI-1521B must be used
for 120ohm strain gages, and the SCXI-1521 must be used for 350ohm
strain gages because they have fixed quarter bridge completion
resistors built into them. If you have a non-standard or less common
strain gage like a 1000ohm or 240ohm, then you must use a module which
enables you to customize your quarter-bridge completion resistor, like
the SCXI-1520 with the SCXI-1314 terminal block.
So, unfortunately there is not a good workaround for you with this module an
d I appologize for your inconvenience.
Logan K#8; Wed, 07 May 2008 00:15:00 GMT