Load cell calibration

Hi there,
New to Labview. Working on a little college assignment and am looking for a little bit of help. I have a micro load cell hooked up to a myDAQ and I'm attempting to calibrate it to get a make-shift weighting scales. I have attached my vi below. So far I have been able to calibrate it to an extent, but the precision is quite poor. It seems to fluctuate +/- 30 grams. I've been told that the error on the load cell is +/- 5g so I would like to get it a little closer to that. Any help would be greatly appreciated.
Load cell
http://www.phidgets.com/products.php?product%20id=3134
Attachments:
Scales new 15_2.vi ‏408 KB

Add a (INAXXX) ampifier with 100 to 400 times amplification ...
The rated output is 1mV/V so you get 5mV at max load and you also need to measure the exitation voltage .. the myDAQ spec tells that it's not exactly 5V ....
If you can't use an external amplifier, use the analog inputs in differential mode and 2V range, and use three 2.2k resistors to divide down (1/3) the supply voltage.
use a low samplerate (twice your line freq) mean as much samples as possible.
Assuming that the supply is only slowly drifting, measure the supply only (50 samples), sensor only (100 samples), and supply again (50 samples)
Mean the supply and the senor output and use the ratio (U_mean_sensor/U_mean_supply) for your calibration
Greetings from Germany
Henrik
LV since v3.1
“ground” is a convenient fantasy
'˙˙˙˙uıɐƃɐ lɐıp puɐ °06 ǝuoɥd ɹnoʎ uɹnʇ ǝsɐǝld 'ʎɹɐuıƃɐɯı sı pǝlɐıp ǝʌɐɥ noʎ ɹǝqɯnu ǝɥʇ'

Similar Messages

Not getting accurate readings off a calibrated load cell

I'm using a Cooper Instruments 200 lb load cell connected to a SCB-68 connector box hooked up to a 6036e DAQ card, and I'm having trouble calibrating it. (I've done this before, but it's been a while, and something just isn't working right.) So, I'm using the calibration wizard (the channels are set as Custom Voltage with Excitation), hanging a bunch of known weights from the cell, entering the values, and all that is going fine. However, when I go to use the load cells (in a very simple VI that just reads the value from the cell), it's reading consistently low by 2-3 pounds. I'm using a 10 V excitation signal, and I set the low end of the Signal Input Range to 0 (it kept wanting to set -5=-5 in the calibration when the low end was -5V, and that was even worse). I've tried modifying a custom scale, and that isn't fixing the problem either. Has anyone encountered this before or have any ideas on what else we can try?
Thanks,
Eric Martell

Hi Eric,
This is a curious problem. Is it every point that has a constant offset or does the offset vary from point to point?
Also what is the model number and sensitivity of your load cell? Have you gotten it to read correctly before? You mentioned that the values were stable out to the fourth decimal place, but haw significant is this decimal place? For instance, when I open the calibration wizard, the values can jump around depending on what I am measuring. If you load cell has a sensitivity of 1 mV/lb, then this could be large variations depending on what the decimal point was when you saved the value.
With regards to my mentioning averaging, when you first click the calibrate button in the DAQ Assistant, the first screen has a Number of Samples to Average control and a Rate control. If you leave the # of samples to average at 1000, but change the rate to 10,000, do the values begin to vary?
Regards, Mallori M.
Mallori M
National Instruments
Global Customer Education Program Mananger
Calculate the time you will save with NI Training

9237 with full-bridge load cell: load cell_null_off_shuntcal.vi throws error 200077

Hi,
I'm trying to use the example
load_cell_null_off_shuntcal.vi with a full-bridge load cell (Honeywell
Model 31, unamplified). I am using LabView 8.6, cDAQ-9172 and NI9237. The
load cell is connected to pins 2,3,6 and 7.
The inputs for the VI front panel
are: internal excitation10V; mV/V 2.1492 (calibration sheet); max weight 10
lbs; bridge resistance 350 ohms (Honeywell specs); 9237 internal shunt
resistance 100 kohms; shunt location R4 (default setting). I have selected
"Do offset null" and "Do shunt cal".
This is the error I receive:
Error -200077 occurred at DAQmx
Perform Shunt Calibration (Bridge).vi:1 Possible reason(s):
Measurements: Requested value is not
a supported value for this property.
Property:
AI.Bridge.ShuntCal.GainAdjust
You Have Requested: -61.980405e3
Valid Values Begin with: 500.0e-3
Valid Values End with: 1.500000
If the "Do shunt cal"
green button is not selected, there is no error. I understand that the Gain
adjust value should be approx 1, whereas the one I get is much larger. The subVI DAQmx PerformShuntCalibration
(bridge).vi contains a "Call library function node" which I don't
know how to interrogate.
Has anyone else had experience
with this error? Do you have any advice on:
1)
How to "see" the calculations being
perfomed inside the "call library function node"?
2)
What the correct shunt element
location for a full bridge load cell is? (although changing this location does
not eliminate the error, I can't find this info).
3)
Anything I may be doing wrong with
my inputs to cause this error?
Thanks,
Claire.
Solved!
Go to Solution.

Hi Claire,
You have to physically connect the SC terminals to one arm of the bridge (normally R3). The terminal is not provided for connecting external resistors.
See example
C:\Program Files\National Instruments\LabVIEW 8.6\examples\DAQmx\Analog In\Measure Strain.llb\Cont Acq Strain Samples (with Calibration) - NI 9237.vi
"A VI inside a Class is worth hundreds in the bush"
യവന്‍ പുലിയാണു കേട്ടാ!!!

9237 + full-bridge load cell: load cell_null_off_shuntcal.vi - error 200077

I'm trying to use
load_cell_null_off_shuntcal.vi with load cell (Honeywell Model 31,
unamplified). I am using LabView 8.6, cDAQ-9172 and NI9237. Inputs:
internal excitation10V; mV/V 2.1492 (calib. sheet); max weight 10 lbs; bridge
resistance 350 ohms (Honeywell specs); 9237 internal shunt resistance 100
kohms; shunt location R4 (default setting). Have selected "Do offset
null" and "Do shunt cal".
Error -200077 occurred at DAQmx
Perform Shunt Calibration
(Bridge).vi:1 Possible reason(s):
Measurements: Requested value is not
a supported value for
this property.
Property:
AI.Bridge.ShuntCal.GainAdjust
You Have Requested: -61.980405e3
Valid Values Begin with: 500.0e-3
Valid Values End with: 1.500000
If "Do shunt cal" green
button not selected, no error. Gain adjust should be approx 1. subVI
DAQmx PerformShuntCalibration (bridge).vi contains "Call library function
node" which is locked (?).
Any ideas?
What is the correct shunt element
location for a full bridge load cell? Changing this location does not eliminate
error.
Solved!
Go to Solution.

Hello CFJ,
The problem is most likely in your external connections of the NI 9237 and the load cell. As referenced in the NI 9237 Operating Instructions and Specifications, page 9, the SC+ and SC- pins should be connected across the resistor specified in the DAQmx Perform Shunt Calibration (Bridge).vi (in the case of a full bridge it would be R3).
Let me know if you are still having issues with your calibration.
Message Edited by Dan_K on 01-22-2009 04:31 PM
Regards,
Dan King

NI 9219 with load cell

Hello,
I am using the NI 9219 with a Futek Load Cell whose specifications are as follows:
Name
Min
Typ
Max
Unit
Channel: 1
Compensated Temperature
60
160
F
Excitation
1
20
Vdc
Hysteresis
-.25
.25
% of R.O.
Input Resistance
744
Ohms nom.
Insulation Resistance
500
Mohms @ 50 Vdc
Nonlinearity
-.25
.25
% of R.O.
Nonrepeatability
-.05
.05
% of R.O.
Operating Temperature
-60
200
F
Output Resistance
700
Ohms nom.
Safe Overload
150
% of R.O.
Temperature Shift Span
-.01
.01
% of Load/F
Temperature Shift Zero
-.01
.01
% of R.O./F
Zero Balance
-1
1
% of R.O.
Capacity
500
lbs
Rated Output
2
mV/V nom.
Calibration Excitation
10
Vdc
I am getting a signal from my load cell which is great, but I was wondering how you can adjust the signal output to have minimal interference from noise, vibrations, etc. and how to program the load cell that it can be calibrated to zero (0) before any data is aquired?
Any help is greatly appreciated!
Thanks,
Yatsco

Hello Yatsco,
Thank you for using NI forums. One thing you will probably want to look into is using the filtering VI's in LabVIEW. A low-pass filter can help to eliminate any high frequency noise from your measurement. Also, take a look at the Field Wiring and Noise Considerations article for some more information on eliminating noise. Lastly, this community example shows how you could calculate the DC offset and compensate for it before measuring your signal. Please let me know if you have any additional questions concerning this application.
Regards,

Load cell

Hi,
I'm using NI 9219 with Honeywell Load Cell model 11. The problem is the excitation voltage for 9219 is 2.7V while the calibrated excitation voltage for the load cell is 5V. When I connected both device, I still get the output from Labview but how can I calibrate the load cell?
Solved!
Go to Solution.

Hi,
Sorry if might look stupid (i know it is...).
On the calibration certificate of the load cell there are several values for several point + the "best match" in mV/V.
When you enter in the calibration mode, it is required to enter 2 points (mV/V and N for both) which values is is best to enter? The extremes ones or some which are close to the range of what you expect to measure?
Then another one... (i may as well since i am a real novice trying to learn). Is there an "AutoZero" option somehow somewhere or do i have to remove the offest by calculation?
Thanks for you time!

Dynamic force control using linear servo actuator + load cell

Hello,
I am designing a test fixture which will allow us to test the performance of actuators we install in our products. I need to apply a constant load to the actuator while it is extending/retracting. I would like to be able to use a linear servo actuator and a load cell on the same axis as the UUT to provide and monitor the load. The actuator under test does not travel at high speeds, its max speed is approximately 1in./sec.
I need to be able to maintain a constant load while the actuator is moving. Therefore I'll need some kind of closed loop system to maintain a velocity such that the load being reported from the load cell is equal to the expected load as the actuator is moving.
I am trying to figure out how to best implement this in a cost effective and time-saving way. I have not purchased any hardware at the moment so am open to suggestions. We do have LabView 2009 with all the toolkits. Would it be best to implement this using a motion controller card or would I be able to get good results using a standard DAQ?
Message Edited by fnaeem on 02-05-2010 05:58 PM

As you have stated correctly, you will need a deterministic closed loop system to accomplish this task. The most cost efficient while reliable solution for this purpose is a motion control board like the PCI-7352. This board provides quadrature encoder inputs for positioning tasks and analog inputs for any other type of control. Torque/force control is a very typical task for this board and it provides a simple API and useful configuration tools.
If cost savings are a primary goal, you could also use a PCI-7342, but for your application I would recommend the PCI-7352, as the PCI-7342 provides only 12-bit ADCs, while the PCI-7352 provides 16-bit ADCs, resulting in a much better resolution of your force feedback signal.
I hope that helps,
Jochen Klier
National Instruments

Data acquisition from a 250N Load cell

Hi ,
I am very new at using the Labview.I am using Labview 6i(PCI 6052E).The load cell(250N) is connected to a pump.The pump has 2 bags.One of them is filled with water and the other is empty.I want to load the bag which is empty from the bag filled with water using the pump.The load cell is connected to the bag which is filled with water.I am trying to aquire a volatge signal continously from a load cell and display it on a chart.
My program has no errors and I am able to run the progam.But it is not aquiring any signal.Could u please help me out.Attached is my code for the same .
-Manasa

Hi Manasa,
Make sure you are handling your errors in your code. You can do this by wiring your error clusters through your VI and then terminate them in a General Error Handler VI. If you are doing this, make sure that your device works in Measurement & Automation Explorer (MAX). Do this by opening a test panel and verifying that you can get a known voltage (like a battery) to read correctly. If you can successfully get a voltage in MAX, try running one of the example programs. You can find them at Help » Find Examples..., then browse to hardware input and output. If you can get an example program that is similar to what you are trying to do to work, try comparing your code to the example.
Please post back if you have any questions. Have a great weekend!
Ryan D.
District Sales Manager for Boston & Northern New England
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.

How can I calibrate load cell?

Hi.
My system is consist of the load cell(excitation:15v), signal conditioner(SC-2043-SG), and DAQ(AT-MIO-16XE-50).
I think there is a difference of excitation between the load cell and DAQ. But,I don't know the exact excitation of DAQ. So I'm thinking about using external power supply to make no difference of excitation betwen the load cell and DAQ. But I'm not sure it is good way or not. Let me know this is good method to calibrate the load cell and how to calibrate the load cell. If the external power supply is needed to the system, where should I connect the power supply? I guess that I should connect the power supply to the signal conditioner.
I would really appreciate a prompt response.
Thanks.

Hi,
The excitation needed for your load cell falls outside the permissible range (check page 5-2 of the manual. For external installation and signal connections, check chapters 2 and 3, respectively.
Regards,
RamziH.

Unable to load Cell Text (Memo A/c) from FDM to HFM..?

Hi All,
I am unable to load Cell Text (Memo a/c) from FDM to HFM. We use Import>validate>export function and use Upsload fucntion in the file to import the data. No errors are shown whilst loading the file and everything gets load except these Memo accounts The issue never arose when we were on version 11.1.1.3. We have recently migrated to 11.1.2.1. I have also checked Application Integration Settings where Cell Text is ticked as enabled.
Can someone help please..
Thanks,
Maneesh

Hi All,
I am unable to load Cell Text (Memo a/c) from FDM to HFM. We use Import>validate>export function and use Upsload fucntion in the file to import the data. No errors are shown whilst loading the file and everything gets load except these Memo accounts The issue never arose when we were on version 11.1.1.3. We have recently migrated to 11.1.2.1. I have also checked Application Integration Settings where Cell Text is ticked as enabled.
Can someone help please..
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Maneesh

Question on Measuring Lift Force for MAV Ornithopter for Student Project using Load Cell

Hey everyone!
I am new to these forums so bare with me, please. I am part of a senior design student group working on making a micro aerial vehicle ornithopter (generates lift by flapping its wings) similar to this Design.
We are using this load cell connected to an AD620 Op-Amp circuit that basically has two input wires from the load cell coming into the op-amp with a gain of 100 (there is an Rg resistor with 500 ohms in the circuit). The load cell and op-amp circuit are both powered correctly with 10 V and +-15 V, respectively. There are two output wires coming out of the circuit. One comes out of the 6th terminal of the op-amp, and one is connected to ground. If we turn on everything and test the output of the circuit with a multimeter there is little if no fluctuation in the output voltage, which is about .25 V with zero load. If we add precise weights and form a linear graph of the output voltage vs. weight, we can find that there is about .0045 volts/gram relationship.
Here comes the part we we are having trouble. It seems as though the circuit it working correctly, but when we try and hook it up to our USB-6221 DAQ Board though the ai0 (or any analog input) and confirm a LabVIEW program to read the output, we get a ton of noise along with a weird looking graph.
Here is a picture of the front panel that shows the output we are getting http://img130.imageshack.us/i/frontpanelg.jpg/
Basically, I would have though we could get a straight line that continuely increases or decreases depending on the load on the load cell. Why would it graph a ton of vertical lines? I would think it would be just one data point per time value?
Here is the simpler block diagram just to test the output: http://img26.imageshack.us/i/blockdiagramsmall.jpg/
Here is the main block diagram that we were going to use to convert to force, etc. but its not working (no need for while loop?): http://img15.imageshack.us/i/blockdiagrambig.jpg/
The properties of the DAQ Assistant VI is as follows:
input range: -10 to 10 v
RSE terminal configuration
acquisition mode: n samples and not sure how many samples we want to read or how fast. we had 1k hz and 100 samples and the image above is basically what we got it the program runs continuously.
I don't know what else I can tell you, except that if anyone helps me you would be like a godsend to our group. It would be very much appreciated
Thanks!!!

As I am unable to look at youor images (the corporate filter here is blocking the url) I can't see what you are describing. I will say that a multimeter will not show fast transitions that will show up in a LabVIEW/DAQ application, so using a meter usually doesn't tell you that much about signal "cleanness". How long are the wires from the op amp/load cell to the DAQ? How long are the wires, and what type (shielded, twisted pairs, untwisted pairs, etc.) from the load cell to the op amp. The output levels of the load cell are usually quite low, so the possibility of also picking up "environmental" electrical noise is very high, and this will be amplified as well. Since the output of the op amp is higher, the noise introduced between it and the input to the DAQ is less of an issue, but there as well. So making sure that signal wires are properly shielded and grounded is important, and there are long papers describing this for low level analog signals. Since the load cells desired output will probably vary relatively slowly (a few Hz) it may also be helpful to put a simple low pass filter before the DAQ.
You should insert the images into your post, as jpg, or png (you have jpg images) Not bmp! (this is for others that might read your post, yours are jpg which should be ok). Generally most of us won't or can't go to links, corporate network filters and corporate policies frown on it, too much maleware lurking at the end of unknown URL's
Putnam
Certified LabVIEW Developer
Senior Test Engineer
Currently using LV 6.1-LabVIEW 2012, RT8.5
LabVIEW Champion

Modbus communication with a load cell

Hello..!
I'm a new user of LV and I try to communicate with a load cell by RS232 modbus.
After installed NI Modbus Library I created a master VI with labview 8.6 using these library, and I can obtain a communication with load cell , these value are added into 1 register U32Bit, and it's okay, if I press a load cell I can see the values go on.( from 0 to 65535) . Now I want to show on front panel the value in KG , as decimal point,, for a right interpretation of value for my customer, so I added a block array to unbundle than I convert a value with I32Bit ( -32768 to 32768 ) with an indicator, but I can't see any values..
I suppose I doing something of wrong ( conversion ), I read some KB, but I can't see a suitable solution..
Can someone give me a link or information to show me an example to convert this value..?
Thanks in advance for any helps..
Configuration of MAster VI:
Read holding register
Starting address 2012 ( query for obtain net value from the load cell)
quantity 1
Slave address: 1
RTU
9600
Com 3
parity none
Solved!
Go to Solution.

Hello Ravens,
I tried to use your good advices and finally I can communicate correctly with my trasducers showing on front panel the right value ( Kg). Has been a problem of conversion from output of register ( U16Bit as 0-65535 ) to I16bit ( -32765 to 32765).
Thanks very much for your help, and I hope to chat again for new challenge...
Have a nice WE
Julio
Attachments:
Comunicazione Modbus load cell.jpg ‏46 KB

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

Closed loop velocity control based on load cell force

Hello,
My application is for a drill, that drills into rocks of various densities for the purpose of collecting rock core samples.
My setup has 2 motors which get controlled, one spins the drill bit at a constant velocity, the other moves the drill mechanism along a Z axis.
For efficient cutting, it is desired to apply a constant force between the drill bit and the rock. I have a load cell which measures the force being exerted by the drill bit on the rock surface, and this force can be adjusted by changing the velocity of the Z axis. So I would like to employ closed loop control to adjust the Z axis velocity to maintain a constant force on the rock.
Platform: cRIO 9073, with NI 9505 & 9215 Modules, Labview 2010 Full with RT and FPGA modules.
The load cell is by Transducer Techniques, and I use their TMO-1 module to condition the signal, the output of which is attached to an input of the 9215 module, where 0-100 lbs equates to 0-8VDC.
The motors and encoders for the Drill and Z axis are connected directly to the 9505 modules.
Right now I am using a modified version the example found in ...\examples\CompactRIO\Module Specific\NI 9505\Velocity Control (closed loop)\Velocity Control (closed loop) - NI 9505.lvproj to accomplish velocity control of the motors.
My questions are:
1) Do I have the appropriate NI hardware/software for this task?
2) With my current hardware setup, what would be an appropriate way to control my Z axis velocity rate based on Analog feedback from the load cell?
3) Development time is a critical factor, so are there any toolkits etc that are easy to get started with that would drastically decrease my development time, or do I already have everything I need?
Thank you for your time
-MK Hokie

1. Your hardware and software look appropriate assuming the motors are compatible with the 9505s. You didn't mention the NI SoftMotion module in your software list which is something you will need.
2. There are a few ways of doing this. One method would be to have a force PID loop that would attempt to maintain a force setpoint by directly outputting values to your torque loop. In this case, the drill would essentially move as fast as it could while maintaining the force setpoint. Another option is to have the force loop output a velocity setpoint. You would then have a velocity PID loop that outputs torque values to the torque loop. By adding this additional velocity loop you could have control over your maximum and minimum velocities. There are likely other alternatives as well, but these are the first two that come to mind.
3. Unfortunately there are no shipping examples that close the loop on force feedback. My advice would be to start with the NI 9505 shipping example and adapt it to your needs. There are quite a few things you will want to change though. Do you know if you will need to use the trajectory generator to move the drill into position before starting the force control?
Assuming you don't need any trajectory generation, you can scrap the entire RT portion of the NI 9505 example and just create the necessary FPGA code. On the FPGA, you won't need the Spline or Synchronization code either because this information would no longer be coming from RT. You could take these out and replace the position loop with a force loop and possibly a velocity loop and your FPGA program would basically be finished. In fact the only real motion IP that you will need is for the encoders (assuming you want velocity control) and PID. Then you would need to create an RT VI that allows you to send down enable, disable, PID gains, and setpoints.
If you do need trajectory generation, you would want to keep most of the example code the way that it is, but then program in a 'Force Mode' that utilizes the force and velocity controly as described above. You could think of it as having two different routines programmed side by side.
Regards,
Burt S

Load cell calibration

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