From Friday, April 19th (11:00 PM CDT) through Saturday, April 20th (2:00 PM CDT), 2024, ni.com will undergo system upgrades that may result in temporary service interruption.
We appreciate your patience as we improve our online experience.
LabVIEW
Fluctuation in torque measurement using NI 9237
Hi,
I have prepared the LabVIEW FPGA program to measure torque meter reading. I am using NI 9237 for the torque meter. I have carried out calibration of torque meter by applying a range of weights and produced relation between voltage output and weight to convert voltage into Nm.
But when I started rotating the torque meter, observed that output voltage is fluctuating a lot and so torque value Nm. I acknowledge that I am using pretty much an old torque meter but it is working fine. I want to ensure that my code is correct for the torque meter. I am using the below code in LabVIEW FPGA to get voltage values from the torque meter (Mod6/AI0).
Could anyone suggest, is this the correct way or not? do I need to add anything else?.
I read in NI 9237 operating instruction that it has different filters like passband and stopband filter. I am not sure how to use it?
Thank you.
Any help will be appreciated.
My first question would be - how are you rotating it? How sure are you that the torque is "constant", for some given level of constant.
The torque sensor might be quite sensitive, and whilst hanging a weight is static and will nicely rest, motion might vary - maybe the motor is going a little faster, a little slower, oscillating around the target speed. How much variation in torque this produces can be significant, depending on the system.
Comparing with some other system doesn't necessarily help - if you connect e.g. a multimeter, probably it does some time-averaging before displaying a reading, which makes it look smoother. Of course, you could do this in LabVIEW too if you wanted, but you have to decide to do it, and then do it.
Is the mean value of your measurement (close to?) what you expect? How large is the variation?
What sort of a wiring setup do you have - how is the sensor connected to the cRIO, is there a slip ring, are you using large AC motors, does the wiring for the sensor have any protection from electrical noise, etc?
Hi,
As shown in below schematic diagram toque meter is installed between the machine (Roots blower, whose power I need to measure) and pully. It is connected with a motor using a belt drive. I am operating a motor using VFD, so I can run the machine at the required RPM. I am measuring RPM as well and it is pretty much stable.
Please refer below table of measured data at a constant speed. variation between maximum and minimum value is too high. So mean value is not representing the correct result.
I am using shielded cabled which has 5 wires, AI+,AI-,EX+,EX-,Extra (using as ground). these 5 wires are connected with RJ50 connection of NI 9237 using a connector available from NI. To avoid noise due to the power supply I have kept all power supply in a separate box.
| Blower Speed | TM Voltage | Torque |
| RPM | (V) | (Nm) |
| 1188.068 | 0.000047 | 0.869199 |
| 1188.334 | 0.000072 | 1.677562 |
| 1188.275 | 0.000109 | 2.92506 |
| 1188.225 | 0.000105 | 2.787978 |
| 1188.38 | 0.000072 | 1.684008 |
| 1188.029 | 0.000086 | 2.17024 |
| 1188.634 | 0.000066 | 1.47826 |
| 1187.741 | 0.000154 | 4.427263 |
| 1188.117 | 0.000083 | 2.041834 |
| 1187.511 | 0.000099 | 2.596112 |
| 1188.159 | 0.00006 | 1.281561 |
| 1188.581 | 0.000108 | 2.890975 |
| 1188.052 | 0.000109 | 2.912542 |
| 1188.844 | 0.000137 | 3.856872 |
| 1187.794 | 0.000077 | 1.85505 |
| 1189.044 | 0.000111 | 2.977117 |
| 1188.728 | 0.000079 | 1.919006 |
| 1188.307 | 0.000145 | 4.119757 |
| 1187.791 | 0.000097 | 2.522861 |
| 1188.081 | 0.0001 | 2.635403 |
Hi Patel,
@patelbrijesh535 wrote:
Full scale of torque meter is 0-50Nm (5kgf m). it is giving output in mV/V. Below is the calibration table, I have applied weight to cover entire range.
You are getting just 1.5mV at full scale input?
Which supply voltage did you use?
Can you attach the manufacturer manual for that torque sensor?
I suspect some problem with excitation or amplification... 1.5mV at full scale seems likely what should be going into an amplifier before measurement.
I took a look through the FPGA properties for a 9237, and at the manual, but didn't see anything that jumped out. You can set the excitation voltage, which might need to be adjusted based on your sensor? Or you can provide an external value, in which case your power supply should be a) at the correct voltage and b) turned on! 🙂
2-4Nm on a 50Nm scale isn't great, but it should be ok (4/50->8% used). 1.5mV on your input scale seems like your problem.
The allowed input is 25mV/V, which with a 3.3V excitation (looks to be the default, you might have changed this?) would make full-scale 82.5mV - and then 1.5/82.5 -> just 1.8%.
@patelbrijesh535 wrote:
I am sorry about manufacturer manual, this is very old torque meter and we don't have manual available for specific model.
I am using 10V internal excitation from NI 9237 module.
You previously wrote:
@patelbrijesh535 wrote:
I am using shielded cabled which has 5 wires, AI+,AI-,EX+,EX-,Extra (using as ground).
How did you identify the wires? Is there no documentation at all available? Or perhaps a part number for the sensor? The manufacturer's name? The manual doesn't necessarily have to be for the specific model (although of course that would be ideal) - sometimes a manual covers a range of similar products?
