How Do I Configure a Load Cell in NI MAX?

Updated Oct 4, 2018

Reported In

Hardware

  • NI-9234
  • NI-9235
  • NI-9236
  • NI-9237
  • PXIe-4330
  • PXIe-4331
  • PXIe-4339

Software

  • Measurement and Automation Explorer (MAX)

Driver

  • NI-DAQmx
  • Traditional NI-DAQ

Issue Details

How do I configure a load cell in NI Measurement & Automation Explorer (NI MAX)?

Solution

The following directions are for configuring a load cell in NI-DAQmx or Traditional NI-DAQ.

NI-DAQmx:
To use a DAQmx Task or Global Channel, complete the following steps:
  1. Create a Force (Bridge) or Force (IEPE)  analog input, depending on your sensor and data acquisition device.
  2. Under the Settings tab configure the Excitation Source for Internal or External and the Excitation Value as appropriate for your transducer.
  3. Configure the Bridge Type as Full Bridge.
  4. If you already have a custom scale created, use the pull-down menu to select the custom scaling for this channel. Otherwise, configure your custom scale by clicking on the wrench symbol to the right of the pull-down menu.
  5. In your application, you will have to perform offset null compensation and shunt calibration programmatically using task or channel properties. A shipping example for LabVIEW can be found in the Example Finder in Help >> Find Examples..., selecting Browse (according to Task) and opening Hardware Input and Output >> NI-DAQmx >> Analog Input >> Bridge Continuous Input.vi. This program contains subVIs that perform offset null compensation and shunt calibration.
Note: The electrical units in the default Bridge Scale in Step 4 is in mV/V.

Traditional NI-DAQ:
To use a virtual channel, complete the following steps:
  1. Right-click on Data Neighborhood in MAX, and select Create New....
  2. Select the appropriate type of channel, Traditional NI-DAQ or DAQmx. (The steps below will be for Traditional NI-DAQ but DAQmx will have the same basic steps).
  3. Select Analog Input.
  4. Enter a name and then a description (the description is optional).
  5. From the next menu, you will want to select Voltage measurement (not strain gauge).
  6. Enter the units (for example, lbs.) and then the range of your sensor. If you have a 50 lb. load cell, then we will want to enter -50 and 50 as our range.
  7. The next screen will ask us to enter a scale. To scale data into a unit other than volts (such as psi), you must create a custom scale. Usually the conversion is linear, and slope and intercept values should be provided by the transducer vendor. You can also choose Map Ranges. For example, if you have a load cell with a +/- 20 mV output, select Map Ranges and then enter 0.02 and -0.02 so that the virtual channel will automatically apply the necessary gain to the readings. Note: If you create a strain gauge virtual channel, all data will be scaled into microstrains.
  8. In the next window, select the SCXI-1520 module from the list and choose the channel of your incoming signal.
  9. Click Finish and you are now done creating the virtual channel.

Additional Information

  • The available excitation values will depend on the module being used. For example, the NI 9235 can only provide 2.0 V, the NI 9236 can only provide 3.3 V and the NI 9237 can provide 2.5 V, 3.3 V, 5 V or 10 V. For more information, refer to your device documentation.
  • Not all hardware supports both internal and external excitation. Refer to your device documentation for further details.
  • If using the NI 9237, see How Do I Configure a Load Cell with the NI 9237.
  • In old versions of NI-DAQmx, you will not find the Force (Bridge) or Force (IEPE) channel types. You will need to create a Custom Voltage with Exitation task and implement a Custom Scale to get the data in the appropriate unit.

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