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:
- Create a Force (Bridge) or Force (IEPE) analog input, depending on your sensor and data acquisition device.
- Under the Settings tab configure the Excitation Source for Internal or External and the Excitation Value as appropriate for your transducer.
- Configure the Bridge Type as Full Bridge.
- 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.
- 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:
- Right-click on Data Neighborhood in MAX, and select Create New....
- 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).
- Select Analog Input.
- Enter a name and then a description (the description is optional).
- From the next menu, you will want to select Voltage measurement (not strain gauge).
- 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.
- 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.
- In the next window, select the SCXI-1520 module from the list and choose the channel of your incoming signal.
- Click Finish and you are now done creating the virtual channel.
- 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.