AIN (Analog Inputs)
A1. My analog input is stuck on some wrong value.
- See Suspicious Values.
A2. My analog input is returning varying values but not the right value.
A3. My readings are too noisy.
- See Too Much Noise.
A4. How do I measure temperature using a thermocouple, RTD, thermistor or other?
- Start on the Temperature Sensors App Note.
A5. My thermocouple readings are wrong.
- Determine if the error is from the cold junction sensor, the A/D conversion, or the signal itself.
- If the cold junction reading is off by a few degrees that error will show up in your calculated thermocouple temperature.
- Remove the thermocouple, and instead jumper the analog input (or both analog inputs for differential) to GND. The thermocouple voltage is now 0.0 volts which is saying both ends of the thermocouple are at the same temperature and thus the thermocouple temperature you calculate will be equal to the cold junction temperature.
- Remove the thermocouple from the system under test and instead just set it next to the LabJack so the thermocouple is measuring air temperature near the LabJack. If the terminals you are connecting to are at air temperature (e.g. CB37 terminals), the expected voltage is 0.0 volts. If the terminals you are connecting to are warmer than air temperature (e.g. T7 terminals), the expected voltage is a negative value dependent on the temperature difference.
- See Thermocouple Complications.
- See Thermocouple Troubleshooting Tips.
A6. I need to monitor a 4-20 mA current loop signal or measure some other current.
- LabJack analog inputs measure voltage. The LJTick-CurrentShunt is an easy way to convert 4-20 mA to voltage. See the Measuring Current App Note.
A7. Should I use differential?
- Sometimes it is required or a good idea. See Why use Differential.
A8. Problem with differential analog inputs.
- The signals cannot be totally floating. See Differential inputs must have a reference.
- See Differential Test.
A9. How do I read from a load cell?
- Most load cells are raw bridge circuits. See the Bridge Circuits App Note.
A10. How do I measure pressure?
- See the Pressure Sensors App Note.
A11. Can I measure AC or DC?
- Yes, both. When you ask for 1 sample from the LabJack you get the voltage at that moment. If the signal is DC, you expect multiple samples over time to return the same value. If the signal is AC, the samples are taken at different points of the waveform and thus will return different values.
- If you want to acquire the waveform for an AC signal, you simply acquire multiple samples over time, which is often done using stream mode. Then if wanted you can do math on the waveform to determine parameters such as max/min, RMS, or frequency.
- On T-series devices you can use the AIN-EF system to acquire multiple samples over time, do some math, and return various values that describe the multiple samples (RMS, Peak-to-Peak, Period, Average, Max/Min).
- See the Measuring 120/240 VAC App Note.
A12. What is the max data rate?
- We have lots of detail for sample rates. U12, U3, U6, UE9, T-Series.
- For stream mode we usually specify the max sample rate. For max scan rate divide the max sample rate by number of channels. SampleRate = ScanRate * NumChannels.
- Extended channels on the Mux80 act just like normal channels. The max sample rate of the LabJack is still the same, you just use a bigger number for NumChannels in the above equation.