What is an analog input? (AI, AIN, ADC) | LabJack
« Close

Datasheets and User Guides

App Notes

Software & Driver


What is an analog input? (AI, AIN, ADC)


AI or AIN = Analog Input
ADC = Analog to Digital Converter

An analog input converts a voltage level into a digital value that can be stored and processed in a computer. Why would you want to measure voltages? There are a multitude of sensors available which convert things like temperature, pressure, etc. into voltages.  The voltages can then be easily measured by various kinds of hardware, such as a LabJack U3-HV, and then read into a computer.  The computer can then convert the voltage value into it's original type (temperature, pressure, etc) and the value can then be stored in a file, emailed to someone, or used to control something else outside of the computer.


Analog Input Example

Get temperature from a sensor using an analog input.

  1. Wire the output of the analog temperature sensor to a U3-HV as shown.
  2. Read the voltage on the computer to know the current temperature. 
  3. This particular sensor outputs 0.01 volts per °F, so 0.76V corresponds with 76°F.

Hardware with Analog Inputs

LabJack U3 USB Analog Input Output Device
LabJack U6 USB Analog Input Output Device
LabJack UE9 USB Ethernet Analog Input Output Device
LabJack T4 USB Ethernet Digital and Analog Input Output Device
LabJack T7 USB Ethernet Wireless 802.11b/g WiFi Analog Input Output Device
LabJack U12 USB Analog Input Output Device


Can we measure standard 4- 20 mA coming from most field instruments with current transmitter on T7-pro AI channels , as its only mentioned voltags ranges ? 

All our devices have voltage inputs.  To measure 4-20 mA current you simply use a shunt resistor or the LJTick-CurrentShunt.  See the Measuring Current (4-20mA) App Note.

can I measure low voltage AC signals 5-7 Vac 

So perhaps you mean a 60 Hz sine wave with an RMS voltage of 7?  That means a max of about +9.9 volts and a min of about -9.9 volts.  Yes, you can measure such a signal.  With the U3 or U6 you would use stream mode to grab at least 1 cycle of the waveform, and then do whatever math you desire on it (e.g. RMS calculation).  With the T7 you can do the same, or use the RMS AIN-EF (analog input extended feature) to do all that and just return a single RMS value.