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FAQ's



What is USB?
USB (Universal Serial Bus) allows the connection of up to 127 devices to a computer. All computers sold today come with at least one USB port. USB is designed to be easy to use.


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.

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.

 

What is an analog output? (AO, DAC)
AO = Analog Output
DAC = Digital to Analog Converter

The LabJack's analog outputs convert digital values from a computer into a variable voltage level presented on an output terminal. This provides an adjustable output.

 

What is a counter?
A counter generally increments an internal register each time a voltage pulse is detected at the counter input. This internal register is then read periodically to determine how many events have occured. Typically used to measure frequency or RPM, accumulate pulses from a tipping bucket precipitation (rain) gauge, and similar counting applications.



What are digital I/O? (IO, D, DIO, FIO, EIO, CIO, MIO)
DIO = Digital Input/Output
IO/D/FIO/EIO/CIO/MIO = Somewhat arbitrary monikers for specific DIO ports on different LabJacks.

Digital I/O stands for Digital Input and Output. Digital Inputs allow a microcontroller to detect logic states, and Digital Outputs allow a microcontroller to output logic states.

Each digital I/O on a LabJack can be individually configured to one of 3 states: input, output-high, or output-low.

Digital Input: A digital input detects if a voltage is above/below a specific threshold. If the voltage is higher than some value, the computer will detect the digital input as high/set/1. If the voltage is lower than some value, the computer will detect the digital input as low/clear/0.

Digital Output: A digital output allows you to control a voltage with a computer. If the computer instructs the output to be high, the output will produce a voltage (generally about 5 or 3.3 volts). If the computer instructs the output to be low, it is connected to ground and produces no voltage.

Example:

Turn an LED On/Off using a digital I/O.
1. Wire the LED as shown. Optionally connect a current-limiting resistor.
2. Set the state of FIO0 to output-high on the computer. The LED will turn on.
3. The LED will turn Off if the state of FIO0 is set to output-low.

 

What do single-ended and differential mean?
Single-ended and differential refer to the reference for a voltage. Single-ended is referred to ground while differential is referred to some other voltage. For a single-ended measurement, the LabJack converts the difference between the voltage at an input and ground. For a differential measurement, the LabJack converts the difference between the voltage at one input and the voltage at another input that is not necessarily ground.

Differential does not refer to whether a signal is positive & negative or positive-only.  The terms for that are bipolar and unipolar.

On the LabJack U3, U12, U6, and T7, analog inputs can set as single-ended or differential via software. Analog inputs on the LabJack UE9 are single-ended only, so an instrumentation amp is needed to convert a differential signal to single-ended, or a pseudo-differential measurement can be made by taking the difference of two single-ended measurements.

 

What does 12- or 16-bit resolution mean?

What is resolution?

Resolution in this context refers to the conversion of an analog voltage to a digital value in a computer (and vice versa). A computer is a digital machine and thus stores a number as a series of ones and zeroes. If you are storing a digital 2-bit number you can store 4 different values: 00, 01, 10, or 11. Now, say you have a device which converts an analog voltage between 0 and 10 volts into a 2-bit digital value for storage in a computer. This device will give digital values as follows:

Voltage 2-Bit Digital Representation

0 to 2.5
2.5 to 5
5 to 7.5
7.5 to 10

00
01
10
11

So in this example, the 2-bit digital value can represent 4 different numbers, and the voltage input range of 0 to 10 volts is divided into 4 pieces giving a voltage resolution of 2.5 volts per bit. A 3-bit digital value can represent 8 (23) different numbers. A 12-bit digital value can represent 4096 (212) different numbers. A 16-bit digital value can represent 65536 (216) different numbers. It might occur to you at this point that a digital input could be thought of as a 1-bit analog to digital converter. Low voltages give a 0 and high voltages give a 1.

In the case of the LabJack U12, a single-ended analog input has a voltage range of -10 volts to +10 volts (20 volt total span) and returns a 12-bit value. This gives a voltage resolution of 20/4096 or 0.00488 volts per bit (4.88 mV/bit).

 

What does it mean to say a device is 12-bit, 16-bit, or 24-bit?

When you see analog input DAQ devices from various manufacturers called 12-bit, 16-bit, or 24-bit, it generally just means they have an ADC (analog to digital converter) that returns that many bits.  When an ADC chip returns 16 bits, it is probably better than a 12-bit converter, but not always.  The simple fact that a converter returns 16-bits says little about the quality of those bits.

It is hard to simply state "the resolution" of a given device. What we like to do, is provide actual measured data that tells you the resolution of a device including typical inherent noise.

If you look at a device called "24-bit" just because it has a converter that returns 24-bits of data per sample, you will find that it typically provides 20 bits effective or 18 bits noise-free (like the UE9-Pro).  The U6-Pro and T7-Pro provide some of the best performance around from a 24-bit ADC, and they do about 22 bits effective or 20 bits noise-free.  You will see with these devices we might mention they have a 24-bit ADC (as that is what people look and search for), but we try not to call them "24-bit" and try to stick with the effective resolution.

Another interesting thing about your typical 24-bit sigma-delta converter, is that you can look at them as only having a 1-bit ADC inside, but with timing and math they can produce 24-bit readings:

http://www.maxim-ic.com/appnotes.cfm/appnote_number/1870/

 

What is an amplifier, PGA or PGIA?
A PGA (Programmable Gain Amplifier) provides variable gain which is controlled in software. It is used to amplify low voltages on analog inputs. Most LabJacks have an internal PGA that can be used to provide small gains in some situations, but for larger gains an external amplifier must be used.