Common DAQ Questions

What LabJack Is Recommended for New Applications?

The LabJack T7 is the most versatile, best bang-for-your-buck DAQ offered by LabJack or anyone else that we know of. Of course, it isn't perfect for every application or project. Compare all LabJack hardware side by side or read a detailed comparison of the different LabJack devices.

 

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).

Compare In-Stock 12, 16 and 24 Bit LabJack Devices

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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 error-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 error-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:

https://www.maximintegrated.com/en/design/technical-documents/tutorials/1/1870.html

Additional Information

Additional device-specific resolution information can be found in the respective device datasheet:

U3 Resolution

U6 Resolution

UE9 Resolution

T4 Resolution

T7 Resolution

What is a LabJack?

LabJacks are USB/Ethernet/WiFi based measurement and automation devices which provide analog inputs/outputs, digital inputs/outputs, and more.  A LabJack is an essential part of a computer-based instrumentation.  If you want to make a computer-based system that acquires readings from various sensors/transducers, and controls various outputs/actuators, you need a LabJack to go between the computer and the various inputs and outputs.

Go to our main FAQ page for more basic questions like "What is DAQ (data acquisition)" and "What is an analog input".

What is DAQ (data acquisition)?

DAQ is short for data acquisition, which is short for data acquisition and control.  The term describes the process of acquiring readings from sensors and transducers (temperature, pressure, strain, etc.), and controlling actuators (relays, solenoids, etc.).  In our case the emphasis is on computer-based DAQ, where the LabJack is the interface that allows a computer to read from sensors and control actuators.

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.

What are counters and timers?

Counters and timers are useful features available on some digital I/O.  On T-series devices they are called digital I/O extended features (DIO-EF).

A counter increments an internal register each time the voltage on a digital input changes from low to high (or vice versa).  This internal register can then be read at any time to get the current count.  Some typical uses are measuring frequency (change in counts over some time period) or monitoring a tipping bucket precipitation (rain) gauge.

A timer can have various capabilities such as PWM output, frequency measurement, pulse width measurement and quadrature counting.

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.

Every LabJack DAQ features analog outputs that appear on the "DAC" terminals. For applications requiring more analog outputs or a larger analog output voltage range than your LabJack has built in, simply add the LJTick-DAC.

The maximum number of expandable analog outputs varies by device.

Visit our LabJack Product Comparison page to review a complete breakdown of analog outputs, resolution, sensor compatibility, communication protocols (USB, Ethernet, WiFi) and software support.

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.

Where Are LabJack Datasheets?

All LabJack Datasheets, App Notes, Quickstart Tutorials, Software, Firmware, Drivers, Examples and everything else are available under the Support Tab

New to Data Acquisition (DAQ)? Not Sure Where to Start?

Our engineers in Colorado, USA, provide real-time live chat Monday-Friday between 9AM-11AM and 2PM-4PM Denver time. Click the chat bar at the bottom right of any page, or see our Contact page for other ways to get in touch with us.

Frequently Asked Support Questions

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.

• See the Troubleshooting Your Analog Input Signal App Note.

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.

Can LabJack be used for Industrial Applications?

LabJack Devices:

• Can comfortably operate within the industrial temperature range (-40°C to 85C)
• Are capable of being mounted via DIN Rail/Snap track
• Integrate with Voltage Dividers for 24+ Volt signals
• NEMA 3 (or greater) enclosures recommended for any outdoor or indoor applications with dust, debris or in condensing humidity environments
• All LabJack products are covered by our industry leading 5 year warranty
• Have OEM Versions available for custom and embedded applications. 
• Drawings and CAD Models Provided 
• LabJack products are very robust, but subject to the influence of user connections.
• LabJack is not liable for any losses, expenses or damages beyond the LabJack device itself.  See our Limitation of Liability for more details.

Drawings, Dimensions, 3D Models, CAD Models

LabJack enclosure and OEM drawings and models are provided in several neutral file formats. Please see the links below to navigate to the correct LabJack.

• LabJack T4
• LabJack T7
• LabJack U3
• LabJack U6
• LabJack U12

What Type of Sensors Can I Connect to LabJack?

LabJack hardware can be connected to nearly any analog or digital sensor. Of course some sensors are easier than others to connect. If you haven't yet purchased your sensors please check out our App Notes for detailed guides and best practices. Generally the best sensors output an analog voltage in the 0-10v DC range. We have many signal conditioning modules we refer to as "Ticks" that make it easy to accept other signals and ranges

• LJTick-Current Shunt for 4-20mA signals
• LJTick-Divider for voltages over 10v
• LJTick-Vref for sensors that require a stable excitation/power source
• LJTick-Resistance for RTDs, Thermistors or resistive sensors
• LJTikc-InAmp for amplifying tiny signals like bridge circuits or thermocouples

Data Acquisition Examples

Read the output of sensors which measure voltage, current, power, temperature, humidity, wind speed, force, pressure, strain, acceleration, RPM, light intensity, sound intensity, gas concentration, position, and many more. A LabJack brings this data into a PC where it can be stored and processed as desired.

Control things like motors, lights, solenoids, relays, valves, and more.

Visit our Blog for detailed examples, case studies and customer projects:

https://shop-labjack-com.myshopify.com/blogs/news/tagged/applications

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.

Explore LabJack's Analog Input App Note