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Software & Driver


Appendix A - Specifications

Specifications at 25 degrees C and Vusb/Vext = 5.0V, except where noted.

Parameter Conditions Min Typical Max Units
USB Cable Length       5 meters
Supply Voltage (1)   4.75 5 5.25 volts
Supply Current (2)     100   mA
Operating Temperature   -40   85 °C
Clock Error ~ 25 °C     ±30 ppm
  -10 to 60 °C     ±50 ppm
  -40 to 85 °C     ±100 ppm
Typ. Command Execution Time (3) USB High-High 0.6     ms
  USB Other 4     ms
Vs Outputs          
Typical Voltage (4) Self-Powered 4.75 5 5.25 volts
  Bus-Powered 4.8 5 5.25  
Maximum Current (4) Self-Powered   400   mA
  Bus-Powered   0   mA
Vm+/Vm- Outputs          
Typical Voltage No-load   ±13   volts
  @ 2.5 mA   ±12   volts
Maximum Current     2.5   mA
10UA & 200UA Current Outputs          
Absolute Accuracy (5) ~ 25 °C   ±0.1 ±0.2 %
Temperature Coefficient See Section 2.5       ppm/°C
Maximum Voltage     VS - 2.0   volts
(1) Device should operate down to about 3.5 volts, with the following considerations. The hi-res converter on the U6-Pro is not specified for operation below 4.75 volts. The voltage drive capability of the current sources will be reduced. The maximum output of the DACs will be limited by VS. The input range of the analog inputs will be reduced approximately 3 volts for each 1 volt that VS is below 4.5 volts.     
(2) Typical current drawn by the U6 itself, not including any user connections     
(3) Total typical time to execute a single Feedback function with no analog inputs. Measured by timing a Windows application that performs 1000 calls to the Feedback function. See Section 3.1 for more timing information     
(4) These specifications are related to the power provided by the host/hub. Self- and bus-powered describes the host/hub. not the U6. Self-powered would apply to USB hubs with a power supply, all known desktop computer USB hosts, and some notebook computer USB hosts. And example of bus powered would be a hub with no power supply, or many PDA ports. The current rating is the maximum current that should be sourced through the U6 and out of the Vs terminals     
(5) This is compared to the value stored during factory calibration     
Parameter Conditions Min Typical Max Units
Analog Inputs          
Typical Input Range (6) Gain=1 -10.5   10.1 volts
Max AIN Voltage to GND (7) Valid Readings -11.5   11.5 volts
Max AIN Voltage to GND (8) No Damage -20   20 volts
Input Bias Current (9)     20   nA
Input Impedance (9)     1  
Source Impedance (9)     1  
Integral Linearity Error Gain=1,10,100     ±0.01 % FS
  Gain=1000     ±0.1 % FS
Absolute Accuracy Gain=1,10,100     ±0.01 % FS
  Gain=1000     ±0.1 % FS
Temperature Drift     15   ppm/°C
Channel Crosstalk (10) < 1kHz   -100   dB
  1kHz - 50kHz   20   dB/dec
Noise (Peak-To-Peak) See Appendix B     <1 μV
Effective Resolution (RMS) See Appendix B     22 bits
Noise-Free Resolution See Appendix B     20 bits
Command/Response Speed See Section 3.1        
Stream Performance See Section 3.2        
(6) Differential or single-ended     
(7) This is the maximum voltage on any AIN pin compared to ground for valid measurements on that channel. For single-ended readings on the channel itself, inputs are limited by the "Typical Input Range" above, and for differential readings consult the signal range tables in Section 2.6.5. Further, if a channel has over 13.0 volts compared to ground, readings on other channels could be affected. Because all even channels are on 1 front-end mux, and all odd channels on a 2nd front-end mux, an overvoltage (>13V) on a single channel will generally affect only even or only odd channels.     
(8) Maximum voltage, compared to ground, to avoid damage to the device. Protection level is the same whether the device is powered or not.     
(9) The key specification here is the maximum source impedance. As long as the source impedance is not over this value, there will be no substantial errors due to impedance problems. For source impedance greater than this value, there are two error sources that need to be considered. First, there is a simple offset error due to the input bias current flowing through the source impedance. Second, if sampling more than 1 channel, there can be a more complex settling error if the analog input system needs to quickly swing from one voltage to another. Required settling time to meet specifications can depend on the source impedance of the signal, channel order, resolution index, and gain/range.     
(10) Typical crosstalk on a grounded AIN pin, with 20Vpp sine wave on
adjacent AIN pin. An adjacent AIN pin refers to multiplexer channel
location not channel number, e.g. AIN0-AIN2 or AIN1-AIN3 pairs.     
Parameter Conditions Min Typical Max Units
Analog Outputs (DAC)          
Nominal Output Range (11) No Load 0.04   4.95 volts
  @ ±2.5 mA 0.255   4.775 volts
Resolution     12   bits
Absolute Accuracy 5% to 95% FS   ±0.1   % FS
Integral Linearity Error     ±0.35 ±1 counts
Differential Linearity Error     ±0.1 ±0.5 counts
Error Due To Loading @ 100 µA   0.1   %
  @ 1 mA   1   %
Souce Impedance     50   Ω
Short Circuit Current (12) Max to GND   50   mA
Time Constant     300   μs
Digital I/O, Timers, Counters          
Low Level Input Voltage   -0.3   0.8 volts
High Level Input Voltage   2   5.8 volts
Maximum Input Voltage (13) FIO -10   10 volts
  EIO/CIO -6   6 volts
Output Low Voltage (14) No Load   0   volts
--- FIO Sinking 1 mA   0.55   volts
--- EIO/CIO Sinking 1 mA   0.18   volts
--- EIO/CIO Sinking 5 mA   0.9   volts
Output High Voltage (14) No Load   3.3   volts
--- FIO Sourcing 1 mA   2.75   volts
--- EIO/CIO Sourcing 1 mA   3.12   volts
--- EIO/CIO Sourcing 5 mA   2.4   volts
Short Circut Current (14) FIO   6   mA
  EIO/CIO   16   mA
Output Impedance (14) FIO   550   Ω
  EIO/CIO   180   Ω
Counter Input Frequency (15)       8 MHz
Input Timer Total Edge Rate (16) No Stream     30000 edges/s
  While Streaming     7000 edges/s
(11) Maximum and minimum analog output voltage is limited by the supply voltages (Vs and GND). The specifications assume Vs is 5.0 volts. Also, the ability of the DAC output buffer to driver voltages close to the power rails, decreases with increasing output current, but in most applications the output is not sinking/source much current as the output voltage approaches GND.     
(12) Continuous short circuit will not cause damage.     
(13) Maximum voltage to avoid damage to the device. Protection works whether the device is powered or not, but continuous voltages over 5.8 volts or less than -0.3 volts are not recommended when the U3 is unpowered, as the voltage will attempt to supply operating power to the U3 possibly causing poor start-up behavior.     
(14) These specifications provide the answer to the question. "How much current can the digital I/O sink or source?". For instance, if EIO0 is configured as output-high and shorted to ground, the current sourced by EIO0 is configured as output-high and shorted to ground, the current sourced by EIO0 into ground will be about 16 mA (3.3/180). If connected to a load that draws 5 mA, EIO0 can provide that current but the voltage will droop to about 2.4 volts instead of the nominal 3.3 volts. If connected to a 180 ohm load to ground, the resulting voltage and current will be about 1.65 volts @ 9 mA.     
(15) Hardware counters. 0 to 3.3 volt square wave.     
(16) To Avoid missing edges, keep the total number of applicable edges on all applicable timers below this limit. See section 2.9 for more information.     


What type of temperature sensors are compatible with LabJack? DS18B20? NTC? RTD? Thanks

The U6 can be used with pretty much any type of temperature sensor.  Silicon type sensors are the easiest/best/cheapest and should be used whenever possible:


If they can't be used, I suggest thermocouples.

I'm measuring current by monitoring the voltage drop across a 500 kilo-ohm resistor using an AIN on a U6-PRO.  The current is 0 to 20 micro-amps.  I need to take a reading 4 times per second.  An electrical engineer advised me to add a 0.1uF capacitor in parallel with the resistor to prevent errors due to voltage drop when the A to D reads the voltage.  Does that make sense?  What do you recommend?

That is a very high source impedance.  My quick suggestion is to use an op-amp or in-amp to buffer the signal.  Is one side of the resistor at GND, or is it a differential reading?  If differential, what is the typical voltage on each side of the resistor compared to GND?

There are many details we can get into for working with a high impedance source.  I suggest you post on our forum to go into more details.

The positive side is at ground, the measured signal will be negative.

There are 2 main problems when working with a high source impedance signal.

1.  Dynamic settling error due to step change:  When the mux system changes from one channel to another, the system must settle from the previous voltage to the new voltage.  If you just sample the same channel repeatedly you don't have to worry about this.

2.  Static error due to bias current:  The analog inputs have a bias current of roughly 20nA, which through a 500k resistor would cause a 10mV offset error.  You could calibrate this out to some extent, but the bias current does change with common-mode voltage.

The solution I recommend is to use a smaller shunt resistor and then add an LJTick-InAmp as a pre-amplifier.

I am currently trying to use my U6 to output 3 volts and 5 volts from DAC0 and DAC1 (both with only a few milliamps), but I'm not sure if I am getting those voltage values.  When I measure the voltage outputs without a load attached, everything is fine, but during operation I am getting a little over 2.5 volts on each output.  Am I just trying to put out too much voltage?

You are on the right page.  See note #10 above.  If your VS is 5.0V or greater, and you set DAC0 to 5.0V with no load, you should see it pretty much go to 5.0V.  If you are drawing 3 mA, that will cause 150 mV drop through the 50 ohms of source impedance so I would expect perhaps 4.8V (source impedance drop plus some drop due to the output op-amp trying to drive a load near the power rail).

If you think your DACs might be damaged and not driving a load properly, test with a simple resistor.  For example, if you set the DAC to 4.0V, you should see 4.0V with no load, but with a 1000 ohm load you would expect about 4.0 * (1000/1050) = 3.8V.

It looks like my resistance is lower than thought (about 100 ohms).  So I am pulling about 50 mA through DAC1, and my voltage is dropping below 3 volts.  Is there another way to get a 5v differential if my resistance is so low? I am trying to switch a mechanical relay that requires 5V, so I can't play with the reistance value really.

I would say you need the LJTick-RelayDriver.  See Section of this U6 User's Guide.