LabJack U12 User Manual

LabJack U12 User’s Guide

Revision 1.00

9/21/2001

LabJack Corporation

www.labjack.com

[e-mail]

For the latest version of the user’s guide, the quickstart guide, or software, go to

www.labjack.com

.

The LabJack U12 is a measurement and automation peripheral that enables the connection of a
PC to the real-world. Although the LabJack U12 has many redundant protection mechanisms, it
is possible, in the case of improper and/or unreasonable use, to damage the LabJack and even
the PC to which it is connected. LabJack Corporation will not be liable for any such damage.

LabJack U12 Warranty

The LabJack U12 comes with a 1 year limited warranty from LabJack Corporation (LC),
covering this product and parts against defects in material or workmanship. The LabJack can
be damaged by misconnection (such as connecting 120 VAC to any of the screw terminals),
and this warranty does not cover damage obviously caused by the customer. If you have a
problem, contact [e-mail]
the customer is responsible for shipping to LC, and LC will pay for the return shipping.

for return authorization. In the case of warranty repairs,

Table Of Contents

1. Installation............................................................................................................................. 5

1.1 Hardware Installation ....................................................................................................... 5

1.2 Software Installation......................................................................................................... 5

2. Hardware Description............................................................................................................ 7

2.1 AI0 – AI7.......................................................................................................................... 8

2.2 AO0 & AO1.................................................................................................................... 10

2.3 IO0 – IO3....................................................................................................................... 11

2.4 D0 – D15 ....................................................................................................................... 11

2.5 CNT............................................................................................................................... 12

2.3 CAL – STB..................................................................................................................... 12

2.4 +5V................................................................................................................................ 12

2.5 GND .............................................................................................................................. 12

3. Example Applications .......................................................................................................... 13

3.1 LJconfig ......................................................................................................................... 13

3.2 LJlogger......................................................................................................................... 14

3.3 LJscope ......................................................................................................................... 17

3.4 LJtest............................................................................................................................. 18

4. Programming Reference ..................................................................................................... 20

4.1 AISample....................................................................................................................... 20

4.2 AIBurst........................................................................................................................... 21

4.3 AIStreamStart ................................................................................................................ 23

4.4 AIStreamRead ...............................................................................................................25

4.5 AIStreamClear ............................................................................................................... 26

4.6 AOUpdate...................................................................................................................... 26

4.7 BitsToVolts .................................................................................................................... 27

4.8 VoltsToBits .................................................................................................................... 27

4.9 Counter.......................................................................................................................... 27

4.10 DigitalIO....................................................................................................................... 28

4.11 GetDriverVersion ......................................................................................................... 28

4.12 GetErrorString.............................................................................................................. 29

4.13 GetFirmwareVersion.................................................................................................... 29

4.14 GetWinVersion.............................................................................................................29

4.15 ListAll........................................................................................................................... 30

4.16 LocalID ........................................................................................................................ 31

4.17 ReEnum....................................................................................................................... 31

4.18 Reset ........................................................................................................................... 31

4.19 Watchdog .................................................................................................................... 31

4.20 ReadMem .................................................................................................................... 32

4.21 WriteMem .................................................................................................................... 33

4.22 BuildOptionBits (ActiveX only) ..................................................................................... 33

4.23 FourPack (ActiveX only) .............................................................................................. 34

A. Specifications...................................................................................................................... 35

Table Of Figures

Figure 2-1. LabJack U12 top surface......................................................................................... 7

Figure 2-2. Single-ended measurement. ................................................................................... 8

Figure 2-3. Differential measurement. ....................................................................................... 9

Figure 2-4. Single-ended measurement with voltage divider circuit. .......................................... 9

Figure 2-5. IO used to detect the state of a switch................................................................... 11

Figure 3-1. LJconfig................................................................................................................. 13

Figure 3-2. LJconfig Change Local ID ..................................................................................... 14

Figure 3-3. LJlogger................................................................................................................ 14

Figure 3-4. LJlogger Configuration .......................................................................................... 15

Figure 3-5. LJlogger Internet Configuration ............................................................................. 16

Figure 3-6. LJlogger HTML Configuration................................................................................ 16

Figure 3-7. LJlogger Trigger Configuration .............................................................................. 17

Figure 3-8. LJscope................................................................................................................. 18

Figure 3-9. LJtest .................................................................................................................... 19

1. Installation

The LabJack U12 requires a PC running Windows 98SE, ME, 2000, or XP. To determine your
operating system version, go to

Start => Settings => Control Panel => System => General

and make sure the version number is 4.10.2222 or higher (Win98SE=4.10.2222,
WinME=4.90.3000, Win2000=5.0.2195, WinXP=5.1.XXXX).

It doesn’t matter if the hardware or software is installed first.

1.1 Hardware Installation

With the PC on and using the included cable, connect the LabJack U12 to the USB port on the
PC or USB hub. The USB cable provides power and communication for the LabJack U12. The
status LED should immediately blink 4 times (at about 4 Hz), and then stay off while the
LabJack enumerates.

Enumeration is the process where the PC’s operating system gathers information from a USB
device that describes it and it’s capabilities. The low-level drivers for the LabJack U12 come
with Windows and enumeration will proceed automatically. The first time a device is
enumerated on a particular PC, it can take a minute or two, and Windows might prompt you
about installing drivers. Accept all the defaults at the Windows prompts, and reboot the PC if
asked to do so. Enumeration occurs whenever the USB cable is connected, and only takes a
few seconds after the first time.

When enumeration is complete, the LED will blink twice and remain on. This means Windows
has enumerated the LabJack properly.

If the LabJack fails to enumerate:

• Make sure you are running Windows OS version 4.10.2222 or higher,

• Try connecting the LabJack to another PC,

• Try connecting a different USB device to the PC,

• Contact LabJack at [e-mail]

.

1.2 Software Installation

Although, the low-level USB drivers for the LabJack are included with Windows, high-level
drivers are needed to send and receive data. The included LabJack CD installs the high-level
drivers, example source code, and example applications.

Close all open applications, especially LabJack related software, and insert the LabJack CD. If
autorun is enabled, the installation program should start automatically. If the installation does
not start, you will have to manually double-click on LabJackVXXX.exe.

When the LabJack installation is finished, it will start the National Instruments LabVIEW Run­Time Engine (LVRTE) setup. The LVRTE is required for the example applications: LJconfig,
LJlogger, LJscope, and LJtest. If prompted to reboot after this installation, go ahead and do so.

To test the installation, start LJconfig by selecting

Start => Programs => LabJack => LJconfig

and make sure 1 LabJack is listed.

2. Hardware Description

The external features of the LabJack U12 are:

• USB connector,

• DB25 digital I/O connector,

• Status LED,

• 30 screw terminals.

The USB connection provides power and communication. No external power supply is needed.
The +5 volt connections available at various locations are outputs, do not connect a power
supply.

Figure 2-1. LabJack U12 top surface.

Figure 2-1 shows the top surface of the LabJack U12. Not shown is the USB and DB25
connector, which are both on the top edge. The DB25 connector provides connections for 16
digital I/O lines, called D0-D15. It also has connections for ground and +5 volts. All
connections besides D0-D15, are provided by the 30 screw terminals shown in Figure 1. Each
individual screw terminal has a label, AI0 through STB.

The status LED blinks 4 times at power-up, and then blinks once and stays on after
enumeration (recognition of the LabJack U12 by the PC operating system). The LED also
blinks during burst and stream operations, unless disabled. The LED can be enabled/disabled
through software using the functions AISample, AIBurst, or AIStreamStart. Since the LED uses
4-5 mA of current, some users might wish to disable it for power-sensitive applications.

2.1 AI0 – AI7

Hardware

The LabJack U12 has 8 screw terminals for analog input signals. These can be configured
individually and on-the-fly as 8 single-ended channels, 4 differential channels, or combinations
in between. Each input has a 12-bit resolution and an input bias current of ±90 µA.

• Single-Ended: The input range for a single-ended measurement is ±10 volts.

• Differential channels can make use of the low noise precision PGA to provide gains up

to 20, giving an effective resolution greater than 16-bits. In differential mode, the voltage
of each AI with respect to ground must be between ±10 volts, but the range of voltage
difference between the 2 AI is a function of gain (G) as follows:

G=1 ±20 volts
G=2 ±10 volts
G=4 ±5 volts
G=5 ±4 volts
G=8 ±2.5 volts
G=10 ±2 volts
G=16 ±1.25 volts
G=20 ±1 volt

The reason the range is ±20 volts at G=1 is that, for example, AI0 could be +10 volts and AI1
could be -10 volts giving a difference of +20 volts, or AI0 could be -10 volts and AI1 could be
+10 volts giving a difference of -20 volts.

Figure 2-2 shows a typical single-ended connection measuring the voltage of a battery. This
same measurement could also be performed with a differential connection to allow the use of
the PGA. In general, any single-ended measurement can be performed using a differential
channel by connecting the voltage to an even-numbered analog input, and grounding the
associated odd-numbered analog input (as shown by the dashed connection to AI1 in Figure 2-

2).

Figure 2-2. Single-ended measurement.

Figure 2-3 shows a typical differential connection measuring the voltage across a current shunt.
A differential connection is required when neither leg of the shunt is at ground potential. Make
sure that the voltage of both AI0 an AI1 with respect to ground is within ±10 volts. For instance,
if the source (Vs) shown in Figure 2-3 is 120 VAC, the difference between AI0 and AI1 might be
small, but the voltage from both AI0 and AI1 to ground will have a maximum value near 170
volts, and will seriously damage the LabJack.

Whether or not the ground (GND) connection is needed (Figure 2-3) will depend on the nature
of Vs.

Figure 2-3. Differential measurement.

Figure 2-4 shows a single-ended connection used to measure the output voltage of a typical
voltage-divider circuit. The voltage divider circuit is a simple way to convert a varying resistance
(thermistor, photoresistor, potentiometer, etc.) to a varying voltage. With nothing connected to
Va, the value of the unknown resistance, R2, can be calculated as:

R2 = Va*R1 / (Vs-Va),

where Vs is the supply voltage (+5V in Figure 2-4).

When Va is connected to AI0, as shown in Figure 2-4, the input bias current of the LabJack
affects the voltage divider circuit, and if the resistance of R1 and R2 is too large, this effect must
be accounted for or eliminated. This is true for any signal with too high of a source impedance.

All measuring devices have maximum analog input bias currents that very from picoamps to
milliamps. The input bias current of the LabJack U12’s analog inputs varies from +70 to -94
microamps (µA). This is similar to an input impedance of about 100 kΩ, but because the current
is nonzero at 0 volts, it is better to model the analog input as a current sink obeying the following
rule:

Iin = 8.181*Va – 11.67 µA

Figure 2-4. Single-ended measurement with voltage divider circuit.

Because the input bias current is known, as a function of input voltage, the simple voltage
divider equation can be modified as follows to account for input bias current:

R2 = Va / [((Vs-Va)/R1) – (8.181µ * Va) + 11.67µ]

As an alternative to the equation above, Va can be buffered by a single-supply rail-to-rail
operational amplifier, and the original simple voltage divider equation can be used. This
solution works for any single-ended signal which stays between 0 and +5 volts. Some op-amp
choices are:

• TLV2462

• LMC6482

• MAX4166

Software

Readings from the analog inputs are returned by the functions AISample, AIBurst, and
AIStreamRead.

AISample returns a single reading of 1-4 channels, and takes up to 20 ms to execute, providing
a maximum date rate of at least 50 Hz per channel. This function also controls the status LED
and sets the state of the IO pins.

AIBurst acquires multiple samples of 1-4 channels at a hardware-timed sample rate of up to
8192 Hz. The acquisition can be triggered based on the change of state of an IO pin. This
function also controls the status LED and returns the states of the IO pins (which are read every
4 samples).

Internally, the actual number of samples collected and transferred by the LabJack during an
AIBurst call is the smallest power of 2, from 64 to 4096, which is at least as big as numSamples.
The execution time of this function, in milliseconds, can be estimated as (auto or turbo mode):

30+(1000*numSamplesActual/sampleRate)+(0.4*numSamplesActual)

numSamples = numScans * numChannels
sampleRate = scanRate * numChannels

AIStreamRead is called periodically during a stream acquisition started by AIStreamStart. Each
call retrieves multiple samples of 1-4 channels from the LabJack stream buffer, along with the
states of the IO pins (read every 4 samples). Hardware-timed sample rates of up 1200 Hz are
available.

2.2 AO0 & AO1

The LabJack U12 has 2 screw terminals for analog output voltages. Each analog output can be
set to a voltage between 0 and the supply voltage (+5 volts nominal) with 10-bits of resolution.

The output voltage is ratiometric with the +5 volt supply, which is generally accurate to ±5% (see
Appendix A). If an output voltage of 5 volts is specified, the resulting output will be 100% of the
supply voltage. Similarly, specifying 2.5 volts actually gives 50% of the supply voltage.

If improved accuracy is needed, measure the +5 volt supply with an analog input channel, and
the actual output voltage can be calculated. For instance, if an analog output of 2.5 volts is

specified and a measurement of +5V returns 5.10 volts, the actual output voltage is 2.55 volts.
Alternatively, the analog output can itself be measured with an analog input.

There is a 1

st

order low-pass filter on each analog output with a 3dB frequency around 22 Hz.

Software

The analog outputs are set using the function AOUpdate, which takes up to 20 ms to execute,
providing a maximum update rate of at least 50 Hz per channel. This function also
controls/reads all 20 digital I/O and the counter.

2.3 IO0 – IO3

Connections to 4 of the LabJack’s 20 digital I/O are made at the screw terminals, and are
referred to as IO0-IO3. Each pin can individually be set to input, output high, or output low.
These 4 channels include a 1.5 k Ω series resistor that provides overvoltage/short-circuit
protection. Each channel also has a 10 MΩ resistor connected to ground.

One common use of a digital input is for measuring the state of a switch as shown in Figure 2-5.
If the switch is open, IO0 reads FALSE. If the switch is closed, IO0 reads TRUE.

Figure 2-5. IO used to detect the state of a switch.

While providing overvoltage/short-circuit protection, the 1.5 k Ω series resistor on each IO pin
also limits the output current capability. For instance, with an output current of 1 mA, the series
resistor will drop 1.5 volts, resulting in an output voltage of about 3.5 volts.

Software

The functions AOUpdate or DigitalIO are used to set the direction, set the state, and/or read the
state, of each IO pin. Both of these functions take up to 20 ms to execute, providing a
maximum update rate of at least 50 Hz per pin.

The function AISample can set/read the state of each IO, and the function Counter reads the
state of each IO.

The functions AIBurst and AIStreamRead, take a reading of the IO states and return it with the
analog data. The states of the 4 IO are read every 4 samples, providing a data rate of up to
2048 Hz per pin.

2.4 D0 – D15

Connections to 16 of the LabJack’s 20 digital I/O are made at the DB25 connector, and are
referred to as D0-D15. These 16 lines have no overvoltage/short-circuit protection, and can
sink or source up to 25 mA each (total sink or source current of 200 mA max for all 16). This
allows the D pins to be used to directly control some relays. All digital I/O are CMOS output and