ADU71 USB to Current Output Interface ( 4-20mA, 0-20mA Transmitter )

The ADU71 USB to Current Output Interface is a USB bus powered current loop source for driving 4-20mA or 0-20mA input devices. The ADU71 can also be used with external resistors to provide 1-5VDC, 0-5VDC or 0-10VDC signals for variable frequency drives, valves etc. The ADU71 internally generated 24VDC loop supply eliminates the need for an external loop power supply. This low-cost USB to Current Output Interface is easy to use with VB, and Visual C++ or .NET via standard HID drivers included with Windows 98,2000,XP,7,8. A mini-driver ( DLL )* is also provided allowing control using standard ASCII commands using familiar readfile , writefile commands. The ADU71 includes a 10' USB cable and is available in a flange mount enclosure with a DIN rail mount option.

IMPORTANT: The ADU71 requires the use of the Aduhid.dll V2.0.  See bottom of this page for download links.

Command Summary

The ADU71 powers up with its output disabled ( High Z ) .  The following commands are used to set the range, output current, slew rate, watchdog settings and check the ADU71 status.

Setting Range and Output Current

The ADU71 operates in either a 4-20mA or a 0-20mA range. The range is set by the commands used to set the desired output current. The current is set using a 16-bit integer number ranging from 00000 ( 0%FS)  to 65535 ( 100% FS )   The commands to set the output current and range are:

WRnnnnn              Sets output current to nnnnn and sets range to 0-20mA ( nnnnn = 00000 to 65535 )

WLnnnnn              Sets output current to nnnnn and sets range to 4-20mA  ( nnnnn = 00000 to 65535 )

Examples;

WR32768               Sets range to 0-20mA and sets current to 32768/65535 X 20 = 10mA

WR65535               Sets range to 0-20mA and sets current to 65535/65535 X 20 = 20mA

WL32768               Sets range to 4-20mA and sets current to 32768/65535 X 16 + 4 = 12mA

WL00000               Sets range to 4-20mA and sets current to 00000/65535 X 16 + 4 = 4mA

Reading Output Current

The ADU71 output current setting can be read back as a 16-bit number from 00000 ( 0% FS ) to 65535 ( 100% FS ). The 16 bit integer number returned represents the current setting and the output current can be calculated depending on which command was used to set the current. 

If the 0-20mA range ( WRnnnnn ) was used to set the output current the output current setting can be calculated using the following formula;

nnnnn/65535 X 20 = Output Current Setting

If the 4-20mA range ( WLnnnnn ) was used to set the output current the output current setting can be calculated using the following formula;

nnnnn/65535 X 16 + 4 = Output Current Setting

The command to read back the present current setting is;

RD                          Returns present current output setting.

For example;

RD

returns...

32768                    

If output current was set with the WRnnnnn command , output current setting is 32768/65535 X 20 = 10mA

If output current was set with the WLnnnnn command , output current setting is 32768/65535 X 16 + 4  = 12mA

RD

returns...

12657                    

If output current was set with the WRnnnnn command , output current setting is 12657/65535 X 20 = 3.86mA

If output current was set with the WLnnnnn command , output current setting is 12657/65535 X 16 + 4  = 7.09mA

Setting the Slew Rate

The ADU71 slew rate can be set to eight different rates ranging from 1ms to 10 seconds. The slew rate is the rate at which the output changes and the specified rate is the time it takes for the output to change from 0% FS to 100% FS. The slew rate settings are:

0    -     1ms

1    -     10ms    ( Default or power-up setting )

2     -    50ms

3     -    100ms

4     -    500ms

5     -    1s

6     -    5s

7      -   10s

To set the slew rate the following command is used;

SRn                 Sets slew rate to desired rate. ( n = 0 to 7 )

Example;

SR3                  Sets slew rate to 100ms

The slew rate can be read back using the following command;

SR                   Returns present slew rate setting

Example

SR

returns...

5                      Slew rate is set to 5 seconds.

 Using the Watchdog Feature

The ADU71 features a host watchdog function that is used to disable the output current if the host application becomes inactive for a specified time period. When enabled, the watchdog timer will be reset with every write to the ADU71 by the host software. 

0    -     OFF      ( Default or power-up setting )

1    -     100ms  

2     -    1s

3     -    5s

4     -    10s

To set the watchdog operation the following command is used;

WDn                 Sets watchdog. ( n = 0 to 4 )

Example;

WD3                  Sets watchdog time to 5 seconds

The watchdog setting can be read back using the following command;

WD                   Returns present watchdog setting

Example

WD

returns...

0                      Watchdog setting is 0. ( OFF )

IMPORTANT:

1. When the watchdog times out, the ADU71 output current will go to zero and the output will switch to high impedance mode.  To re-enable the output after a watchdog timeout occurs use either the WRnnnnn or WLnnnnn command.

 2. If the host computer goes to sleep and suspends the USB connection,  the ADU71 will turn off the output immediately regardless of watchdog timer settings.

Using the Status Feature

The ADU71 features a status function that returns a numeric indication of the ADU71 operating status. The five operating status conditions are:

0    -     Loop Output Disabled      ( Default or power-up setting )

1    -     Loop Enabled   ( No fault )  

2     -    Slew  Active  ( Not a fault condition. Simply an indication that the output is presently slewing )

3     -    Loop is OPEN  ( Fault condition )

4     -    Over Temperature  ( Fault condition.  ADU71 core above 150C )

The operating status can be read back using the following command;

STA                   Returns present status.

Example;

STA

returns...

1                      Loop is enabled and no fault is detected.

The ADU71 Reset Command

The ADU71 features a reset command than can be used to return the ADU71 to the power on state at any time.

The reset command is ;

RST

ADU71 Test Software and V2.0 DLL

The ADU71 is a Full Speed USB product and requires the use of the new Aduhid.dll Ver 2.0 or higher.

The V2.0 DLL and V2.0 AduHidTest Software can be downloaded here:

ADUHidTest V2.0 and Dll  ( 32 Bit )  ( Operates on both 32 and 64-bit computers)

ADUHidTest V2.0 and Dll  ( 64 Bit )  ( Use this one only if developing 64-bit applications.)

An AduHidTest tutorial is available in our programming section, or by clicking HERE.

Back to Products Page