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2638A DAQ unit (multiplexor) example in COMPASS

Fluke 2638A Multiplexer Setup Using its Internal DMM to Read Volts

This is from the Sample/Example 2638A Support Device that is already in the COMPASS for Pressure (v5.0.50 and higher) new install database as an example. If you don’t already see this in your database as a Support Device then you can get it from the hidden example database. See the COMPASS help file for instructions on how to search for, and use, example setups. Also this web page, COMPASS Example Database

This example only shows the voltage output setup but the other outputs; amps, frequency and ohms are setup in the same way. For voltage output the 1586A Super-DAQ works the same way so this method and setup will also work for the 1586A when using it to calibrate pressure devices.


The same information is in the attached file to download, save or print.

The information on the Calibration tab is optional.

In the 2638A Support Device setup, go to the Communications Tab. Here is a view for RS232 setup using the USB output on the 2638A. Note that the Command Terminator can be set to CR or CR LF by remote commands to the 2638A. If the replies are on the same line, or the next line (erroneously) check this setting in the 2638A.


Go to the Output Tab and select the Voltage ScanList output

Output Tab, [Edit Output] Button, Raw Output

 Output Tab, [Edit Output] Button, Final Output


Output Tab, [Edit Commands] Button

Output Tab, [Edit Commands] Button, Read Command. Should look like this.

A ReplyParser macro named "ParseScanListRead" is used to parse the comma-separated reply that is received from the 2638A. If you don't have this macro in the drop-down list, see the below attached file to copy and paste it into a new macro in the COMPASS Macro Editor.


Save any changes by pressing the disk icon, then press the [OK] button to close this window.

Go to the Set Tab, select the “MUX Ch ScanList” output then click the [Edit Set] Button.

Set Tab, [Edit Set] Button, Raw Set

Set Tab, [Edit Set] Button, Final Set


Set Tab, [Edit Commands] Button

Set Tab, [Edit Commands] Button, Initialize Command, for MUX Ch ScanList. A GetCommand macro named "CreateScanList2638A" is used to create the command that will be sent to the 2638A to set the active channels. If you don't have this macro in the drop-down list, see the below attached file to copy and paste it into a new macro in the COMPASS Macro Editor.

The rate is set to fast with the RATE FAST command (change if desired, see the 2638A Programmer's guide for more information).

Set Tab, [Edit Commands] Button, Set Command. COMPASS needs a reply to we just use the *IDN? command. The reply is not used for anything.

 Save any changes by pressing the disk icon, then press the [OK] button to close this window.

Comments tab, all comments are optional. Setup Info section is shown during test initialization.


Now run a manual test to check if it’s working by this menu path;. [Run],<Run Manual Test>.

Ten identical DUTs are chosen for this example. Choose more than one of the same DUT by double-clicking it again. COMPASS will ask you how many of them you want in the test.

Enter the serial number, check the "Use Multiplexor" box, then enter the multiplexer channel in the “Channel” box. The CreateScanList2638A will automatically change a channel entered as 1 to 20 into 101 to 120 (card 1), and from 21 to 40 into 201 to 220 (card 2), and 41 to 60 into 301 to 320 (card 3). The channel will automatically increment for any more DUTs. Edit as necessary. Choose the 2638A output as the Voltage(V) device at the bottom left.


For the multiplexer choose the 2638A output labeled “MUX Ch ScanList”. Choose a Reference Pressure and Test Pressure Control devices if you want to.

The setup and macros work for Auxiliary devices also.

The screen for the 2638A shows that it has two outputs; a read output “Voltage Scan List” and a set output “MUX Ch ScanList”

Slider to left

Slider to right

If you chose an Auxiliary device its setup screen appears next. It's on channel 18 (118) in this example.

The final verification screen. Make sure the 2638A is not in DMM mode when pressing the [Finish] button or it will error and not work.

Here is the COMPASS Run Window

The interface spy is shown to the right of the 2638A's window. Display it by clicking on the yellow value for an output (like Voltage ScanList) and selecting “Display Interface Spy” from the drop-down list. More details on this here, Display Interface Spy in COMPASS for Pressure

Note that the 2638A is switching from channel 1 to 10 (and 18 for the Aux device), and the voltage is being read for each channel appropriately.

The 2638A web page is here, 2638A

End of Article

If you have questions please contact Fluke Calibration Pressure or Flow Technical Support at the below link or by calling 1.877.355.3225

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