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Agilent 34970 Multiplexor with internal DMM example in COMPASS, power supply monitoring also

Agilent 34970A Multiplexer Setup Using its Internal DMM to Read Volts

15-August-2016 - Added additional output to Read Voltage from a Power Supply on a specific channel. See blue screen-shots at end of article for this feature. Starts at page 11 of the attached pdf file.

The below screen-shots are from the Example 34970A Support Device that is already in the COMPASS for Pressure 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 setup sends a discrete command to the 34970A for each reply from the 34970.

There's another method shown in the COMPASS Help File that is typically faster and quieter (therefore it's preferred). It sends one command to the 34970A to get all replies from the 34970A. It uses a macro to combine the COMPASS commands into one command, and is considerably faster. For this method search the COMPASS Help File for the phrase "Scanned Outputs" and read that page. The needed macro text is on that page. Here is a snippet of that page.

This example only shows the voltage output setup but the other outputs; amps, frequency and ohms are setup in the same way.

In the 34970A Support Device setup, go to the Communications Tab. Here is a view for IEEE/GPIB setup.

Here is a view for RS232 setup.


Go to the Output Tab and select the V via MUX output

Output Tab, [Edit Output] Button, Raw Output


Output Tab, [Edit ] Output Button, Final Output


Output Tab, [Edit Commands] Button, Initialize Command. When setting up as GPIB/IEEE - if the setup has a SYSTEM:REMOTE command as an initialization command the multiplexer will not switch channels. Select the INIT command and press the X above the blue/white question mark to delete this command if it is there. If you are using the 34970A in RS232 mode then this initialization command should be here.

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

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 (V)” output then click the [Edit Commands] Button.

Set Tab, [Edit Set] Button, Raw Output

Set Tab, [Edit Set] Button, Final Output

Set Tab, [Edit Commands] Button, Initialize Command, for Mux(v). If using IEEE don’t use SYSTEM:REMOTE command because it will give ERROR 514 on the 34970A. Press the X above the blue/white question mark to delete this command if it is there. If using RS232 leave the initialization command.

Set Tab, [Edit Commands] Button, Set Command, for MUX(v)

The (@[x]) text will be replaced by the multiplexer channel number when COMPASS sends this command to the 34970A. The MEAS:VOLT:DC? command is both a read and set command. It sets the DMM to volts DC, sets the channel per the specified channel during test initialization and measures the voltage. The READ? command in the Output tab is used by COMPASS to read the voltage value for the DUT.

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

Set Tab, The “Mux Channel” output is typically used when the 34970A will be used as a multiplexer only and the internal DMM will not be used. An example would be to use the 34970A to use an external DMM to read voltage on the multiple channels of the 34970A. “Mux Channel” is not used in this example.

If using GPIB/IEEE it's a good idea to verify/change settings in the [Tools], <Options>, <Interface> tab. The "Use multiple threads for IEEE-488 interface box" being checked can be important when using as a multiplexer.

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

Two 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.

Set the multiplexer channel in the “Channel” box. The channel will automatically increment for any more DUTs. Edit as necessary.


For the multiplexer choose the “Mux(V)” output not the “Mux Channel” Output. Choose a Reference Pressure and Test Pressure Control devices if you want to.

The screen for the 34970A shows that it has two outputs; a read output “V via Mux” and a set output “Mux (V)”

If the Auxiliary setup screen appears don't select the DMM or MUX in this screen.

The final verification screen.

Here is the COMPASS Run Window

The interface spy is shown on this COMPASS Run window. Display it by clicking on the yellow value for an output (like V via Mux) 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 34970 is switching from channel 101 to 104 and the voltage is being read for each channel appropriately.



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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