Using the NI 1127 switch with NI 4070 how can I scan current measurements?

[dbngc]

How can I scan through channels and make current measurements without losing power to the device under test.  Or at least only break a connection for a small amount of time when a measurement is asked for?

[chericks1]

Hi dbngc,

If you are able to provide a diagram or example showing where and how you are measuring currents within the device(s) under test, I would be able to assist you better in designing a test solution. 

Without this information, the best advice I can give is that you maintain power to the device under test when connecting the NI PXI-4070 DMM to your circuit.  After the NI PXI-4070 is connected, disconnect the initial circuit to allow the current to flow completely through the NI PXI-4070.  Before moving to the next measurement, reconnect the initial circuit.  Continue with this procedure to prevent losing power to the device(s) under test.

The NI SCXI-1127 switch module can be used as a multiplexer with its channels connected to each circuit where you want to break it, and its COM connected to the NI PXI-4070.  Another general-purpose relay, or multiplexer (depending on the device(s) under test and measurement locations), can be used to disconnect the initial current loop to allow the current to flow completely through the NI SCXI-1127 and NI PXI-4070.

Let me know if you have any questions!

Chad Erickson
Switch Product Support Engineer
NI - USA

[dbngc]

Basically, I'm stressing 20 parts by applying a certain voltage across them.  The parts are wired in series.  The 1127 switch would have to be initially closed.  In order to measure current across each part, I have to break all the connections and only close the connection to the part being measured.  Scan through the other parts the same way.  Once the measurements are completed, close all connections again to continue the stress.  See the attachment.

thanks

[chericks1]

Hi dbngc,

May I ask what is the reasoning behind measuring current between the individual DUTs?  Ideally, it appears the current should be the same at each measurement location. 

In this configuration, it appears you may need one general purpose relay between Vcc and Dut 1, between each Dut x and x+1, and Dut 20 and Gnd to disconnect the initial circuit to allow the current to flow through the DMM and switch modules. 

Can this setup be reconstructed such that Vcc is connected to each DUT in parallel?

Thanks!

Chad Erickson
Switch Product Support Engineer
NI - USA

[dbngc]

The parts are capacitors so as the part degrades, the leakage current increases.  I could measure the total current as you suggest, but that would not tell me which part degraded and by how much.  To do that I have to measure the current indivually for each device.  To maintain a constant voltage (since the voltage will drop as well) we have a feedback loop on the power supply to compensate, keeping the devices at a constant voltage.  The setup will work if I could somehow programmatically close all the swtiches on the 1127.  By default the 1127 switches are all open then I can only connect a pair at a time.  I need to be able to close the switches at once. 

[chericks1]

Hi dbngc,

When using the SCXI-1127 as a multiplexer, you are allowed to connect only one channel to COM at a time.  However, if you control individual relays on the module using the relay API, you can connect every channel to COM simultaneously.  Keep in mind the relays are in a DPST arrangement, so closing one relay actually connects two channels (i.e. ch0+ and ch0-) to COM.  Refer to the Hardwire Diagram of the SCXI-1127 in the NI Switches Help for more information.

I have to say I don't fully understand the configuration.  Even if you can connect all channels simultaneously, how does that help?  Don't you still need a general purpose relay in between each Dut in addition to the SCXI-1127?  The SCXI-1127 connecting to the DMM and the general purpose relay disconnecting the previous current path?

I've attached the configuration I was thinking of earlier when I mentioned connecting Vcc to each DUT in parallel.  The advantage of this configuration is that you could supply a constant voltage.  The disadvantage is that you would require two SCXI-1127s.  One to connect to the DMM and one to disconnect the previous path.

Hope this helps!

Chad Erickson
Switch Product Support Engineer
NI - USA

[dbngc]

This exactly what I wanted.  All I need to know now is how to close all the switches on the 1127.

[chericks1]

Hi dbngc,

There are multiple programming methods to control the SCXI-1127.  Two options are the NI-Switch and DAQmx Switch APIs.  Both of these options provide relay VIs and functions to control individual SCXI-1127 relays.

NI-Switch
niSwitch Relay Control VI
niSwitch_RelayControl function

DAQmx Switch
DAQmx Switch Close Relays VI
DAQmxSwitchCloseRelays function
DAQmx Switch Open Relays VI
DAQmxSwitchOpenRelays function

Refer to the Hardware Diagram attached below (from the NI Switches Help) that shows the name of each individual relay within the SCXI-1127.  Note that multiple relays may need to be connected to create a channel to COM connection.  For example, to route CH8+ / CH8- to COM0+ / COM0-, relays "CH8" and "BC01" must be closed.  As mentioned before, also note that closing individual relays actually connects two channels at a time (i.e. CH0+ and CH0-).

Let me know if you have further questions!

Chad Erickson
Switch Product Support Engineer
NI - USA