How can I send a trig out from my PXI system

[SamEJ]

I have a PXI 4072 DMM and PXI 2532 switch box and 2640 terminal block. The switch is configured as a 4*128 matrix and is connected to an external current stimulator. The stimulator requires a trigger input and to accurately synchronize the system I would like to use a trigger generated NI PXI system and route it to the stimulator. How can I do this?

I have been trying to use the AUX I/O but I can't seem to get any pulse out of the trigger out.

[mallorim · Accepted solution]

Hello Sam,

With regards to working with triggers with a DMM and a Switch, both of these modules use triggers to perform handshaking scanning- basically using triggers to synchronize the 2532 connecting channels to the common for DMM Measurement. The process is as follows:

1. The Switch makes a new connection: ch 1 to COM.

2. The switch settles and sends a "Switch Advanced" trigger to a TTL line on fht PXI Backplane: PXI_Trig0

3. The DMM watches this TTL and when it sees the trigger, it knows that the switch connection is good and it can now take an accurate measurement.

4. The DMM is done taking the measurement and sends a "Measurement Complete" trigger to the backplane: PXI_Trig1

5. The Switch was watching this second line, and uses the MC Trigger to advance to the next item in its scan list.

Some things to note: Switch Executive is not capable of scanning with triggers. 

Also, these trigger locations (PXI_Trig0 and PXI_Trig1 in the example above) are configured by the user. Take a look at the Example Program niSwitch DMM Switch Handshaking to see how the NI-DMM and NI-Switch triggers are configured.  It is possible to output the DMM Measurement Complete trigger to the AUX connector on the front of the DMM. The AUX connector is meant to be used when a DMM is controlling a switch in an SCXI Chassis, like out SCXI-1130. The SCXI-1357 can be used with and AUX cable to let the DMM control the SCXI chassis and send the trigger to the SCXI switch.

I guess the question for you is what trigger exactly do you want to export to your simulator? I told you above about the triggers the DMM and Switch use. However, if you want to use some sort of initial start trigger to synchronize things you might be out of luck.  The DMM and Switch have no way of generating such a trigger, and even if they did, you cannot use either of these to access the PXI chassis's trig lines. You would need some other module in the chassis that you could take advantage of, for instance a PXI-6651 to provide access to the Trig lines if you use the Switch advanced trigger, or a DAQ card with a counter to generate a pulse that you can use as a trigger.

Regards,

Mallori M.

[SamEJ]

Hi Mallorim,

Since the DMM cannot send an output trigger to the stimulator, I am using a serial port on the computer and getting LV to break the RTS state and using this as an input trigger to the stimulator. The stimulator is now being triggered but I'm unable to record the pulses generated from the stimulator. The stimlulator has a 60us delay from when it receives the trigger.....

The VI also uses switch executive to connect to switch the signal between the columns. 

I can view the pulses generated by the stimulator on the CRO, but I am unable to synchronize the DMM recording with the stimulator? I'm attaching the VI, could you tell me what I may be doing wrong?

Regards

Sam

[mallorim]

Hi Sam,

I wanted to clarify the order of things in your system. So as I understand it, you have a simulator which needs to be triggered to generate an output. This output is then routed through a switch to the DMM where it takes .

How many outputs does the simulator have, how many channels of the switch do you need to scan through and take a measurement?

And what is the order of the switches needed? For instance, you mentioned that the simulator needs an input trigger. Are you also triggering the DMM and the Switch connection?

You mentioned that you were unable to acquire the simulator data with the DMM. Something to check is are you properly triggering the DMM's acquisitions? On the front panel, there is a trigger source control. Immediate means that the DMM will begin acquiring points as soon as the DMM Initiate.vi is executed. External means that a trigger is coming in from the Auxiliary connector. Software means that a user presses a software button on the front panel- the change in state of the boolean value executes a case structure where a software trigger is sent to the DMM. In your VI right now, there is no front panel boolean so your software trigger is sent as soon as the case structure executes.

I also noticed in the attached VI that you are only performing finite acquisition. It is possible that you are  finishing the acquisition before the similation had begun? I would recommend increasing the number of samples to acquire or perhaps doing continuous waveform acquisition as seen in one of the example programs. Check out Cont Acq Multiple Samples- SW Sample Trig.vi

Regards,

Mallori