PXI processes synchronisation/timing

[miraz]

Hello, I'm a LV newbie and I would like to get some hint on precise timing and synchronisation, please... I have not found any suitable example so I'm posting it here.

What I want to do is a simple spectroscopy: step the voltage at a High Voltage power supply and at each step perform a (let say) 20 seconds measurement. The measurement means counting TTL pulses from the detector setup and simultaneously reading the values from a high precision voltmeter every ~2 seconds.

I have a PXI-1042 system with PXI-6221 M series DAQ, PCI-6601 and other modules. The TTL pulses go simply via BNC cable to the SCB-68 box and are counted on one digital input channel of the PXI-6221, works fine. The expected count rate coming from the detector is rather low, max. 100 Hz. Also the communication with the HV power supply (RS232) and voltmeter (GPIB) is flawless. The only and biggest problem is the overall synchronisation 🙂

Please have a look on the attached figure, it shows what I would like to get, in principle. The attached VI is the first attempt, not working properly: the stepping of the HV power supply is not "waiting" for the specified period of time on each step but it sets new and new values... I'm also unsure about the proper use of the Timed Loops. 

Could someone please check the timing structures in the VI and provide better solution? I'm pretty sure that the hardware provides great possibilities of precise timing but I have no experience with that yet 😞 Any hints would be much appreciated!

[Marco_Brauner]

Hi, 

when you think about timing and synchronization of multiple measurement units inside a program, you have to distinguish a few things.

As far as I could see in your VI, you want to achieve that the edge counting of the counter and the measurement of the high voltage should be synchronized in some way.

Should they start together and run for 20 secs or should every analog measurement be taken at a certain edge arriving at the ctr input? This would be hardware triggering.

You also can do software triggering and syncing with the timed structures. Please tell me what you desire.

Marco Brauner NIG 

[miraz]

Hello Marco, many thanks for Your reply!

What I would need is to start simultaneously the counter of the pulses and the voltmeter readout. These two processes should run "together" but "independently" - one should not influence the other one.

The pulses represent signals from a detector, they come randomly and with a low rate, max. 100 Hz. So the counter should "run all the time" - with some high frequency, 1 kHz or so (?).

On the other hand, the voltmeter readout should happen regularly, every about 2 seconds. Precisely, one readout takes ~1.8 sec, and I would like to have a possibility to adjust this time in the program.

These counter and voltmeter processes should run precisely for some given time - for example 20 seconds, possibly adjustable by the user before the program starts.

I am able to run both processes but I do not know how to make them run together for precisely e.g. 20 seconds...? Could You please suggest some suitable timed structures?

[Marco_Brauner]

Hi, 

I know your last post has been since quite a while.

Anyway, here is an example for you. 

M. Brauner NIG 

[miraz]

Hallo Marco,

thanks a lot for Your reply! Unfortunately, I can not open Your vi because it's version 9.0 and I have only LV version 8.6 here... Could You please post here the example in version 8.6 ? Many thanks, Miroslav

Message Edited by miraz on 03-04-2010 04:15 AM

[Marco_Brauner]

Hi Miroslav,

here it is for LV 8.6

regards

M. Brauner NIG