Triggering and Recording for specific duration

[nnnsh]

Enclosed is the VI which I am using to trigger a electrical circuit for generating a spark.

My system is very simple wherein I am generating spark in a vessel (by a triggred electrical pulse to HV generator) and measuring the pressure and temperature for a specified time of X and Y seconds after the spark.

Part A:

On a single Boolean input (TRUE) I would like to have following:  

1. The Trigger pulse (USB 6009 device) should start and last for say 1.5 sec. which is input to my electrical circuit. Two DAQ max is used since current from one port is not sufficient to trigger the HV generator - electrical circuit.

2. At the same time the pressure inside the vessel should be recorded for X sec. only (writing to file)
3. Simultaneously the temperature should also be recorded for Y sec. only (writing to file)

In the present VI, I have to keep the “Auto fire and record” button pressed to write the data to file. I have set up preset time for the trigger pulse.

 

After triggering and recording for specific time 1.5, X and Y sec. the Boolean should go to FALSE position since long duration pulse to electrical circuit can be damaging.

*** REQUEST SOME-ONE HELP ON THIS MATTER ASAP. ****

Part B:

Later I have to record the values of current and voltage measured at three locations by Tektronix TDS 3034B Scope (channel 1, 2  and 3) for a duration of 300 nano-seconds after the spark has occurred (i.e. say P sec. after trigger pulse and recording till P + 300 duration)

This simple logic seems to be more difficult than, I expected, can some one please help
/ suggest in the right direction. (**VI attached**)

Sorry for the language – New to Labview and not an electrical engineer. So pl. explain.

THANKS

Email: nnnsh@yahoo.com

[nnnsh]

Hope the VI file gets attached 

[xseadog]

Hi nnnsh

Welcome to Labview

A pulse is usually a short duration ! 1.5 secs in electrical terms is a very long pulse. I have not got the specs for the 6009 in front of me but sounds like you are pushing the current parameter. Have you thought about using a relay ?

Your vi as it stands in its present form will only capture 4 samples for you pressure measurement and 12 samples for your temperature. You need to amend the number of samples that you wish to capture!

Your description appears to be a motor ? If this is the case then you need to be capturing at least 1024 samples so that you obtain the correct pressure map profile. remember the less you capture the more difficult it is to attain a useful  profile.

you also need to delete one of your DAQ tasks. 'Merge your sampling channels into one task!

Suggest that you check out the examples provided by NI under Help option.

Its late
so If I have time  to morrow I 'l see if i can dig up an appropiate example-- no promises

xseadog

[nnnsh]

Thanks xseadog the quick and point-wise reply.

My system is a combustion chamber, wherein I am mixing methane and air and carrying out explosion within the chamber with a capacitive spark discharge. Its not mere a capacitive spark but a circuit is designed for generating HV across the spark electrodes. FOR WHICH the trigger pulse is required.

The pulse (5 V and 0.85 mA) is used in the primary of the HV generator which is prepared to give me output of around 40- 50 KV. This HV is then used to generate spark.

I understand that 1.5 sec is bit long time, but with very small duration pulse the necessary voltage is not generated, hence I requested for 1.5 sec., which I wish to modify to smallest value. Maybe the inherent time lag in the system requires that this pulse is for specific duration.

All measurement pressure, temperature, current (voltage) values starts after the spark is generated. As advised I will increase the number of samples.

A nudge in direction of how to delete one “DAQ task and merging the channels” will be helpful. I am also presently working on that.

I have extensively searched the NI examples and only after that put a question in discussion forum.

further help requested

THANKS

[xseadog]

Hi

what DAQ card are you intending to use?

xseadog

[nnnsh]

Hi,

The DAQ card is NI USB 6009 (http://sine.ni.com/nips/cds/view/p/lang/en/nid/14605)

The Digital output is 5 V (max.) and 8.5 mA  per channel as per the specifications.

Well I want the trigger current to be more than 10 mA, hence two ports are used.

Thanks

[xseadog]

Hi

attached screen shot highlights an example you should attempt to use.

cont Acq&Graph Voltage -Analog SW trigger.vi

Rather than attempt to run before you can crawl I suggest that you wire up the pressure sensor to AI0. Provide a current source independant of USB 6009 to
fire the HV generator. in first instant just use a sflick switch!

If you have set up system then your graph will illustrate the pressure profile.

Remember to set up the USB 6009 in your MAX  configuration before hand.

With regard to the current source I would look at using a relay controlled by the 6009 rather than using the 6009 directly

xseadog

[xseadog]

Hi

what actual sensor are you using to detect pressure deviation?

like wise what termal couples are you using?

xseadog

[nnnsh]

Hi xseadog,

Sincere apologies for inordinate delay in reply.

Was blocked up with actually setting up the experiment in physical sense. Keeping all the bits and pieces in right place.

The pressure sensor / transducer is Omega PX219 with output 0 – 5 V. Recording pressure reading every 0.001sec. immediately after the spark trigger (USB 6009 signal) is switched ON. (through labview)

The temperature is K type thermocouple. Recording temp every 1/12 sec.(0.0833 sec) after spark.

I have made a provision to trigger the spark manually – through push button. But this mode requires me to start recording press and temp., before pushing the button to generate spark. Hence keen on using the trigger initiated through Labview.

Regarding relay controlled by the 6009, I understand that circuit is similar to that. The HV is generated through an EHT pulse generator, which is ready now, the only thing is it requires a trigger of 5 V and more than 10 mA.

Manually when we generate spark, we do not require the USB 6009, so we get spark every time when button is pushed, it was only during the Labview trigging we diagnose this prob. And hence clubbed the two channels of 6009.

As of now the loop time “Auto fire and record” which is the key for firing –spark generation –runs every 1.011 sec. can you suggest, how to reduce the loop time ?.

Does the DAQ’s consumes time or which step consumes more time. I would request your comments.

Thanks for the continuous help / replies.

nnnsh