how to wait a few seconds after switch action

[木虫]

How to Reduce Errors When Switching Low-Voltage or current Signals？

Recently NI website uploaded a "low_level_measurements_resource_kit", which said you should wait a few seconds after the relay is closed because these relays needs a constant current to be supplied to them in order to maintain a given state or positon.  But when you scan a list channels(break before make mode and no action mode) you can not add time-lapse after SWTICH action. In other words it is hard to wait a few senconds after relays action. I did not find this in LabVIEW examples also.

I'd like to know that how can I achieve what suggested in  low_level_measurements_resource_kit?

Thanks advance

[chericks1]

Hi 木虫 ,

Are you performing a measurement after each relay closure?  If so, when configuring the measurement device, select a trigger delay to increase the settling time. 

With a NI DMM, you can set the trigger delay with the niDMM Configure Trigger VI.  The Trigger Delay (sec) input specifies the time the DMM waits after it has received a trigger before taking a measurement.

Attached is more details on the niDMM Configure Trigger VI.

Hope this helps!

Chad Erickson
Switch Product Support Engineer
NI - USA

[小木虫]

thanks for your help.  I use niswitch DMM switch synchronous scanning example in my test. I did not find what you suggest in attched file. Whether this example can not be used for what I want to carry out? Whether I should use niswitch DMM switch handshaking example? what is the difference between this two example?

Best regards

[chericks1]

Hi 小木虫 ,

With the Synchronous Scanning example, you specify the appropriate amount of time between DMM measurements with the niDMM Configure Multi Point VI's Sample Interval (sec) input. 

Use this example when you want a programmed delay interval between DMM measurements.
Use the Handshaking example when you want hardware triggers to determine when the switch actuates and DMM measures.

Hope this helps!

Chad Erickson
Switch Product Support Engineer
NI - USA

[小木虫]

Hi,Chad Erickson, thank you very much for your help.

I have a question now: which example do you think is precise when used for measuring a list of channels (voltage)?  According to the suggestions on NI website, I think handshaking mode would be better.

 I think these two examples must be programmed for different aim.

Best regards

小木虫

[木虫]

Hi,Chad Erickson,thanks for your help,i have a new question now:

Whether the software scanning (in attached fig.) can achieve "delay 50 ms after relay action and then measure ..."? If it does not work, how can I achieve this aim using software scanning example?

On the other hand, when i measure a list currents, I can not find the module to setup time delay (as that in handshaking example).

Best regards

小木虫

[chericks1]

Hi 小木虫,

I agree that handshaking is ideal because software is eliminated, resulting in a hardware deterministic process, and tighter integration between the DMM and switch devices.  Deterministic timing is desired by many of our customers for multiple reasons; especially when optimizing for speed.  

When a software delay or repetitive time interval is desired between measurements, handshaking or synchronous scanning can be used.  If a variable or user-modifiable time interval is desired, software scanning is available.

Let me know if you have further questions!

Best regards,

Chad Erickson
Switch Product Support Engineer
NI - USA

[chericks1]

Hi 小木虫,

This is a response to your post on 08-04-2008 01:42 AM, where you asked the following questions:

Whether the software scanning (in attached fig.) can achieve "delay 50 ms after relay action and then measure ..."? If it does not work, how can I achieve this aim using software scanning example?

As shown in the picture, adding a software wait will work.  The next VI in this sequence would make the measurement.

On the other hand, when i measure a list currents, I can not find the module to setup time delay (as that in handshaking example).

I may not understand this comment.  I assume you are asking how to program a time delay with software scanning.  Am I correct?  If so, then you are correct in adding a software wait (as shown in your attached picture above).

Hope this helps!

Chad Erickson
Switch Product Support Engineer
NI - USA 

[木虫]

Hi ,Chad Erickson, thanks for your answers.

I tested handshaking example and found some questions:

When I setup time delay (10 or50 ms) in DMM measurement strigger.vi, the handshaking example doenn't work and some error was reported when the programe was stopped"max time exceeded before operation completed". When the time delay is 0, this example works well. But at this time, some results are obviously wrong(compared to that measured using synchronization example).  I measured  more than 3 channels(voltage about -100mV) in above test. I do not know whether some parameters should be setup correctly before test?

Another question is: why while loop is used in handshaking example? why not connect niDMM initiate. vi directly to niDMM fetch multi points.vi just as that in synchronization example.

Best regards

小木虫

[chericks1]

Hi 小木虫,

The "max time exceeded before operation completed" error is likely reported because the niDMM Fetch Multi Point VI is not completed within the time interval specified by its Maximum Time (msec) input.  Try increasing the value of Maximum Time (msec) to avoid this error.

The results may differ because the Trigger Delay (sec) input of the niDMM Configure Trigger VI appears to only affect the first measurement of a continuous acquisition.  The subsequent measurements do not have a delay inserted after their respective triggers.  If you require a repetitive delay to be inserted after each trigger, increase the settling time of the DMM by including a niDMM Property Node and the Settle Time property.  Once the property node is dropped on the block diagram, select Configuration >> Advanced >> Settle Time. 

The while loop is used in the handshaking example because the acquisition is continuous.  The Sample Count input of the niDMM Configure Multi Point VI is intentionally set to 0, and the DMM will continue fetching multiple points until the user stops the VI.  On the other hand, the sychronous scanning example performs a multi point acquisition.  After the specified number of samples has been acquired, the VI is finished.  If you want the user to stop an acquisition, a while loop is appropriate.

Best regards,

Chad Erickson

Switch Product Support Engineer
NI - USA