CLD prep. guide, page 9, 7b-6

[Blokk]

"Warn user of errors that result due to changes to the system clock if using the
Get Date/Time in Seconds function"

This is not really clear to me, could someone give me an example? Is this a scenario, when the user changes the op system clock? How can we detect such an action?

I imagine, I could add another input terminal to "tell" to the timing subVI how fast I will call it to check if the time elapsed yet (for example 25 msec). If the subVI detects that between two calls more time elapsed than 25 msec (maybe a bit higher value, like 40 msec, and not checking if we are at pause condition case), we can assume the user changed the windows clock, and we report a warning or error...

Is this correct, or I am in a confusion here? 🙂

thanks!

[JÞB]

Lets assume you are waiting a polite period like 1 second from now.  The User changes the OS Clock to sometime last week Your 1 second delay just became due to expire in a week.  

How do you code around it?  Don't.  Train the IT dept to protect the user from themselves in a reasonable manner.

Joe Engineer in his sandbox lab can probably tolerate the behavior.  Your test collecting quality records should probably both have the system time locked out and require user training with the statement "And that's why you can't reset the clock." 

[Blokk]

Ok, I understand your point. But why is this statement in the prep guide? I guess they do not deduct points if we do not code such a OS time change tester..? 🙂

I hope you do not mind if I ask another closely related question:

Here I read some useful tips for CLD exam:

http://forums.ni.com/t5/Certification/CLD-Tips-you-can-t-have-too-many/td-p/2145314

(see below)

The second sentence is obvious, if I need only simple funcionality, I can use the Express VI, like in the prep guide example CLD 1.

The first sentence mentions functions: pause, restart, stop, reset to zero.

I just do not understand what are "stop" and "restart" functions? If I have such a timer with a FGV, I can pause it or reset to zero, and set autoreset state. There is no such a action as "stop" and "restart"...

• Practice coding a timer that can be Paused, Restarted, Stopped, and Reset to Zero. Practice coding this timer from scratch. There are several examples on the forums of these timers.

• Practice using the Timer express VI (don't reinvent the wheel if this timer will work for you. NI does not deduct points for using this VI, and it is in fact a very useful tool)"

[JÞB · Accepted solution]

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@Blokk wrote:

Ok, I understand your point. But why is this statement in the prep guide? I guess they do not deduct points if we do not code such a OS time change tester..? 🙂

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I would assume so you add the relevant comment to the vi "#Deployment - Must prevent OS Timer changes using appropriate method".  I'm almost certain no one will deduct points for doing that!

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I hope you do not mind if I ask another closely related question:

Here I read some useful tips for CLD exam:

http://forums.ni.com/t5/Certification/CLD-Tips-you-can-t-have-too-many/td-p/2145314

(see below)

The second sentence is obvious, if I need only simple funcionality, I can use the Express VI, like in the prep guide example CLD 1.

The first sentence mentions functions: pause, restart, stop, reset to zero.

I just do not understand what are "stop" and "restart" functions? If I have such a timer with a FGV, I can pause it or reset to zero, and set autoreset state. There is no such a action as "stop" and "restart"...

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Simple to do additional states (Actions) that are not "Basic Express timer" functionality but may be requrements of the exam.  There are some good examples available

[Blokk]

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Jeff·Þ·Bohrer wrote:

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Simple to do additional states (Actions) that are not "Basic Express timer" functionality but may be requrements of the exam.  There are some good examples available

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I did not really find such functions, like the stop action. (I searched the LV forum with keyword stop timer)

What I do not understand, is more general: what a stop action mean? If I have a timer subVI, I call it every lets say 50 msec in a loop, lets say it is a state in a state machine. I can see the point in functions like "reset", "set autoreset" and "pause". But what can I do with a "stop" action? Or is this action would be simply a stored state inside the subVI (shift register), so the user could abort the timer in the main VI at another location?

[Blokk]

anyway, never mind, I guess I will see such examples in the CLD sample exams when I get there after the prep guide practices.

thanks for info,

regards!