# LabVIEW

cancel
Showing results for
Did you mean:

Solved!
Go to solution

## Re: Data logging every 10 seconds

The input consists of temperature values using an RTD sensor. It's not a sine.

Message 11 of 19
(625 Views)

## Re: Data logging every 10 seconds

@Ezzow wrote:

The input consists of temperature values using an RTD sensor. It's not a sine.

It isn't a straight line either. A constant is the derivative of a straight line, IIRC. The dy isn't constant, so the derivative isn't constant.

That derivative looks to me like the derivative of it's input.

Message 12 of 19
(613 Views)

## Re: Data logging every 10 seconds

Hmm, I think there are straight lines in  each interval 🤔

It looks like the same signal only with a delay 🧐

Message 13 of 19
(608 Views)

## Re: Data logging every 10 seconds

@Ezzow wrote:

Hmm, I think there are straight lines in  each interval 🤔

It looks like the same signal only with a delay 🧐

And\or reversed (the y scale is flipped)...

The straight intervals look like lines between points to me. Hard to tell, even if I'd run the VI, I won't get that data.

Of course a cosine is a delayed sine...

Could it be that the init is true by default?

Message 14 of 19
(603 Views)

## Re: Data logging every 10 seconds

The problem is that when I hold the sensor in my hand and wait till I get approximately a constant value its derivative looks exactly the same when logically it shouldn't. That's why I think it's only a delayed input.

Yes ofc the cosinus is a delayed sine and vice versa .. but what makes you think that a signal coming from a sensor could behave like a sine signal?

What do you mean by "init" ? It would help a lot if you reformulate the question

Message 15 of 19
(590 Views)

## Re: Data logging every 10 seconds

@Ezzow wrote:

Yes ofc the cosinus is a delayed sine and vice versa .. but what makes you think that a signal coming from a sensor could behave like a sine signal?

Just that the signal looked, at the first glance, like 1 phase of a sine, the derivative looked like one phase of a cosine.

It obviously isn't like that, so please forget that remark.

Message 16 of 19
(579 Views)
Solution
Accepted by Ezzow

## Re: Data logging every 10 seconds

@Ezzow wrote:

What do you mean by "init" ? It would help a lot if you reformulate the question

The derivative x(t).vi you're using isn't correct.

The VI you want is derivative x(t) PtByPT, and that one has an init input.

The PtByPt version assumes straming data, continuing where the previous iteration stopped. The VI you're using now doesn't, it calculates the incoming data, and that's it.

Message 17 of 19
(577 Views)

## Re: Data logging every 10 seconds

Thank you @CARY! That is exactly the VI I was looking for.

Even though I didn't understand what is the difference to the derivative x(t).

I'm using a CompactRio 9047. The write to measurement file VI doesn't save data in my Computer. I read in the forum that the ConmpactRio must has its own storage and I have to use methodes like FTP adress or networks streams to save data in my host-PC. However, I don't know how to it ..

Message 18 of 19
(551 Views)

## Re: Data logging every 10 seconds

@Ezzow wrote:

Thank you @CARY! That is exactly the VI I was looking for.

Even though I didn't understand what is the difference to the derivative x(t).

The Derivative x(t).vi takes a signal and processes it. The PtByPt variation takes a signal each iteration, and processes the signal as one continuous stream.

@Ezzow wrote:

I'm using a CompactRio 9047. The write to measurement file VI doesn't save data in my Computer. I read in the forum that the ConmpactRio must has its own storage and I have to use methodes like FTP adress or networks streams to save data in my host-PC. However, I don't know how to it ..

Write to measurement file VI should store data locally just fine, but you have to give it a valid path. The cRIO has it's own file system, and not all folders can be used for storage (some might be write protected).

I don't have recent experiences with the Linux based cRIOs, but a static path like "C:\" will most certainly fail. In stead, try to use the Temporary Directory function, and a build path to set a file name..

If you want your data stored on the PC (and the PC is always available), you could stream the data in stead of transporting the file. For instance with a network stream.

Message 19 of 19
(529 Views)