periodic X-Axis in reports

[nimic]

Hello

I am currently performing engine measurements. Typically, pressure signals are periodic in 720° crank angle.

If I plot pressure vs. angle, I get an overlay of all revolutions measured. If I sum up or integrate the angle, angle values get very large and don't reflect the angular position.

Is there a way to make the X-Axis 'wrap' at 720°, similar to having a scale of time seconds (which obviously does wrap around at 60 secs)?

thank you for your help

Michael

[Brad_Turpin]

Hi Michael,

Do your Angle channel values go back to 0 each time they get to 760, or do they keep counting up to 1520, 2280, 3040, etc.?  If they keep counting, then you can convert all the Angle channel values to their corresponding values between 0 and 760.  Once your Angle values are repeating between 0 and 760, you can plot the measurements as a scatter plot with only markers.  If you need to see lines from left to right but not lines from right to left (at the wrap point), then you can insert a NoValue row before the Angle channel values drop back to 0.

I'm not yet sure what you want and what you lack.  A data file would help clear some of this up.

Brad Turpin
DIAdem Product Support Engineer

National Instruments

[Gianni_P]

Hi Brad,

I believe he is dealing with the opposite scenario that with what you described. The angles don't continue past 720 (1440, 2160... etc.), they start over again at 0. This means that he is getting mulitple signals from 0 to 720 overlapped, rather than having them one after the other.

Therefore, the x-axis should be something like: 0, 180, 360, 540, 720/0, 180, 360, 540, etc. rather than 0, 180, 360, 540, 720, 900, 1080.

My only solution is to convert the angles into a fraction. For example, 180/760  is 0.25. Then you have to create a scipt which identifies how many revolutions are contained within your data, and u can plot the x-axis as follows:

1, 1.25, 1.5 ...., 2, 2.25, etc. But, this requires that all ove the angles are converted into a fraction (angle/720).

It's not pretty, and I'm sure there is a better way, but it will work...

[Brad_Turpin]

Hi nimic,

Could you please comment on which angle scenario you have?  Also, would you please describe exactly what you want to see on your graph-- in particular on the X axis?

Brad Turpin
DIAdem Product Support Engineer
National Instruments

[Gianni_P]

Hello, So, it turns out that I now need help with this kind of plot, and I don't know if a solution was prosposed. I'll try to explain the problem a bit better in general terms.

Take a clock. Numbers 1 to 12 all around. Suppose each hour position represent a measurement. So, there are 12 measurements being taken around a circular object. If I want to plot the "profile" of these measurements on a standard plot, I would put 1 to 12 on the x axis, and the measurements on the y axis. BUT, on the plot, the 1st and 12th measurements are at opposite ends of the graph, while in reality, they represent side-by-side measurements, since they are on a circle.

Or, suppose I want the plot to start at the 5th measurement and end on the 4th measurement (instead of 1 to 12). In other words, what if I don't want to start plotting from the measurement at the top of the circle?

Or (and this is what the previous poster was trying to get at), what if I want to plot 1 through 12, several times? Since my measurements are changing in time, the profile from 1 to 12 is also changing. If I want to see multiple profiles together, I don't want them stacked on top of eachother. Instead, I want the x-axis to read as follows:

1, 2, 3, ...... , 10, 11, 12, 1, 2, 3, ......... , 10, 11, 12, 1, 2, 3, 4, ......., 11, 12, 1, 2, etc.

|---------1st cycle-----------| |---------2nd cycle-------------| |-----------3rd cycle--------| |--------

Thanks in advance.

Message Edited by Gianni_P on 09-11-2009 07:48 AM

[Brad_Turpin]

Hi Gianni,

Thank you for clarifying.  What you requested on the x axis is actually pretty easy to do.  First graph the Y channel vs. its array index (leave the X channel in the graph dialog for that curve blank).  Then set the curve type to "line and points" ("line and symbol" in older DIAdem versions).  Now go into the curve configuration and set up symbols to display from the X channel in the Data Portal-- you want them to display at about -5% vertically and at their respective position horizontally.

If you send me data, I can make the TDR for you,

Brad Turpin

DIAdem Product Support Engineer
National Instruments

[Gianni_P]

Thanks Brad.

I don't quite follow your instructions, particularaly the part about the symbols...

In any case, I have another solution. I created a Text/String channel and plotted that on the x-axis. Its great, because it puts any string on the axis, so it doesn't even have to be numeric. In the case with the 12 measurements around a circular object, I created 13 entries, whereby I start and end with the 12th one. The resulting plot has 12 at the "0" position, then 1 through 12 afterwards. This will also work with angles in degrees (as the thread starter wanted) or anything else that is periodic.

[AndreasH_Ha · Accepted solution]

Hello nimic,

reading through your initial question, I was wondering whether the earlier replies answered your question. From working with engine data (combustion analysis) in DIAdem, I would think that you are trying to display pressure data from several cycles. In the graph, you would like to see one cycle after the other (see picture). When you plot your data versus its index (no data for x-axis), the labels on the x-axes would show the index instead of a repeated sequence of 0, 180,360, 540,0, 180,360, 540.....

But you are already close. Please take a look at the second graph in the bitmap below. Is this what you want ? If so, all you need to do is plot your data versus its index and then define the following formatting for the labels of the x-axes :"@@CFV Mod 720@@". Then you want to change the x-axes scaling from automatic to "Ticks manual". Set the tick value to 360.

Let me know if this is what you need.