Autoscale

[andybdjuk]

HI, i am currently plotting the output of my wind turbine against time . Every time i walk past the PC i Autoscale both axis to give me a nicer graph.

Is there a way of allowing the graph to autoscale automatically as the data comes in?

Warmest regards

[AzeoTech]

Of course. The Scale From and Scale To parameters of the graph are expressions, so you can put formula in there. Lets say you are plotting a channel called WindTurbine. For ScaleFrom you'd do:

min(WindTurbine)

and ScaleTo you'd do:

max(WindTurbine)

you might want a little room, so maybe you'd do:

min(WindTurbine) - min(WindTurbine) * 0.1

max(WindTurbine) + max(WindTurbine) * 0.1

You will, of course, need to thaw your axes to have these scalings take effect. Doing AutoScale will freeze the Y axis.

[RJE]

Will that work just for the graph window only?

I have a graph of amps vs time, if there is a large peak I have to autoscale to see how high it is, lets say 35 amps. The y axis becomes 0 - 35. As the amps drops down to say 4 and the graph moves along so that the line is all at 4, autoscaling will not change the y axis to 0 - 4.

It seems the peak value in the channel history is setting the autoscale y value.

[AzeoTech]

That's exactly what is happening. Doing min(channelname) does the min of the entire history. If you only want it to use, say, the last 60 points, you'd do:

min(channelname[0,59])

You could also do, say, the last 60 seconds worth of points:

min(channelname[systime(),systime()-60])

[BeeHay]

min(channelname[systime(),systime()-60])

Can you do this for variables?

Or in my case, V.Chans?

[AzeoTech]

Certainly, provided there is a history. Channels, variables and V.Chans act the same when when you are retrieving data from them. They just work different when you are assigning values to them:

variable = 3

makes variable equal to 3

channel = 3

sets the output channel to 3 (calling the driver), and if successful, updates the channel history, moving older data back one place. If channel is an input, nothing will happen

v.channel = 3

updates the history, making 3 the [0] value and moving everything else back one place