Sweep Chart Problems in Patient Monitor

[Dr Tallman]

I have built a simple patient monitor that "looks up" and plots four tables of numbers. The basic diagram is shown below in Sweep Chart.JPG.

Also, the VI I use to read the tables is shown in Waveform Read.JPG. These are relatively short tables containing between 300-400 elements.

Alone, this works very well but when put into a larger system, two things happen that are unexpected.

1) The sweep chart erases after it reaches the right border. This doesn't happen all the time but seems almost random

2) the chart hesitates after reading each table. This only happens in the vi. that has an A/D option. This does not happen in the exact same vi that uses a numerical control instead of the A/D input

What external conditions would give rise to these two problems?

By the way, I am using the NI USB-6009 with a DAQ Assistant Express vi. sampling 2 channels.

Thanks in advance for your help.

Richard Tallman

[Dr Tallman]

Correction!

The sweep chart isn't actually erasing. It is taking the last value at the right border and quickly plotting it across the entire chart (thus erasing the old data) and continuing normally from the left. This is what it looks like at that point.

Any ideas why that would happen? Thanks again.

Richard

[Michael Aivaliotis]

I think this is what it's suppose to do since you are using a chart? You are updating the chart from inside the loop with new data. Once the chart buffer is full it will sweep from the beginning again. What is the update mode? Switch it to strip chart and see if that helps.

[Dr Tallman]

The Strip Chart and Scope Chart modes work exactly as advertised. The Scope chart keeps the old data about 1/2 the time.(see below).

I have tried playing with the "Chart History Length" (is that the same as the Chart Buffer?) but that doesn't seem to have any effect.

[Dr Tallman]

For those who may be interested, I finally found out what was happening. After working with NI and going back and forth, it was considered a glitch (apparently also happening in versions of LabView more recent than mine, 8.5). I discovered that putting anything on top of the chart (label, line decoration etc.) caused the problem. The lines and labels you see on my chart were added on top as decorations and lines. Removing them, resulted in perfect behavior.

[ShaunR]

For those who may be interested, I finally found out what was happening. After working with NI and going back and forth, it was considered a glitch (apparently also happening in versions of LabView more recent than mine, 8.5). I discovered that putting anything on top of the chart (label, line decoration etc.) caused the problem. The lines and labels you see on my chart were added on top as decorations and lines. Removing them, resulted in perfect behavior.

Did they give you a CAR number for it or was there already one registered.?

[Dr Tallman]

Yes they did. The CAR number is 297680.