problems formatting the x-axis (chart)

[snoowfroog@hotmail.com]

Hello I'm a student and I've some problems measuring the waveform of an akku charger (2-3h total measure-time). The main problem is the wrong update rate of the time (x) axis (I choosed "relativ time" mode). For example: I get a trigger signal (only in charging mode) and have then up to 3 or 4ms time to measure. After that short space the values will be incorrect. I use a DAQ-6020E Pad(USB) with Trig1(PFI0 Pin 11). Now, LabView displays the data correctly in delta time = 1s. But when I compared the update rate with a watch, I recognized that the actual rate is about 1.7s and not just a second, so the total time of the waveform is 1.4h instead of 2.5h. The second problem is that if I first measure the discharging of the akku ( I
don't have a trigger signal at that time) and have to detect the starting of the trigger signal when the akku charger change to charging mode. I used the normal AI-Read.vi to detect the trigger edge and change then the trigger typ of the AI-Start.vi from "No Trigger" to "Trigger A", but this was to slow. It would be very helpful to me if somebody could give me an advice to solve the problem. Thank you. Andreas

[Filipe A.]

Hello;

Everytime you correlate any DAQ operation with a Software call in Labview or any other programming language, you will not get a hardware precision on that operation. Then you can expect a delay of a couple of miliseconds if you are using Software calls together with DAQ. Regarding your second question, if the signal you are intending to detect is TTL, you can use one of the general purpose counters of that equipment of your, to monitor the counter value. Then, when the counter has a value different from zero at its register value, that means the trigger already happened.
Hope this helps.
Filipe