Hi everyone,
I am using a NI PCI-6602 to record photon arrival times. Basically, it counts the number of rising edges on the 80MHz sample clock that occur between two rising
edges on the photon TTL signal. The array of integers can be converted to times by multiplying by 12.5ns. Please find my VI for the task and its subVI attached.
I have two problems:
1) I want to do this same measurement for two photon detector channels. I have set up two independent channels. My aim is to correlate the signals with a delay between them. I am able to implement a delay in the software, but from my data there appears to be a small inherent delay between the start of each channel.
The amount of delay is seemingly random and occurs in both the positive and negative direction. In the VI I have attached, I tried using the Arm Start Trigger in order to get both channels to start acquisition at the same time, but while this reduced the severity of the delay, it has not removed it completely. There is still a delay of between 1 and 500 microseconds. Have I implemented the Arm Start Trigger correctly, or is there another way to go about solving this?
2) I regularly receive an error stating that "data was overwritten before it could be read by the system". The number of samples that has been collected before this error varies wildly and also varies between the counters on the board. I had a theory that the sample transfer rate was not good enough, but according to the manual, the transfer rate should be about 2000kS/s. This is more than enough considering that the photon count rate is less than 50k/s. The PC I'm using has a PCI graphics card too. Is it possible that this is limiting the sampling rate? Here are the PC specs: Intel Pentium D processor (3.0GHz), 2GB RAM, nVidia GeForce 7300 LE graphics card.
Thanks in advance.