Counting analog pulses from a photon multiplier tube

[scol]

Hi,

I am trying to work out if it is possible to count random negative analog pulses from a photon multiplier tube (PMT) with any of the NI multifunction DAQ or counter/timer boards? 

Firstly, the properties of the PMT output are as follows (single photon response):

•  1.5 ns FWHM
•  -50 mV to -400 mV (random due to the amplification process in the PMT)
• Up to 5 million counts per second (higher rates cause the detector to overload) arriving at random times. 

All I would like to do is to do simple event counting or buffered event counting.

All the counters seem to only be able to count digital TTL pulses. In that case I have some external signal conditioning electronics in mind which will convert the pulses to positive 5V CMOS logic pulses (which according to this website is suitable for the counter inputs). It also contains a dicriminator circuit to ignore pulses below a threshold. With this signal, I am planning to send to a NI USB multifunction DAQ BNC counter input for event/buffered event counting.

However, in the hope to keep the cost of my system down, I was hoping there might be a way to set an analog trigger to create a TTL pulse from one of NI boards, therefore altogether side-stepping the need for external signal conditioning??

Any help would be gratefully received.

Kind regards

Sean

[Henrik_Volkers · Accepted solution]

You might need to strech the pulse to meet the minimum pulse length of the counter input.

I know you want to do it without extra signal conditioning ... however we build a signalconditioner for our task with a MAX961ESA  comparator driven by the 5V provided ...  the layout is in the datasheet 😉

As a simple pulse strecher I would try a simple RC lowpass before the comparator input . 

[johnsold · Accepted solution]

Sean,

The cost of a high speed comparator and a one shot multivibrator to stretch the pulses is far less than the cost of any board with analog triggering capability to respond to the PMT pulses.

Lynn

[scol]

Thanks Henrik and Lynn. Your help is appreciated!

[johnsold]

Since you marked my post as the solution and indicated that both posts helped, you should also give kudos to Henrik's post.  Kudos are another way of saying thank you that gets counted by the Forum's "scorekeepers."

Lynn