Generation of square wave by varying the amplitude at regular time intervals.

[GiridharYadav]

Dear John,

Thanks for your reply

I had already mentioned the details of the pulses like as shown below

Coming to the characteristics of these pulses

1. Rise time of the pulse = 0.1micro second

2. Fall time (Decay time) = 1 micro second

3. Average pulse rate <= 5000 pulses/second.

4. Amplitude of the pulse will varying between 0 to 5V/ (10V variable)

Duration of the pulse = Rise time + fall time = 1.1 micro second.

For the pulse height analysis cant we use Histogram function?

From these pulses I need to separate the standard pulses with 5V amplitude which are randomly distributed.

Coming to the pulse shape, if it is some what important.

Multi Channel Scalar:

In this MCS those pulse counts that are obtained from the Pulse height analysis were stored in some channels where each channel is opened for some particular time i.e. 100 micro seconds. A graph is to be plotted between Counts / unit time and Channels. Channel number is fixed like 2000 channels. So total time taken for 2000*100micro seconds = 0.2 second which is the sweep time for the above process. After 300 such sweeps the MCS stops. The stored data needs to be filed into some memory. Then the amplitude of the square wave is changed.

which is used as the reference signal for varying the gamma ray frequency, so with this different types of pulses will be obtained which are need to be analyzed.(Example consider the Doppler effect)

Actually this I am having one traditional setup for the above process in which MCDWIN S/W is used. and MCA card is used. 

Still if you have any query let me know?

Thankss and Regards

A.Giridhar Yadav.

[NI-Bongo]

Hi Gamma Ray,

I just wanted to make sure there was no high time between the rising edge and the decay.  A
high-speed digitizer should be able to achieve sampling rates that will resolve a pulse with these characteristics.  There is a Histogram function in LabVIEW, but you need to first extract the peaks from the signal.  Otherwise, all the samples will be plotted in the histogram, not just the peaks.  Here is a Developer Zone article on how to extract the peaks from your data.

Peak Detection Using LabVIEW and Measurement Studio
http://zone.ni.com/devzone/cda/tut/p/id/3770

From there, you can use the Histogram VIs to plot the data.  You can find it in Functions»Mathematics»Probability & Statistics»Histogram.vi. 

What is not clear to me still is what you mean by "Channels" for the Multi Channel Scalar.  Are you saying you want to now take the same data from above, look at it in small time intervals, and simply count the number of pulses in each interval?  You can use the same peak data you extracted for the histogram, but this time you would have to create bins for the 100 microsecond interval and find the total number of peaks in each bin.  I'm not aware of a function that does this automatically, but you could certainly create a program that would do so by iterating through the peak data and using it's "location" value to find which bin should be incremented.

I'm still not sure of the purpose of the square wave signal.  Is this being used as a gate to eliminate peaks of a lower frequency than the reference?  If so, this gating could be done in software by removing peaks below the threshold before creating the histogram of the number of pulses vs. time.


LabVIEW for Measurement and Data Analysis
http://zone.ni.com/devzone/cda/tut/p/id/3566

[johnsold]

John,

In the language of radio isotope measurements the channels refer to the peak amplitudes of the pulses. The pulses are typically the output from one or two photomultiplier tubes (PMT). The PMTs record the light emitted when the radioactive particles pass through a scintillating medium. The medium absorbs the energy of particles and then emits light as the energy imparted to outer shell electrons by the absorption process is released when the electrons drop back to the ground state. The energy of the particles is distributed around a peak value. Multiple atoms or molecules of the scintillating medium are excited by the passage of each particle. The magnitude of the PMT output pulse is proportional to the number of photons emitted and thus proportional to the energy of the particle.

Some instruments have a very large dynamic range and use a logarithmic amplifier between the PMT and the analyzer.

A Multi Channel Analyzer is a device which can measure the amplitude of the peaks of the pulses and sort them into bins or "Channels."

A hardware approach would be to build a peak capture and hold circuit and digitize the captured peaks. The Virtual Instrument approach would be to digitize the output of the PMT (or log amp), find the peaks in software, and then sort into the channels. Because the traditional channel boundaries may not line up with the quantization levels of the digitizer, a higher resolution digitizer may be needed.

Lynn

[GiridharYadav]

Dear john,

Thank you for UR cooperation. I need the same support till I complete this project.

So, we can do this project using LabVIEW. But what I need is the appropriate DAQ card for acquiring the pulses and generating the variable amplitude square wave. So, I need your help in this. Still do you have any queries excpt that generation of square wave.

Thanks and Regards

A.Giridhar Yadav

[NI-Bongo]

Hello A.Giridhar Yadav,

Because you want to ensure that you are measuring the pulse height accurately, you definitely want a sampling rate of at least 10MHz, but 20MHz would be better.  Our Multifunction DAQ devices do not attain high enough sampling rates to accurately reproduce your signals without external signal conditioning.  These rates require a high-speed digitizer.  The article below will give you an idea of what you need to consider when choosing a digitizer.

Top 10 Things to Consider when Selecting a Digitizer/Oscilloscope
http://zone.ni.com/devzone/cda/tut/p/id/4333

This means that you would need a separate device for generating the square wave.  Almost any of our Multifunction DAQ devices can generate a 10Hz Square Wave.  If you want a very high precision signal source, you could also go with a Function Generator or Arbitrary Waveform Generator.  These are a lot more flexible for generating signals, but also more specialized to signal generation.

Data Acquisition Products
http://www.ni.com/dataacquisition/

Signal Generators
http://www.ni.com/signalgenerators/

Depending on which form factor you prefer, there are different options available.  PXI is robust and reliable.  PCI is easily integrated into an already existing machine.  USB is more portable.  I can have someone contact you if you'd like to discuss your options further.