Hi Tim, 
sorry for not providing all the details.  
I have actually searched NI website including forums but they dont have the drivers for 4142b.  And the instrument is with GPIB - USB controller.   
I will try to work on your suggestion. 
Thanks 
Robin 
 
Hello Mark,  
Thanks for your suggestion, I have read the commands and I will try to learn how to use them in LabVIEW. 
And I saw that post too.  I guess I am not the only one.  
Thanks, 
Robin