data acquisions in two timed loops sometimes dont reads the input signal

Hello..

  I am using a timed loop inside the master while loop, in which i do data acquisition for 6 sensors. Kindly see the attachment to get a overview. Also i have a infinite while loop (or atleast it should run at 100ms) controlling the pressure in the system. while running NI DAQ reads zero value in an arbitrary iteration (eg shown below) and then starts give the actual value thereafter. This applies to all the 6 sensors, however not all goes to zero at the same time, only one goes. Also i didnt find a periodicity of this zero signal. This does not happen frequently, maybe one or two in 5 minutes..

for eg., acquired value from sensor 

2.32

2.33

2.32

2.22

0.00<------

2.22

2.24

2.34 etc..

Thanks Muthu