System description
 
 
 FINUDA Straw tube detector employees 2424 alluminized-mylar straws with a diameter of 15 mm and a straw length of ~ 2.6 m. Straws are operated with a mixture of Argon + Ethane (50%+50%) and the total straw volume of ~ 1m3  is flown at a rate of 2 m3/day.
 
 
 
Number of straws 2424  
Straw volume 0.5  l
Total volume 1000  l
Gas mixture Argon+Ethane  
Argon percentage 50  %
Ethane percentage 50  %
Minimum mixture flow rate 50  l/h
Minimum flow on a single layer (404 straws) 5  l/h
Maximum flow on a single layer (404 straws) 100  l/h
Straw operating pressure 50  mb
Maximum straw pressure (software safety limit) 100  mb
Maximum straw pressure (hardware safety limit) 200-250  mb
 
 
 

 
Ramp inversion and primary decompression
 
Both argon and ethane bottles are divided in two ramps (left and right) located in gas rooms adjacent to Astra Lab. For argon when the bottle pressure of  ramp under use goes below 10 bar, automatic ramp inversion is done and an alarm signal is generated to indicate the necessity of changing gas bottles. Ethane bottles are placed on an electronic balance and a ramp inversion takes place when the gas weight in the ramp under use goes below 2 kg. Gas pressure is reduced to 5 bar in the inversion units and sent to filtering rack.
 

Gas filtering

Line pressure regulators are used to set the outlet pressure at filtering rack to 0.7 bar both for argon and ethane. Gas filters and all other hardware related to distribution system is located inside Astra Lab.
 

Gas mixing

Electronic mass flow meters with a full scale of 420 Nl/h are used to mix argon and ethane in a 50/50 volume ratio. Mixture pressure and temperature is monitored electronically. In addition to electronic mass flow meters, both argon and ethane flows can visually be seen on rotameters. In case of necessity, flow can be set to bypass the electronic mass flow meters and the rotameters can be used to regulate the flow.

 
Layer distribution patch panels
 
Output for the mixing rack is fed in parallel to 6 layer distributors. Gas flow, pressure and temperature can be read through electronic transducers both at the inlet and the outlet side. Mass flow meters (which can be bypassed) followed by rotameters are used to set the input flow for each of the six straw layers. Each layer distributor provides 7 black rilsan tubes used as flow lines. Each line is used to provide gas to a group of 60 straws in parallel. Outgoing flow from straws is collected in a similar manner (7 blue rilsan tubes each from the group of 60 straws in parallel). On its return path gas from the six layers is collected together and fed to the exhaust line which brings it outside the Astra lab.
 

Control software

A Labview program running on PCSTCON uses the serial ports with RS232 protocol and can be used to read all the transducers (temperature, pressure and gas flow) and set the gas flow for individual straw layers.
 

Pressure safety

Hardware and software safety protection is provided to avoid that gas pressure inside
straws exceed the specified level.