A PROGRESS REPORT ON PHASE-II OF BASCULE BRIDGE PROJECT.

We will discuss the following three aspects of the work that has been done up till now as part of Phase-II, they are

1.DAQ boards (Data acquisition system)

2.Temperature measurement

3.Strain gages for stress measurement

DATA ACQUISITION

As per the requirements of our current problem, we have to measure the temperature and stress at various critical points on the THG assembly. We have estimated that we would need about 10 channels each of temperature and strain. Now, we have before us a lot of options, about the type of DAQ system to be employed. These vary from simple plug-in boards( from OMEGA) with on-board signal conditioning, that directly take inputs from the sensors to a fully integrated DAQ system(from MEME) for measuring stress.

Detailed specifications of the desired data acquisition system:

Step –I: Measurement of residual stress. The data acquisition system should be capable of storing these stress values, and later on add them to the stresses induced during the cooling process

Step-II: Measurement of temperatures and strains (stresses) when the assembly is immersed in liquid nitrogen. Here, since we will be measuring parameters, when the assembly is under liquid nitrogen (-321 degree Fahrenheit), the sensors (thermocouples and strain gages) and the connecting wires should be able to withstand the temperature of the liquid nitrogen, and pass on the signals from the sensors attached to the assembly to the data acquisition system lying outside the tank of liquid nitrogen.

TECHNICAL SPECIFICATIONS

1.Channels: 16 for temperature and 16 for strains.

2.Scan rate: 1 reading per minute.

3.Duration of the test: order of 50 hours 4. Data Manipulation abilities: The data acquisition system should be able to do the following:

(i) Cold junction compensation for the thermocouples (ii) Signal conditioning (iii) Store the data and plot graphs of the variables, against each other and against time. (iv) Suitable software, so that the operator of the system need not write any separate programs.

We are searching for DAQ systems from different vendors like National instruments, HP, etc. We have also searched for portable computers with slots for DAQ boards, which would result in a mobile testing apparatus.

TEMPERATURE MEASUREMENT

We will be employing about 16 type “E” thermocouples (OMEGA) for measuring the temperature. The connecting wires will be insulated with Teflon, which can endure the temperature of liquid nitrogen.

STRAIN MEASUREMENT

We will be employing about 16 strain rosettes at various critical points on the THG, to record the stress state. Also, the residual stresses developed in each cylinder will be recorded and later added to the assembly stresses to get the total stresses, induced in each of the three components.