Question

The strain measuring device used to measure the convergence between the roof and floor at a remote location of a mine is

• A. Tell tale bore hole extensometer
• B. Magnetic ring multipoint bore hole extensometer
• C. Remote convergence recorder
• D. Load cells

Hint:

Break down the name of the instrument to understand its function:
- Convergence: Measures roof-to-floor closure.
- Recorder: Logs the data over time.
- Remote: Can be read from a safe distance.
The name perfectly describes the instrument's purpose.

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
The question asks for an instrument that specifically measures roof-to-floor convergence (the coming together of the roof and floor) and can be read from a remote location.

Step 2: Detailed Explanation:
Let's analyze the instruments:
-

Extensometers (A and B): These instruments are installed in boreholes to measure movement within the rock mass.
They measure the displacement between different points along the length of the borehole, not the total convergence between the roof and floor surfaces.
A "tell tale" is a simple mechanical device for visual indication of roof movement, not a remote recorder.
-

Load Cells: These instruments measure force or pressure, for example, the load acting on a roof support.
They do not directly measure displacement or convergence.
-

Remote Convergence Recorder: This instrument is specifically designed for the purpose described.
It consists of a sensor unit that is installed between the roof and floor.
The sensor measures the change in distance between its two ends as the roof and floor converge.
This measurement is converted into an electrical signal and transmitted via a cable to a readout unit or data logger located in a safe,

remote location.
This allows for continuous and safe monitoring of convergence in inaccessible or hazardous areas.

Step 3: Final Answer:
The device used to measure convergence remotely is a remote convergence recorder.
This corresponds to option (C).