Recording Instrument, Strip Chart and Circular Chart Recorders

Recording devices are used where a continuous record of a variable quantity is required. The recording device is mainly useful for more than three reasons which are as follows.

(i) The process operator gives the command to observe the deviation of the variable amount of the machine in any direction.

(ii) Records are needed to find out the past value of an amount.

(iii) Recording devices are not used where only a simple indicator is sufficient. There are two different types of recording charts used in recording type industry instruments which are as follows.

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Strip Chart Recorder 

Strip Chart Recorder is used to record the amount of change with time and this indicator is used in pointer meter instruments and resistance thermometers. Its construction and working are as follows.

Construction and Working

This chart is forced on a supply roll which is driven by a motor. The speed of this chart is kept at about 2 inches/hour. Strip chart recording pyrometers and resistance thermometers are also used in a variety of instruments. The chart used in this is about 10 inches.

The strip chart recorder used in the Galvan meter type instrument is not like this, it is usually 6 inches wide and the line is slightly inclined rather than straight, so the movement of the pen in this type of instrument is in the form of an arc.

Advantages 

1. Chart speed is also available for a very long range. 

2. It does not need to be changed frequently. 

3. Long running process can be easily recorded.

Limitation of Strip Chart Recorders 

1. It is difficult to keep and it is not so easy to use to give instructions. 

2. The maximum visible length of the chart is usually 8 inches.

Circular Chart Recorders

Circular chart recorders are used in most of all types of industries.

Construction and Working

It consists of a circular chart that is clamped at its geometrical center and rotates through its center and is rotated with the help of a motor. The speed of rotation of the chart is controlled in such a way that it completes only one round in contact. The recording pen moves between the minimum marking line and the maximum marking line as the variable amount changes.

An indicating pointer also moves around the circular chart, indicating the variable amount on the recording scale like a clock needle. Circular chart records are mainly made of two sizes, one about 8 inches in diameter and the other 12 inches in diameter. Used in industrial work, an 8-inch diameter chart is used where recording does not require much accuracy.

Advantages

1. These charts are flat and easy to hold. Can be easily carried from one place to another. 

2. The entire record of a process is viewed at a glance. 

3. The recording device usually allows the recording mechanism of the rotational motion measurement and recording. 

4. It is possible to record four different variables at the same time in this chart.

Limitation of Circular Chart Recorder

1. There is some difficulty in reading the readings received on the side of the center of the chart. 

2. This chart is changed after 4.8 or 12 hours in any process.

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