What is Strip Chart Recorder?

What is Strip Chart Recorder?

A chart recorder is an electromechanical instrument used to record or store various mechanical as well as electrical data on paper or chart. It can record multiple inputs on strip charts or circle charts using different colored pens.

Figure: Strip Chart Recorder Diagram

Strip Chart Recorder Application

Strip Chart Recorder is widely used to collect and record data. Single and multi-channel models are available in the market and most of today’s recorders available in the market have options to record data in digital format too.

Strip Chart Recorder Components

The following are the components of strip chart recorder.

  • Pen (Stylus)
  • Chart Paper
  • Chart Paper drive mechanism
  • Event Marker
  • Signal Conditioning System

Pen: It is used for marking data.

Chart Paper: In the Strip chart recorder, this chart paper is in the form of a strip. This strip is rolled and rotates under the pen as time passes.

Chart Paper Drive Mechanism: We need to move the chart paper under the pen to store the data. Users can adjust the speed of the moving paper (chart).

Event Marker: This marker is used to indicate the amount of time it takes to record fluctuations.

Signal Conditioning System: Signal conditioning system consist of Discrete circuits, Filters, Amplifiers, DAC, ADC etc.

Strip Chart Recorder Working Principle:

The working principle of a strip chart recorder is to record data on a continuous roll of chart paper moving at a constant speed. The recorder records the difference of one of the more variables with respect to time.

To reduce noise and interference the recorder’s input DC signal is first filtered and then pre-amplified. This conditioned signal is carried to the servo amplifier, which is constantly compared to the feedback signal evolved by the servo potentiometer.

The difference between these two signals is a positive or negative error signal, which is used to drive a servo motor connected to a servo potentiometer in one direction to reduce the error signal to zero. Since the recorder plate is automatically connected to the servo motor and servo potentiometer, its position on the graph represents the accuracy of the input signal and the continuous registration of the graph.

Methods to Record Data on the Strip

There are various methods we used to record the data on the strip paper. They are

  • Pen and Ink Stylus
  • Electric Writing
  • Thermal composition
  • Impact Printing
  • Optical Writing

1. Pen and ink stylus

The stylus is inked from the refillable reservoir by capillary action. Modern technology has replaced these pens with disposable fiber tip pens. In addition, the multichannel operation can be performed, i.e. at any given moment, a maximum of six pens can be used to record data. When using multiple pens, stagnation of the pens is required to avoid mechanical interference.

2. Electrical writing

In this technique, we use a special chart paper to record the data. This paper has a paper base coated with colored paint (black, blue or red), which is then coated on a thin surface of aluminum.

Electrical writing is based on the electrostatic p rinciple.

The stylus (pen) consists of a tungsten wire moving on an aluminum surface. Marking on paper is done by applying 35 V possibilities to the stylus. This causes an electric discharge, which removes the aluminum and reveals the colored paint.

3. Thermal composition

In this system, a special moving pen is used which is heated by passing an electric current. This system requires a heat sensitive paper that changes its color when heat is applied.

4. Impact printing

A carbon ribbon is located between the pointer mechanism and the paper in the original impact printing system, which provides ink for data recording. Marking on the chart by pressing the pointer mechanism.

The basic advantage of impact printing in pen and ink mode is that it can record data in up to 20 variables simultaneously.This is achieved with the help of a wheel with a corresponding ink pad that provides ink for the symbol on the wheel. The wheel moves across the paper in response to the recorded variable.

In some systems, pressure-sensitive paper is used. Marking on paper is done with a chopper bar, which puts pressure on the paper.

5. Optical Writing

In optical writing, a special photo-sensitive chart paper, sensitiveUltra violet light is used to record the data. This technology is mostly used in galvanometer systems.

Ultraviolet light is used to reduce the unwanted effects of ambient light. Paper can be expanded in daylight or artificial light without the need for special chemicals, which is not possible with normal light.

The pointer is attached to the stylus in most of the system.

Paper drive system: Paper drive system The paper must be moved at a uniform speed. A spring-wound mechanism often uses a synchronous motor to drive the paper.

Chart speed: Chart speed is a term used to describe the moving rate of the recording paper on a strip chart recorder. It is determined by mechanical gear trains. If the chart speed is known, the duration of the recorded signal can be calculated