# Characteristics of Instruments Static and Dynamic [PDF]

Contents

In this article, we shall learn the different characteristics of static and dynamic instruments. We have also provided a PDF for the same

Measuring instruments are a device that indicates the measured quantity into broadly displayed information. It can directly show the measured value or it can show the equivalent value to the known measure value of the same quantity. To do the perfect performance, an instrument should have some quality. We have broadly classified the characteristic of an instrument into two types which are as follows

• Static Characteristic
• Dynamic Characteristic

## Static Characteristic

So let’s start with static characteristics, this type of characteristic generally not change so much with the time, you can say this static characteristic most probably constant with the time.

## Types of Static Characteristics

These are some of the standards characteristics of static instruments

• Sensitivity
• Magnification
• Scale Interval
• Calibration
• Repeatability
• Discrimination
• Precision
• Accuracy
• Reproducibility
• Hysteresis
• Linearity

#### Sensitivity

• Sensitivity is defined as the displacement of indicating device of the instrument with respect o the measured quantity.
• Mathematically Sensitivity is equal to Scale Spacing/Scale Division.

#### Magnification

• Magnification means the increase of the magnitude of the output signal of the measuring devices many times to make the output reading more visible or readable.
• Generally greater the magnification smaller is the range of the instrument.

#### Scale Interval

• Scale interval is the difference between two successive scale marks in units of the measured quantity.
• Due to this factor, we can say that the device is accurate to show the value of the measured quantity.

• Readability means how we can take the measurement quite easily, this is also an important factor of the instrument.

#### Calibration

• Calibration of any instrument is necessary to measure the quantity in terms of the standard unit.
• It is the pre-measurement process, where we need to calibrate the particular device with the stranded value, however, generally this is carried out by the manufacturer of that particular instrument so that the instrument should give the zero output for zero input and similarly the maximum output for the maximum input nearly in a linear scale (Y=mx).

#### Repeatability

• Repeatability means the measuring device can show the same value or nearly about the same value for the same quantity when the measurements are carried out by the same observer, same instrument, same environmental condition, same method, and same interval of time.
• Precision is also associated with this.

#### Discrimination

• Discrimination is the ability of any measuring device to show very smaller changes in the measured quantity.

#### Precision

• Precision is generally the repeatability of the measuring process that means when we kept constant the other variable factor if we repeat the measurement process the instrument should give us nearly about the same result continuously.
• Mathematically or quantitatively the precision can be expressed as:

#### Accuracy

• When the measured value is very much closer than the true value then that is called accuracy, If the difference between the measured value and true value is less then we can say the instrument is much more accurate but if the difference between the true value and the measured value is more then we can say the instrument is less accurate.

#### Reproducibility

• Reproducibility is a degree of closeness within a period.

#### Hysteresis

• Hysteresis can be expressed as the difference between the indication of a measuring device when the value of the measured quantity is reached by increasing or decreasing that quantity.
• Mathematically it can be expressed by

#### Linearity

Linearity is the ratio of maximum deviation from the linear characteristic as a % of full-scale output.

## Dynamic Characteristic

Dynamic characteristic means that the input variable changes rapidly with time.

## Types of Dynamic Characteristic

These are some of the standards characteristics of Dynamic instruments

• Responses Time
• Dynamic Error
• Lag
• Step Response
• Ramp Response
• Standard Signals
• Overshoot
• Dynamic Error
• Fidelity

#### Response Time

• Response Time can be defined as the time which passes after a sudden change in the measured quantity until the device gives us different reading from the true value.

#### Dynamic Error

• A dynamic error is a difference between the true value changing with time to the actual value shown by the instruments over time. It is also called a measurement error.

#### Lag

• It is time to respond to that particular instrument when we change the input. This time is called Lag.

#### Lags are Two- Types

Retardation Lags

• That means when we change the measured quantity the device also changes its value in a faster way.

Time delay lag

• Time delay lag means the device changes its value after some time even when the measured quantity changes.

#### Step Response

• When the measuring device measures one steady step value to another steady step value, the in-between response time between these two values is called Step Response.

#### Ramp Response

• In ramp response, the value of response time in-between two responses changes very slowly with time.

#### Standard Signals

• It is very hard for us to know the types of signals easily as the signal is in random nature.

For study purposes, the dynamic characteristic of signal there is some signal equations is developed which are as follows

• Ramp input
• Step input
• Parabolic input
• Impulse input

#### Overshoot

• In any instrument, the moving indicator also has some mass due to having mass it has some inertia too, so when we give the input to the instrument it deflects from its zero position to some sort of reading position however due to the inertia initially the pointer moves beyond of the reading. This is called overshoot.
• However, the galvanometer-based device have some minimal overshoot.

#### Dynamic Error

• Dynamic Error is the difference between the training value to the indicated value given by the device if we don’t consider any static error.

#### Fidelity

Fidelity means the system can reproduce the output in the same as the input.

These are the measuring devices where we find dynamic characteristics

• Potentiometer
• Thermocouple
• Seismic Sensor
• Step response performance
• Frequency Response Performance
• Bandwidth and Natural Frequency

## FAQ

#### What Are The Characteristics Of Instrument?

The Characteristics of the Instruments are broadly classified into two categories

• Static Characteristic
• Dynamic Characteristic

#### What Are The Dynamic Characteristics Of Instrument?

The Dynamic Characteristic of Instruments are as follows

• Responses Time
• Dynamic Error
• Lag
• Step Response
• Ramp Response
• Standard Signals

#### What Are The Static Characteristics Of Instrument?

The Static Characteristics of Instrument are as follows

• Magnification
• Scale Interval